We Keep Coding

Fill in shape with lines at a specified angle

I need to create line segments within a shape and not just a visual pattern - I need to know start and end coordinates for those lines that are within a given boundary (shape). I'll go through what I have and explain the issues I'm facing
I have a closed irregular shape (can have dozens of sides) defined by [x, y] coordinates
shape = [
[150,10], // x, y
[10,300],
[150,200],
[300,300]
];
I calculate and draw the bounding box of this shape
I then draw my shape on the canvas
Next, I cast rays within the bounding box with a set spacing between each ray. The ray goes from left to right incrementing by 1 pixel.
Whenever a cast ray gets to a pixel with RGB values of 100, 255, 100 I then know it has entered the shape. I know when it exits the shape if the pixel value is not 100, 255, 100. Thus I know start and end coordinates for each line within my shape and if one ray enters and exits the shape multiple times - this will generate all line segments within that one ray cast.
For the most part it works but there are issues:
It's very slow. Perhaps there is a better way than casting rays? Or perhaps there is a way to optimize the ray logic? Perhaps something more intelligent than just checking for RGB color values?
How do I cast rays at a different angle within the bounding box? Now it's going left to right, but how would I fill my bounding box with rays cast at any specified angle? i.e.:
I don't care about holes or curves. The shapes will all be made of straight line segments and won't have any holes inside them.
Edit: made changes to the pixel RGB sampling that improve performance.
canvas = document.getElementById('canvas');
ctx = canvas.getContext('2d');
lineSpacing = 15;
shape = [
[150,10], // x, y
[10,300],
[150,200],
[300,300]
];
boundingBox = [
[Infinity,Infinity],
[-Infinity,-Infinity]
]
// get bounding box coords
for(var i in shape) {
if(shape[i][0] < boundingBox[0][0]) boundingBox[0][0] = shape[i][0];
if(shape[i][1] < boundingBox[0][1]) boundingBox[0][1] = shape[i][1];
if(shape[i][0] > boundingBox[1][0]) boundingBox[1][0] = shape[i][0];
if(shape[i][1] > boundingBox[1][1]) boundingBox[1][1] = shape[i][1];
}
// display bounding box
ctx.fillStyle = 'rgba(255,0,0,.2)';
ctx.fillRect(boundingBox[0][0], boundingBox[0][1], boundingBox[1][0]-boundingBox[0][0], boundingBox[1][1]-boundingBox[0][1]);
// display shape (boundary)
ctx.beginPath();
ctx.moveTo(shape[0][0], shape[0][1]);
for(var i = 1; i < shape.length; i++) {
ctx.lineTo(shape[i][0], shape[i][1]);
}
ctx.closePath();
ctx.fillStyle = 'rgba(100,255,100,1)';
ctx.fill();
canvasData = ctx.getImageData(0, 0, canvas.width, canvas.height).data;
// loop through the shape in vertical slices
for(var i = boundingBox[0][1]+lineSpacing; i <= boundingBox[1][1]; i += lineSpacing) {
// send ray from left to right
for(var j = boundingBox[0][0], start = false; j <= boundingBox[1][0]; j++) {
x = j, y = i;
pixel = y * (canvas.width * 4) + x * 4;
// if pixel is within boundary (shape)
if(canvasData[pixel] == 100 && canvasData[pixel+1] == 255 && canvasData[pixel+2] == 100) {
// arrived at start of boundary
if(start === false) {
start = [x,y]
}
} else {
// arrived at end of boundary
if(start !== false) {
ctx.strokeStyle = 'rgba(0,0,0,1)';
ctx.beginPath();
ctx.moveTo(start[0], start[1]);
ctx.lineTo(x, y);
ctx.closePath();
ctx.stroke();
start = false;
}
}
}
// show entire cast ray for debugging purposes
ctx.strokeStyle = 'rgba(0,0,0,.2)';
ctx.beginPath();
ctx.moveTo(boundingBox[0][0], i);
ctx.lineTo(boundingBox[1][0], i);
ctx.closePath();
ctx.stroke();
}
<canvas id="canvas" width="350" height="350"></canvas>

This is a pretty complex problem that I am trying to simplify as much as possible. Using the line intersection formula we can determin where the ray intersects with the shape at every edge. What we can do is loop through each side of the shape while check every rays intersection. If they intersect we push those coordinates to an array.
I have tried to make this as dynamic as possible. You can pass the shape and change the number of rays and the angle. As for the angle it doesn't take a specific degree (i.e. 45) but rather you change the start and stop y axis. I'm sure if you must have the ability to put in a degree we can do that.
It currently console logs the array of intersecting coordinates but you can output them however you see fit.
The mouse function is just to verify that the number match up. Also be aware I am using toFixed() to get rid of lots of decimals but it does convert to a string. If you need an integer you'll have to convert back.
let canvas = document.getElementById("canvas");
let ctx = canvas.getContext("2d")
canvas.width = 300;
canvas.height = 300;
ctx.fillStyle = "violet";
ctx.fillRect(0,0,canvas.width,canvas.height)
//Shapes
let triangleish = [
[150,10], // x, y
[10,300],
[150,200],
[300,300]
]
let star = [ [ 0, 85 ], [ 75, 75 ], [ 100, 10 ], [ 125, 75 ],
[ 200, 85 ], [ 150, 125 ], [ 160, 190 ], [ 100, 150 ],
[ 40, 190 ], [ 50, 125 ], [ 0, 85 ] ];
let coords = [];
//Class that draws the shape on canvas
function drawShape(arr) {
ctx.beginPath();
ctx.fillStyle = "rgb(0,255,0)";
ctx.moveTo(arr[0][0], arr[0][1]);
for (let i=1;i<arr.length;i++) {
ctx.lineTo(arr[i][0], arr[i][1]);
}
ctx.fill();
ctx.closePath();
}
//pass the shape in here to draw it
drawShape(star)
//Class to creat the rays.
class Rays {
constructor(x1, y1, x2, y2) {
this.x1 = x1;
this.y1 = y1;
this.x2 = x2;
this.y2 = y2;
this.w = canvas.width;
this.h = 1;
}
draw() {
ctx.beginPath();
ctx.strokeStyle = 'black';
ctx.moveTo(this.x1, this.y1)
ctx.lineTo(this.x2, this.y2)
ctx.stroke();
ctx.closePath();
}
}
let rays = [];
function createRays(angle) {
let degrees = angle * (Math.PI/180)
//I am currently creating an array every 10px on the Y axis
for (let i=0; i < angle + 45; i++) {
//The i will be your start and stop Y axis. This is where you can change the angle
let cx = canvas.width/2 + (angle*2);
let cy = i * 10;
let x1 = (cx - 1000 * Math.cos(degrees));
let y1 = (cy - 1000 * Math.sin(degrees));
let x2 = (cx + 1000 * Math.cos(degrees));
let y2 = (cy + 1000 * Math.sin(degrees));
rays.push(new Rays(x1, y1, x2, y2))
}
}
//enter angle here
createRays(40);
//function to draw the rays after crating them
function drawRays() {
for (let i=0;i<rays.length; i++) {
rays[i].draw();
}
}
drawRays();
//This is where the magic happens. Using the line intersect formula we can determine if the rays intersect with the objects sides
function intersectLines(coord1, coord2, rays) {
let x1 = coord1[0];
let x2 = coord2[0];
let y1 = coord1[1];
let y2 = coord2[1];
let x3 = rays.x1;
let x4 = rays.x2;
let y3 = rays.y1;
let y4 = rays.y2;
//All of this comes from Wikipedia on line intersect formulas
let d = (x1 - x2)*(y3 - y4) - (y1 - y2)*(x3 - x4);
if (d == 0) {
return
}
let t = ((x1 - x3)*(y3 - y4) - (y1 - y3)*(x3 - x4)) / d;
let u = ((x2 - x1)*(y1 - y3) - (y2 - y1)*(x1 - x3)) / d;
//if this statement is true then the lines intersect
if (t > 0 && t < 1 && u > 0) {
//I have currently set it to fixed but if a string does not work for you you can change it however you want.
//the first formula is the X coord of the interect the second is the Y
coords.push([(x1 + t*(x2 - x1)).toFixed(2),(y1 + t*(y2 - y1)).toFixed(2)])
}
return
}
//function to call the intersect function by passing in the shapes sides and each ray
function callIntersect(shape) {
for (let i=0;i<shape.length;i++) {
for (let j=0;j<rays.length;j++) {
if (i < shape.length - 1) {
intersectLines(shape[i], shape[i+1], rays[j]);
} else {
intersectLines(shape[0], shape[shape.length - 1], rays[j]);
}
}
}
}
callIntersect(star);
//just to sort them by the Y axis so they they show up as in-and-out
function sortCoords() {
coords.sort((a, b) => {
return a[1] - b[1];
});
}
sortCoords()
console.log(coords)
//This part is not needed only added to verify number matched the mouse posit
let mouse = {
x: undefined,
y: undefined
}
let canvasBounds = canvas.getBoundingClientRect();
addEventListener('mousemove', e => {
mouse.x = e.x - canvasBounds.left;
mouse.y = e.y - canvasBounds.top;
ctx.clearRect(0, 0, canvas.width, canvas.height)
drawCoordinates();
})
function drawCoordinates() {
ctx.font = '15px Arial';
ctx.fillStyle = 'black';
ctx.fillText('x: '+mouse.x+' y: '+mouse.y, mouse.x, mouse.y)
}
function animate() {
ctx.clearRect(0, 0, canvas.width, canvas.height)
ctx.fillStyle = "violet";
ctx.fillRect(0,0,canvas.width,canvas.height)
for (let i=0;i<rays.length; i++) {
rays[i].draw();
}
drawShape(star)
drawCoordinates();
requestAnimationFrame(animate)
}
animate()
<canvas id="canvas"></canvas>

