This function is similar to the existing ImageAlphaBlending() function in that it affects the way pixel drawing will be done during any kind of drawing function. It extends the functionality by allowing you to use one of the effect modes (listed below).
"effect" takes one of the values:
IMG_EFFECT_REPLACE
Use pixel replacement (equivalent of ImageAlphaBlending(FALSE))
IMG_EFFECT_NORMAL
Use normal pixel blending (equivalent of ImageAlphaBlending(TRUE))
IMG_EFFECT_OVERLAY
Use the overlay routine. Overlay has the effect that black background pixels will remain black, white background pixels will remain white, but grey background pixels will take the colour of the foreground pixel.