I'm trying to pixelate an animation.. I have a .png image where I cut in frames. I have a scrollbar who gives a number, which is the new size of every pixel. (rasterSize)
I already did it for an image and it's working.
http://bht-homework.com/RMA/PIX_PRES1/
But for animation it looks like doesn't calculate the first pixels.
http://bht-homework.com/RMA/PIX_PRES2/
var imgData=context.getImageData(0,0,img.width,img.height);// width is 190,height 240
for (var x = 0; x < spriteSizeWidth; x++) {
for (var y = 0; y < spriteSizeHeight; y++) {
var rasterX = ((x / rasterSize) | 0) * rasterSize;
var rasterY = ((y / rasterSize) | 0) * rasterSize;
var rasterValIndex = (rasterX + rasterY * imgData.width) * 4;
r=imgData.data[rasterValIndex];
g=imgData.data[rasterValIndex + 1];
b=imgData.data[rasterValIndex + 2];
a=imgData.data[rasterValIndex + 3];
context.fillStyle="rgba(" +r+","+g+","+b+","+a+")";
context.fillRect(x,y,rasterSize,rasterSize);
}
}
Does someone has an idea how to fix it?
Thanks!
Though it might look as it would skip the first few pixels of your image, it actually just draws the blocks at the wrong position. It's offset by rasterSize.
You need to shift back the pixels to the correct position.
So simply replace
context.fillRect(x, y, rasterSize, rasterSize);
by
context.fillRect(x - rasterSize, y - rasterSize, rasterSize, rasterSize);
Every rectangle has x and y coordinates, width and height.
The total width of the screen is maxWidth and total height is maxHeight.
I have an array containing all the already drawn rectangles.
I am working on an web App where users will be drawing rectangles on the screen using their mouse. For that I am using Javascript to draw on the canvas element.
The challenge is that the rectangles must not intersect at any given point.
I am trying to avoid this kind of case:
or this:
This is how the output I am aiming for should look like:
What I basically need is an Algorithm (preferably in JavaScript) that can help locating enough space to draw a rectangle knowing its axis, height and width.
BM67 Box packing.
This is a method I use to pack rectangles. I made it up myself to create sprite sheets.
How it works.
You maintain two arrays, one holds rectangles of available spaces (space array), and the other rectangles you have placed.
You start by adding to the space array a rectangle that covers the whole area to be filled. This rectangle represents available space.
When you add a rectangle to fit you search the available space rectangles for a rectangle that will fit the new rectangle. If you can not find a rectangle that is bigger or sane size as the one you want to add there is no room.
Once you have found a place to put the rectangle, check all the available space rectangles to see if any of them overlap the new added rectangle. If any overlap you slice it up along the top, bottom, left and right, resulting in up to 4 new space rectangles. There are some optimisation when you do this to keep the number of rectangles down but it will work without the optimisations.
It's not that complicated and reasonably efficient compared to some other methods. It is particularly good when the space starts to run low.
Example
Below is a demo of it filling the canvas with random rectangles. It's on a animation loop to show the process, so is very much slowed down.
Gray boxes are the ones to fit. Red show the current spacer boxes. Each box has a 2 pixel margin. See top of code for demo constants.
Click the canvas to restart.
const boxes = []; // added boxes
const spaceBoxes = []; // free space boxes
const space = 2; // space between boxes
const minW = 4; // min width and height of boxes
const minH = 4;
const maxS = 50; // max width and height
// Demo only
const addCount = 2; // number to add per render cycle
const ctx = canvas.getContext("2d");
canvas.width = canvas.height = 1024;
// create a random integer
const randI = (min, max = min + (min = 0)) => (Math.random() * (max - min) + min) | 0;
// itterates an array
const eachOf = (array, cb) => { var i = 0; const len = array.length; while (i < len && cb(array[i], i++, len) !== true ); };
// resets boxes
function start(){
boxes.length = 0;
spaceBoxes.length = 0;
spaceBoxes.push({
x : space, y : space,
w : canvas.width - space * 2,
h : canvas.height - space * 2,
});
}
// creates a random box without a position
function createBox(){
return { w : randI(minW,maxS), h : randI(minH,maxS) }
}
// cuts box to make space for cutter (cutter is a box)
function cutBox(box,cutter){
var b = [];
// cut left
if(cutter.x - box.x - space > minW){
b.push({
x : box.x, y : box.y,
w : cutter.x - box.x - space,
h : box.h,
})
}
// cut top
if(cutter.y - box.y - space > minH){
b.push({
x : box.x, y : box.y,
w : box.w,
h : cutter.y - box.y - space,
})
}
// cut right
if((box.x + box.w) - (cutter.x + cutter.w + space) > space + minW){
b.push({
x : cutter.x + cutter.w + space,
y : box.y,
w : (box.x + box.w) - (cutter.x + cutter.w + space),
h : box.h,
})
}
// cut bottom
if((box.y + box.h) - (cutter.y + cutter.h + space) > space + minH){
b.push({
x : box.x,
y : cutter.y + cutter.h + space,
w : box.w,
h : (box.y + box.h) - (cutter.y + cutter.h + space),
})
}
return b;
}
// get the index of the spacer box that is closest in size to box
function findBestFitBox(box){
var smallest = Infinity;
var boxFound;
eachOf(spaceBoxes,(sbox,index)=>{
if(sbox.w >= box.w && sbox.h >= box.h){
var area = sbox.w * sbox.h;
if(area < smallest){
smallest = area;
boxFound = index;
}
}
})
return boxFound;
}
// returns an array of boxes that are touching box
// removes the boxes from the spacer array
function getTouching(box){
var b = [];
for(var i = 0; i < spaceBoxes.length; i++){
var sbox = spaceBoxes[i];
if(!(sbox.x > box.x + box.w + space || sbox.x + sbox.w < box.x - space ||
sbox.y > box.y + box.h + space || sbox.y + sbox.h < box.y - space )){
b.push(spaceBoxes.splice(i--,1)[0])
}
}
return b;
}
// Adds a space box to the spacer array.
