I have a matrix of pixels in RAM memory, e.g. 1000x1000 pixels. I send it to GPU using
gl.texImage2D(gl.TEXTURE_2D, 0, gl.RGBA, 1000,1000, 0, gl.RGBA, gl.UNSIGNED_BYTE, pixels);
Which works great. But then I change some pixels, located in rectangle x=50, y=50, width =100, height=100. Sending the whole 1000x1000px picture again takes too much time, I would like to send only changed sub-area to the GPU.
I have tired
gl.texSubImage2D(gl.TEXTURE_2D, 0, 50,50, 100,100, gl.RGBA, gl.UNSIGNED_BYTE, pixels);
but it seems, that parameter "pixels" should be the sub-area of 100x100 pixels. Copying out a sub-area from a large picture also takes too much time. Can I somehow specify a sub-rectangle for source pixels in RAM? Maybe somehow using
UPDATE: I discovered that it is possible in WebGL 2.0 (= OpenGL ES 3.0) using gl.pixelStorei() by changing PACK_ROW_LENGTH, PACK_SKIP_ROWS, PACK_SKIP_PIXELS parameters. Too bad WebGL 2.0 is not supported in most of devices now :(