Find how many columns and rows along a circle is - javascript

So the following code will make an array of circles. I want to be able to click on a circle and have a popup tell me how many rows and columns along that circle is starting from (1,1).
Does anyone know how to do this?
var c = document.getElementById("myCanvas");
var ctx = c.getContext("2d");
var gCanvasElement = ctx;
ctx.strokeStyle="#FF0000";
ctx.strokeRect(20,20,800,600);
// Positions are hardcoded to make sure that circle starts from the right place
var startX = 55;
var startY = 55;
console.clear();
for(var i=1;i<=8;i++){
console.group(i);
for(var j=1;j<=i;j++){
ctx.beginPath();
ctx.strokeStyle='green';
//radius is hardcoded to 30 for testing purpose
ctx.arc(startX*j + (j-1)*10,startY*i + (i-1)*10,30,0,2*Math.PI);
ctx.stroke();
//console log
console.group(j);
console.log(startX*j + (j-1)*10);
console.log(startY*i + (i-1)*10);
console.groupEnd(j);
}
console.groupEnd(i);
}

As I've written in my comment canvas is just a raster image. It does not store shapes unlike vector graphics (SVG). So you need to use math to find if the user clicked the circle or not.
http://jsfiddle.net/tarabyte/Jct6j/
function distance(x1, y1, x2, y2) { //helper to get distance between 2 points
return Math.sqrt((x2-x1)*(x2-x1) + (y2-y1)*(y2-y1));
}
function center(i) { //helper to get coordinates of i-th circle
return (i*2-1)*radius + (i-1)*step/2;
}
c.addEventListener('click', function(ev){ //click lister
var x = ev.pageX - c.offsetLeft - (startX - radius), //normalized coords
y = ev.pageY - c.offsetTop - (startY - radius), //normalized coords
grid = 2*radius + step/2,
i, j, d;
if(x < 0 || y < 0) { return;} //out of circles
//cell inside your grid
i = Math.ceil(x/grid);
j = Math.ceil(y/grid);
if(i > j) { return;} //out of circles
d = distance(x, y, center(i), center(j));
if(d > radius) {return;} //to far from center
console.log(i, j);
}, false);

Related

Javascript 3d Terrain Without Three.js

I have searched around but I can't find anything like what I'm trying to do that doesn't use Three.js in some way (I can't use Three.js because my computer is too old to support Webgl). Here's what I've got so far:
HTML:
<!DOCTYPE html>
<html>
<head>
<script type="text/javascript" src="terrain.js"></script>
<title>Terrain</title>
</head>
<body>
<canvas id="canvas" height="400" width="400"></canvas>
</body>
</html>
Javascript:
var canvas, ctx, row1 = [], row2 = [], intensity = 15, width = 20, height = 20, centery = 200, centerx = 200, minus, delta = 1.6, nu = .02;
window.onload = function() {
canvas = document.getElementById('canvas'), ctx = canvas.getContext('2d');
ctx.lineStyle = '#000'
for (var i = 0; i < height; i++) {
row2 = [];
minus = 200
for (var j = 0; j < width; j++) {
row2[j] = {
x: centerx - (minus * (delta * (nu * i))),
y: Math.floor(Math.random() * intensity) + (height * i)
}
minus -= height;
}
ctx.beginPath();
ctx.moveTo(row2[0].x,row2[0].y)
for (var k = 1; k < row2.length; k++) {
ctx.lineTo(row2[k].x,row2[k].y)
if (k == row2.length) {ctx.clostPath()}
}
ctx.stroke();
if (row1[0] && row2[0]) {
for (var l = 0; l < row2.length; l++) {
ctx.beginPath();
ctx.moveTo(row2[l].x,row2[l].y)
ctx.lineTo(row1[l].x,row1[l].y)
ctx.closePath();
ctx.stroke();
}
}
row1 = row2;
}
}
Currently, the result looks like a Christmas tree but I want it to look more like actual 3d wireframe terrain.
3D wire frame basics
3D can be done on any systems that can move pixels. Thought not by dedicated hardware Javascript can do alright if you are after simple 3d.
This answers shows how to create a mesh, rotate and move it, create a camera and move it, and project the whole lot onto the 2D canvas using simple moveTo, and lineTo calls.
This answer is a real rush job so apologies for the typos (if any) and messy code. Will clean it up in the come few days (if time permits). Any questions please do ask in the comments.
Update
I have not done any basic 3D for some time so having a little fun I have added to the answer with more comments in the code and added some extra functionality.
vec3 now has normalise, dot, cross functions.
mat now has lookat function and is ready for much more if needed.
mesh now maintains its own world matrix
Added box, and line that create box and line meshs
Created a second vector type vec3S (S for simple) that is just coordinates no functionality
Demo now shows how to add more objects, position them in the scene, use a lookat transform
Details about the code.
The code below is the basics of 3D. It has a mesh object to create objects out of 3D points (vertices) connected via lines.
Simple transformation for rotating, moving and scaling a model so it can be placed in the scene.
A very very basic camera that can only look forward, move up,down, left,right, in and out. And the focal length can be changed.
Only for lines as there is no depth sorting.
The demo does not clip to the camera front plane, but rather just ignores lines that have any part behind the camera;
You will have to work out the rest from the comments, 3D is a big subject and any one of the features is worth a question / answer all its own.
Oh and coordinates in 3D are origin in center of canvas. Y positive down, x positive right, and z positive into the screen. projection is basic so when you have perspective set to 400 than a object at 400 units out from camera will have a one to one match with pixel size.
var ctx = canvas.getContext("2d");
// some usage of vecs does not need the added functionality
// and will use the basic version
const vec3Basic = { x : 0, y : 0, z: 0};
const vec3Def = {
// Sets the vector scalars
// Has two signatures
// setVal(x,y,z) sets vector to {x,y,z}
// setVal(vec) set this vector to vec
setVal(x,y = x.y,z = x.z + (x = x.x) * 0){
this.x = x;
this.y = y;
this.z = z;
},
// subtract v from this vector
// Has two signatures
// setVal(v) subtract v from this returning a new vec3
// setVal(v,vec) subtract v from this returning result in retVec
sub(v,retVec = vec3()){
retVec.x = this.x - v.x;
retVec.y = this.y - v.y;
retVec.z = this.z - v.z;
return retVec;
},
// Cross product of two vectors this and v.