I'm not an expert, but maybe you could do something like this:
Generate the points that constitute the borders.
Organize them in a convenient structure, e.g. an object with the y as key, and an array of x as values.
2.1. i.e. each item in the object would constitute all points of all borders in a single y.
Iterate over the object and generate the segments for each y.
3.1. e.g. if the array of y=12 contains [ 10, 20, 60, 80 ] then you would generate two segments: [ 10, 12 ] --> [ 20, 12 ] and [ 60, 12 ] --> [ 80, 12 ].
To generate the borders' points (and to answer your second question), you can use the line function y = a*x + b.
For example, to draw a line between [ 10, 30 ] and [ 60, 40 ], you would:
Solve a and b by substituting x and y for both points and combining these two formulas (with standard algebra):
For point #1: 30 = a*10 + b
For point #2: 40 = a*60 + b
b = 30 - a*10
40 = a*60 + (30 - a*10)
a*60 - a*10 = 40 - 30
50*a = 10
a = 0.2
30 = a*10 + b
30 = 0.2*10 + b
b = 30 - 2
b = 28
With a and b at hand, you get the function for your specific line:
y = 0.2*x + 28
With that, you can calculate the point of the line for any y. So, for example, the x of the point right under the first point ([ 10, 30 ]) would have a y of 31, and so: 31 = 0.2*x + 28, and so: x = 15. So you get: [ 15, 31 ].
You may need a bit of special handling for:
Vertical lines, because the slope is "infinite" and calculating it would cause division by zero.
Rounding issues. For some (probably most) pixels you will get real x values (i.e. non-integer). You can Math.round() them, but it can cause issues, like:
8.1. Diagonal rays may not actually hit a border point even when they go through a border. This will probably require additional handling (like checking points around and not just exactly the pixels the ray lies on).
8.2. The points your algorithm generate may (slightly) differ from the points that appear on the screen when you use libraries or built-in browser functionality to draw the shape (depending on the implementation of their drawing algorithms).

