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I have an Html5 canvas which i am drawing squares to.
The canvas itself is roughly the size of the window.
When i detect a click on a square i would like to translate the canvas so that the square is roughly in the center of the window. Any insights, hints, or straight-forward replies are welcome.
Here is what i tried so far:
If a square is at point (1000, 1000) I would simply translate the canvas (-1000, -1000). I know i need to add an offset so that it is centered in the window. However, the canvas always ends up off of the visible window (too far in the upper-left corner somewhere).
A more complex scenario:
Ultimately i would like to be able to center on a clicked object on a canvas that is transformed (rotated & skewed). I'm going for an isometric effect which seems to work really well. I'm wondering if this transformation affects the centering logic/math at all?
Transforming from screen to world and back
When working with non standard axis (or projections) such as isometrix it is always best to use a transformation matrix. It will cover every possible 2D projection with the same simple functions.
The coordinates of the iso world are called world coordinates. All you objects are stored as world coordinates. When you render them you project those coordinates to the screen coordinates using a transformation matrix.
The matrix, not a movie.
The matrix represents the direction and size in screen coordinates of the world
x and y axis and the screen location of the world origin (0,0)
For iso that is
x axis across 1 down 0.5
y axis across -1 down 0.5
z axis up 1 (-1 as up is the reverse of down) but this example does not use z
So the matrix as an array
const isoMat = [1,0.5,-1,0.5,0,0]; // ISO (pixel art) dimorphic projection
The first two are the x axis, the next two the y axis and the last two values are the screen coordinates of the origin.
Use the matrix to transform points
You apply a matrix to a point, this transforms the point from one coordinate system to another. You can also convert back via a inverse transform.
World to screen
You will need to convert from world coordinates to screen coordinates.
function worldToScreen(pos,retPos){
retPos.x = pos.x * isoMat[0] + pos.y * isoMat[2] + isoMat[4];
retPos.y = pos.x * isoMat[1] + pos.y * isoMat[3] + isoMat[5];
}
In the demo I ignore the origin as I set that at the center of the canvas at all times. Thus remove the origin from that function
function worldToScreen(pos,retPos){
retPos.x = pos.x * isoMat[0] + pos.y * isoMat[2];
retPos.y = pos.x * isoMat[1] + pos.y * isoMat[3];
}
Screen to world.
You will also need to convert from the screen coordinates to the world. For this you need to use the inverse transform. It's a bit like the inverse of multiply a * 2 = b is the inverse of b / 2 = a
There is a standard method for calculating the inverse matrix as follows
const invMatrix = []; // inverse matrix
// I call the next line cross, most call it the determinant which I
// think is stupid as it is effectively a cross product and is used
// like you would use a cross product. Anyways I digress
const cross = isoMat[0] * isoMat[3] - isoMat[1] * isoMat[2];
invMatrix[0] = isoMat[3] / cross;
invMatrix[1] = -isoMat[1] / cross;
invMatrix[2] = -isoMat[2] / cross;
invMatrix[3] = isoMat[0] / cross;
Then we have a function that converts from the screen x,y to the world position
function screenToWorld(pos,retPos){
const x = pos.x - isoMat[4];
const y = pos.y - isoMat[5];
retPos.x = x * invMatrix[0] + y * invMatrix[2];
retPos.y = x * invMatrix[1] + y * invMatrix[3];
}
So you get the mouse coords as screen pixels, use the above function to convert to world coords. Then you can use the world coords to find the object you are looking for.
To move a world object to the screen center you convert its coords to screen coords, add the position on the screen (the canvas center) and set the transform matrix origin to that location.
The demo
The demo creates a set of boxes in world coordinates. It sets the 2D context transform to the isoMat (isometric projection) via ctx.setTransform(
Every frame I convert the mouse screen coords to world coords then use that to check which box the mouse is over.
If the mouse button is down I then convert that box from world coords to screen and add the screen center. To smooth the step the new screen center is chased (smoothed)..