// Cross product can be thought of as get the vector
// that is perpendicular to the plane described by the two vector we are crossing
// Has two signatures
// cross(vec); // returns a new vec3 as the cross product of this and vec
// cross(vec, retVec); // set retVec as the cross product
cross (v, retVec = vec3()){
retVec.x = this.y * v.z - this.z * v.y;
retVec.y = this.z * v.x - this.x * v.z;
retVec.z = this.x * v.y - this.y * v.x;
return retVec;
},
// Dot product
// Dot product of two vectors if both normalized can be thought of as finding the cos of the angle
// between two vectors. If not normalised the dot product will give you < 0 if v points away from
// the plane that this vector is perpendicular to, if > 0 the v points in the same direction as the
// plane perpendicular to this vector. if 0 then v is at 90 degs to the plane this is perpendicular to
// Using vector dot on its self is the same as getting the length squared
// dot(vec3); // returns a number as a float
dot (v){ return this.x * v.x + this.y * v.y + this.z * this.z },
// normalize normalizes a vector. A normalized vector has length equale to 1 unit
// Has two signitures
// normalise(); normalises this vector returning this
// normalize(retVec); normalises this vector but puts the normalised vector in retVec returning
// returning retVec. Thiis is unchanged.
normalize(retVec = this){
// could have used len = this.dot(this) but for speed all functions will do calcs internaly
const len = Math.sqrt(this.x * this.x + this.y * this.y + this.z * this.z);
// it is assumed that all vector are valid (have length) so no test is made to avoid
// the divide by zero that will happen for invalid vectors.
retVec.x = this.x / len;
retVec.y = this.y / len;
retVec.z = this.z / len;
}
}
// Created as a singleton to close over working constants
const matDef = (()=>{
// to seed up vector math the following closed over vectors are used
// rather than create and dispose of vectors for every operation needing them
// Currently not used
const V1 = vec3();
return {
// The matrix is just 3 pointers one for each axis
// They represent the direction and scale in 3D of each axis
// when you transform a point x,y,z you move x along the x axis,
// then y along y and z along the z axis
xAxis : null,
yAxis : null,
zAxis : null,
// this is a position x,y,z and represents where in 3D space an objects
// center coordinate (0,0,0) will be. It is simply added to a point
// after it has been moved along the 3 axis.
pos : null,
// This function does most of the 3D work in most 3D environments.
// It rotates, scales, translates, and a whole lot more.
// It is a cut down of the full 4 by 4 3D matrix you will find in
// Libraries like three.js
transformVec3(vec,retVec = {}){
retVec.x = vec.x * this.xAxis.x + vec.y * this.yAxis.x + vec.z * this.zAxis.x + this.pos.x;
retVec.y = vec.x * this.xAxis.y + vec.y * this.yAxis.y + vec.z * this.zAxis.y + this.pos.y;
retVec.z = vec.x * this.xAxis.z + vec.y * this.yAxis.z + vec.z * this.zAxis.z + this.pos.z;
return retVec;
},
// resets the matrix
identity(){ // default matrix
this.xAxis.setVal(1,0,0); // x 1 unit long in the x direction
this.yAxis.setVal(0,1,0); // y 1 unit long in the y direction
this.zAxis.setVal(0,0,1); // z 1 unit long in the z direction
this.pos.setVal(0,0,0); // and position at the origin.
},
init(){ // need to call this before using due to the way I create these
// objects.
this.xAxis = vec3(1,0,0);
this.yAxis = vec3(0,1,0);
this.zAxis = vec3(0,0,1);
this.pos = vec3(0,0,0);
return this; // must have this line for the constructor function to return
},
setRotateY(amount){
var x = Math.cos(amount);
var y = Math.sin(amount);
this.xAxis.x = x;
this.xAxis.y = 0;
this.xAxis.z = y;
this.zAxis.x = -y;
this.zAxis.y = 0;
this.zAxis.z = x;
},
// creates a look at transform from the current position
// point is a vec3.
// No check is made to see if look at is at pos which will invalidate this matrix
// Note scale is lost in this operation.
lookAt(point){
// zAxis along vector from pos to point
this.pos.sub(point,this.zAxis).normalize();
// use y as vertical reference
this.yAxis.x = 0;
this.yAxis.y = 1;
this.yAxis.z = 0;
// get x axis perpendicular to the plane described by z and y axis
// need to normalise as z and y axis may not be at 90 deg
this.yAxis.cross(this.zAxis,this.xAxis).normalize();
// Get the y axis that is perpendicular to z and x axis
// Normalise is not really needed but rounding errors can be problematic
// so the normalise just fixes some of the rounding errors.
this.zAxis.cross(this.xAxis,this.yAxis).normalize();
},
}
})();
// Mesh object has buffers for the
// model as verts
// transformed mesh as tVerts
// projected 2D verts as dVerts (d for display)
// An a array of lines. Each line has two indexes that point to the
// vert that define their ends.
// Buffers are all preallocated to stop GC slowing everything down.
const meshDef = {
addVert(vec){
this.verts.push(vec);
// vec3(vec) in next line makes a copy of the vec. This is important
// as using the same vert in the two buffers will result in strange happenings.