This is a mashup of Justin's answer and code from my proposed question.
One issue was generating rays at a set angle and a set distance from each other. To have rays be equal distances apart at any angle we can use a vector at a 90 degree angle and then place a new center point for the next line.
We can start at the exact midpoint of our boundary and then spread out on either side.
Red line is the center line, green dots are the vector offset points for the next line.
Next I modified Justin's intersect algorithm to iterate by ray and not side, that way I get interlaced coordinates where array[index] is the start point of a segment and array[index+1] is the end point.
And by connecting the lines we get a shape that is filled with lines inside its boundaries at set distances apart
Issues:
I had to inflate the boundary by 1 pixel otherwise certain shapes would fail to generate paths
I'd like rays to be some what aligned. It's hard to explain, but here's an example of 6 triangles rotated at 60 degree increments that form a hexagon with their inner lines also offset by 60 degree increments. The top and bottom triangle inner lines do not join those of the outside triangles. This is an issue with the cast rays. Ideally I'd like them to join and be aligned with the outer most edge if that makes sense. Surely there is a better way to cast rays than this...
canvas = document.getElementById('canvas');
ctx = canvas.getContext('2d');
lineSpacing = 12;
angle = 45;
shapes = [
[[143.7,134.2], [210.4,18.7], [77.1,18.7]],
[[143.7,134.2], [77.1,18.7], [10.4,134.2]],
[[143.7,134.2], [10.4,134.2], [77.1,249.7]],
[[143.7,134.2], [77.1,249.7], [210.4,249.7]],
[[143.7,134.2], [210.4,249.7], [277.1,134.2]],
[[143.7,134.2], [277.1,134.2], [210.4,18.7]]
];
for(var i in shapes) {
lines = getLineSegments(shapes[i], 90+(-60*i), lineSpacing);
for(var i = 0; i < lines.length; i += 2) {
start = lines[i];
end = lines[i+1];
ctx.beginPath();
ctx.lineWidth = 1;
ctx.strokeStyle = 'rgba(0,0,0,1)';
ctx.moveTo(start[0], start[1]);
ctx.lineTo(end[0], end[1]);
ctx.closePath();
ctx.stroke();
}
}
function getLineSegments(shape, angle, lineSpacing) {
boundingBox = [
[Infinity,Infinity],
[-Infinity,-Infinity]
]
// get bounding box coords
for(var i in shape) {
if(shape[i][0] < boundingBox[0][0]) boundingBox[0][0] = shape[i][0];
if(shape[i][1] < boundingBox[0][1]) boundingBox[0][1] = shape[i][1];
if(shape[i][0] > boundingBox[1][0]) boundingBox[1][0] = shape[i][0];
if(shape[i][1] > boundingBox[1][1]) boundingBox[1][1] = shape[i][1];
}
boundingBox[0][0] -= 1, boundingBox[0][1] -= 1;
boundingBox[1][0] += 1, boundingBox[1][1] += 1;
// display shape (boundary)
ctx.beginPath();
ctx.moveTo(shape[0][0], shape[0][1]);
for(var i = 1; i < shape.length; i++) {
ctx.lineTo(shape[i][0], shape[i][1]);
}
ctx.closePath();
ctx.fillStyle = 'rgba(100,255,100,1)';
ctx.fill();
boundingMidX = ((boundingBox[0][0]+boundingBox[1][0]) / 2);
boundingMidY = ((boundingBox[0][1]+boundingBox[1][1]) / 2);
rayPaths = [];
path = getPathCoords(boundingBox, 0, 0, angle);
rayPaths.push(path);
/*ctx.beginPath();
ctx.lineWidth = 1;
ctx.strokeStyle = 'red';
ctx.moveTo(path[0][0], path[0][1]);
ctx.lineTo(path[1][0], path[1][1]);
ctx.closePath();
ctx.stroke();*/
getPaths:
for(var i = 0, lastPaths = [path, path]; true; i++) {
for(var j = 0; j < 2; j++) {
pathMidX = (lastPaths[j][0][0] + lastPaths[j][1][0]) / 2;
pathMidY = (lastPaths[j][0][1] + lastPaths[j][1][1]) / 2;
pathVectorX = lastPaths[j][1][1] - lastPaths[j][0][1];
pathVectorY = lastPaths[j][1][0] - lastPaths[j][0][0];
pathLength = Math.sqrt(pathVectorX * pathVectorX + pathVectorY * pathVectorY);
pathOffsetPointX = pathMidX + ((j % 2 === 0 ? pathVectorX : -pathVectorX) / pathLength * lineSpacing);
pathOffsetPointY = pathMidY + ((j % 2 === 0 ? -pathVectorY : pathVectorY) / pathLength * lineSpacing);
offsetX = pathOffsetPointX-boundingMidX;
offsetY = pathOffsetPointY-boundingMidY;
path = getPathCoords(boundingBox, offsetX, offsetY, angle);
if(
path[0][0] < boundingBox[0][0] ||
path[1][0] > boundingBox[1][0] ||
path[0][0] > boundingBox[1][0] ||
path[1][0] < boundingBox[0][0]
) break getPaths;
/*ctx.fillStyle = 'green';
ctx.fillRect(pathOffsetPointX-2.5, pathOffsetPointY-2.5, 5, 5);
ctx.beginPath();
ctx.lineWidth = 1;
ctx.strokeStyle = 'black';
ctx.moveTo(path[0][0], path[0][1]);
ctx.lineTo(path[1][0], path[1][1]);
ctx.closePath();
ctx.stroke();*/
rayPaths.push(path);
lastPaths[j] = path;
}
}
coords = [];
function intersectLines(coord1, coord2, rays) {
x1 = coord1[0], x2 = coord2[0];
y1 = coord1[1], y2 = coord2[1];
x3 = rays[0][0], x4 = rays[1][0];
y3 = rays[0][1], y4 = rays[1][1];
d = (x1 - x2)*(y3 - y4) - (y1 - y2)*(x3 - x4);
if (d == 0) return;
t = ((x1 - x3)*(y3 - y4) - (y1 - y3)*(x3 - x4)) / d;
u = ((x2 - x1)*(y1 - y3) - (y2 - y1)*(x1 - x3)) / d;
if (t > 0 && t < 1 && u > 0) {
coords.push([(x1 + t*(x2 - x1)).toFixed(2),(y1 + t*(y2 - y1)).toFixed(2)])
}
return;
}
function callIntersect(shape) {
for (var i = 0; i < rayPaths.length; i++) {
for (var j = 0; j< shape.length; j++) {
if (j < shape.length - 1) {
intersectLines(shape[j], shape[j+1], rayPaths[i]);
} else {
intersectLines(shape[0], shape[shape.length - 1], rayPaths[i]);
}
}
}
}
callIntersect(shape);
return coords;
}
function getPathCoords(boundingBox, offsetX, offsetY, angle) {
coords = [];
// add decimal places otherwise can lead to Infinity, subtract 90 so 0 degrees is at the top
angle = angle + 0.0000000000001 - 90;
boundingBoxWidth = boundingBox[1][0] - boundingBox[0][0];
boundingBoxHeight = boundingBox[1][1] - boundingBox[0][1];
boundingMidX = ((boundingBox[0][0]+boundingBox[1][0]) / 2);
boundingMidY = ((boundingBox[0][1]+boundingBox[1][1]) / 2);
x = boundingMidX + offsetX, y = boundingMidY + offsetY;
dx = Math.cos(Math.PI * angle / 180);
dy = Math.sin(Math.PI * angle / 180);
for(var i = 0; i < 2; i++) {
bx = (dx > 0) ? boundingBoxWidth+boundingBox[0][0] : boundingBox[0][0];
by = (dy > 0) ? boundingBoxHeight+boundingBox[0][1] : boundingBox[0][1];
if(dx == 0) ix = x, iy = by;
if(dy == 0) iy = y, ix = bx;
tx = (bx - x) / dx;
ty = (by - y) / dy;
if(tx <= ty) {
ix = bx, iy = y + tx * dy;
} else {
iy = by, ix = x + ty * dx;
}
coords.push([ix, iy]);
dx = -dx;
dy = -dy;
}
return coords;
}
<canvas id="canvas" width="500" height="500"></canvas>
canvas = document.getElementById('canvas');
ctx = canvas.getContext('2d');
lineSpacing = 10;
angle = 45;
shape = [
[200,10], // x, y
[10,300],
[200,200],
[400,300]
];
lines = getLineSegments(shape, angle, lineSpacing);
for(var i = 0; i < lines.length; i += 2) {
start = lines[i];
end = lines[i+1];
ctx.beginPath();
ctx.lineWidth = 1;
ctx.strokeStyle = 'rgba(0,0,0,1)';
ctx.moveTo(start[0], start[1]);
ctx.lineTo(end[0], end[1]);
ctx.closePath();
ctx.stroke();
}
function getLineSegments(shape, angle, lineSpacing) {
boundingBox = [
[Infinity,Infinity],
[-Infinity,-Infinity]
]
// get bounding box coords
for(var i in shape) {
if(shape[i][0] < boundingBox[0][0]) boundingBox[0][0] = shape[i][0];
if(shape[i][1] < boundingBox[0][1]) boundingBox[0][1] = shape[i][1];
if(shape[i][0] > boundingBox[1][0]) boundingBox[1][0] = shape[i][0];
if(shape[i][1] > boundingBox[1][1]) boundingBox[1][1] = shape[i][1];
}
boundingBox[0][0] -= 1, boundingBox[0][1] -= 1;
boundingBox[1][0] += 1, boundingBox[1][1] += 1;
// display bounding box
ctx.fillStyle = 'rgba(255,0,0,.2)';
ctx.fillRect(boundingBox[0][0], boundingBox[0][1], boundingBox[1][0]-boundingBox[0][0], boundingBox[1][1]-boundingBox[0][1]);
// display shape (boundary)
ctx.beginPath();
ctx.moveTo(shape[0][0], shape[0][1]);
for(var i = 1; i < shape.length; i++) {
ctx.lineTo(shape[i][0], shape[i][1]);
}
ctx.closePath();
ctx.fillStyle = 'rgba(100,255,100,1)';
ctx.fill();
boundingMidX = ((boundingBox[0][0]+boundingBox[1][0]) / 2);
boundingMidY = ((boundingBox[0][1]+boundingBox[1][1]) / 2);
rayPaths = [];
path = getPathCoords(boundingBox, 0, 0, angle);
rayPaths.push(path);
/*ctx.beginPath();
ctx.lineWidth = 1;
ctx.strokeStyle = 'red';
ctx.moveTo(path[0][0], path[0][1]);
ctx.lineTo(path[1][0], path[1][1]);
ctx.closePath();
ctx.stroke();*/
getPaths:
for(var i = 0, lastPaths = [path, path]; true; i++) {
for(var j = 0; j < 2; j++) {
pathMidX = (lastPaths[j][0][0] + lastPaths[j][1][0]) / 2;
pathMidY = (lastPaths[j][0][1] + lastPaths[j][1][1]) / 2;
pathVectorX = lastPaths[j][1][1] - lastPaths[j][0][1];
pathVectorY = lastPaths[j][1][0] - lastPaths[j][0][0];
pathLength = Math.sqrt(pathVectorX * pathVectorX + pathVectorY * pathVectorY);
pathOffsetPointX = pathMidX + ((j % 2 === 0 ? pathVectorX : -pathVectorX) / pathLength * lineSpacing);
pathOffsetPointY = pathMidY + ((j % 2 === 0 ? -pathVectorY : pathVectorY) / pathLength * lineSpacing);
offsetX = pathOffsetPointX-boundingMidX;
offsetY = pathOffsetPointY-boundingMidY;
path = getPathCoords(boundingBox, offsetX, offsetY, angle);
if(
path[0][0] < boundingBox[0][0] ||
path[1][0] > boundingBox[1][0] ||
path[0][0] > boundingBox[1][0] ||
path[1][0] < boundingBox[0][0]
) break getPaths;
/*ctx.fillStyle = 'green';
ctx.fillRect(pathOffsetPointX-2.5, pathOffsetPointY-2.5, 5, 5);
ctx.beginPath();
ctx.lineWidth = 1;
ctx.strokeStyle = 'black';
ctx.moveTo(path[0][0], path[0][1]);
ctx.lineTo(path[1][0], path[1][1]);
ctx.closePath();
ctx.stroke();*/
rayPaths.push(path);
lastPaths[j] = path;
}
}
coords = [];
function intersectLines(coord1, coord2, rays) {
x1 = coord1[0], x2 = coord2[0];
y1 = coord1[1], y2 = coord2[1];
x3 = rays[0][0], x4 = rays[1][0];
y3 = rays[0][1], y4 = rays[1][1];
d = (x1 - x2)*(y3 - y4) - (y1 - y2)*(x3 - x4);
if (d == 0) return;
t = ((x1 - x3)*(y3 - y4) - (y1 - y3)*(x3 - x4)) / d;
u = ((x2 - x1)*(y1 - y3) - (y2 - y1)*(x1 - x3)) / d;
if (t > 0 && t < 1 && u > 0) {
coords.push([(x1 + t*(x2 - x1)).toFixed(2),(y1 + t*(y2 - y1)).toFixed(2)])
}
return;
}
function callIntersect(shape) {
for (var i = 0; i < rayPaths.length; i++) {
for (var j = 0; j< shape.length; j++) {
if (j < shape.length - 1) {
intersectLines(shape[j], shape[j+1], rayPaths[i]);
} else {
intersectLines(shape[0], shape[shape.length - 1], rayPaths[i]);
}
}
}
}
callIntersect(shape);
return coords;
}
function getPathCoords(boundingBox, offsetX, offsetY, angle) {
coords = [];
// add decimal places otherwise can lead to Infinity, subtract 90 so 0 degrees is at the top
angle = angle + 0.0000000000001 - 90;
boundingBoxWidth = boundingBox[1][0] - boundingBox[0][0];
boundingBoxHeight = boundingBox[1][1] - boundingBox[0][1];
boundingMidX = ((boundingBox[0][0]+boundingBox[1][0]) / 2);
boundingMidY = ((boundingBox[0][1]+boundingBox[1][1]) / 2);
x = boundingMidX + offsetX, y = boundingMidY + offsetY;
dx = Math.cos(Math.PI * angle / 180);
dy = Math.sin(Math.PI * angle / 180);
for(var i = 0; i < 2; i++) {
bx = (dx > 0) ? boundingBoxWidth+boundingBox[0][0] : boundingBox[0][0];
by = (dy > 0) ? boundingBoxHeight+boundingBox[0][1] : boundingBox[0][1];
if(dx == 0) ix = x, iy = by;
if(dy == 0) iy = y, ix = bx;
tx = (bx - x) / dx;
ty = (by - y) / dy;
if(tx <= ty) {
ix = bx, iy = y + tx * dy;
} else {
iy = by, ix = x + ty * dx;
}
coords.push([ix, iy]);
dx = -dx;
dy = -dy;
}
return coords;
}
<canvas id="canvas" width="500" height="500"></canvas>

Why circles are vibrating on collision (Canvas)