Well you should be able to work it out in the code, any problems ask in the comments.
const ctx = canvas.getContext("2d");
const moveSpeed = 0.4;
const boxMin = 20;
const boxMax = 50;
const boxCount = 100;
const boxArea = 2000;
// some canvas vals
var w = canvas.width;
var h = canvas.height;
var cw = w / 2; // center
var ch = h / 2;
var globalTime;
const U = undefined;
// Helper function
const doFor = (count, cb) => { var i = 0; while (i < count && cb(i++) !== true); };
const eachOf = (array, cb) => { var i = 0; const len = array.length; while (i < len && cb(array[i], i++, len) !== true ); };
const setOf = (count, cb) => {var a = [],i = 0; while (i < count) { a.push(cb(i ++)) } return a };
const randI = (min, max = min + (min = 0)) => (Math.random() * (max - min) + min) | 0;
const rand = (min, max = min + (min = 0)) => Math.random() * (max - min) + min;
// mouse function and object
const mouse = {x : 0, y : 0, button : false, world : {x : 0, y : 0}}
function mouseEvents(e){
mouse.x = e.pageX;
mouse.y = e.pageY;
mouse.button = e.type === "mousedown" ? true : e.type === "mouseup" ? false : mouse.button;
}
["down","up","move"].forEach(name => document.addEventListener("mouse"+name,mouseEvents));
// boxes in world coordinates.
const boxes = [];
function draw(){
if(this.dead){
ctx.fillStyle = "rgba(0,0,0,0.5)";
ctx.fillRect(this.x,this.y,this.w,this.h);
}
ctx.strokeStyle = this.col;
ctx.globalAlpha = 1;
ctx.strokeRect(this.x,this.y,this.w,this.h);
// the rest is just overkill
if(this.col === "red"){
this.mr = 10;
}else{
this.mr = 1;
}
this.mc += (this.mr-this.m) * 0.45;
this.mc *= 0.05;
this.m += this.mc;
for(var i = 0; i < this.m; i ++){
const m = this.m * (i + 1);
ctx.globalAlpha = 1-(m / 100);
ctx.strokeRect(this.x-m,this.y-m,this.w,this.h);
}
}
// make random boxes.
function createBoxes(){
boxes.length = 0;
boxes.push(...setOf(boxCount,()=>{
return {
x : randI(cw- boxArea/ 2, cw + boxArea/2),
y : randI(ch- boxArea/ 2, ch + boxArea/2),
w : randI(boxMin,boxMax),
h : randI(boxMin,boxMax),
m : 5,
mc : 0,
mr : 5,
col : "black",
dead : false,
draw : draw,
isOver : isOver,
}
}));
}
// use mouse world coordinates to find box under mouse
function isOver(x,y){
return x > this.x && x < this.x + this.w && y > this.y && y < this.y + this.h;
}
var overBox;
function findBox(x,y){
if(overBox){
overBox.col = "black";
}
overBox = undefined;
eachOf(boxes,box=>{
if(box.isOver(x,y)){
overBox = box;
box.col = "red";
return true;
}
})
}
function drawBoxes(){
boxes.forEach(box=>box.draw());
}
// next 3 values control the movement of the origin
// rather than move instantly the currentPos chases the new pos.
const currentPos = {x :0, y : 0};
const newPos = {x :0, y : 0};
const chasePos = {x :0, y : 0};
// this function does the chasing
function updatePos(){
chasePos.x += (newPos.x - currentPos.x) * moveSpeed;
chasePos.y += (newPos.y - currentPos.y) * moveSpeed;
chasePos.x *= moveSpeed;
chasePos.y *= moveSpeed;
currentPos.x += chasePos.x;
currentPos.y += chasePos.y;
}
// ISO matrix and inverse matrix plus 2world and 2 screen
const isoMat = [1,0.5,-1,0.5,0,0];
const invMatrix = [];
const cross = isoMat[0] * isoMat[3] - isoMat[1] * isoMat[2];
invMatrix[0] = isoMat[3] / cross;
invMatrix[1] = -isoMat[1] / cross;
invMatrix[2] = -isoMat[2] / cross;
invMatrix[3] = isoMat[0] / cross;
function screenToWorld(pos,retPos){
const x = pos.x - isoMat[4];
const y = pos.y - isoMat[5];
retPos.x = x * invMatrix[0] + y * invMatrix[2];
retPos.y = x * invMatrix[1] + y * invMatrix[3];
}
function worldToScreen(pos,retPos){
retPos.x = pos.x * isoMat[0] + pos.y * isoMat[2];// + isoMat[4];
retPos.y = pos.x * isoMat[1] + pos.y * isoMat[3];// + isoMat[5];
}
// main update function
function update(timer){
// standard frame setup
globalTime = timer;
ctx.setTransform(1,0,0,1,0,0); // reset transform
ctx.globalAlpha = 1; // reset alpha
if(w !== innerWidth || h !== innerHeight){
cw = (w = canvas.width = innerWidth) / 2;
ch = (h = canvas.height = innerHeight) / 2;
createBoxes();
}else{
ctx.clearRect(0,0,w,h);
}
ctx.fillStyle = "black";
ctx.font = "28px arial";
ctx.textAlign = "center";
ctx.fillText("Click on a box to center it.",cw,28);
// update position
updatePos();
isoMat[4] = currentPos.x;
isoMat[5] = currentPos.y;
// set the screen transform to the iso matrix
// all drawing can now be done in world coordinates.