// Check if it is insid, too small, or can be joined to another befor adding.
// will not add if not needed.
function addSpacerBox(box){
var dontAdd = false;
// is to small?
if(box.w < minW || box.h < minH){ return }
// is same or inside another
eachOf(spaceBoxes,sbox=>{
if(box.x >= sbox.x && box.x + box.w <= sbox.x + sbox.w &&
box.y >= sbox.y && box.y + box.h <= sbox.y + sbox.h ){
dontAdd = true;
return true;
}
})
if(!dontAdd){
var join = false;
// check if it can be joinded with another
eachOf(spaceBoxes,sbox=>{
if(box.x === sbox.x && box.w === sbox.w &&
!(box.y > sbox.y + sbox.h || box.y + box.h < sbox.y)){
join = true;
var y = Math.min(sbox.y,box.y);
var h = Math.max(sbox.y + sbox.h,box.y + box.h);
sbox.y = y;
sbox.h = h-y;
return true;
}
if(box.y === sbox.y && box.h === sbox.h &&
!(box.x > sbox.x + sbox.w || box.x + box.w < sbox.x)){
join = true;
var x = Math.min(sbox.x,box.x);
var w = Math.max(sbox.x + sbox.w,box.x + box.w);
sbox.x = x;
sbox.w = w-x;
return true;
}
})
if(!join){ spaceBoxes.push(box) }// add to spacer array
}
}
// Adds a box by finding a space to fit.
function locateSpace(box){
if(boxes.length === 0){ // first box can go in top left
box.x = space;
box.y = space;
boxes.push(box);
var sb = spaceBoxes.pop();
spaceBoxes.push(...cutBox(sb,box));
}else{
var bf = findBestFitBox(box); // get the best fit space
if(bf !== undefined){
var sb = spaceBoxes.splice(bf,1)[0]; // remove the best fit spacer
box.x = sb.x; // use it to position the box
box.y = sb.y;
spaceBoxes.push(...cutBox(sb,box)); // slice the spacer box and add slices back to spacer array
boxes.push(box); // add the box
var tb = getTouching(box); // find all touching spacer boxes
while(tb.length > 0){ // and slice them if needed
eachOf(cutBox(tb.pop(),box),b => addSpacerBox(b));
}
}
}
}
// draws a box array
function drawBoxes(list,col,col1){
eachOf(list,box=>{
if(col1){
ctx.fillStyle = col1;
ctx.fillRect(box.x+ 1,box.y+1,box.w-2,box.h - 2);
}
ctx.fillStyle = col;
ctx.fillRect(box.x,box.y,box.w,1);
ctx.fillRect(box.x,box.y,1,box.h);
ctx.fillRect(box.x+box.w-1,box.y,1,box.h);
ctx.fillRect(box.x,box.y+ box.h-1,box.w,1);
})
}
// Show the process in action
ctx.clearRect(0,0,canvas.width,canvas.height);
var count = 0;
var handle = setTimeout(doIt,10);
start()
function doIt(){
ctx.clearRect(0,0,canvas.width,canvas.height);
for(var i = 0; i < addCount; i++){
var box = createBox();
locateSpace(box);
}
drawBoxes(boxes,"black","#CCC");
drawBoxes(spaceBoxes,"red");
if(count < 1214 && spaceBoxes.length > 0){
count += 1;
handle = setTimeout(doIt,10);
}
}
canvas.onclick = function(){
clearTimeout(handle);
start();
handle = setTimeout(doIt,10);
count = 0;
}
canvas { border : 2px solid black; }
<canvas id="canvas"></canvas>
Update
Improving on the above algorithm.
Turned algorithm into an object
Improved speed by finding better fitting spacer via weighting the fit on the aspect ratio
Added placeBox(box) function that adds a box without checking if it fits. It will be placed at its box.x, box.y coordinates
See code example below on usage.