I have been creating a clone of agar.io and I don't understand why the circles start vibrating when they touch each other. Below is my code:
var
canvas,
ctx,
width = innerWidth,
height = innerHeight,
mouseX = 0,
mouseY = 0;
var
camera = {
x: 0,
y: 0,
update: function(obj) {
this.x = obj.x - width / 2;
this.y = obj.y - height / 2;
}
},
player = {
defaultMass: 54,
x: 0,
y: 0,
blobs: [],
update: function() {
for (var i = 0; i < this.blobs.length; i++) {
var x = mouseX + camera.x - this.blobs[i].x;
var y = mouseY + camera.y - this.blobs[i].y;
var length = Math.sqrt(Math.pow(x, 2) + Math.pow(y, 2));
var speed = 54 / this.blobs[i].mass;
this.blobs[i].velX = x / length * speed * Math.min(1, Math.pow(x / this.blobs[i].mass, 2));
this.blobs[i].velY = y / length * speed * Math.min(1, Math.pow(x / this.blobs[i].mass, 2));
this.blobs[i].x += this.blobs[i].velX;
this.blobs[i].y += this.blobs[i].velY;
for (var j = 0; j < this.blobs.length; j++) {
if (j != i && this.blobs[i] !== undefined) {
var blob1 = this.blobs[i];
var blob2 = this.blobs[j];
var dist = Math.sqrt(Math.pow(blob2.x - blob1.x, 2) + Math.pow(blob2.y - blob1.y, 2));
if (dist < blob1.mass + blob2.mass) {
if (this.blobs[i].x < this.blobs[j].x) {
this.blobs[i].x--;
} else if (this.blobs[i].x > this.blobs[j].x) {
this.blobs[i].x++;
}
if (this.blobs[i].y < this.blobs[j].y) {
this.blobs[i].y--;
} else if ((this.blobs[i].y > this.blobs[j].y)) {
this.blobs[i].y++;
}
}
}
}
}
this.x += (mouseX - width / 2) / (width / 2) * 1;
this.y += (mouseY - height / 2) / (height / 2) * 1
},
split: function(cell) {
cell.mass /= 2;
this.blobs.push({
x: cell.x,
y: cell.y,
mass: cell.mass
});
},
draw: function() {
for (var i = 0; i < this.blobs.length; i++) {
ctx.fillStyle = "red";
ctx.beginPath();
ctx.arc(-camera.x + this.blobs[i].x, -camera.y + this.blobs[i].y, this.blobs[i].mass, 0, Math.PI * 2);
ctx.fill();
ctx.closePath();
}
}
};
function handleMouseMove(e) {
mouseX = e.clientX;
mouseY = e.clientY;
}
function setup() {
canvas = document.getElementById("game");
ctx = canvas.getContext("2d");
canvas.width = width;
canvas.height = height;
addEventListener("mousemove", handleMouseMove);
player.blobs.push({
x: 0,
y: 0,
mass: player.defaultMass
});
player.blobs.push({
x: 100,
y: 100,
mass: player.defaultMass / 2
});
player.blobs.push({
x: 100,
y: 100,
mass: player.defaultMass * 2
});
var loop = function() {
update();
draw();
requestAnimationFrame(loop);
}
requestAnimationFrame(loop);
}
function update() {
camera.update(player.blobs[0]);
player.update();
}
function draw() {
ctx.fillStyle = "#fff";
ctx.fillRect(0, 0, width, height);
player.draw();
}
setup();
body {
margin: 0;
padding: 0;
}
<canvas id="game">kindly update your browser.</canvas>

Separating circles
Your separation code was not correct. Use the vector between them to get the new pos.
The vector between them
To find if two circles are intercepting find the length of the vector from one to the next
The two circles.
var cir1 = {x : 100, y : 100, r : 120}; // r is the radius
var cir2 = {x : 250, y : 280, r : 150}; // r is the radius
The vector from cir2 to cir1
var vx = cir2.x - cir1.x;
var vy = cir2.y - cir1.y;
The length of the vector
var len = Math.sqrt(x * x + y * y);
// or use the ES6 Math.hypot function
/* var len = Math.hypot(x,y); */
The circles overlap if the sum of the radii is greater than the length of the vector between them
if(cir1.r + cir2.r > len){ // circles overlap
Normalise the vector
If they overlap you need to move one away from the other. There are many ways to do this, the simplest way is to move one circle along the line between them.
First normalise the vector from cir1 to cir2 by dividing by its (vector) length.
vx \= len;
vy \= len;
Note that the length could be zero. If this happens then you will get NaN in further calculations. If you suspect you may get one circle at the same location as another the easiest way to deal with the zero move one circle a little.
// replace the two lines above with
if(len === 0){ // circles are on top of each other
vx = 1; // move the circle (abstracted into the vector)
}else{
vx \= len; // normalise the vector
vy \= len;
}
Move circle/s to just touch
Now you have the normalised vector which is 1 unit long you can make it any length you need by multiplying the two scalars vx, vy with the desired length which in this case is the sum of the two circles radii.
var mx = vx * (cir1.r + cir2.r); // move distance
var my = vy * (cir1.r + cir2.r);
.Only use one of the following methods.
You can now position one of the circles the correct distance so that they just touch
// move cir1
cir1.x = cir2.x - mx;
cir1.y = cir2.y - my;
Or move the second circle
cir2.x = cir1.x + mx;
cir2.y = cir1.y + my;
Or move both circles but you will have to first find the proportional center between the two
var pLen = cir1.r / (cir1.r + cir2.r); // find the ratio of the radii
var cx = cir1.x + pLen * vx * len; // find the proportional center between
var cy = cir1.y + pLen * vy * len; // the two circles
Then move both circles away from that point by their radii
cir1.x = cx - vx * cir1.r; // move circle 1 away from the shared center
cir1.y = cy - vy * cir1.r;
cir2.x = cx + vx * cir2.r; // move circle 2 away from the shared center
cir2.y = cy + vy * cir2.r;
DEMO
Copy of OP's snippet with mods to fix problem by moving the the first circle blob1 away from the second blob2 and assuming they will never be at the same spot (no divide by zero)
var
canvas,
ctx,
width = innerWidth,
height = innerHeight,
mouseX = 0,
mouseY = 0;
var
camera = {
x: 0,
y: 0,
update: function(obj) {
this.x = obj.x - width / 2;
this.y = obj.y - height / 2;
}
},
player = {
defaultMass: 54,
x: 0,
y: 0,
blobs: [],
update: function() {
for (var i = 0; i < this.blobs.length; i++) {
var x = mouseX + camera.x - this.blobs[i].x;
var y = mouseY + camera.y - this.blobs[i].y;
var length = Math.sqrt(Math.pow(x, 2) + Math.pow(y, 2));
var speed = 54 / this.blobs[i].mass;
this.blobs[i].velX = x / length * speed * Math.min(1, Math.pow(x / this.blobs[i].mass, 2));
this.blobs[i].velY = y / length * speed * Math.min(1, Math.pow(x / this.blobs[i].mass, 2));
this.blobs[i].x += this.blobs[i].velX;
this.blobs[i].y += this.blobs[i].velY;
for (var j = 0; j < this.blobs.length; j++) {
if (j != i && this.blobs[i] !== undefined) {
var blob1 = this.blobs[i];
var blob2 = this.blobs[j];
var x = blob2.x - blob1.x; // get the vector from blob1 to blob2
var y = blob2.y - blob1.y; //
var dist = Math.sqrt(x * x + y * y); // get the distance between the two blobs
if (dist < blob1.mass + blob2.mass) { // if the distance is less than the 2 radius
// if there is overlap move blob one along the line between the two the distance of the two radius
x /= dist; // normalize the vector. This makes the vector 1 unit long
y /= dist;
// multiplying the normalised vector by the correct distance between the two
// and subtracting that distance from the blob 2 give the new pos of
// blob 1
blob1.x = blob2.x - x * (blob1.mass + blob2.mass);
blob1.y = blob2.y - y * (blob1.mass + blob2.mass);
}
}
}
}
this.x += (mouseX - width / 2) / (width / 2) * 1;
this.y += (mouseY - height / 2) / (height / 2) * 1
},
split: function(cell) {
cell.mass /= 2;
this.blobs.push({
x: cell.x,
y: cell.y,
mass: cell.mass
});
},
draw: function() {
for (var i = 0; i < this.blobs.length; i++) {
ctx.fillStyle = "red";
ctx.beginPath();
ctx.arc(-camera.x + this.blobs[i].x, -camera.y + this.blobs[i].y, this.blobs[i].mass, 0, Math.PI * 2);
ctx.fill();
ctx.closePath();
}
}
};
function handleMouseMove(e) {
mouseX = e.clientX;
mouseY = e.clientY;
}
function setup() {
canvas = document.getElementById("game");
ctx = canvas.getContext("2d");
canvas.width = width;
canvas.height = height;
addEventListener("mousemove", handleMouseMove);
player.blobs.push({
x: 0,
y: 0,
mass: player.defaultMass
});
player.blobs.push({
x: 100,
y: 100,
mass: player.defaultMass / 2
});
player.blobs.push({
x: 100,
y: 100,
mass: player.defaultMass * 2
});
var loop = function() {
update();
draw();
requestAnimationFrame(loop);
}
requestAnimationFrame(loop);
}
function update() {
camera.update(player.blobs[0]);
player.update();
}
function draw() {
ctx.fillStyle = "#fff";
ctx.fillRect(0, 0, width, height);
player.draw();
}
setup();
body {
margin: 0;
padding: 0;
}
<canvas id="game">kindly update your browser.</canvas>