ctx.setTransform(isoMat[0], isoMat[1], isoMat[2], isoMat[3], isoMat[4], isoMat[5]);
// convert the mouse to world coordinates
screenToWorld(mouse,mouse.world);
// find box under mouse
findBox(mouse.world.x, mouse.world.y);
// if mouse down and over a box
if(mouse.button && overBox){
mouse.button = false;
overBox.dead = true; // make it gray
// get the screen coordinates of the box
worldToScreen({
x:-(overBox.x + overBox.w/2),
y:-(overBox.y + overBox.h/2),
},newPos
);
// move it to the screen center
newPos.x += cw;
newPos.y += ch;
}
// forget what the following function does, think it does something like draw boxes, but I am guessing.. :P
drawBoxes();
requestAnimationFrame(update);
}
requestAnimationFrame(update);
canvas { position : absolute; top : 0px; left : 0px; }
<canvas id="canvas"></canvas>
I need to check if an image exists in another image using JavaScript, I need to know what are the best approaches (algorithm) and solutions (ex: librarie) to do this operations
I explained what I need to do in this image:
Using the GPU to help in image processing.
Using the 2D API and some simple tricks you can exploit the GPUs power to speed up Javascript.
Difference
To find an image you need to compare the pixels you are looking for (A) against the pixels in the image (B). If the difference between the Math.abs(A-B) === 0 then the pixels are the same.
A function to do this may look like the following
function findDif(imageDataSource, imageDataDest, xx,yy)
const ds = imageDataSource.data;
const dd = imageDataDest.data;
const w = imageDataSource.width;
const h = imageDataSource.height;
var x,y;
var dif = 0;
for(y = 0; y < h; y += 1){
for(x = 0; x < w; x += 1){
var indexS = (x + y * w) * 4;
var indexD = (x + xx + (y + yy) * imageDataDest.width) * 4;
dif += Math.abs(ds[indexS]-dd[indexD]);
dif += Math.abs(ds[indexS + 1]-dd[indexD + 1]);
dif += Math.abs(ds[indexS + 2]-dd[indexD + 2]);
}
}
return dif;
}
var source = sourceCanvas.getContext("2d").getImageData(0,0,sourceCanvas.width,sourceCanvas.height);
var dest = destinationCanvas.getContext("2d").getImageData(0,0,destinationCanvas.width,destinationCanvas.height);
if(findDif(source,dest,100,100)){ // is the image at 100,100?
// Yes image is very similar
}
Where the source is the image we are looking for and the dest is the image we want to find it in. We run the function for every location that the image may be and if the result is under a level then its a good chance we have found it.
But this is very very slow in JS. This is where the GPU can help.
Using the ctx.globalCompositeOperation = "difference"; operation we can speed up the process as it will do the difference calculation for us
When you render with the comp operation "difference" the resulting pixels are the difference between the pixels you are drawing and those that are already on the canvas. Thus if you draw on something that is the same the result is all pixels are black (no difference)
To find a similar image in the image you render the image you are testing for at each location on the canvas that you want to test for. Then you get the sum of all the pixels you just rendered on, if the result is under a threshold that you have set then the image under that area is very similar to the image you are testing for.
But we still need to count all the pixels one by one.
A GPU mean function
The comp op "difference" already does the pixel difference calculation for you, but to get the sum you can use the inbuilt image smoothing.
After you have rendered to find the difference you take that area and render it at a smaller scale with ctx.imageSmoothingEnabled = true the default setting. The GPU will do something similar to an average and can reduce the amount of work JS has to do by several orders of magnitude.
