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Vertex color alpha not working

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I am writing a particle system using point sprites and I am using vertex color blending for it. This works well and the particles change color. I am using .png textures for the particles and the texture transparency works. But when I lower the alpha value in the vertex color nothing happens. I've tried every render state I can think of but nothing works. I'm guessing it has something to do with the D3D_BLEND state. What am I doing wrong?

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You must use the diffuse colour alpha as secondary input to the alpha operation.
Try this:

// modulate texture alpha
device->SetTextureStageState( 0, D3DTSS_ALPHAOP, D3DTOP_MODULATE );
// use diffuse colour as second alpha argument
device->SetTextureStageState( 0, D3DTSS_ALPHAARG2, D3DTA_DIFFUSE );

// use alpha from source pixel
device->SetRenderState( D3DRS_SRCBLEND, D3DBLEND_SRCALPHA );
// use 1-alpha for destination pixel

// optional - enable alpha testing
device->SetRenderState( D3DRS_ALPHATESTENABLE, TRUE );


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