var
canvas,
ctx,
width = innerWidth,
height = innerHeight,
mouseX = 0,
mouseY = 0;
var
camera = {
x: 0,
y: 0,
update: function(obj) {
this.x = obj.x - width / 2;
this.y = obj.y - height / 2;
}
},
player = {
defaultMass: 54,
x: 0,
y: 0,
blobs: [],
update: function() {
for (var i = 0; i < this.blobs.length; i++) {
var x = mouseX + camera.x - this.blobs[i].x;
var y = mouseY + camera.y - this.blobs[i].y;
var length = Math.sqrt(Math.pow(x, 2) + Math.pow(y, 2));
var speed = 54 / this.blobs[i].mass;
this.blobs[i].velX = x / length * speed * Math.min(1, Math.pow(x / this.blobs[i].mass, 2));
this.blobs[i].velY = y / length * speed * Math.min(1, Math.pow(x / this.blobs[i].mass, 2));
this.blobs[i].x += this.blobs[i].velX;
this.blobs[i].y += this.blobs[i].velY;
for (var j = 0; j < this.blobs.length; j++) {
if (j != i && this.blobs[i] !== undefined) {
var blob1 = this.blobs[i];
var blob2 = this.blobs[j];
var dist = Math.sqrt(Math.pow(blob2.x - blob1.x, 2) + Math.pow(blob2.y - blob1.y, 2));
if (dist < blob1.mass + blob2.mass) {
if (this.blobs[i].x < this.blobs[j].x) {
this.blobs[i].x--;
} else if (this.blobs[i].x > this.blobs[j].x) {
this.blobs[i].x++;
}
if (this.blobs[i].y < this.blobs[j].y) {
this.blobs[i].y--;
} else if ((this.blobs[i].y > this.blobs[j].y)) {
this.blobs[i].y++;
}
}
}
}
}
this.x += (mouseX - width / 2) / (width / 2) * 1;
this.y += (mouseY - height / 2) / (height / 2) * 1
},
split: function(cell) {
cell.mass /= 2;
this.blobs.push({
x: cell.x,
y: cell.y,
mass: cell.mass
});
},
draw: function() {
for (var i = 0; i < this.blobs.length; i++) {
ctx.fillStyle = "red";
ctx.beginPath();
ctx.arc(-camera.x + this.blobs[i].x, -camera.y + this.blobs[i].y, this.blobs[i].mass, 0, Math.PI * 2);
ctx.fill();
ctx.closePath();
}
}
};
function handleMouseMove(e) {
mouseX = e.clientX;
mouseY = e.clientY;
}
function setup() {
canvas = document.getElementById("game");
ctx = canvas.getContext("2d");
canvas.width = width;
canvas.height = height;
addEventListener("mousemove", handleMouseMove);
player.blobs.push({
x: 0,
y: 0,
mass: player.defaultMass
});
player.blobs.push({
x: 100,
y: 100,
mass: player.defaultMass / 2
});
player.blobs.push({
x: 100,
y: 100,
mass: player.defaultMass * 2
});
var loop = function() {
update();
draw();
requestAnimationFrame(loop);
}
requestAnimationFrame(loop);
}
function update() {
camera.update(player.blobs[0]);
player.update();
}
function draw() {
ctx.fillStyle = "#fff";
ctx.fillRect(0, 0, width, height);
player.draw();
}
setup();
body {
margin: 0;
padding: 0;
}
<canvas id="game">kindly update your browser.</canvas>

Canvas onClick add to array

I got this HTML5 canvas project I'm struggling with.
Basically I'm trying to add a new particle on click.
And the particles is pushed to the particles array, but
the particle does not show. I can see that the particle is pushed to the array with the mouse coordinates, but it doesn't seem like the last particle is drawn.
What am I doing wrong?
See example.
// Request animation frame
var requestAnimationFrame = window.requestAnimationFrame ||
window.mozRequestAnimationFrame ||
window.webkitRequestAnimationFrame ||
window.msRequestAnimationFrame;
// Canvas
var canvas = document.getElementById('canvas');
var ctx = canvas.getContext('2d');
// Set full-screen
canvas.width = window.innerWidth;
canvas.height = window.innerHeight;
// Options
var num = 100; // Number of particles to draw
var size = 2; // Particle size
var color = '#dd64e6'; // Particle color
var min_speed = .3; // Particle min speed
var max_speed = 2; // Particle max speed
var dist = 100; // Max distance before line gets cut
var dist_sq = dist * dist; // Dist squared
var line_width = 2; // Line width
var background = '#181b23'; // Background color
var line_color = '#1d2631'; // Line color
var fps = 60;
var now, delta;
var then = Date.now();
var interval = 1000 / fps;
if (/Android|webOS|iPhone|iPad|iPod|BlackBerry|IEMobile|Opera Mini/i.test(navigator.userAgent)) {
num = 10;
fps = 29;
}
// Particles array
var particles = [];
for (var i = 0; i < num; i++) {
particles.push(
new create_particle(false, false)
);
}
// Lets animate the particle
function draw() {
// Loop
requestAnimationFrame(draw);
now = Date.now();
delta = now - then;
if (delta > interval) {
then = now - (delta % interval);
// Background
ctx.fillStyle = background;
ctx.fillRect(0, 0, canvas.width, canvas.height);
// Lets draw particles from the array now
draw_particles();
}
}
// Draw particles
function draw_particles() {
for (var t = 0; t < num; t++) {
// This particle
var p = particles[t];
for (var q = t + 1; q < num; q++) {
// Check X first, maybe we don't need to
// calculate Y
var x = particles[q].x - p.x;
if ((x *= x) < dist_sq) {
// Check passed, calculate Y
var y = particles[q].y - p.y;
if (x + (y * y) < dist_sq) {
// Check passed, draw line
draw_line(p.x, p.y, particles[q].x, particles[q].y);
}
}
}
// Color
ctx.fillStyle = color;
// Circle path
ctx.beginPath();
ctx.arc(p.x, p.y, p.radius, Math.PI * 2, false);
ctx.fill();
// Lets use the velocity now
p.x += p.vx;
p.y += p.vy;
// If there is only 1 particle
// show X, Y, and velocity
if (num === 1) {
ctx.fillText('Y:' + p.y, 20, 20);
ctx.fillText('X:' + p.x, 20, 40);
ctx.fillText('YV:' + p.vy, 20, 60);
ctx.fillText('XV:' + p.vx, 20, 80);
}
// To prevent the balls from moving out of the canvas
if (p.x < size) p.vx *= (p.vx / -p.vx);
if (p.y < size) p.vy *= (p.vy / -p.vy);
if (p.x > canvas.width - size) p.vx *= (-p.vx / p.vx);
if (p.y > canvas.height - size) p.vy *= (-p.vy / p.vy);
}
}
// Return a particle object
function create_particle(xPos, yPos) {
// Position
if (xPos == false && yPos == false) {
this.x = Math.random() * canvas.width;
this.y = Math.random() * canvas.height;
} else {
this.x = xPos;
this.y = yPos;
}
// Velocity
this.vx = random_int_between(min_speed, max_speed);
this.vy = random_int_between(min_speed, max_speed);
// Size
this.radius = size;
console.log('particle created at: ' + this.x + ', ' + this.y);
}
// Returns an random integer, positive or negative
// between the given value
function random_int_between(min, max) {
var num = Math.floor(Math.random() * max) - min;
num *= Math.floor(Math.random() * 2) == 1 ? 1 : -1;
return num;
}
// Draw a line between 2 particles
// given the particles x and y position
function draw_line(p_x, p_y, p2_x, p2_y) {
ctx.beginPath();
ctx.lineWidth = line_width;
ctx.strokeStyle = line_color;
ctx.moveTo(p_x, p_y);
ctx.lineTo(p2_x, p2_y);
ctx.stroke();
}
// When the canvas is clicked
// add new particle
function clicked(e) {
var mouseXpos, mouseYpos;
if (e.offsetX) {
mouseXpos = e.offsetX;
mouseYpos = e.offsetY;
} else if (e.layerX) {
mouseXpos = e.layerX;
mouseYpos = e.layerY;
}
particles.push(
new create_particle(mouseXpos, mouseYpos)
);
}
canvas.addEventListener('click', function(e) {
clicked(e);
}, false);
draw();
<!DOCTYPE html>
<html>
<head>
<style>
* {margin:0;padding:0;overflow:hidden;}
</style>
</head>
<body>
<canvas id="canvas">{{-- The background --}}</canvas>
</body>
</html>