Example
The example is the same as the above example but have added randomly place boxes before fitting boxes.
Demo displays the boxes and spacer boxes as it goes to show how it works. Click the canvas to restart. Hold [shift] key and click canvas to restart without displaying intermediate results.
Pre placed boxes are blue.
Fitted boxes are gray.
Spacing boxes are red and will overlap.
When holding shift the fitting process is stopped at the first box tat does not fit. The red boxes will show area that are available but unused.
When showing progress the function will keep adding boxes ignoring non fitting boxes until out of room.
const minW = 4; // min width and height of boxes
const minH = 4;
const maxS = 50; // max width and height
const space = 2;
const numberBoxesToPlace = 20; // number of boxes to place befor fitting
const fixedBoxColor = "blue";
// Demo only
const addCount = 2; // number to add per render cycle
const ctx = canvas.getContext("2d");
canvas.width = canvas.height = 1024;
// create a random integer randI(n) return random val 0-n randI(n,m) returns random int n-m, and iterator that can break
const randI = (min, max = min + (min = 0)) => (Math.random() * (max - min) + min) | 0;
const eachOf = (array, cb) => { var i = 0; const len = array.length; while (i < len && cb(array[i], i++, len) !== true ); };
// creates a random box. If place is true the box also gets a x,y position and is flaged as fixed
function createBox(place){
if(place){
const box = {
w : randI(minW*4,maxS*4),
h : randI(minH*4,maxS*4),
fixed : true,
}
box.x = randI(space, canvas.width - box.w - space * 2);
box.y = randI(space, canvas.height - box.h - space * 2);
return box;
}
return {
w : randI(minW,maxS),
h : randI(minH,maxS),
}
}
//======================================================================
// BoxArea object using BM67 box packing algorithum
// https://stackoverflow.com/questions/45681299/algorithm-locating-enough-space-to-draw-a-rectangle-given-the-x-and-y-axis-of
// Please leave this and the above two lines with any copies of this code.
//======================================================================
//
// usage
// var area = new BoxArea({
// x: ?, // x,y,width height of area
// y: ?,
// width: ?,
// height : ?.
// space : ?, // optional default = 1 sets the spacing between boxes
// minW : ?, // optional default = 0 sets the in width of expected box. Note this is for optimisation you can add smaller but it may fail
// minH : ?, // optional default = 0 sets the in height of expected box. Note this is for optimisation you can add smaller but it may fail
// });
//
// Add a box at a location. Not checked for fit or overlap
// area.placeBox({x : 100, y : 100, w ; 100, h :100});
//
// Tries to fit a box. If the box does not fit returns false
// if(area.fitBox({x : 100, y : 100, w ; 100, h :100})){ // box added
//
// Resets the BoxArea removing all boxes
// area.reset()
//
// To check if the area is full
// area.isFull(); // returns true if there is no room of any more boxes.
//
// You can check if a box can fit at a specific location with
// area.isBoxTouching({x : 100, y : 100, w ; 100, h :100}, area.boxes)){ // box is touching another box
//
// To get a list of spacer boxes. Note this is a copy of the array, changing it will not effect the functionality of BoxArea
// const spacerArray = area.getSpacers();
//
// Use it to get the max min box size that will fit
//
// const maxWidthThatFits = spacerArray.sort((a,b) => b.w - a.w)[0];
// const minHeightThatFits = spacerArray.sort((a,b) => a.h - b.h)[0];
// const minAreaThatFits = spacerArray.sort((a,b) => (a.w * a.h) - (b.w * b.h))[0];
//
// The following properties are available
// area.boxes // an array of boxes that have been added
// x,y,width,height // the area that boxes are fitted to
const BoxArea = (()=>{
const defaultSettings = {
minW : 0, // min expected size of a box
minH : 0,
space : 1, // spacing between boxes
};
const eachOf = (array, cb) => { var i = 0; const len = array.length; while (i < len && cb(array[i], i++, len) !== true ); };
function BoxArea(settings){
settings = Object.assign({},defaultSettings,settings);
this.width = settings.width;
this.height = settings.height;
this.x = settings.x;
this.y = settings.y;
const space = settings.space;
const minW = settings.minW;
