mTextureUV
Vec4 = [0, 0, 1, 1] The rectangle to draw, as {left, top, right, bottom} in pixels of the source
resolution. Left and right are divided by mTextureSourceResolutionWidth, top and
bottom by mTextureSourceResolutionHeight.
The result is used as it comes out: no half-pixel inset, and no clamp to the texture.