Well since no one else answered this other than in a comment, I thought I would answer it so that others might not wonder about the same thing.
The problem is that you use a variable "num" to hold the number of particles. If you instead use "particles.length" you can
// Request animation frame
var requestAnimationFrame = window.requestAnimationFrame ||
window.mozRequestAnimationFrame ||
window.webkitRequestAnimationFrame ||
window.msRequestAnimationFrame;
// Canvas
var canvas = document.getElementById('canvas');
var ctx = canvas.getContext('2d');
// Set full-screen
canvas.width = window.innerWidth;
canvas.height = window.innerHeight;
// Options
var num = 100; // Number of particles to draw
var size = 2; // Particle size
var color = '#dd64e6'; // Particle color
var min_speed = .3; // Particle min speed
var max_speed = 2; // Particle max speed
var dist = 100; // Max distance before line gets cut
var dist_sq = dist * dist; // Dist squared
var line_width = 2; // Line width
var background = '#181b23'; // Background color
var line_color = '#1d2631'; // Line color
var fps = 60;
var now, delta;
var then = Date.now();
var interval = 1000 / fps;
if (/Android|webOS|iPhone|iPad|iPod|BlackBerry|IEMobile|Opera Mini/i.test(navigator.userAgent)) {
num = 10;
fps = 29;
}
// Particles array
var particles = [];
for (var i = 0; i < num; i++) {
particles.push(
new create_particle(false, false)
);
}
// Lets animate the particle
function draw() {
// Loop
requestAnimationFrame(draw);
now = Date.now();
delta = now - then;
if (delta > interval) {
then = now - (delta % interval);
// Background
ctx.fillStyle = background;
ctx.fillRect(0, 0, canvas.width, canvas.height);
// Lets draw particles from the array now
draw_particles();
}
}
// Draw particles
function draw_particles() {
for (var t = 0; t < particles.length; t++) {
// This particle
var p = particles[t];
for (var q = t + 1; q < particles.length; q++) {
// Check X first, maybe we don't need to
// calculate Y
var x = particles[q].x - p.x;
if ((x *= x) < dist_sq) {
// Check passed, calculate Y
var y = particles[q].y - p.y;
if (x + (y * y) < dist_sq) {
// Check passed, draw line
draw_line(p.x, p.y, particles[q].x, particles[q].y);
}
}
}
// Color
ctx.fillStyle = color;
// Circle path
ctx.beginPath();
ctx.arc(p.x, p.y, p.radius, Math.PI * 2, false);
ctx.fill();
// Lets use the velocity now
p.x += p.vx;
p.y += p.vy;
// If there is only 1 particle
// show X, Y, and velocity
if (num === 1) {
ctx.fillText('Y:' + p.y, 20, 20);
ctx.fillText('X:' + p.x, 20, 40);
ctx.fillText('YV:' + p.vy, 20, 60);
ctx.fillText('XV:' + p.vx, 20, 80);
}
// To prevent the balls from moving out of the canvas
if (p.x < size) p.vx *= (p.vx / -p.vx);
if (p.y < size) p.vy *= (p.vy / -p.vy);
if (p.x > canvas.width - size) p.vx *= (-p.vx / p.vx);
if (p.y > canvas.height - size) p.vy *= (-p.vy / p.vy);
}
}
// Return a particle object
function create_particle(xPos, yPos) {
// Position
if (xPos == false && yPos == false) {
this.x = Math.random() * canvas.width;
this.y = Math.random() * canvas.height;
} else {
this.x = xPos;
this.y = yPos;
}
// Velocity
this.vx = random_int_between(min_speed, max_speed);
this.vy = random_int_between(min_speed, max_speed);
// Size
this.radius = size;
console.log('particle created at: ' + this.x + ', ' + this.y);
}
// Returns an random integer, positive or negative
// between the given value
function random_int_between(min, max) {
var num = Math.floor(Math.random() * max) - min;
num *= Math.floor(Math.random() * 2) == 1 ? 1 : -1;
return num;
}
// Draw a line between 2 particles
// given the particles x and y position
function draw_line(p_x, p_y, p2_x, p2_y) {
ctx.beginPath();
ctx.lineWidth = line_width;
ctx.strokeStyle = line_color;
ctx.moveTo(p_x, p_y);
ctx.lineTo(p2_x, p2_y);
ctx.stroke();
}
// When the canvas is clicked
// add new particle
function clicked(e) {
var mouseXpos, mouseYpos;
if (e.offsetX) {
mouseXpos = e.offsetX;
mouseYpos = e.offsetY;
} else if (e.layerX) {
mouseXpos = e.layerX;
mouseYpos = e.layerY;
}
particles.push(
new create_particle(mouseXpos, mouseYpos)
);
}
canvas.addEventListener('click', function(e) {
clicked(e);
}, false);
draw();
<!DOCTYPE html>
<html>
<head>
<style>
* {margin:0;padding:0;overflow:hidden;}
</style>
</head>
<body>
<canvas id="canvas">{{-- The background --}}</canvas>
</body>
</html>
I will dare to go outside the scope of our problem because you could prevent such issues in the future by utilizing Array.prototype.forEach, and move the drawing of the dots and constrain them to new functions. With the added benefit of simplifying your code.
// Draw particles
function draw_particles() {
particles.forEach(function(p,pi){
particles.forEach(function(p2,p2i){
if(pi === p2i){
return;
}
// Check X first, maybe we don't need to
// calculate Y
var x = p2.x - p.x;
if ((x *= x) < dist_sq) {
// Check passed, calculate Y
var y = p2.y - p.y;
if (x + (y * y) < dist_sq) {
// Check passed, draw line
draw_line(p.x, p.y, p2.x, p2.y);
draw_dot(p);
constrain(p);
}
}
});
});
}
// Draw particle
function draw_dot(p){
// Color
ctx.fillStyle = color;
// Circle path
ctx.beginPath();
ctx.arc(p.x, p.y, p.radius, Math.PI * 2, false);
ctx.fill();
ctx.closePath();
// Lets use the velocity now
p.x += p.vx;
p.y += p.vy;
// If there is only 1 particle
// show X, Y, and velocity
if (particles.length === 1) {
ctx.fillText('Y:' + p.y, 20, 20);
ctx.fillText('X:' + p.x, 20, 40);
ctx.fillText('YV:' + p.vy, 20, 60);
ctx.fillText('XV:' + p.vx, 20, 80);
}
}
// Constrain particle movement
function constrain(p){
// To prevent the balls from moving out of the canvas
if (p.x < size) p.vx *= (p.vx / -p.vx);
if (p.y < size) p.vy *= (p.vy / -p.vy);
if (p.x > canvas.width - size) p.vx *= (-p.vx / p.vx);
if (p.y > canvas.height - size) p.vy *= (-p.vy / p.vy);
}
Using Array.prototype.length and Array.prototype.forEach reduces the risk of heading into issues of array indices.

How do I allow a 2D shape to wrap around a canvas using WebGL?

I have created a simple animation in WebGL (html & javascript) where a 2D shape is animated and manipulated on a canvas. The default animation is shape moving to the right at a set speed and then using "WASD" changes its direction. The shape moves in the given direction indefinitely, even after it is off of the canvas and out of the clip-space. I would like to have the shape wrap around the canvas instead of just continuing even after it is unseen. For example, if the shape is moving to the right and moves completely off of the canvas, I would like it to appear on left side still moving to the right and continue cycling. Same goes for if it is moving left or up or down.
Any suggestions on how to implement this?