this.tVerts.push(vec3S(vec)); // transformed verts pre allocated so GC does not bite
this.dVerts.push({x:0,y:0}); // preallocated memory for displaying 2d projection
// when x and y are zero this means that it is not visible
return this.verts.length - 1;
},
addLine(index1,index2){
this.lines.push(index1,index2);
},
transform(matrix = this.matrix){
for(var i = 0; i < this.verts.length; i++){
matrix.transformVec3(this.verts[i],this.tVerts[i]);
}
},
eachVert(callback){
for(var i = 0; i < this.verts.length; i++){
callback(this.tVerts[i],i);
}
},
eachLine(callback){
for(var i = 0; i < this.lines.length; i+= 2){
var ind1 = this.lines[i];
var v1 = this.dVerts[ind1]; // get the start
if(v1.x !== 0 && v1.y !== 0){ // is valid
var ind2 = this.lines[i+ 1]; // get end of line
var v2 = this.dVerts[ind2];
if(v2.x !== 0 && v2.y !== 0){ // is valid
callback(v1,v2);
}
}
}
},
init(){ // need to call this befor using
this.verts = [];
this.lines = [];
this.dVerts = [];
this.tVerts = [];
this.matrix = mat();
return this; // must have this line for the construtor function to return
}
}
const cameraDef = {
projectMesh(mesh){ // create a 2D mesh
mesh.eachVert((vert,i)=>{
var z = (vert.z + this.position.z);
if(z < 0){ // is behind the camera then ignor it
mesh.dVerts[i].x = mesh.dVerts[i].y = 0;
}else{
var s = this.perspective / z;
mesh.dVerts[i].x = (vert.x + this.position.x) * s;
mesh.dVerts[i].y = (vert.y + this.position.y) * s;
}
})
},
drawMesh(mesh){ // renders the 2D mesh
ctx.beginPath();
mesh.eachLine((v1,v2)=>{
ctx.moveTo(v1.x,v1.y);
ctx.lineTo(v2.x,v2.y);
})
ctx.stroke();
}
}
// vec3S creates a basic (simple) vector
// 3 signatures
//vec3S(); // return vec 1,0,0
//vec3S(vec); // returns copy of vec
//vec3S(x,y,z); // returns {x,y,z}
function vec3S(x = {x:1,y:0,z:0},y = x.y ,z = x.z + (x = x.x) * 0){ // a 3d point
return Object.assign({},vec3Basic,{x, y, z});
}
// vec3S creates a basic (simple) vector
// 3 signatures
//vec3S(); // return vec 1,0,0
//vec3S(vec); // returns copy of vec
//vec3S(x,y,z); // returns {x,y,z}
function vec3(x = {x:1,y:0,z:0},y = x.y ,z = x.z + (x = x.x) * 0){ // a 3d point
return Object.assign({},vec3Def,{x,y,z});
}
function mat(){ // matrix used to rotate scale and move a 3d point
return Object.assign({},matDef).init();
}
function mesh(){ // this is for storing objects as points in 3d and lines conecting points
return Object.assign({},meshDef).init();
}
function camera(perspective,position){ // this is for displaying 3D
return Object.assign({},cameraDef,{perspective,position});
}
// grid is the number of grids x,z and size is the overal size for x
function createLandMesh(gridx,gridz,size,maxHeight){
var m = mesh(); // create a mesh
var hs = size/2 ;
var step = size / gridx;
for(var z = 0; z < gridz; z ++){
for(var x = 0; x < gridx; x ++){
// create a vertex. Y is random
m.addVert(vec3S(x * step - hs, (Math.random() * maxHeight), z * step-hs)); // create a vert
}
}
for(var z = 0; z < gridz-1; z ++){
for(var x = 0; x < gridx-1; x ++){
if(x < gridx -1){ // dont go past end
m.addLine(x + z * gridx,x + 1 + z * gridx); // add line across
}
if(z < gridz - 1){ // dont go past end
m.addLine(x + z * (gridx-1),x + 1 + (z + 1) * (gridx-1));
}
}
}
return m;
}
function createBoxMesh(size){
var s = size / 2;
var m = mesh(); // create a mesh
// add bottom
m.addVert(vec3S(-s,-s,-s));
m.addVert(vec3S( s,-s,-s));
m.addVert(vec3S( s, s,-s));
m.addVert(vec3S(-s, s,-s));
// add top verts
m.addVert(vec3S(-s,-s, s));
m.addVert(vec3S( s,-s, s));
m.addVert(vec3S( s, s, s));
m.addVert(vec3S(-s, s, s));
// add lines
/// bottom lines
m.addLine(0,1);
m.addLine(1,2);
m.addLine(2,3);
m.addLine(3,0);
/// top lines
m.addLine(4,5);
m.addLine(5,6);
m.addLine(6,7);
m.addLine(7,4);
// side lines
m.addLine(0,4);
m.addLine(1,5);
m.addLine(2,6);
m.addLine(3,7);
return m;
}
function createLineMesh(v1 = vec3S(),v2 = vec3S()){
const m = mesh();
m.addVert(v1);
m.addVert(v2);
m.addLine(0,1);
return m;
}
//Create a land mesh grid 20 by 20 and 400 units by 400 units in size
var land = createLandMesh(20,20,400,20); // create a land mesh
var box = createBoxMesh(50);
var box1 = createBoxMesh(25);
var line = createLineMesh(); // line conecting boxes
line.tVerts[0] = box.matrix.pos; // set the line transformed tVect[0] to box matrix.pos
line.tVerts[1] = box1.matrix.pos; // set the line transformed tVect[0] to box1 matrix.pos
var cam = camera(200,vec3(0,0,0)); // create a projection with focal len 200 and at 0,0,0
box.matrix.pos.setVal(0,-100,400);
box1.matrix.pos.setVal(0,-100,400);
land.matrix.pos.setVal(0,100,300); // move down 100, move away 300
var w = canvas.width;
var h = canvas.height;
var cw = w / 2; // center of canvas
var ch = h / 2;
function update(timer){
// next section just maintains canvas size and resets state and clears display
if (canvas.width !== innerWidth || canvas.height !== innerHeight) {
cw = (w = canvas.width = innerWidth) /2;
ch = (h = canvas.height = innerHeight) /2;
}
ctx.setTransform(1,0,0,1,0,0); // reset transform
ctx.globalAlpha = 1; // reset alpha
ctx.fillStyle = "black";
ctx.fillRect(0,0,canvas.width,canvas.height);
// end of standard canvas maintenance
// render from center of canvas by setting canvas origin to center
ctx.setTransform(1,0,0,1,canvas.width / 2,canvas.height / 2)
land.matrix.setRotateY(timer/1000); // set matrix to rotation position
land.transform();
// move the blue box
var t = timer/1000;
box1.matrix.pos.setVal(Math.sin(t / 2.1) * 100,Math.sin( t / 3.2) * 100, Math.sin(t /5.3) * 90+300);
// Make the cyan box look at the blue box
box.matrix.lookAt(box1.matrix.pos);
// Transform boxes from local to world space
box1.transform();
box.transform();
// set camera x,y pos to mouse pos;
cam.position.x = mouse.x - cw;
cam.position.y = mouse.y - ch;
// move in and out
if (mouse.buttonRaw === 1) { cam.position.z -= 1 }
if (mouse.buttonRaw === 4) {cam.position.z += 1 }
// Converts mesh transformed verts to 2D screen coordinates