Now instead of 100s or 1000s of pixels you can reduce it down to as little at 4 or 16 depending on the accuracy you need.
An example.
Using these methods you can get a near realtime image in image search with just the basic numerical analysis.
Click to start a test. Results are shown plus the time it took. The image that is being searched for is in the top right.
//------------------------------------------------------------------------
// Some helper functions
var imageTools = (function () {
var tools = {
canvas(width, height) { // create a blank image (canvas)
var c = document.createElement("canvas");
c.width = width;
c.height = height;
return c;
},
createImage : function (width, height) {
var i = this.canvas(width, height);
i.ctx = i.getContext("2d");
return i;
},
image2Canvas(img) {
var i = this.canvas(img.width, img.height);
i.ctx = i.getContext("2d");
i.ctx.drawImage(img, 0, 0);
return i;
},
copyImage(img){ // just a named stub
return this.image2Canvas(img);
},
};
return tools;
})();
const U = undefined;
const doFor = (count, callback) => {var i = 0; while (i < count && callback(i ++) !== true ); };
const setOf = (count, callback) => {var a = [],i = 0; while (i < count) { a.push(callback(i ++)) } return a };
const randI = (min, max = min + (min = 0)) => (Math.random() * (max - min) + min) | 0;
const rand = (min, max = min + (min = 0)) => Math.random() * (max - min) + min;
const randA = (array) => array[(Math.random() * array.length) | 0];
const randG = (min, max = min + (min = 0)) => Math.random() * Math.random() * Math.random() * Math.random() * (max - min) + min;
// end of helper functions
//------------------------------------------------------------------------
function doit(){
document.body.innerHTML = ""; // clear the page;
var canvas = document.createElement("canvas");
document.body.appendChild(canvas);
var ctx = canvas.getContext("2d");
// a grid of 36 images
canvas.width = 6 * 64;
canvas.height = 6 * 64;
console.log("test");
// get a random character to look for
const digit = String.fromCharCode("A".charCodeAt(0) + randI(26));
// get some characters we dont want
const randomDigits = setOf(6,i=>{
return String.fromCharCode("A".charCodeAt(0) + randI(26));
})
randomDigits.push(digit); // add the image we are looking for
var w = canvas.width;
var h = canvas.height;
// create a canvas for the image we are looking for
const imageToFind = imageTools.createImage(64,64);
// and a larger one to cover pixels on the sides
const imageToFindExtend = imageTools.createImage(128,128);
// Draw the character onto the image with a white background and scaled to fit
imageToFindExtend.ctx.fillStyle = imageToFind.ctx.fillStyle = "White";
imageToFind.ctx.fillRect(0,0,64,64);
imageToFindExtend.ctx.fillRect(0,0,128,128);
ctx.font = imageToFind.ctx.font = "64px arial black";
ctx.textAlign = imageToFind.ctx.textAlign = "center";
ctx.textBaseline = imageToFind.ctx.textBaseline = "middle";
const digWidth = imageToFind.ctx.measureText(digit).width+8;
const scale = Math.min(1,64/digWidth);
imageToFind.ctx.fillStyle = "black";
imageToFind.ctx.setTransform(scale,0,0,scale,32,32);
imageToFind.ctx.fillText(digit,0,0);
imageToFind.ctx.setTransform(1,0,0,1,0,0);
imageToFindExtend.ctx.drawImage(imageToFind,32,32);
imageToFind.extendedImage = imageToFindExtend;
// Now fill the canvas with images of other characters
ctx.fillStyle = "white";
ctx.setTransform(1,0,0,1,0,0);
ctx.fillRect(0,0,w,h);
ctx.fillStyle = "black";
ctx.strokeStyle = "white";
ctx.lineJoin = "round";
ctx.lineWidth = 12;
// some characters will be rotated 90,180,-90 deg
const dirs = [
[1,0,0,1,0,0],
[0,1,-1,0,1,0],
[-1,0,0,-1,1,1],
[0,-1,1,0,0,1],
]
// draw random characters at random directions
doFor(h / 64, y => {
doFor(w / 64, x => {
const dir = randA(dirs)
ctx.setTransform(dir[0] * scale,dir[1] * scale,dir[2] * scale,dir[3] * scale,x * 64 + 32, y * 64 + 32);
const d = randA(randomDigits);
ctx.strokeText(d,0,0);
ctx.fillText(d,0,0);
});
});