You have to draw it 2 to 4 times depending on if you want to wrap both left/right and top/bottom
Assume we only want to wrap around horizontally. If the player is near the left edge we need to also draw the player 1 screen width to the right. If the player is near the right edge we need to draw the player again one screen to the left. Same with up and down
Here's an example using canvas 2D but the only difference for WebGL is you'd draw using WebGL. The concept is the same.
Example:
var x = 150;
var y = 100;
var vx = 0;
var vy = 0;
const maxSpeed = 250;
const acceleration = 1000;
const ctx = document.querySelector("canvas").getContext("2d");
const keys = {};
const LEFT = 65;
const RIGHT = 68;
const DOWN = 83;
const UP = 87;
const width = ctx.canvas.width;
const height = ctx.canvas.height;
var then = 0;
function render(now) {
now *= 0.001; // seconds
const deltaTime = now - then;
then = now;
ctx.clearRect(0, 0, width, height);
if (keys[UP]) { vy -= acceleration * deltaTime; }
if (keys[DOWN]) { vy += acceleration * deltaTime; }
if (keys[LEFT]) { vx -= acceleration * deltaTime; }
if (keys[RIGHT]) { vx += acceleration * deltaTime; }
// keep speed under max
vx = absmin(vx, maxSpeed);
vy = absmin(vy, maxSpeed);
// move based on velociy
x += vx * deltaTime;
y += vy * deltaTime;
// wrap
x = euclideanModulo(x, width);
y = euclideanModulo(y, height);
// draw player 4 times
const xoff = x < width / 2 ? width : -width;
const yoff = y < height / 2 ? height : -height;
drawPlayer(x, y);
drawPlayer(x + xoff, y);
drawPlayer(x, y + yoff);
drawPlayer(x + xoff, y + yoff);
requestAnimationFrame(render);
}
requestAnimationFrame(render);
function drawPlayer(x, y) {
ctx.fillStyle = "blue";
ctx.strokeStyle = "red";
ctx.lineWidth = 4;
ctx.beginPath();
ctx.arc(x, y, 20, 0, Math.PI * 2, false);
ctx.fill();
ctx.stroke();
}
function absmin(v, max) {
return Math.min(Math.abs(v), max) * Math.sign(v);
}
function euclideanModulo(n, m) {
return ((n % m) + m) % m;
}
window.addEventListener('keydown', e => {
keys[e.keyCode] = true;
});
window.addEventListener('keyup', e => {
keys[e.keyCode] = false;
});
canvas {
display: block;
border: 1px solid black;
}
<canvas></canvas>
<p><span style="color:red;">click here</span> then use ASWD to move</p>
A WebGL version changes no code related to wrapping.
var x = 150;
var y = 100;
var vx = 0;
var vy = 0;
const maxSpeed = 250;
const acceleration = 1000;
const gl = document.querySelector("canvas").getContext("webgl");
const keys = {};
const LEFT = 65;
const RIGHT = 68;
const DOWN = 83;
const UP = 87;
const width = gl.canvas.width;
const height = gl.canvas.height;
var program = setupWebGL();
var positionLoc = gl.getAttribLocation(program, "position");
var then = 0;
function render(now) {
now *= 0.001; // seconds
const deltaTime = now - then;
then = now;
if (keys[UP]) { vy -= acceleration * deltaTime; }
if (keys[DOWN]) { vy += acceleration * deltaTime; }
if (keys[LEFT]) { vx -= acceleration * deltaTime; }
if (keys[RIGHT]) { vx += acceleration * deltaTime; }
// keep speed under max
vx = absmin(vx, maxSpeed);
vy = absmin(vy, maxSpeed);
// move based on velociy
x += vx * deltaTime;
y += vy * deltaTime;
// wrap
x = euclideanModulo(x, width);
y = euclideanModulo(y, height);
// draw player 4 times
const xoff = x < width / 2 ? width : -width;
const yoff = y < height / 2 ? height : -height;
drawPlayer(x, y);
drawPlayer(x + xoff, y);
drawPlayer(x, y + yoff);
drawPlayer(x + xoff, y + yoff);
requestAnimationFrame(render);
}
requestAnimationFrame(render);
function drawPlayer(x, y) {
gl.useProgram(program);
// only drawing a single point so no need to use a buffer
gl.vertexAttrib2f(
positionLoc,
x / width * 2 - 1,
y / height * -2 + 1);
gl.drawArrays(gl.POINTS, 0, 1);
}
function absmin(v, max) {
return Math.min(Math.abs(v), max) * Math.sign(v);
}
function euclideanModulo(n, m) {
return ((n % m) + m) % m;
}
window.addEventListener('keydown', e => {
keys[e.keyCode] = true;
});
window.addEventListener('keyup', e => {
keys[e.keyCode] = false;
});
function setupWebGL() {
const vs = `
attribute vec4 position;
void main() {
gl_Position = position;
gl_PointSize = 40.;
}
`;
const fs = `
void main() {
gl_FragColor = vec4(1,0,1,1);
}
`;
// compiles and links shaders and assigns position to location 0
return twgl.createProgramFromSources(gl, [vs, fs]);
}
canvas {
display: block;
border: 1px solid black;
}
<canvas></canvas>
<p><span style="color:red;">click here</span> then use ASWD to move</p>
<script src="https://twgljs.org/dist/3.x/twgl-full.min.js"></script>
If you don't want the player appear on both sides then your question has nothing to do with graphics, you just wait until the player's x position is at least screenWidth + haflPlayerWidth which means they're completely off the right side and then you set their x position to -halfPlayerWidth which will put them just off the left and visa versa
var x = 150;
var y = 100;
var vx = 0;
var vy = 0;
const maxSpeed = 250;
const acceleration = 1000;
const ctx = document.querySelector("canvas").getContext("2d");
const keys = {};
const LEFT = 65;
const RIGHT = 68;
const DOWN = 83;
const UP = 87;
const width = ctx.canvas.width;
const height = ctx.canvas.height;
const playerSize = 40;
const halfPlayerSize = playerSize / 2;
var then = 0;
function render(now) {
now *= 0.001; // seconds
const deltaTime = now - then;
then = now;
ctx.clearRect(0, 0, width, height);
if (keys[UP]) { vy -= acceleration * deltaTime; }
if (keys[DOWN]) { vy += acceleration * deltaTime; }
if (keys[LEFT]) { vx -= acceleration * deltaTime; }
if (keys[RIGHT]) { vx += acceleration * deltaTime; }
// keep speed under max
vx = absmin(vx, maxSpeed);
vy = absmin(vy, maxSpeed);
// move based on velociy
x += vx * deltaTime;
y += vy * deltaTime;
// wrap
x = euclideanModulo(x + halfPlayerSize, width + playerSize) - halfPlayerSize;
y = euclideanModulo(y + halfPlayerSize, height + playerSize) - halfPlayerSize;
// draw player
drawPlayer(x, y);
requestAnimationFrame(render);
}
requestAnimationFrame(render);
function drawPlayer(x, y) {
ctx.fillStyle = "blue";
ctx.strokeStyle = "red";
ctx.lineWidth = 4;
ctx.beginPath();
ctx.arc(x, y, halfPlayerSize, 0, Math.PI * 2, false);
ctx.fill();
ctx.stroke();
}
function absmin(v, max) {
return Math.min(Math.abs(v), max) * Math.sign(v);
}
function euclideanModulo(n, m) {
return ((n % m) + m) % m;
}
window.addEventListener('keydown', e => {
keys[e.keyCode] = true;
});
window.addEventListener('keyup', e => {
keys[e.keyCode] = false;
});
canvas {
display: block;
border: 1px solid black;
}
<canvas></canvas>
<p><span style="color:red;">click here</span> then use ASWD to move</p>
this code probably needs an explanation
x = euclideanModulo(x + haflPlayerSize, width + playerSize) - haflPlayerSize;
y = euclideanModulo(y + haflPlayerSize, height + playerSize) - haflPlayerSize;
First off euclideanModulo is just like normal % modulo operator, it returns the remainder after division, except euclidean modulo keeps the same remainder even for negative numbers. In other words
3 % 5 = 3
8 % 5 = 3
13 % 5 = 3
-2 % 5 = -2
-7 % 5 = -2
-12 % 5 = -2
but
3 euclideanMod 5 = 3
8 euclideanMod 5 = 3
13 euclideanMod 5 = 3
-2 euclideanMod 5 = 3
-7 euclideanMod 5 = 3
-12 euclideanMod 5 = 3
So it's a super easy way to wrap things.
x = euclideanModulo(x, screenWidth)
Is similar to
if (x < 0) x += screenWidth;
if (x >= screenWidth) x -= screenWidth;
Except those would fail if x > screenWidth * 2 for example where as the one using euclideanModulo would not.
So, back to
x = euclideanModulo(x + haflPlayerSize, width + playerSize) - haflPlayerSize;
y = euclideanModulo(y + haflPlayerSize, height + playerSize) - haflPlayerSize;
We know the player (in this case a circle) has its position at its center. So, we know when its center is half the playerSize off the left or right of the screen it's completely off the screen and we therefore want to move it to the other side. That means we can imagine the screen is really width + halfPlayerSize + halfPlayerSize wide. The first halfPlayerSize is for the stepping off the left side, the second halfPlayerSize is for stepping off the right side. In other words it's just width + playerSize wide. We then want the player to wrap from left to right when x < -halfPlayerSize. So we add halfPlayerSize to the player's position, then do the euclideanModulo which will wrap the position, then subtract that halfPlayerSize back out.

