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PlayStation 2 alpha-blending modes
[PlayStation 2]

The GS rasterization chip of the PlayStation 2 supports a subset of the standard alpha-blending modes, as shown in the table below. Here, "#" indicates that the mode is supported and "." that it is not. The blending example demonstrates the usage of the available modes. 

        Source:|  ZERO | ONE |  SRCALPHA | INVSRCALPHA | DESTALPHA | INVDESTALPHA
   ------------+-------+-----+-----------+-------------+-----------+-------------
   Destination |       |     |           |             |           |
               |       |     |           |             |           |
           ZERO|   #   |  #  |     #     |      #      |     #     |      #
            ONE|   #   |  #  |     #     |      .      |     #     |      .
       SRCALPHA|   #   |  #  |     .     |      #      |     .     |      .
    INVSRCALPHA|   #   |  .  |     #     |      .      |     .     |      .
   DESTSRCALPHA|   #   |  #  |     .     |      .      |     .     |      #
   INVDESTALPHA|   #   |  .  |     .     |      .      |     #     |      .
Note:
The reason for this non-standard blending functionality is that the GS uses the following blending equation:
 Cdst = (A - B)*C + D

Where A, B and D may be one of Csrc, Cdst or zero and C may be Asrc, Adst or a fixed value. Compared this with the standard blending equation, shown here:

 Cdst = BLENDSRC*Csrc + BLENDDST*Cdst

Whilst this restricts the GS from achieving all the blend modes in the above table, it also allows it to achieve some extra modes such as subtractive (as opposed to additive) blending. Refer to the GS manual for further details (the above equations do not cover all relevant details, such as the alpha test, destination alpha test and PABE flag).

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