ctx.setTransform(1,0,0,1,0,0);
// get a copy of the canvas
const saveCan = imageTools.copyImage(ctx.canvas);
// function that finds the images
// image is the image to find
// dir is the matrix direction to find
// smapleSize is the mean sampling size samller numbers are quicker
function checkFor(image,dir,sampleSize){
const can = imageTools.copyImage(saveCan);
const c = can.ctx;
const stepx = 64;
const stepy = 64;
// the image that will contain the reduced means of the differences
const results = imageTools.createImage(Math.ceil(w / stepx) * sampleSize,Math.ceil(h / stepy) * sampleSize);
const e = image.extendedImage;
// for each potencial image location
// set a clip area and draw the source image on it with
// comp mode "difference";
for(var y = 0 ; y < h; y += stepy ){
for(var x = 0 ; x < w; x += stepx ){
c.save();
c.beginPath();
c.rect(x,y,stepx,stepy);
c.clip();
c.globalCompositeOperation = "difference";
c.setTransform(dir[0],dir[1],dir[2],dir[3],x +32 ,y +32 );
c.drawImage(e,-64,-64);
c.restore();
}
}
// Apply the mean (reducing nnumber of pixels to check
results.ctx.drawImage(can,0,0,results.width,results.height);
// get the pixel data
var dat = new Uint32Array(results.ctx.getImageData(0,0,results.width,results.height).data.buffer);
// for each area get the sum of the difference
for(var y = 0; y < results.height; y += sampleSize){
for(var x = 0; x < results.width; x += sampleSize){
var val = 0;
for(var yy = 0; yy < sampleSize && y+yy < results.height; yy += 1){
var i = x + (y+yy)*results.width;
for(var xx = 0; xx < sampleSize && x + xx < results.width ; xx += 1){
val += dat[i++] & 0xFF;
}
}
// if the sum is under the threshold we have found an image
// and we mark it
if(val < sampleSize * sampleSize * 5){
ctx.strokeStyle = "red";
ctx.fillStyle = "rgba(255,0,0,0.5)";
ctx.lineWidth = 2;
ctx.strokeRect(x * (64/sampleSize),y * (64/sampleSize),64,64);
ctx.fillRect(x * (64/sampleSize),y * (64/sampleSize),64,64);
foundCount += 1;
}
}
}
}
var foundCount = 0;
// find the images at different orientations
var now = performance.now();
checkFor(imageToFind,dirs[0],4);
checkFor(imageToFind,dirs[1],6); // rotated images need larger sample size
checkFor(imageToFind,dirs[2],6);
checkFor(imageToFind,dirs[3],6);
var time = performance.now() - now;
var result = document.createElement("div");
result.textContent = "Found "+foundCount +" matching images in "+time.toFixed(3)+"ms. Click to try again.";
document.body.appendChild(result);
// show the image we are looking for
imageToFind.style.left = (64*6 + 16) + "px";
imageToFind.id = "lookingFor";
document.body.appendChild(imageToFind);
}
document.addEventListener("click",doit);
canvas {
border : 2px solid black;
position : absolute;
top : 28px;
left : 2px;
}
#lookingFor {
border : 4px solid red;
}
div {
border : 2px solid black;
position : absolute;
top : 2px;
left : 2px;
}
Click to start test.
Not perfect
The example is not perfect and will sometimes make mistakes. There is a huge amount of room for improving both the accuracy and the speed. This is just something I threw together as an example to show how to use the GPU via the 2D API. Some further maths will be needed to find the statistically good results.
This method can also work for different scales, and rotations, you can even use some of the other comp modes to remove colour and normalize contrast. I have used a very similar approch to stabilize webcam by tracking points from one frame to the next, and a veriaty of other image tracking uses.
This is for an air app but I'm sure it's a common issue for other things.
I've really been struggling to work out the best way to size tiles in a grid. I've got something like the code below, which kind of works but the problem I'm having is that the whole thing scales down too much on small screens.
I'm trying to find an optimum way of scaling a number of tiles so they fit the screen and stay the largest size possible. I could implement scrolling but I'd like to avoid that.