cam.projectMesh(land);
cam.projectMesh(box);
cam.projectMesh(box1);
cam.projectMesh(line);
// Draw each mesh in turn
ctx.strokeStyle = "#0F0";
cam.drawMesh(land);
ctx.strokeStyle = "#0FF";
cam.drawMesh(box);
ctx.strokeStyle = "#00F";
cam.drawMesh(box1);
ctx.strokeStyle = "#F00";
cam.drawMesh(line);
ctx.setTransform(1,0,0,1,cw,ch / 4);
ctx.font = "20px arial";
ctx.textAlign = "center";
ctx.fillStyle = "yellow";
ctx.fillText("Move mouse to move camera. Left right mouse move in out",0,0)
requestAnimationFrame(update);
}
requestAnimationFrame(update);
// A mouse handler from old lib of mine just to give some interaction
// not needed for the 3d
var mouse = (function () {
var m; // alias for mouse
var mouse = {
x : 0, y : 0, // mouse position
buttonRaw : 0,
buttonOnMasks : [0b1, 0b10, 0b100], // mouse button on masks
buttonOffMasks : [0b110, 0b101, 0b011], // mouse button off masks
bounds : null,
event(e) {
m.bounds = m.element.getBoundingClientRect();
m.x = e.pageX - m.bounds.left - scrollX;
m.y = e.pageY - m.bounds.top - scrollY;
if (e.type === "mousedown") { m.buttonRaw |= m.buttonOnMasks[e.which - 1] }
else if (e.type === "mouseup") { m.buttonRaw &= m.buttonOffMasks[e.which - 1] }
e.preventDefault();
},
start(element) {
m.element = element === undefined ? document : element;
"mousemove,mousedown,mouseup".split(",").forEach(name => document.addEventListener(name, mouse.event) );
document.addEventListener("contextmenu", (e) => { e.preventDefault() }, false);
return mouse;
},
}
m = mouse;
return mouse;
})().start(canvas);
canvas { position:absolute; top : 0px; left : 0px;}
<canvas id="canvas"></canvas>

Rotating Images & Pixel Collision Detection

I've got this game in this plunker.
When the swords are not rotating, it all works fine (you can check by uncommenting lines 221 and commenting out 222-223). When they are rotating like in the plunker above, the collision doesn't work well.
I guess that's because the "getImageData" remembers the old images, but I gather it's an expensive thing to recalculate over and over again.
Is there a better way to rotate my images and make this work? Or do I have to recalculate their pixel map?
Code of the culprit:
for (var i = 0; i < monsters.length; i++) {
var monster = monsters[i];
if (monster.ready) {
if (imageCompletelyOutsideCanvas(monster, monster.monsterImage)) {
monster.remove = true;
}
//else {
//ctx.drawImage(monster.monsterImage, monster.x, monster.y);
drawRotatedImage(monster.monsterImage, monster.x, monster.y, monster);
monster.rotateCounter += 0.05;
//}
}
}
Geometric solution
To do this via a quicker geometry solution.
The simplest solution is a line segment with circle intersection algorithm.
Line segment.
A line has a start and end described in a variety of ways. In this case we will use the start and end coordinates.
var line = {
x1 : ?,
y1 : ?,
x2 : ?,
y2 : ?,
}
Circle
The circle is described by its location and radius
var circle = {
x : ?,
y : ?,
r : ?,
}
Circle line segment Intersect
The following describes how I test for the circle line segment collision. I don't know if there is a better way (most likely there is) but this has served me well and is reliable with the caveat that line segments must have length and circles must have area. If you can not guarantee this then you must add checks in the code to ensure you don't get divide by zeros.
Thus to test if a line intercepts the circle we first find out how far the closest point on the line (Note a line is infinite in size while a line segment has a length, start and end)
// a quick convertion of vars to make it easier to read.
var x1 = line.x1;
var y1 = line.y1;
var x2 = line.x2;
var y2 = line.y2;
var cx = circle.x;
var cy = circle.y;
var r = circle.r;
The result of the test, will be true if there is a collision.
var result; // the result of the test
Convert the line to a vector.
var vx = x2 - x1; // convert line to vector
var vy = y2 - y1;
var d2 = (vx * vx + vy * vy); // get the length squared
Get the unit distance from the circle of the near point on the line. The unit distance is a number from 0, to 1 (inclusive) and represents the distance along the vector of a point. if the value is less than 0 then the point is before the vector, if greater then 1 the point is past the end.
I know this by memory and forget the concept. Its the dot product of the line vector and the vector from the start of the line segment to the circle center divided by the line vectors length squared.
// dot product of two vectors is v1.x * v2.x + v1.y * v2.y over v1 length squared
u = ((cx - x1) * vx + (cy - y1) * vy) / d2;
Now use the unit position to get the actual coordinate of the point on the line closest to the circle by adding to the line segment start position the line vector times the unit distance.
// get the closest point
var xx = x1 + vx * u;
var yy = y1 + vy * u;
Now we have a point on the line, we calculate the distance from the circle using pythagoras square root of the sum of the two sides squared.
// get the distance from the circle center
var d = Math.hypot(xx - cx, yy - cy);
Now if the line (not line segment) intersects the circle the distance will be equal or less than the circle radius. Otherwise the is no intercept.
if(d > r){ //is the distance greater than the radius
result = false; // no intercept
} else { // else we need some more calculations
To determine if the line segment has intercepted the circle we need to find the two points on the circle's circumference that the line has crossed. We have the radius and the distance the circle is from the line. As the distance from the line is always at right angles we have a right triangle with the hypot being the radius and one side being the distance found.
Work out the missing length of the triangle. UPDATE see improved version of the code from here at bottom of answer under "update" it uses unit lengths rather than normalise the line vector.