Determine when number has stopped increasing

You're in a javascript loop:
The loop spits out random numbers increasing or decreasing by 1. It starts at 10 and begins to loop:
10, 9, 8, 7, 6, 7, 8, 9, 8, 7, 6, 5, 4, 3, 4, 5, 6, 7, 6
I want to log the peak numbers. So in the list above that would be 10, 9, 7
So I assume I would need to log the last 3 numbers as the script loops. 2 numbers ago(a), 1 number ago(b), current number(c) and check if c<b && a<b then log b if that turned out to be true.
I'm unsure of how to actually store those 3 numbers without them being overwritten. So say I did let current = [current number]; because it's a loop that would always be the current number, but how would I store the previous 2 numbers without having them constant be overwritten while remaining in the loop?
UPDATE:
I'm trying to grab the y value for when the ball bounces highest. So if it bounces 3 times I would have 3 y values (when the ball reached its peak 3 times).
The numbers are being logged in the console.
*** Run the code in full page view
'use strict';
// Todo
// - Make the ball spin
// - Make the ball squish
// - Add speed lines
// - Clear only the ball not the whole canvas
(function () {
const canvas = document.getElementsByClassName('canvas')[0],
c = canvas.getContext('2d');
// -----------------------------------
// Resize the canvas to be full screen
// -----------------------------------
window.addEventListener('resize', resizeCanvas, false);
function resizeCanvas() {
canvas.width = window.innerWidth;
canvas.height = window.innerHeight;
// ---------
// Variables
// ---------
var circleRadius = 40,
circleHeight = circleRadius * 2,
x = (canvas.width/2) - circleRadius, // inital x position of the ball
y = (canvas.height/2) - circleRadius, // inital y position of the ball
fallHeight = y,
vx = 0, // velocity
vy = 0, // velocity
groundHeight = circleHeight,
bouncePoints = [],
gravity = 0.8,
dampening = 0.5,
pullStrength = 0.04,
segments = 4,
bezieCircleFormula = (4/3)*Math.tan(Math.PI/(2*segments)), // http://stackoverflow.com/a/27863181/2040509
pointOffset = {
positive: bezieCircleFormula*circleRadius,
negative: circleRadius-(bezieCircleFormula*circleRadius)
},
// Each side has 3 points, bezier 1, circle point, bezier 2
// These are listed below in clockwise order.
// So top has: left bezier, circle point, right bezier
// Right has: top bezier, circle point, bottom bezier
circlePoints = {
top: [
[x+pointOffset.negative, y],
[x+circleRadius, y],
[x+pointOffset.positive+circleRadius, y]
],
right: [
[x+circleHeight, y+pointOffset.negative],
[x+circleHeight, y+circleRadius],
[x+circleHeight, y+pointOffset.positive+circleRadius]
],
bottom: [
[x+pointOffset.positive+circleRadius, y+circleHeight],
[x+circleRadius, y+circleHeight],
[x+pointOffset.negative, y+circleHeight]
],
left: [
[x, y+pointOffset.positive+circleRadius],
[x, y+circleRadius],
[x, y+pointOffset.negative]
]
};
// --------------------
// Ball squish function
// --------------------
// For `side` you can pass `top`, `right`, `bottom`, `left`
// For `amount` use an interger
function squish (side, squishAmount) {
for (let i = 0; i < circlePoints[side].length; i++) {
if (side === 'top') {
circlePoints[side][i][1] += squishAmount;
} else if (side === 'right') {
circlePoints[side][i][0] -= squishAmount;
} else if (side === 'bottom') {
circlePoints[side][i][1] -= squishAmount;
} else if (side === 'left') {
circlePoints[side][i][0] += squishAmount;
}
}
}
// ------------------
// Animation Function
// ------------------
function render () {
// Clear the canvas
c.clearRect(0, 0, canvas.width, canvas.height);
// -----------------
// Draw the elements
// -----------------
// Ground
c.beginPath();
c.fillStyle = '#9cccc8';
c.fillRect(0, canvas.height - groundHeight, canvas.width, groundHeight);
c.closePath();
// Shadow
let distanceFromGround = parseFloat(((y - canvas.height/2) + circleHeight) / (canvas.height/2 - groundHeight/2)).toFixed(4),
shadowWidth = circleRadius * (1-distanceFromGround+1),
shadowHeight = circleRadius/6 * (1-distanceFromGround+1),
shadowX = (x + circleRadius) - shadowWidth/2,
shadowY = canvas.height - groundHeight/2,
shadowOpacity = 0.15 * distanceFromGround; // The first value here represents the opacity that will be used when the ball is touching the ground
c.beginPath();
c.fillStyle = 'rgba(0,0,0, ' + shadowOpacity + ')';
c.moveTo(shadowX, shadowY);
c.bezierCurveTo(shadowX, shadowY - shadowHeight, shadowX + shadowWidth, shadowY - shadowHeight, shadowX + shadowWidth, shadowY);
c.bezierCurveTo(shadowX + shadowWidth, shadowY + shadowHeight, shadowX, shadowY + shadowHeight, shadowX, shadowY);
c.fill();
c.closePath();
// Bezier circle
c.beginPath();
c.fillStyle = '#cf2264';
c.moveTo(circlePoints.left[1][0], circlePoints.left[1][1]);
c.bezierCurveTo(circlePoints.left[2][0], circlePoints.left[2][1], circlePoints.top[0][0], circlePoints.top[0][1], circlePoints.top[1][0], circlePoints.top[1][1]);
c.bezierCurveTo(circlePoints.top[2][0], circlePoints.top[2][1], circlePoints.right[0][0], circlePoints.right[0][1], circlePoints.right[1][0], circlePoints.right[1][1]);
c.bezierCurveTo(circlePoints.right[2][0], circlePoints.right[2][1], circlePoints.bottom[0][0], circlePoints.bottom[0][1], circlePoints.bottom[1][0], circlePoints.bottom[1][1]);
c.bezierCurveTo(circlePoints.bottom[2][0], circlePoints.bottom[2][1], circlePoints.left[0][0], circlePoints.left[0][1], circlePoints.left[1][0], circlePoints.left[1][1]);
c.stroke();
c.closePath();
// -------------------------------
// Recalculate circle co-ordinates
// -------------------------------
circlePoints = {
top: [
[x+pointOffset.negative, y],
[x+circleRadius, y],
[x+pointOffset.positive+circleRadius, y]
],
right: [
[x+circleHeight, y+pointOffset.negative],
[x+circleHeight, y+circleRadius],
[x+circleHeight, y+pointOffset.positive+circleRadius]
],
bottom: [
[x+pointOffset.positive+circleRadius, y+circleHeight],
[x+circleRadius, y+circleHeight],
[x+pointOffset.negative, y+circleHeight]
],
left: [
[x, y+pointOffset.positive+circleRadius],
[x, y+circleRadius],
[x, y+pointOffset.negative]
]
};
// -----------------
// Animation Gravity
// -----------------
// Increment gravity
vy += gravity;
// Increment velocity
y += vy;
x += vx;
// ----------
// Boundaries
// ----------
// Bottom boundary
if (y + circleHeight > canvas.height - groundHeight/2) {
y = canvas.height - groundHeight/2 - circleHeight;
vy *= -1;
// Dampening
vy *= dampening;
vx *= dampening;
// If the Y velocity is less than the value below, stop the ball
if (vy > -2.4) {
dampening = 0;
}
fallHeight = fallHeight*dampening;
}
// Right boundary
if (x + circleHeight > canvas.width) {
x = canvas.width - circleHeight;
vx *= -1;
// Dampening
vy *= dampening;
vx *= dampening;
}
// Left boundary
if (x + circleHeight < 0 + circleHeight) {
x = 0;
vx *= -1;
// Dampening
vy *= dampening;
vx *= dampening;
}
// Top boundary
if (y < 0) {
y = 0;
vy *= -1;
// Dampening
vy *= dampening;
vx *= dampening;
}
console.log(y);
requestAnimationFrame(render);
}
// -----------
// Click event
// -----------
canvas.addEventListener('mousedown', function (e) {
let dx = e.pageX - x,
dy = e.pageY - y;
if (dampening === 0) {
dampening = 0.5;
}
vx += dx * pullStrength;
vy += dy * pullStrength;
});
render();
}
resizeCanvas();
})();
body{
margin: 0;
}
canvas {
background: #ddf6f5;
display: block;
}
<canvas class="canvas"></canvas>

for(var a=0,b=1,c=2; c < input.length;)
{
if(input[b] > input[a] && input[b] > input[c])
{
console.log(input[b]);
}
a++;b++;c++;
}

As I explained, push them into the array.
var nums = [10, 9, 8, 7, 6, 7, 8, 9, 8, 7, 6, 5, 4, 3, 4, 5, 6, 7, 6];
var peaks = [];
nums.forEach(function(val, index, arr){
var isPrevLess = index==0 || arr[index-1]<val, //is the last number less
isNextLess = index==arr.length-1 || arr[index+1]<val; //is the next number less
if (isPrevLess && isNextLess) { //if both are less it is a peak
peaks.push(val);
}
});
console.log(peaks);

If I understand correctly, array arr of length l has a peak at position i if any of these is fulfilled:
0 = i < l-1 and arr[i] > arr[i+1]
0 < i < l-1 and arr[i-1] < arr[i] > l-1
0 < i = l-1 and arr[i] > arr[i-1]
0 = i = l-1
Then, you can use
var peaks = arr.filter(function(n, i, a) {
return (i===0 || n > a[i-1]) && (i===a.length-1 || n > arr[i+1]);
});

You really should post a function that does what you say, then your attempt at a solution. Since that's missing…
function foo(startNum, count) {
var prev = -Infinity;
var sense = 'up';
var curr = startNum;
for (var i=0; i<count; i++) {
// Randomly add or subtract one from current
curr += Math.random() < 0.5? -1 : 1;
// If it's a peak, do something. If it's not a peak, do something else
if (sense == 'up' && curr < prev) { // Hit peak
document.write('<br>peak: ' + prev + ' going ' + sense);
} else {
document.write('<br>Not peak: ' + prev + ' going ' + sense);
}
// Prepare for next loop
sense = prev > curr? 'down' : prev < curr? 'up' : sense;
prev = curr;
}
}
foo(10,20);