Is it possible to directly alter individual pixels within a canvas, rather than retrieving the entire buffer using ctx.getImageData and then pasting it back with ctx.putImageData? This is crucial in order to avoid the costly process of copying data every time a frame is updated.
A way to modify specific regions is by following these steps:
var imageData = ctx.getImageData(x, y, width, height);
Once the modifications are done, place the modified image back in its original position:
ctx.putImageData(imageData, x, y);
If you want to work with a single pixel at coordinates x/y:
var imageData = ctx.getImageData(x, y, 1, 1);
/// convert the pixel to grayscale
var gray = data[0] * 0.2126 + data[1] * 0.7152 +data[2] * 0.0722;
imageData.data[0] = gray; /// r
imageData.data[1] = gray; /// g
imageData.data[2] = gray; /// b
imageData.data[3] = 255; /// alpha
/// put the modified pixel back
ctx.putImageData(imageData, x, y);
For simple color changes, utilizing fillRect(), rect(), and fill() for multiple rectangles would suffice. However, for more intricate modifications (as assumed here), extracting and working on regions individually can be beneficial.
For the most efficient way to individually modify pixels, adjust the fillStyle and then utilize fillRect(x ,y, 1, 1). This method has shown to be significantly faster on the latest versions of Firefox (50 times) and Chrome (20%). Check out the performance test results at http://jsperf.com/fillrect-vs-putimagedata.
Edit: After considering @markE's input, I updated the performance test link: http://jsperf.com/fillrect-vs-putimagedata/4. It appears that changing draw color with ctx.fillStyle=... and using fillRect afterwards can yield similar or even better results compared to putImageData in Firefox and Chrome. However, Safari performs best with fillStyle changes (though it seems to matter only for consistent colors).
Ultimately, using fillRect over putImageData is recommended only for solid color fills in Chrome and Firefox. Safari seems to prefer avoiding binary image representations.
(It's advisable to conduct tests on various devices to observe any performance differences, especially on Safari when dealing with varying colors).
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