// ld for line distance is the square root of the hyp subtract side squared
var ld = Math.sqrt(r * r - d * d);
Now add that distance to the point we found on the line xx, yy to do that normalise the line vector (makes the line vector one unit long) by dividing the line vector by its length, and then to multiply it by the distance found above
var len = Math.sqrt(d2); // get the line vector length
var nx = (vx / len) * ld;
var ny = (vy / len) * ld;
Some people may see that I could have used the Unit length and skipped a few calculations. Yes but I can be bothered rewriting the demo so will leave it as is
Now to get the to intercept points by adding and subtracting the new vector to the point on the line that is closest to the circle
ix1 = xx + nx; // the point furthest alone the line
iy1 = xx + ny;
ix2 = xx - nx; // the point in the other direction
iy2 = xx - ny;
Now that we have these two points we can work out if they are in the line segment but calculating the unit distance they are on the original line vector, using the dot product divide the squared distance.
var u1 = ((ix1 - x1) * vx + (iy1 - y1) * vy) / d2;
var u2 = ((ix2 - x1) * vx + (iy1 - y1) * vy) / d2;
Now some simple tests to see if the unit postion of these points are on the line segment
if(u1 < 0){ // is the forward intercept befor the line segment start
result = false; // no intercept
}else
if(u2 > 1){ // is the rear intercept after the line end
result = false; // no intercept
} else {
// though the line segment may not have intercepted the circle
// circumference if we have got to here it must meet the conditions
// of touching some part of the circle.
result = true;
}
}
Demo
As always here is a demo showing the logic in action. The circle is centered on the mouse. There are a few test lines that will go red if the circle touches them. It will also show the point where the circle circumference does cross the line. The point will be red if in the line segment or green if outside. These points can be use to add effects or what not
I am lazy today so this is straight from my library. Note I will post the improved math when I get a chance.
Update
I have improved the algorithm by using unit length to calculate the circle circumference intersects, eliminating a lot of code. I have added it to the demo as well.
From the Point where the distance from the line is less than the circle radius
// get the unit distance to the intercepts
var ld = Math.sqrt(r * r - d * d) / Math.sqrt(d2);
// get that points unit distance along the line
var u1 = u + ld;
var u2 = u - ld;
if(u1 < 0){ // is the forward intercept befor the line
result = false; // no intercept
}else
if(u2 > 1){ // is the backward intercept past the end of the line
result = false; // no intercept
}else{
result = true;
}
}
var demo = function(){
// the function described in the answer with extra stuff for the demo
// at the bottom you will find the function being used to test circle intercepts.
/** GeomDependancies.js begin **/
// for speeding up calculations.
// usage may vary from descriptions. See function for any special usage notes
var data = {
x:0, // coordinate
y:0,
x1:0, // 2nd coordinate if needed
y1:0,
u:0, // unit length
i:0, // index
d:0, // distance
d2:0, // distance squared
l:0, // length
nx:0, // normal vector
ny:0,
result:false, // boolean result
}
// make sure hypot is suported
if(typeof Math.hypot !== "function"){
Math.hypot = function(x, y){ return Math.sqrt(x * x + y * y);};
}
/** GeomDependancies.js end **/
/** LineSegCircleIntercept.js begin **/
// use data properties
// result // intercept bool for intercept
// x, y // forward intercept point on line **
// x1, y1 // backward intercept point on line
// u // unit distance of intercept mid point
// d2 // line seg length squared
// d // distance of closest point on line from circle
// i // bit 0 on for forward intercept on segment
// // bit 1 on for backward intercept
// ** x = null id intercept points dont exist
var lineSegCircleIntercept = function(ret, x1, y1, x2, y2, cx, cy, r){
var vx, vy, u, u1, u2, d, ld, len, xx, yy;
vx = x2 - x1; // convert line to vector
vy = y2 - y1;
ret.d2 = (vx * vx + vy * vy);
// get the unit distance of the near point on the line
ret.u = u = ((cx - x1) * vx + (cy - y1) * vy) / ret.d2;
xx = x1 + vx * u; // get the closest point
yy = y1 + vy * u;
// get the distance from the circle center
ret.d = d = Math.hypot(xx - cx, yy - cy);
if(d <= r){ // line is inside circle
// get the distance to the two intercept points
ld = Math.sqrt(r * r - d * d) / Math.sqrt(ret.d2);
// get that points unit distance along the line
u1 = u + ld;
if(u1 < 0){ // is the forward intercept befor the line
ret.result = false; // no intercept
return ret;
}
u2 = u - ld;
if(u2 > 1){ // is the backward intercept past the end of the line
ret.result = false; // no intercept
return ret;
}
ret.i = 0;
if(u1 <= 1){
ret.i += 1;
// get the forward point line intercepts the circle
ret.x = x1 + vx * u1;
ret.y = y1 + vy * u1;
}else{
ret.x = x2;
ret.y = y2;
}
if(u2 >= 0){
ret.x1 = x1 + vx * u2;
ret.y1 = y1 + vy * u2;
ret.i += 2;
}else{
ret.x1 = x1;
ret.y1 = y1;
}
// tough the points of intercept may not be on the line seg
// the closest point to the must be on the line segment
ret.result = true;
return ret;
}
ret.x = null; // flag that no intercept found at all;
ret.result = false; // no intercept
return ret;
}
/** LineSegCircleIntercept.js end **/
// mouse and canvas functions for this demo.