Is there a less convaluted/more effective way of arranging and scaling tiles to fit in a space?
var scaleFactor:Number = Model.appScale * this.scaleX;
var gap:Number = 10 /scaleFactor;
var _width:Number = stage.fullScreenWidth / scaleFactor;
var sampleWidth:Number = sample.width;
var sampleHeight:Number = sample.height;
var _scale:Number = 1;
var colWidth:Number = sampleWidth + gap;
var totalWidth:Number;
var columns:Number = 0;
var rows:Number = 0;
do{
rows ++;
columns = Math.ceil(_children.length/rows);
totalWidth = columns * colWidth;
if(rows > Math.sqrt(_children.length) && totalWidth > _width)
_scale = (_width/totalWidth) * _scale;
totalWidth = columns * colWidth * _scale;
}
while(totalWidth > _width)
var top:Number = - ((rows * (sampleHeight + gap)) + (gap *2)) * _scale;
// if it's too big scale it down
var pt:Point = localToGlobal(new Point(0, 0));
if(Math.abs(top) > pt.y/scaleFactor){
_scale = (((pt.y - (bg.height + gap))/scaleFactor)/Math.abs(top)) * _scale;
top = -pt.y/scaleFactor;
}
var col:int = 0;
var row:int = 0;
for each(var button:MenuRenderer in _children)
{
Tweener.addTween(button,{
x : _0x + (((sampleWidth + gap) * _scale) * col),
y : top + (((sampleHeight + gap) * _scale) * row),
scaleX: _scale,
scaleY: _scale,
time: 0.05 * button.order,
transition: "easeInOut"
});
col ++;
if(col == columns)
{
row ++;
col = 0;
}
}
i was trying to move the physics body by changing its coordinate in scheduler and i used this code. if i run this code in browser it will work but after js binding it doesn't work on mac or ios. Physics body doesn't move at all on these devices
init: function{
var mass = 1;
var width = 1, height = 1;
this.playerBody = new cp.Body(mass , cp.momentForBox(mass, width, height));
this.space.addBody(this.playerBody);
this.schedule(this.move);
},
move: function(dt){
this.space.step(dt);
this.playerBody.getPos().x += 2 * dt;
this.playerBody.getPos().y += 2 * dt;
}
Try removing that getPos() from those lines, leave them at: this.playerBody.p.x += 2 * dt;. I think that's most likely the cause of your problem.
Additionally, avoid manipulating the coordinates yourself and let the physics engine handle everything.
For example, you could assign the velocity by hand like this:
init: function{
var mass = 1;
var width = 1, height = 1;
var vx = 1, vy = 1;
this.playerBody = new cp.Body(mass , cp.momentForBox(mass, width, height));
this.space.addBody(this.playerBody);
this.playerBody.vx = vx;
this.playerBody.vy = vy;
this.schedule(this.move);
},
move: function(dt){
this.space.step(dt);
}
Or, if you want to give a "bump" to the object in a certain direction, you could use applyImpulse like this:
init: function{
var mass = 1;
var width = 1, height = 1;
var fx = 1, fy = 1;
this.playerBody = new cp.Body(mass , cp.momentForBox(mass, width, height));
this.space.addBody(this.playerBody);
this.playerBody.applyImpuse(cp.v(fx, fy), cp.v(0,0));
this.schedule(this.move);
},
move: function(dt){
this.space.step(dt);
}
Or, if you want to apply a constant force to the object, change applyImpulse to applyForce in that last example.
Note: the cp.v(0,0) parameter is telling the engine to apply the force to the center of the object, so it should not rotate.
PS: if (and only if) you happen to see some strange behaviour with the physics simulation, look at this answer.
after adding few lines my player started to move in mac
init: function{
var mass = 1;
var width = 1, height = 1;
this.playerBody = new cp.Body(mass , cp.momentForBox(mass, width, height));
this.space.addBody(this.playerBody);
this.schedule(this.move);
},
move: function(dt){
this.space.step(dt);
var a = this.playerBody.local2World(this.playerBody.p);
a.y += 2 * dt;
a.x += 2 * dt ;
a = this.playerBody.world2Local(a);
this.playerBody.p = a;
}
but i don't have explanation of this code
When I'm use:
var shape:Shape = new new Shape();
shape.graphics.lineStyle(2,0);
shape.graphics.lineTo(10,10);
addChild(shape);
I get the black line I want, but I also get grey pixels floating around next to them. Is there a way to turn off whatever smoothing/anti-aliasing is adding the fuzzy pixels?