const minH = settings.minH;
const boxes = []; // added boxes
const spaceBoxes = [];
this.boxes = boxes;
// cuts box to make space for cutter (cutter is a box)
function cutBox(box,cutter){
var b = [];
// cut left
if(cutter.x - box.x - space >= minW){
b.push({
x : box.x, y : box.y, h : box.h,
w : cutter.x - box.x - space,
});
}
// cut top
if(cutter.y - box.y - space >= minH){
b.push({
x : box.x, y : box.y, w : box.w,
h : cutter.y - box.y - space,
});
}
// cut right
if((box.x + box.w) - (cutter.x + cutter.w + space) >= space + minW){
b.push({
y : box.y, h : box.h,
x : cutter.x + cutter.w + space,
w : (box.x + box.w) - (cutter.x + cutter.w + space),
});
}
// cut bottom
if((box.y + box.h) - (cutter.y + cutter.h + space) >= space + minH){
b.push({
w : box.w, x : box.x,
y : cutter.y + cutter.h + space,
h : (box.y + box.h) - (cutter.y + cutter.h + space),
});
}
return b;
}
// get the index of the spacer box that is closest in size and aspect to box
function findBestFitBox(box, array = spaceBoxes){
var smallest = Infinity;
var boxFound;
var aspect = box.w / box.h;
eachOf(array, (sbox, index) => {
if(sbox.w >= box.w && sbox.h >= box.h){
var area = ( sbox.w * sbox.h) * (1 + Math.abs(aspect - (sbox.w / sbox.h)));
if(area < smallest){
smallest = area;
boxFound = index;
}
}
})
return boxFound;
}
// Exposed helper function
// returns true if box is touching any boxes in array
// else return false
this.isBoxTouching = function(box, array = []){
for(var i = 0; i < array.length; i++){
var sbox = array[i];
if(!(sbox.x > box.x + box.w + space || sbox.x + sbox.w < box.x - space ||
sbox.y > box.y + box.h + space || sbox.y + sbox.h < box.y - space )){
return true;
}
}
return false;
}
// returns an array of boxes that are touching box
// removes the boxes from the array
function getTouching(box, array = spaceBoxes){
var boxes = [];
for(var i = 0; i < array.length; i++){
var sbox = array[i];
if(!(sbox.x > box.x + box.w + space || sbox.x + sbox.w < box.x - space ||
sbox.y > box.y + box.h + space || sbox.y + sbox.h < box.y - space )){
boxes.push(array.splice(i--,1)[0])
}
}
return boxes;
}
// Adds a space box to the spacer array.
// Check if it is inside, too small, or can be joined to another befor adding.
// will not add if not needed.
function addSpacerBox(box, array = spaceBoxes){
var dontAdd = false;
// is box to0 small?
if(box.w < minW || box.h < minH){ return }
// is box same or inside another box
eachOf(array, sbox => {
if(box.x >= sbox.x && box.x + box.w <= sbox.x + sbox.w &&
box.y >= sbox.y && box.y + box.h <= sbox.y + sbox.h ){
dontAdd = true;
return true; // exits eachOf (like a break statement);
}
})
if(!dontAdd){
var join = false;
// check if it can be joined with another
eachOf(array, sbox => {
if(box.x === sbox.x && box.w === sbox.w &&
!(box.y > sbox.y + sbox.h || box.y + box.h < sbox.y)){
join = true;
var y = Math.min(sbox.y,box.y);
var h = Math.max(sbox.y + sbox.h,box.y + box.h);
sbox.y = y;
sbox.h = h-y;
return true; // exits eachOf (like a break statement);
}
if(box.y === sbox.y && box.h === sbox.h &&
!(box.x > sbox.x + sbox.w || box.x + box.w < sbox.x)){
join = true;
var x = Math.min(sbox.x,box.x);
var w = Math.max(sbox.x + sbox.w,box.x + box.w);
sbox.x = x;
sbox.w = w-x;
return true; // exits eachOf (like a break statement);
}
})
if(!join){ array.push(box) }// add to spacer array
}
}
// Adds a box by finding a space to fit.
// returns true if the box has been added
// returns false if there was no room.
this.fitBox = function(box){
if(boxes.length === 0){ // first box can go in top left
box.x = space;
box.y = space;
boxes.push(box);
var sb = spaceBoxes.pop();
spaceBoxes.push(...cutBox(sb,box));
}else{
var bf = findBestFitBox(box); // get the best fit space
if(bf !== undefined){
var sb = spaceBoxes.splice(bf,1)[0]; // remove the best fit spacer
box.x = sb.x; // use it to position the box
box.y = sb.y;
spaceBoxes.push(...cutBox(sb,box)); // slice the spacer box and add slices back to spacer array
boxes.push(box); // add the box
var tb = getTouching(box); // find all touching spacer boxes
while(tb.length > 0){ // and slice them if needed
eachOf(cutBox(tb.pop(),box),b => addSpacerBox(b));
}
} else {
return false;
}
}
return true;
}
// Adds a box at location box.x, box.y
// does not check if it can fit or for overlap.