/** fullScreenCanvas.js begin **/
var canvas = (function(){
var canvas = document.getElementById("canv");
if(canvas !== null){
document.body.removeChild(canvas);
}
// creates a blank image with 2d context
canvas = document.createElement("canvas");
canvas.id = "canv";
canvas.width = window.innerWidth;
canvas.height = window.innerHeight;
canvas.style.position = "absolute";
canvas.style.top = "0px";
canvas.style.left = "0px";
canvas.style.zIndex = 1000;
canvas.ctx = canvas.getContext("2d");
document.body.appendChild(canvas);
return canvas;
})();
var ctx = canvas.ctx;
/** fullScreenCanvas.js end **/
/** MouseFull.js begin **/
var canvasMouseCallBack = undefined; // if needed
var mouse = (function(){
var mouse = {
x : 0, y : 0, w : 0, alt : false, shift : false, ctrl : false,
interfaceId : 0, buttonLastRaw : 0, buttonRaw : 0,
over : false, // mouse is over the element
bm : [1, 2, 4, 6, 5, 3], // masks for setting and clearing button raw bits;
getInterfaceId : function () { return this.interfaceId++; }, // For UI functions
startMouse:undefined,
};
function mouseMove(e) {
var t = e.type, m = mouse;
m.x = e.offsetX; m.y = e.offsetY;
if (m.x === undefined) { m.x = e.clientX; m.y = e.clientY; }
m.alt = e.altKey;m.shift = e.shiftKey;m.ctrl = e.ctrlKey;
if (t === "mousedown") { m.buttonRaw |= m.bm[e.which-1];
} else if (t === "mouseup") { m.buttonRaw &= m.bm[e.which + 2];
} else if (t === "mouseout") { m.buttonRaw = 0; m.over = false;
} else if (t === "mouseover") { m.over = true;
} else if (t === "mousewheel") { m.w = e.wheelDelta;
} else if (t === "DOMMouseScroll") { m.w = -e.detail;}
if (canvasMouseCallBack) { canvasMouseCallBack(m.x, m.y); }
e.preventDefault();
}
function startMouse(element){
if(element === undefined){
element = document;
}
"mousemove,mousedown,mouseup,mouseout,mouseover,mousewheel,DOMMouseScroll".split(",").forEach(
function(n){element.addEventListener(n, mouseMove);});
element.addEventListener("contextmenu", function (e) {e.preventDefault();}, false);
}
mouse.mouseStart = startMouse;
return mouse;
})();
if(typeof canvas === "undefined"){
mouse.mouseStart(canvas);
}else{
mouse.mouseStart();
}
/** MouseFull.js end **/
// helper function
function drawCircle(ctx,x,y,r,col,col1,lWidth){
if(col1){
ctx.lineWidth = lWidth;
ctx.strokeStyle = col1;
}
if(col){
ctx.fillStyle = col;
}
ctx.beginPath();
ctx.arc( x, y, r, 0, Math.PI*2);
if(col){
ctx.fill();
}
if(col1){
ctx.stroke();
}
}
// helper function
function drawLine(ctx,x1,y1,x2,y2,col,lWidth){
ctx.lineWidth = lWidth;
ctx.strokeStyle = col;
ctx.beginPath();
ctx.moveTo(x1,y1);
ctx.lineTo(x2,y2);
ctx.stroke();
}
var h = canvas.height;
var w = canvas.width;
var unit = Math.ceil(Math.sqrt(Math.hypot(w, h)) / 32);
const U80 = unit * 80;
const U60 = unit * 60;
const U40 = unit * 40;
const U10 = unit * 10;
var lines = [
{x1 : U80, y1 : U80, x2 : w /2, y2 : h - U80},
{x1 : w - U80, y1 : U80, x2 : w /2, y2 : h - U80},
{x1 : w / 2 - U10, y1 : h / 2 - U40, x2 : w /2, y2 : h/2 + U10 * 2},
{x1 : w / 2 + U10, y1 : h / 2 - U40, x2 : w /2, y2 : h/2 + U10 * 2},
];
function update(){
var i, l;
ctx.clearRect(0, 0, w, h);
drawCircle(ctx, mouse.x, mouse.y, U60, undefined, "black", unit * 3);
drawCircle(ctx, mouse.x, mouse.y, U60, undefined, "yellow", unit * 2);
for(i = 0; i < lines.length; i ++){
l = lines[i]
drawLine(ctx, l.x1, l.y1, l.x2, l.y2, "black" , unit * 3)
drawLine(ctx, l.x1, l.y1, l.x2, l.y2, "yellow" , unit * 2)
// test the lineSegment circle
data = lineSegCircleIntercept(data, l.x1, l.y1, l.x2, l.y2, mouse.x, mouse.y, U60);
// if there is a result display the result
if(data.result){
drawLine(ctx, l.x1, l.y1, l.x2, l.y2, "red" , unit * 2)
if((data.i & 1) === 1){
drawCircle(ctx, data.x, data.y, unit * 4, "white", "red", unit );
}else{
drawCircle(ctx, data.x, data.y, unit * 2, "white", "green", unit );
}
if((data.i & 2) === 2){
drawCircle(ctx, data.x1, data.y1, unit * 4, "white", "red", unit );
}else{
drawCircle(ctx, data.x1, data.y1, unit * 2, "white", "green", unit );
}
}
}
requestAnimationFrame(update);
}
update();
}
// resize if needed by just starting again
window.addEventListener("resize",demo);
// start the demo
demo();
... and here's how to find the sword blade lines when the sword is moved & rotated
Start by finding the vertices of the original sword blade and saving them in an array.
var pts=[{x:28,y:42},{x:69,y:3},{x:83,y:1},{x:83,y:19},{x:42,y:57}];
When the sword rotates, each blade vertex point will rotate around the rotation point. In your case the rotation point is the center of the image.
Gray rect is the rectangular border of the image
Blue dot is one sword vertex (at the tip of the blade)
Green dot is at the center of the image (== the rotation point)
Green line is the distance from center-image to vertex
Blue circle is the path the blade tip will follow as it rotates 360 degrees
The green line will change its angle depending on the image's rotation.
