sceGuBlendFunc usage ?

[hlide]

I would like to convert some glBlend* operations in GU sceGuBlendFunc, but i have some difficulties because there are some not even defined in pspgl.

The only one I could be sure (according what I found out in PSPGL) is the following two :

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(1.0 x Cd + 1.0 x Cs) :

    glBlendFunc(GL_ONE,GL_ONE);
    glBlendEquationEXT(GL_FUNC_ADD_EXT);

--->

    sceGuBlendFunc(GU_ADD, GU_FIX, GU_FIX, 0xffffff, 0xffffff);

and

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(1.0 x Cd - 1.0 x Cs) :

    glBlendFunc(GL_ONE,GL_ONE);
    glBlendEquationEXT(GL_FUNC_REVERSE_SUBTRACT_EXT);

--->

    sceGuBlendFunc(GU_REVERSE_SUBTRACT, GU_FIX, GU_FIX, 0xffffff, 0xffffff);

there are other two I dunno how to translate :

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(0.5 x Cs + 0.5 x Cd) :

    glBlendColorEXT(0.0,0.0,0.0,0.5);
    glBlendFunc(GL_CONSTANT_ALPHA,GL_CONSTANT_ALPHA);
    glBlendEquationEXT(GL_FUNC_ADD_EXT);

--->

    sceGuBlendFunc(GU_ADD, ?, ?, ?, ?);

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(1.0 x Cd + 0.25 x Cs) :

    glBlendColorEXT(0.0,0.0,0.0,0.5);
    glBlendFunc(GL_CONSTANT_ALPHA,GL_ONE);
    glBlendEquationEXT(GL_FUNC_ADD_EXT);


--->

    sceGuBlendFunc(GU_ADD, ?, GU_FIX, ?, 0xffffff);

I hope someone knows the answer :/

[hlide]

anyone to help me ? i'm lost :(

I would be expecting something like :

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(0.5 x Cs + 0.5 x Cd) :

    glBlendColorEXT(0.0,0.0,0.0,0.5);
    glBlendFunc(GL_CONSTANT_ALPHA,GL_CONSTANT_ALPHA);
    glBlendEquationEXT(GL_FUNC_ADD_EXT);

--->

    sceGuBlendFunc(GU_ADD, GU_FIX, GU_FIX, 0x7f7f7f, 0x7f7f7f);

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(1.0 x Cd + 0.25 x Cs) :

    glBlendColorEXT(0.0,0.0,0.0,0.5);
    glBlendFunc(GL_CONSTANT_ALPHA,GL_ONE);
    glBlendEquationEXT(GL_FUNC_ADD_EXT);


--->

    sceGuBlendFunc(GU_ADD, GU_FIX, GU_FIX, 0x3f3f3f, 0xffffff);

Can anybody correct my code if i'm wrong ?

[hlide]

Up : please tell me if i'm wrong :'(

[chp]

Looks about right, yes. If you want to read it more easily you can use the macros available, so something like this ...

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sceGuBlendFunc(GU_ADD, GU_FIX, GU_FIX, GU_COLOR(0.25f,0.25f,0.25f,0.25f), GU_COLOR(1,1,1,1));

... would multiply the input source pixel with 0.25 and add it to the destination, much like you have written yourself already.

[hlide]

Great ! thx chp !

well there is something i don't understand :

PSPGL defines GL_ONE as being equivalent to GU_COLOR(255, 255, 255, 0) and not to GU_COLOR(255, 255, 255, 255).

Is there any difference between :

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sceGuBlendFunc(GU_ADD, GU_FIX, GU_FIX, GU_COLOR(0.25f,0.25f,0.25f,0.25f), GU_COLOR(1,1,1,1));

and

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sceGuBlendFunc(GU_ADD, GU_FIX, GU_FIX, GU_COLOR(0.25f,0.25f,0.25f, 0), GU_COLOR(1,1,1, 0));

and

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sceGuBlendFunc(GU_ADD, GU_FIX, GU_FIX, GU_COLOR(0,0,0,0.25f), GU_COLOR(0,0,0,1));

?

[chp]

It probably depends on how you want the alpha-component of the color to affect the input. I have not properly tested how the alpha-vs-alpha blending is done on the PSP. On the PS2 the alpha-channel wasn't affected by blending, which is stopping me from answering which approach that is the correct one.