Yes, it is possible to draw pixel-perfect shapes, even with anti-aliasing on. Pixel-hinting is a must. The other half of the equation is to actually issue the drawing commands with whole-pixel coordinates.
For example, you can draw a pixel-perfectly-symmetrical rounded-rectangle with 4px radius curves with the following code. Pay careful attention to what the code is doing, particularly how the offsets relate to the border thickness.
First, keep in mind that when you're drawing filled shapes, the rasterization occurs up to, but no including the right/lower edges of the outline. So to draw a 4x4 pixel filled square, you can just call drawRect(0,0,4,4). That covers pixels 0,1,2,3,4 (5 pixels), but since it doesn't rasterize the right and lower edges, it ends up being 4 pixels. On the other hand, if you're drawing just the outline (without filling it), then you need to call drawRect(0,0,3,3), which will cover pixels 0,1,2,3, which is 4 pixels. So you actually need slightly different dimensions for the fill vs the outline to get pixel-perfect sizes.
Suppose you wanted to draw a button that's 50px wide, 20px tall, with a 4px radius on its rounded edges, which are 2px thick. In order to ensure that exactly 50x20 pixels are covered, and the outside edge of the 2px thick line buts up against the edge pixels without overflowing, you have to issue the drawing command exactly like this. You must use pixel hinting, and you must offset the rectangle by 1px inward on all sides (not half a pixel, but exactly 1). That places the center of the line exactly between pixels 0 and 1, such that it ends up drawing the 2px wide line through pixels 0 and 1.
Here is an example method that you can use:
public class GraphicsUtils
{
public static function drawFilledRoundRect( g:Graphics, x:Number, y:Number, width:Number, height:Number, ellipseWidth:Number = 0, ellipseHeight:Number = 0, fillcolor:Number = 0xFFFFFF, fillalpha:Number = 1, thickness:Number = 0, color:Number = 0, alpha:Number = 1, pixelHinting:Boolean = false, scaleMode:String = "normal", caps:String = null, joints:String = null, miterLimit:Number = 3 )
{
if (!isNaN( fillcolor))
{
g.beginFill( fillcolor, fillalpha );
g.drawRoundRect( x, y, width, height, ellipseWidth, ellipseHeight );
g.endFill();
}
if (!isNaN(color))
{
g.lineStyle( thickness, color, alpha, pixelHinting, scaleMode, caps, joints, miterLimit );
g.drawRoundRect( x, y, width, height, ellipseWidth, ellipseHeight );
}
}
}
Which you'd want to call like this:
var x:Number = 0;
var y:Number = 0;
var width:Number = 50;
var height:Number = 20;
var pixelHinting:Boolean = true;
var cornerRadius:Number = 4;
var fillColor:Number = 0xffffff; //white
var fillAlpha:Number = 1;
var borderColor:Number = 0x000000; //black
var borderAlpha:Number = 1;
var borderThickness:Number = 2;
GraphicsUtils.drawFilledRoundRect( graphics, x + (borderThickness / 2), y + (borderThickness / 2), width - borderThickness, height - borderThickness, cornerRadius * 2, cornerRadius * 2, fillColor, fillAlpha, borderThickness, borderColor, borderAlpha, pixelHinting );
That will produce a pixel-perfectly-symmetrical 2px thick filled rounded rectangle that covers exactly a 50x20 pixel region.
Its very important to notice that using a borderThickness of zero is somewhat non-sensical, and will result in an rectangle oversized by 1 pixel, because it's still drawing a one-pixel wide line, but it's failing to subtract the width (since its zero), hence you'll get an oversized rectangle.
In summary, use the algorithm above, where you add half the border thickness to the x and y coordinates, and subtract the whole border thickness from the width and height, and always use a minimum thickness of 1. That will always result in a rectangle with a border that occupies and does not overflow a pixel region equivalent to the given width and height.
