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How can I alphablend only certain parts of a texture in DX 9?

Answer 1

A:

So you have setup the alpha on the texture you wish to overlay such that 0 is transparent (ie shows whats underneath) and 1 is opaque (ie shows the overlay texture)?

If so then you just need to set up a a simple blend mode:

pDevice->SetRenderState( D3DRS_SRCBLEND, D3DBLEND_SRCALPHA );
pDevice->SetRenderState( D3DRS_DESTBLEND, D3DBLEND_INVSRCALPHA );
pDevice->SetRenderState( D3DRS_ALPHABLENDENABLE, TRUE );

Make sure you draw the background first! Also note that values between 0 and 1 represent a linear interpolation between background and the overlay texture.

Goz 2010-09-02 22:59:01

I enabled alphablending and did everything else you said, but it seems that whenever I set these render states : pDevice->SetRenderState( D3DRS_SRCBLEND, D3DBLEND_SRCALPHA ); pDevice->SetRenderState( D3DRS_SRCBLEND, D3DBLEND_INVSRCALPHA ); The textures are shown all black. Oh, and by the way, my game is 2D, and I've been wondering the whole day if the RHW in the FVF I'm using has anything to do with the problems I'm having. Big thanks again, in advance!Oh, and I hope I didn't misuse the comments.

C4theWin 2010-09-03 12:44:40

What colour is the background? What are the vertex colours set to?

Goz 2010-09-03 13:09:34

The background color is D3DCOLOR_XRGB(150, 200, 255). Vertex colors are all D3DCOLOR_ARGB(255, 255, 255, 255), though I tried some other colors too.

C4theWin 2010-09-04 08:59:15

Then it might be handy to see your texture and its alpha channel.

Goz 2010-09-04 15:49:46

The code here is setting the Source-Blend factor twice. For standard alpha-blending, you want `pDevice->SetRenderState( D3DRS_DSTBLEND, D3DBLEND_INVSRCALPHA );`

Alan 2010-09-05 15:28:26

LOL well spotted Alan. Updated my answer!

Goz 2010-09-05 16:29:21

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How can I alphablend only certain parts of a texture in DX 9?

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