this.placeBox = function(box){
boxes.push(box); // add the box
var tb = getTouching(box); // find all touching spacer boxes
while(tb.length > 0){ // and slice them if needed
eachOf(cutBox(tb.pop(),box),b => addSpacerBox(b));
}
}
// returns a copy of the spacer array
this.getSpacers = function(){
return [...spaceBoxes];
}
this.isFull = function(){
return spaceBoxes.length === 0;
}
// resets boxes
this.reset = function(){
boxes.length = 0;
spaceBoxes.length = 0;
spaceBoxes.push({
x : this.x + space, y : this.y + space,
w : this.width - space * 2,
h : this.height - space * 2,
});
}
this.reset();
}
return BoxArea;
})();
// draws a box array
function drawBoxes(list,col,col1){
eachOf(list,box=>{
if(col1){
ctx.fillStyle = box.fixed ? fixedBoxColor : col1;
ctx.fillRect(box.x+ 1,box.y+1,box.w-2,box.h - 2);
}
ctx.fillStyle = col;
ctx.fillRect(box.x,box.y,box.w,1);
ctx.fillRect(box.x,box.y,1,box.h);
ctx.fillRect(box.x+box.w-1,box.y,1,box.h);
ctx.fillRect(box.x,box.y+ box.h-1,box.w,1);
})
}
// Show the process in action
ctx.clearRect(0,0,canvas.width,canvas.height);
var count = 0;
var failedCount = 0;
var timeoutHandle;
var addQuick = false;
// create a new box area
const area = new BoxArea({x : 0, y : 0, width : canvas.width, height : canvas.height, space : space, minW : minW, minH : minH});
// fit boxes until a box cant fit or count over count limit
function doIt(){
ctx.clearRect(0,0,canvas.width,canvas.height);
if(addQuick){
while(area.fitBox(createBox()));
count = 2000;
}else{
for(var i = 0; i < addCount; i++){
if(!area.fitBox(createBox())){
failedCount += 1;
break;
}
}
}
drawBoxes(area.boxes,"black","#CCC");
drawBoxes(area.getSpacers(),"red");
if(count < 5214 && !area.isFull()){
count += 1;
timeoutHandle = setTimeout(doIt,10);
}
}
// resets the area places some fixed boxes and starts the fitting cycle.
function start(event){
clearTimeout(timeoutHandle);
area.reset();
failedCount = 0;
for(var i = 0; i < numberBoxesToPlace; i++){
var box = createBox(true); // create a fixed box
if(!area.isBoxTouching(box,area.boxes)){
area.placeBox(box);
}
}
if(event && event.shiftKey){
addQuick = true;
}else{
addQuick = false;
}
timeoutHandle = setTimeout(doIt,10);
count = 0;
}
canvas.onclick = start;
start();
body {font-family : arial;}
canvas { border : 2px solid black; }
.info {position: absolute; z-index : 200; top : 16px; left : 16px; background : rgba(255,255,255,0.75);}
<div class="info">Click canvas to reset. Shift click to add without showing progress.</div>
<canvas id="canvas"></canvas>
Try the following:
iterate through the existing rectangles from top to bottom, based on the top boundary of each existing rectangle
while proceeding in top-to-bottom order, maintain a list of "active rectangles":
adding each succeeding rectangle based on its top boundary as an active rectangle, and
removing active rectangles based on their bottom boundary
(you can do this efficiently by using a priority queue)
also keep track of the gaps between active rectangles:
adding an active rectangle will end all gaps that overlap it, and (assuming it doesn't overlap any existing rectangles) start a new gap on each side
removing an active rectangle will add a new gap (without ending any)
note that multiple active gaps may overlap each other -- you can't count on having exactly one gap between active rectangles!
Check your new rectangle (the one you want to place) against all gaps. Each gap is itself a rectangle; you can place your new rectangle if it fits entirely inside some gap.
This kind of method is called a sweep-line algorithm.
You may have to check whether your current point is inside the area of any of the current rectangles. You can use the following code to test that (stolen from here)
In the array you are having, store the rectangle details in the following way
var point = {x: 1, y: 2};
var rectangle = {x1: 0, x2: 10, y1: 1, y2: 7};
Following will be your function to test whether any given point is inside any given rectangle.
function isPointInsideRectangle(p, r) {
return
p.x > r.x1 &&
p.x < r.x2 &&
p.y > r.y1 &&
p.y < r.y2;
}
I am not sure how you are going to implement this -
On mouse down
Always during drawing (This may be too much of a work).
On mouse up (this will be my preference. You can cancel the drawing if the test did not pass, with possible explanation for the user somewhere in the canvas)
Hope this will get you starting.
I'm building a website which uses jQuery to allow users to add widgets to a page, drag them around and resize them (the page is fixed width and infinite height.) The issue that I'm having is that when adding a new widget to the page I have to find a free space for it (the widgets cannot overlap and I'd like to favour spaces at the top of the page.)
I've been looking at various packing algorithms and none of them seem to be suitable. The reason why is that they are designed for packing all of the objects in to the container, this means that all of the previous rectangles are laid out in a uniform way. They often line up an edge of the rectangle so that they form rows/columns, this simplifies working out what will fit where in the next row/column. When the user can move/resize widgets at will these algorithms don't work well.
I thought that I had a partial solution but after writing some pseudo code in here I’ve realized that it won’t work. A brute force based approach would work, but I'd prefer something more efficient if possible. Can anyone suggest a suitable algorithm? Is it a packing algorithm that I'm looking for or would something else work better?
