glTexSubImage split to more updates


I need help how to split glTexSubImage3D into small parts. Why? Because its more faster than whole image.

My discovery: using small parts ex: 1024*1024 times 1x1 pixel is a lot faster than 1 time 1024x1024.

1 time change looks:

GLfuncs->glTexSubImage3D(type, 0, 0, 0, 0, width, height, layer, GL_RGBA, GL_FLOAT, texels);

Split change using glTexSubImage3D offsets(ofc that code is in two “for” cycles):

GLfuncs->glTexSubImage3D(type, 0, x, y, 0, 1, 1, layer, GL_RGBA, GL_FLOAT, texels);

What’s my fault? I see just first pixel of this all(others are 0). So my offset data is somehow wrong, I don’t know where can be mistake.
Also this texture is updated per frame. If you have better idea how to do this whole easier or faster give me advice!