You can calculate the position of the blade tip at any angle of rotation like this:
// [cx,cy] = the image centerpoint (== the rotation point)
// [vx,vy] = the coordinate position of the blade tip
// Calculate the distance and the angle between the 2 points
var dx=vx-cx;
var dy=vy-cy;
var distance=Math.sqrt(dx*dx+dy*dy);
var originalAngle=Math.atan2(dy,dx);
// rotationAngle = the angle the image has been rotated expressed in radians
var rotatedX = cx + distance * Math.cos(originalAngle + rotationAngle);
var rotatedY = cy + distance * Math.sin(originalAngle + rotationAngle);
Here's example code and a Demo that tracks blade vertices while being moved and rotated:
var canvas=document.getElementById("canvas");
var ctx=canvas.getContext("2d");
var cw=canvas.width;
var ch=canvas.height;
function reOffset(){
var BB=canvas.getBoundingClientRect();
offsetX=BB.left;
offsetY=BB.top;
}
var offsetX,offsetY;
reOffset();
window.onscroll=function(e){ reOffset(); }
window.onresize=function(e){ reOffset(); }
var isDown=false;
var startX,startY;
var sword={
img:null,
rx:0,
ry:0,
angle:0,
pts:[{x:28,y:42},{x:69,y:3},{x:83,y:1},{x:83,y:19},{x:42,y:57}],
// precalculated properties -- for efficiency
radii:[],
angles:[],
halfWidth:0,
halfHeight:0,
//
initImg:function(img){
var PI2=Math.PI*2;
this.img=img;
this.halfWidth=img.width/2;
this.halfHeight=img.height/2;
for(var i=0;i<this.pts.length;i++){
var dx=this.halfWidth-this.pts[i].x;
var dy=this.halfHeight-this.pts[i].y;
this.radii[i]=Math.sqrt(dx*dx+dy*dy);
this.angles[i]=((Math.atan2(dy,dx)+PI2)%PI2)-Math.PI;
}
},
// draw sword with translation & rotation
draw:function(){
var img=this.img;
var rx=this.rx;
var ry=this.ry;
var angle=this.angle;
ctx.translate(rx,ry);
ctx.rotate(angle);
ctx.drawImage(img,-this.halfWidth,-this.halfHeight);
ctx.rotate(-angle);
ctx.translate(-rx,-ry);
},
// recalc this.pts after translation & rotation
calcTrxPts:function(){
var trxPts=[];
for(var i=0;i<this.pts.length;i++){
var r=this.radii[i];
var ptangle=this.angles[i]+this.angle;
trxPts[i]={
x:this.rx+r*Math.cos(ptangle),
y:this.ry+r*Math.sin(ptangle)
};
}
return(trxPts);
},
}
// load image & initialize sword object & draw scene
var img=new Image();
img.onload=function(){
// set initial sword properties
sword.initImg(img);
sword.rx=150;
sword.ry=75;
sword.angle=0; //(Math.PI/8);
// draw scene
drawAll();
// listen for mouse events
$("#canvas").mousedown(function(e){handleMouseDown(e);});
$("#canvas").mousemove(function(e){handleMouseMove(e);});
$("#canvas").mouseup(function(e){handleMouseUpOut(e);});
$("#canvas").mouseout(function(e){handleMouseUpOut(e);});
// listen for mousewheel events
$("#canvas").on('DOMMouseScroll mousewheel',function(e){
e.preventDefault();
e.stopPropagation();
var e=e || window.event; // old IE support
sign=((e.originalEvent.wheelDelta||e.originalEvent.detail*-1)>0)?1:-1;
sword.angle+=Math.PI/45*sign;
drawAll();
});
}
img.src = 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";
/////////////////////
// helper functions
/////////////////////
function drawAll(){
ctx.clearRect(0,0,cw,ch);
sword.draw();
drawHitArea();
}
function drawHitArea(){
// lines
var trxPts=sword.calcTrxPts();
ctx.beginPath();
ctx.moveTo(trxPts[0].x,trxPts[0].y);
for(var i=1;i<trxPts.length;i++){
ctx.lineTo(trxPts[i].x,trxPts[i].y);
}
ctx.closePath();
ctx.strokeStyle='red';
ctx.stroke();
// dots
for(var i=0;i<trxPts.length;i++){
ctx.beginPath();
ctx.arc(trxPts[i].x,trxPts[i].y,3,0,Math.PI*2);
ctx.closePath();
ctx.fillStyle='blue';
ctx.fill();
}
}
function getClosestPointOnLineSegment(line,x,y) {
//
lerp=function(a,b,x){ return(a+x*(b-a)); };
var dx=line.x1-line.x0;
var dy=line.y1-line.y0;
var t=((x-line.x0)*dx+(y-line.y0)*dy)/(dx*dx+dy*dy);
var lineX=lerp(line.x0, line.x1, t);
var lineY=lerp(line.y0, line.y1, t);
return({x:lineX,y:lineY,isOnSegment:(t>=0 && t<=1)});
};
function handleMouseDown(e){
// tell the browser we're handling this event
e.preventDefault();
e.stopPropagation();
startX=parseInt(e.clientX-offsetX);
startY=parseInt(e.clientY-offsetY);
// Put your mousedown stuff here
isDown=true;
}
function handleMouseUpOut(e){
// tell the browser we're handling this event
e.preventDefault();
e.stopPropagation();
// clear the isDragging flag
isDown=false;
}
function handleMouseMove(e){
if(!isDown){return;}
// tell the browser we're handling this event
e.preventDefault();
e.stopPropagation();
// calc distance moved since last drag
mouseX=parseInt(e.clientX-offsetX);
mouseY=parseInt(e.clientY-offsetY);
var dx=mouseX-startX;
var dy=mouseY-startY;
startX=mouseX;
startY=mouseY;
// drag the sword to new position
sword.rx+=dx;
sword.ry+=dy;
drawAll();
}
body{ background-color: ivory; }
#canvas{border:1px solid red; }
<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.9.1/jquery.min.js"></script>
<h6>Drag sword and<br>Rotate sword using mousewheel inside canvas<br>Red "collision" lines follow swords translation & rotation.</h6>
<h5></h5>
<canvas id="canvas" width=300 height=300></canvas>

How can canvas coordinates be converted into tile coordinates?

So I have a canvas with an isometric tile map drawn on it, which looks perfect.
In the event listener at the bottom of the script, I grab the cursor's coordinates inside the canvas. How could I find out which tile the cursor is hovering over?
var cs = document.getElementById('board');
var c = cs.getContext("2d")
var gridWidth=100
var gridHeight=50
var tilesX = 12, tilesY = 12;
var spriteWidth=gridWidth
var spriteHeight=img.height/img.width*gridWidth
cs.width = window.innerWidth //spriteWidth*10
cs.height = window.innerHeight //spriteHeight*10
var ox = cs.width/2-spriteWidth/2
var oy = (tilesY * gridHeight) / 2
window.onresize=function(){
cs.width = window.innerWidth //spriteWidth*10
cs.height = window.innerHeight //spriteHeight*10
ox = cs.width/2-spriteWidth/2
oy = (tilesY * gridHeight) / 2
draw()
}
draw();
function renderImage(x, y) {
c.drawImage(img, ox + (x - y) * spriteWidth/2, oy + (y + x) * gridHeight/2-(spriteHeight-gridHeight),spriteWidth,spriteHeight)
}
function draw(){
for(var x = 0; x < tilesX; x++) {
for(var y = 0; y < tilesY; y++) {
renderImage(x,y)
}
}
}
cs.addEventListener('mousemove', function(evt) {
var x = evt.clientX,
y = evt.clientY;
console.log('Mouse position: ' + x + ',' + y);
}, false);
Sorry for pasting such lengthy code, but all of it is there just to lay the isometric grid.
EDIT: Also, how could I get the top left coordinates of the tile image to relay it?
Assuming you've arranged your tiles where the leftmost column and topmost row are zero:
var column = parseInt(mouseX / tileWidth);
var row = parseInt(mouseY / tileHeight);
BTW, if you eventually move your canvas off the top-left of the page then you must adjust your mouse coordinates by the canvas offset.
