Enumeration of commonly used render state blocks.
An implementation of RenderEffect should provide helper methods for applying render state values based on the items of this enumeration. Those should be named as
Transparent geometry using alpha-blending.
This preset enables order-dependent alpha compositing with the over operator:
A_out = A_src + A_dst * (1 - A_src) C_out = (C_src * A_src + C_dst * A_dst * (1 - A_src)) / A_out
(C_src,A_src) represents the fragment that is being rasterized,
(C_dst,A_dst) represents the fragment that is present in the target buffer and
(C_out,A_out) represents the resulting fragment that will be written to the buffer. All three tuples use straight alpha. Assuming that the target buffer stores fragments with premultiplied alpha, the following applies:
C_dstPre = C_dst * A_dst C_outPre = C_out * A_out
This leads to the final equations that are actually performed by the GPU:
A_out = A_src + A_dst * (1 - A_src) C_outPre = C_src * A_src + C_dstPre * (1 - A_src)