Thanks
Ok, I've worked out a solution. I didn't like the idea of a brute force based approach because I thought it would be inefficient, what I realized though is if you can look at which existing widgets are in the way of placing the widget then you can skip large portions of the grid.
Here is an example: (the widget being placed is 20x20 and page width is 100px in this example.)
This diagram is 0.1 scale and got messed up so I've had to add an extra column
*123456789A*
1+---+ +--+1
2| | | |2
3| | +--+3
4| | 4
5+---+ 5
*123456789A*
We attempt to place a widget at 0x0 but it doesn't fit because there is a 50x50 widget at that coordinate.
So we then advance the current x coordinate being scanned to 51 and check again.
We then find a 40x30 widget at 0x61.
So we then advance the x coordinate to 90 but this doesn't leave enough room for the widget being placed so we increment the y coordinate and reset x back to 0.
We know from the previous attempts that the widgets on the previous line are at least 30px high so we increase the y coordinate to 31.
We encounter the same 50x50 widget at 0x31.
So we increase x to 51 and find that we can place a widget at 51x31
Here is the javascript:
function findSpace(width, height) {
var $ul = $('.snap-layout>ul');
var widthOfContainer = $ul.width();
var heightOfContainer = $ul.height();
var $lis = $ul.children('.setup-widget'); // The li is on the page and we dont want it to collide with itself
for (var y = 0; y < heightOfContainer - height + 1; y++) {
var heightOfShortestInRow = 1;
for (var x = 0; x < widthOfContainer - width + 1; x++) {
console.log(x + '/' + y);
var pos = { 'left': x, 'top': y };
var $collider = $(isOverlapping($lis, pos, width, height));
if ($collider.length == 0) {
// Found a space
return pos;
}
var colliderPos = $collider.position();
// We have collided with something, there is no point testing the points within this widget so lets skip them
var newX = colliderPos.left + $collider.width() - 1; // -1 to account for the ++ in the for loop
x = newX > x ? newX : x; // Make sure that we are not some how going backwards and looping forever
var colliderBottom = colliderPos.top + $collider.height();
if (heightOfShortestInRow == 1 || colliderBottom - y < heightOfShortestInRow) {
heightOfShortestInRow = colliderBottom - y; // This isn't actually the height its just the distance from y to the bottom of the widget, y is normally at the top of the widget tho
}
}
y += heightOfShortestInRow - 1;
}
//TODO: Add the widget to the bottom
}
Here is the longer and more less elegant version that also adjusts the height of the container (I've just hacked it together for now but will clean it up later and edit)
function findSpace(width, height,
yStart, avoidIds // These are used if the function calls itself - see bellow
) {
var $ul = $('.snap-layout>ul');
var widthOfContainer = $ul.width();
var heightOfContainer = $ul.height();
var $lis = $ul.children('.setup-widget'); // The li is on the page and we dont want it to collide with itself
var bottomOfShortestInRow;
var idOfShortestInRow;
for (var y = yStart ? yStart : 0; y <= heightOfContainer - height + 1; y++) {
var heightOfShortestInRow = 1;
for (var x = 0; x <= widthOfContainer - width + 1; x++) {
console.log(x + '/' + y);
var pos = { 'left': x, 'top': y };
var $collider = $(isOverlapping($lis, pos, width, height));
if ($collider.length == 0) {
// Found a space
return pos;
}
var colliderPos = $collider.position();
// We have collided with something, there is no point testing the points within this widget so lets skip them
var newX = colliderPos.left + $collider.width() - 1; // -1 to account for the ++ in the for loop
x = newX > x ? newX : x; // Make sure that we are not some how going backwards and looping forever
colliderBottom = colliderPos.top + $collider.height();
if (heightOfShortestInRow == 1 || colliderBottom - y < heightOfShortestInRow) {
heightOfShortestInRow = colliderBottom - y; // This isn't actually the height its just the distance from y to the bottom of the widget, y is normally at the top of the widget tho
var widgetId = $collider.attr('data-widget-id');
if (!avoidIds || !$.inArray(widgetId, avoidIds)) { // If this is true then we are calling ourselves and we used this as the shortest widget before and it didnt work
bottomOfShortestInRow = colliderBottom;
idOfShortestInRow = widgetId;
}
}
}
y += heightOfShortestInRow - 1;
}
if (!yStart) {