If you want to see it in action, just copy and paste the following code block into a new AS3 Flash Project on the main timeline and run it, as is, since it includes everything necessary to run:
import flash.display.StageScaleMode;
import flash.display.StageAlign;
import flash.events.Event;
import flash.utils.getTimer;
import flash.display.Sprite;
import flash.display.Graphics;
stage.scaleMode = flash.display.StageScaleMode.NO_SCALE;
stage.align = flash.display.StageAlign.TOP_LEFT;
stage.frameRate = 60;
draw();
function draw():void
{
var x:Number = 10;
var y:Number = 10;
var width:Number = 50;
var height:Number = 20;
var pixelHinting:Boolean = true;
var cornerRadius:Number = 4;
var fillColor:Number = 0xffffff; //white
var fillAlpha:Number = 1;
var borderColor:Number = 0x000000; //black
var borderAlpha:Number = 1;
var borderThickness:Number = 2;
var base:Number = 1.6;
var squares:int = 10;
var rows = 4;
var thicknessSteps:Number = 16;
var thicknessFactor:Number = 4;
var offset:Number;
var maxBlockSize:Number = int(Math.pow( base, squares ));
var globalOffset:Number = maxBlockSize; //leave room on left for animation
var totalSize:Number = powerFactorial( base, squares );
var colors:Array = new Array();
for (i = 1; i <= squares; i++)
colors.push( Math.random() * Math.pow( 2, 24 ) );
for (var j:int = 0; j < thicknessSteps; j++)
{
var cycle:Number = int(j / rows);
var subCycle:Number = j % rows;
offset = cycle * totalSize;
y = subCycle * maxBlockSize;
borderThickness = (j + 1) * thicknessFactor;
for (var i:int = 0; i < squares; i++)
{
cornerRadius = Math.max( 8, borderThickness );
borderColor = colors[i];
x = globalOffset + offset + powerFactorial( base, i ); //int(Math.pow( base, i - 1 ));
width = int(Math.pow( base, i + 1 ));
height = width;
if (borderThickness * 2 > width) //don't draw if border is larger than area
continue;
drawFilledRoundRect( graphics, x + (borderThickness / 2), y + (borderThickness / 2), width - borderThickness, height - borderThickness, cornerRadius * 2, cornerRadius * 2, fillColor, fillAlpha, borderThickness, borderColor, borderAlpha, pixelHinting );
}
}
var start:uint = flash.utils.getTimer();
var duration:uint = 5000;
var sprite:Sprite = new Sprite();
addChild( sprite );
var gs:Graphics = sprite.graphics;
addEventListener( flash.events.Event.ENTER_FRAME,
function ( e:Event ):void
{
var t:uint = (getTimer() - start) % duration;
if (t > (duration / 2))
borderThickness = ((duration-t) / (duration/2)) * thicknessSteps * thicknessFactor;
else
borderThickness = (t / (duration/2)) * thicknessSteps * thicknessFactor;
//borderThickness = int(borderThickness);
cornerRadius = Math.max( 8, borderThickness );
borderColor = colors[squares - 1];
x = 0;
y = 0;
width = int(Math.pow( base, squares ));
height = width;
if (borderThickness * 2 > width) //don't draw if border is larger than area
return;
gs.clear();
drawFilledRoundRect( gs, x + (borderThickness / 2), y + (borderThickness / 2), width - borderThickness, height - borderThickness, cornerRadius * 2, cornerRadius * 2, fillColor, fillAlpha, borderThickness, borderColor, borderAlpha, pixelHinting );
}, false, 0, true );
}
function powerFactorial( base:Number, i:int ):Number
{
var result:Number = 0;
for (var c:int = 0; c < i; c++)
{
result += int(Math.pow( base, c + 1 ));
}
return result;
}
function drawFilledRoundRect( g:Graphics, x:Number, y:Number, width:Number, height:Number, ellipseWidth:Number = 0, ellipseHeight:Number = 0, fillcolor:Number = 0xFFFFFF, fillalpha:Number = 1, thickness:Number = 0, color:Number = 0, alpha:Number = 1, pixelHinting:Boolean = false, scaleMode:String = "normal", caps:String = null, joints:String = null, miterLimit:Number = 3 )
{
if (!isNaN( fillcolor))
{
g.beginFill( fillcolor, fillalpha );
g.drawRoundRect( x, y, width, height, ellipseWidth, ellipseHeight );
g.endFill();
}
if (!isNaN(color))
{
g.lineStyle( thickness, color, alpha, pixelHinting, scaleMode, caps, joints, miterLimit );
g.drawRoundRect( x, y, width, height, ellipseWidth, ellipseHeight );
}
}
Try turning on pixelHinting:
shape.graphics.lineStyle(2, 0, 1, true);
More about pixelHinting here.
You can't turn off antialiasing completely. If you want a sharp, pixelated line then unfortunately you have to draw pixel by pixel, using a Bitmap and setPixel()