dest alpha

lukas · Post by **lukas** » Sat Dec 26, 2009 7:06 am

has anybody tried using dest alpha? it seems it doesnt work for me neither when i'm trying to blend nor when i do a screenshot ( its all set to 0 even if i clear with 0xff). maybe i'm missing some state?

Raphael · Post by **Raphael** » Sat Dec 26, 2009 7:47 am

PSP does not support destination alpha. The framebuffer alpha channel is used as stencil buffer bits.
You can however use the clear enable bit to write to destination alpha at least through the primitives vertex color (as is done in sceGuClear to "clear" the stencil bits).

Code: Select all

sceGuSendCommandi&#40;211, GU_STENCIL_BUFFER_BIT<<8|0x1&#41;;
sceGuDrawArray&#40;....&#41;;
sceGuSendCommandi&#40;211, 0&#41;;

This will render the vertex colors alpha component into the destination stencil/alpha bits (iirc even with the interpolation done by smooth shading). However, this unfortunately still doesn't render texture alpha component.

lukas · Post by **lukas** » Sat Dec 26, 2009 8:00 am

all alpha related stuff appears to be sooo broken on psp. no possibility to sum vertex and texture alpha, no dest blending. that's frustrating. thanks for quick reply though