Different ways the alpha channel of pixels affects blending.
|alphamultiply||Color channel values are multiplied by the alpha channel during blending.|
|premultiplied||Color channels are not multiplied by the alpha channel. This should be used if the pixels being drawn have already been blended, or "pre-multiplied", by the alpha channel.|
The premultiplied mode should be used if pixels being drawn have already been blended, or "pre-multiplied", by the alpha channel. This happens when rendering a framebuffer that contains pixels with transparent alpha values, since the stored color values have already been faded by alpha and don't need to be faded a second time with the alphamultiply blend mode.