Reputation: 80
I would like to be run an iteration of a loop every x seconds.
Every iteration will change the value of a pixel and paint the changed image to the canvas.
So far I have this:
for(let i=0;i<width;i++){ //Rows
for(o=i*(width*4);o<i*(width*4)+(width*4);o+=4){//pixels in current row
imgData.data[o] = 255
}
ctx.putImageData(imgData, xPos, yPos);
}
Which successfully changes all pixels in the image to be 255 red. However, this happens all at the same time. I would like this to happen a pixel a time every x seconds.
Any guidance?
Upvotes: 0
Views: 103
Reputation: 21881
A version with setTimeout()
(or requestAnimationFrame()
) and without the use of global variables (and without all the "complicated" math):
const modifyPixel = (function(canvas) {
const context = canvas.getContext("2d");
const imageData = context.getImageData(0, 0, canvas.width, canvas.height);
return function(index = 0) {
if (index >= imageData.data.length) {
return;
}
imageData.data[index] = 255;
context.putImageData(imageData, 0, 0);
index += 4;
setTimeout(function() {
modifyPixel(index + 4);
}, 50);
};
}(document.querySelector("canvas")));
(function init() {
const canvas = document.querySelector("canvas");
const context = canvas.getContext("2d");
context.beginPath();
context.rect(0, 0, canvas.width, canvas.height);
context.fillStyle = "green";
context.fill();
}());
const modifyPixel = (function(canvas) {
const context = canvas.getContext("2d");
const imageData = context.getImageData(0, 0, canvas.width, canvas.height);
return function(index = 0) {
if (index >= imageData.data.length) {
return;
}
imageData.data[index] = 255;
context.putImageData(imageData, 0, 0);
index += 4;
setTimeout(function() {
modifyPixel(index + 4);
}, 50);
};
}(document.querySelector("canvas")));
modifyPixel();
<canvas style="width:200px; height:200px" width="50px" height="50px"></canvas>
Upvotes: 1
Reputation: 12891
If you want this to happen a pixel every second you shouldn't use the outer for-loop at all. Instead use a global variable which holds the position of the current pixel. With each interval increment that variable and put the changed imageData to the canvas.
Something like:
var originalWidth = width;
var currentPixel = 0;
function update() {
for (o = currentPixel * (originalWidth * 4); o < currentPixel * (originalWidth * 4) + (originalWidth * 4); o += 4) {
imgData.data[o] = 255;
}
ctx.putImageData(imgData, xPos, yPos);
if (currentPixel + 1 < originalWidth) {
currentPixel++
} else {
clearInterval(intervalId);
}
}
var intervalId = setInterval(update, 1000);
Upvotes: 2