// No space was found so create some
var idsToAvoid = [];
for (var attempts = 0; attempts < widthOfContainer; attempts++) { // As a worse case scenario we have lots of 1px wide colliders
idsToAvoid.push(idOfShortestInRow);
heightOfContainer = $ul.height();
var maxAvailableRoom = heightOfContainer - bottomOfShortestInRow;
var extraHeightRequired = height - maxAvailableRoom;
if (extraHeightRequired < 0) { extraHeightRequired = 0;}
$ul.height(heightOfContainer + extraHeightRequired);
var result = findSpace(width, height, bottomOfShortestInRow, idsToAvoid);
if (result.top) {
// Found a space
return result;
}
// Got a different collider so lets try that next time
bottomOfShortestInRow = result.bottom;
idOfShortestInRow = result.id;
if (!bottomOfShortestInRow) {
// If this is undefined then its broken (because the widgets are bigger then their contianer which is hardcoded atm and resets on f5)
break;
}
}
debugger;
// Something has gone wrong so we just stick it on the bottom left
$ul.height($ul.height() + height);
return { 'left': 0, 'top': $ul.height() - height };
} else {
// The function is calling itself and we shouldnt recurse any further, just return the data required to continue searching
return { 'bottom': bottomOfShortestInRow, 'id': idOfShortestInRow };
}
}
function isOverlapping($obsticles, tAxis, width, height) {
var t_x, t_y;
if (typeof (width) == 'undefined') {
// Existing element passed in
var $target = $(tAxis);
tAxis = $target.position();
t_x = [tAxis.left, tAxis.left + $target.outerWidth()];
t_y = [tAxis.top, tAxis.top + $target.outerHeight()];
} else {
// Coordinates and dimensions passed in
t_x = [tAxis.left, tAxis.left + width];
t_y = [tAxis.top, tAxis.top + height];
}
var overlap = false;
$obsticles.each(function () {
var $this = $(this);
var thisPos = $this.position();
var i_x = [thisPos.left, thisPos.left + $this.outerWidth()]
var i_y = [thisPos.top, thisPos.top + $this.outerHeight()];
if (t_x[0] < i_x[1] && t_x[1] > i_x[0] &&
t_y[0] < i_y[1] && t_y[1] > i_y[0]) {
overlap = this;
return false;
}
});
return overlap;
}
I'm programming a HTML5 < canvas > project that involves zooming in and out of images using the scroll wheel.
I want to zoom towards the cursor like google maps does but I'm completely lost on how to calculate the movements.
What I have: image x and y (top-left corner); image width and height; cursor x and y relative to the center of the canvas.
In short, you want to translate() the canvas context by your offset, scale() it to zoom in or out, and then translate() back by the opposite of the mouse offset. Note that you need to transform the cursor position from screen space into the transformed canvas context.
ctx.translate(pt.x,pt.y);
ctx.scale(factor,factor);
ctx.translate(-pt.x,-pt.y);
Demo: http://phrogz.net/tmp/canvas_zoom_to_cursor.html
I've put up a full working example on my website for you to examine, supporting dragging, click to zoom in, shift-click to out, or scroll wheel up/down.
The only (current) issue is that Safari zooms too fast compared to Chrome or Firefox.
I hope, these JS libraries will help you:
(HTML5, JS)
Loupe
http://www.netzgesta.de/loupe/
CanvasZoom
https://github.com/akademy/CanvasZoom
Scroller
https://github.com/zynga/scroller
As for me, I'm using loupe. It's awesome!
For you the best case - scroller.
I recently needed to archive same results as Phrogz had already done but instead of using context.scale(), I calculated each object size based on ratio.
This is what I came up with. Logic behind it is very simple. Before scaling, I calculate point distance from edge in percentages and later adjust viewport to correct place.
It took me quite a while to come up with it, hope it saves someones time.
$(function () {
var canvas = $('canvas.main').get(0)
var canvasContext = canvas.getContext('2d')
var ratio = 1
var vpx = 0
var vpy = 0
var vpw = window.innerWidth
var vph = window.innerHeight
var orig_width = 4000
var orig_height = 4000
var width = 4000
var height = 4000
$(window).on('resize', function () {
$(canvas).prop({
width: window.innerWidth,
height: window.innerHeight,
})
}).trigger('resize')
$(canvas).on('wheel', function (ev) {
ev.preventDefault() // for stackoverflow
var step
if (ev.originalEvent.wheelDelta) {
step = (ev.originalEvent.wheelDelta > 0) ? 0.05 : -0.05
}
if (ev.originalEvent.deltaY) {
step = (ev.originalEvent.deltaY > 0) ? 0.05 : -0.05
}
if (!step) return false // yea..