Here's an example of how to calculate mouse position:
// references to the canvas element and its context
var canvas=document.getElementById("canvas");
var ctx=canvas.getContext("2d");
// get the offset position of the canvas on the web page
var BB=canvas.getBoundingClientRect();
var offsetX=BB.left;
var offsetY=BB.top;
// listen for mousedown events
canvas.onmousedown=handleMousedown;
function handleMousedown(e){
// tell the browser we will handle this event
e.preventDefault();
e.stopPropagation();
// calculate the mouse position
var mouseX=e.clientX-offsetX;
var mouseY=e.clientY-offsetY;
}

Canvas javascript event based on a object

I need to do an action onclick of a particular (point) or a rectangle in a canvas.
Example:
$(document).ready(function(){
var canvas = $('#myCanvas').get(0);
if (!canvas.getContext) { return; }
var ctx = canvas.getContext('2d');
ctx.fillRect(150,140,8,8);
ctx.fillRect(200,120,8,8);
ctx.fillRect(200,160,8,8);
});
I need to connect two points with a line and another two points with a curve using javascript .How can i do this?
You need to maintain the regions yourselves. There are no objects on a canvas, only pixels and the browser does not know anything about it.
Demo here
You can do something like this (simplified):
// define the regions - common for draw/redraw and check
var rect1 = [150,140,8,8];
var rect2 = [200,120,8,8];
var rect3 = [200,160,8,8];
var regions = [rect1, rect2, rect3];
Now on your init you can use the same array to render all the rectangles:
$(document).ready(function(){
var canvas = $('#myCanvas').get(0);
if (!canvas.getContext) { return; }
var ctx = canvas.getContext('2d');
//use the array also to render the boxes
for (var i = 0, r; r = regions[i]; i++) {
ctx.fillRect(r[0],r[1],r[2],r[3]);
}
});
On the click event you check the array to see if the mouse coordinate (corrected for canvas) is inside any of the rectangles:
$('#myCanvas').on('click', function(e){
var pos = getMousePos(this, e);
// check if we got a hit
for (var i = 0, r; r = regions[i]; i++) {
if (pos.x >= r[0] && pos.x <= (r[0] + r[2]) &&
pos.y >= r[1] && pos.y <= (r[1] + r[3])) {
alert('Region ' + i + ' was hit');
}
}
});
//get mouse position relative to canvas
function getMousePos(canvas, evt) {
var rect = canvas.getBoundingClientRect();
return {
x: evt.clientX - rect.left,
y: evt.clientY - rect.top
};
}
Also remember to redraw the canvas if the window is re-sized or for other reason clears the canvas (browser dialogs etc.).
To connect the boxes you need to store the first hit position and when you get a second hit draw a line between them.
Demo with lines here
Add to the global vars and also make canvas and context available from global (see fiddle for related modifications in onready):
var x1 = -1, y1;
var canvas = myCanvas;
var ctx = canvas.getContext('2d');
And in the click event:
$('#myCanvas').on('click', function(e){
var pos = getMousePos(this, e);
for (var i = 0, r; r = regions[i]; i++) {
if (pos.x >= r[0] && pos.x <= (r[0] + r[2]) &&
pos.y >= r[1] && pos.y <= (r[1] + r[3])) {
//first hit? then store the coords
if (x1 === -1) {
x1 = pos.x;
y1 = pos.y;
} else {
//draw line from first point to this
ctx.beginPath();
ctx.moveTo(x1, y1);
ctx.lineTo(pos.x, pos.y);
ctx.stroke();
x1 = -1; //reset (or keep if you want continuous lines).
};
}
}
});

Using midpoint circle algorithm to generate points of a filled circle

I need to generate and store the coordinates of each point of a filled circle of say, radius 10 in Javascript.
It seems like the best way to do this would be to use the midpoint circle algorithm, but I'm not sure how to adapt it to find every point in the circle. The coordinates are going to be stored as objects in an array.
Could someone help me with the implementation?
Personally I think it would probably be faster in this case to test all pixels in the bounding box for their distance to the center. If <= r then the point is in the circle and should be pushed onto your array.
function distance(p1, p2)
{
dx = p2.x - p1.x; dx *= dx;
dy = p2.y - p1.y; dy *= dy;
return Math.sqrt( dx + dy );
}
function getPoints(x, y, r)
{
var ret = [];
for (var j=x-r; j<=x+r; j++)
for (var k=y-r; k<=y+r; k++)
if (distance({x:j,y:k},{x:x,y:y}) <= r) ret.push({x:j,y:k});
return ret;
}
You loop through all the possible points and you run the Point-In-Circle check on them.
Something like the following would suffice...
var result = [];
var d = 10;
var r = d / 2;
var rr = r*r;
for(var y=0; y<d; y++)
for(var x=0; x<d; x++)
if((x-r)*(x-r)+(y-r)*(y-r) < rr)
result.push({"x": x, "y": y});
Modifying the above algorithm to handle other (more complex) shapes/path/polygons would be difficult. For a more generic solution you could use HTML5 CANVAS. You create a canvas, get the 2d context draw all of your shapes/paths/polygons in solid black then iterate through the pixel data and find the pixels with an alpha channel greater than 0 (or 127 if you want to alleviate false positives from anti-aliasing).
var r = 5; // radius of bounding circle
//
// set up a canvas element
//
var canvas = document.createElement("canvas");
canvas.width = r*2;
canvas.height = r*2;
canvas.style.width = (r*2) + "px";
canvas.style.height = (r*2) + "px";
var ctx = canvas.getContext("2d");
ctx.fillStyle = "#000";
//
// draw your shapes/paths/polys here
//
ctx.beginPath();
ctx.arc(r, r, r, 0, Math.PI*2, true);
ctx.closePath();
ctx.fill();
//
// process the pixel data
//
var imageData = ctx.getImageData(0,0,(r*2),(r*2));
var data = imageData.data;
var result = [];
var str = "";
for(var y = 0; y<(r*2); y++) {
for(var x = 0; x<(r*2); x++) {
var pixelOffset = (y * (r*2) + x) * 4;
if(data[pixelOffset+3] > 127) {
result.push({x: x, y: y});
str += "(" + x + ", " + y + ") "; // debug
}
}
}
//
// debug/test output
//
document.body.innerHTML += str;
document.body.appendChild(canvas);
alert(result.length);

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