var new_ratio = ratio + step
var min_ratio = Math.max(vpw / orig_width, vph / orig_height)
var max_ratio = 3.0
if (new_ratio < min_ratio) {
new_ratio = min_ratio
}
if (new_ratio > max_ratio) {
new_ratio = max_ratio
}
// zoom center point
var targetX = ev.originalEvent.clientX || (vpw / 2)
var targetY = ev.originalEvent.clientY || (vph / 2)
// percentages from side
var pX = ((vpx * -1) + targetX) * 100 / width
var pY = ((vpy * -1) + targetY) * 100 / height
// update ratio and dimentsions
ratio = new_ratio
width = orig_width * new_ratio
height = orig_height * new_ratio
// translate view back to center point
var x = ((width * pX / 100) - targetX)
var y = ((height * pY / 100) - targetY)
// don't let viewport go over edges
if (x < 0) {
x = 0
}
if (x + vpw > width) {
x = width - vpw
}
if (y < 0) {
y = 0
}
if (y + vph > height) {
y = height - vph
}
vpx = x * -1
vpy = y * -1
})
var is_down, is_drag, last_drag
$(canvas).on('mousedown', function (ev) {
is_down = true
is_drag = false
last_drag = { x: ev.clientX, y: ev.clientY }
})
$(canvas).on('mousemove', function (ev) {
is_drag = true
if (is_down) {
var x = vpx - (last_drag.x - ev.clientX)
var y = vpy - (last_drag.y - ev.clientY)
if (x <= 0 && vpw < x + width) {
vpx = x
}
if (y <= 0 && vph < y + height) {
vpy = y
}
last_drag = { x: ev.clientX, y: ev.clientY }
}
})
$(canvas).on('mouseup', function (ev) {
is_down = false
last_drag = null
var was_click = !is_drag
is_drag = false
if (was_click) {
}
})
$(canvas).css({ position: 'absolute', top: 0, left: 0 }).appendTo(document.body)
function animate () {
window.requestAnimationFrame(animate)
canvasContext.clearRect(0, 0, canvas.width, canvas.height)
canvasContext.lineWidth = 1
canvasContext.strokeStyle = '#ccc'
var step = 100 * ratio
for (var x = vpx; x < width + vpx; x += step) {
canvasContext.beginPath()
canvasContext.moveTo(x, vpy)
canvasContext.lineTo(x, vpy + height)
canvasContext.stroke()
}
for (var y = vpy; y < height + vpy; y += step) {
canvasContext.beginPath()
canvasContext.moveTo(vpx, y)
canvasContext.lineTo(vpx + width, y)
canvasContext.stroke()
}
canvasContext.strokeRect(vpx, vpy, width, height)
canvasContext.beginPath()
canvasContext.moveTo(vpx, vpy)
canvasContext.lineTo(vpx + width, vpy + height)
canvasContext.stroke()
canvasContext.beginPath()
canvasContext.moveTo(vpx + width, vpy)
canvasContext.lineTo(vpx, vpy + height)
canvasContext.stroke()
canvasContext.restore()
}
animate()
})
<!DOCTYPE html>
<html>
<head>
<title></title>
<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
</head>
<body>
<canvas class="main"></canvas>
</body>
</html>
I took #Phrogz's answer as a basis and made a small library that enables canvas with dragging, zooming and rotating.
Here is the example.
var canvas = document.getElementById('canvas')
//assuming that #param draw is a function where you do your main drawing.
var control = new CanvasManipulation(canvas, draw)
control.init()
control.layout()
//now you can drag, zoom and rotate in canvas
You can find more detailed examples and documentation on the project's page
Faster
Using ctx.setTransform gives you more performance than multiple matrix calls ctx.translate, ctx.scale, ctx.translate.
No need for complex transformation inversions as and expensive DOM matrix calls tp converts point between zoomed and screen coordinate systems.
Flexible
Flexibility as you don't need to use ctx.save and ctx.restore if you are rendering content at using different transforms. Returning to the transform with ctx.setTransform rather than the potentially frame rate wreaking ctx.restorecall
Easy to invert the transform and get the world coordinates of a (screen) pixel position and the other way round.
Examples
Using mouse and mouse wheel to zoom in and out at mouse position
An example using this method to scale page content at a point (mouse) via CSS transform CSS Demo at bottom of answer also has a copy of the demo from the next example.
And an example of this method used to scale canvas content at a point using setTransform
How
Given a scale and pixel position you can get the new scale as follow...
const origin = {x:0, y:0}; // canvas origin
var scale = 1; // current scale
function scaleAt(x, y, scaleBy) { // at pixel coords x, y scale by scaleBy
scale *= scaleBy;
origin.x = x - (x - origin.x) * scaleBy;
origin.y = y - (y - origin.y) * scaleBy;
}
To position the canvas and draw content
ctx.setTransform(scale, 0, 0, scale, origin.x, origin.y);
ctx.drawImage(img, 0, 0);
To use if you have the mouse coordinates
const zoomBy = 1.1; // zoom in amount
scaleAt(mouse.x, mouse.y, zoomBy); // will zoom in at mouse x, y
scaleAt(mouse.x, mouse.y, 1 / zoomBy); // will zoom out by same amount at mouse x,y
To restore the default transform
ctx.setTransform(1,0,0,1,0,0);
The inversions
To get the coordinates of a point in the zoomed coordinate system and the screen position of a point in the zoomed coordinate system
Screen to world
function toWorld(x, y) { // convert to world coordinates
x = (x - origin.x) / scale;
y = (y - origin.y) / scale;
return {x, y};
}
World to screen
function toScreen(x, y) {
x = x * scale + origin.x;
y = y * scale + origin.y;
return {x, y};
}