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ALPHAOP madness

Started by Marc aka Foddex Apr 27, 2004 at 7:26 AM 3 replies 800+ views

Original Post

Apr 27, 2004 at 7:26 AM

[I use DirectX 7!] Hi all, I''m kinda lost with the DirectX ALPHAOP render state. I''m used to OpenGL, where you can simply call functions like this:

//for alpha blending:

  glEnable(GL_BLEND);
  glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);

//for alpha testing:

  glEnable(GL_ALPHA_TEST);
  glAlphaFunc(GL_EQUAL, reference_value);

With Direct3D I''ve found the following functions, which are pretty equal:

//for alpha blending:

  m_d3ddevice->SetRenderState( D3DRENDERSTATE_ALPHABLENDENABLE, TRUE );
  m_d3ddevice->SetRenderState( D3DRENDERSTATE_SRCBLEND,  D3DBLEND_SRCALPHA );
  m_d3ddevice->SetRenderState( D3DRENDERSTATE_DESTBLEND, D3DBLEND_INVSRCALPHA );

//for alpha testing:

  m_d3ddevice->SetRenderState( D3DRENDERSTATE_ALPHATESTENABLE, TRUE );
  m_d3ddevice->SetRenderState( D3DRENDERSTATE_ALPHAREF, reference_value);
  m_d3ddevice->SetRenderState( D3DRENDERSTATE_ALPHAFUNC, D3DCMP_EQUAL );

What I don''t understand though is that ALPHAOP stuff... how do I configure the ALPHAOP renderstate so that it works like OpenGL? In other words, is it possible to setup the ALPHAOP renderstate once, after which I can simply use the functions above to enable alpha testing/blending? I ask this, because I''ve found out that the following piece of code sets up the the ALPHAOP stuff for proper alpha blending:

  m_d3ddevice->SetTextureStageState(i, D3DTSS_ALPHAOP,   D3DTOP_SELECTARG1);
  m_d3ddevice->SetTextureStageState(i, D3DTSS_ALPHAARG1, D3DTA_DIFFUSE);

But the code for proper alpha testing is:

  m_d3ddevice->SetTextureStageState(i, D3DTSS_ALPHAOP, D3DTOP_SELECTARG1 );
  m_d3ddevice->SetTextureStageState(i, D3DTSS_ALPHAARG1, D3DTA_TEXTURE );
  m_d3ddevice->SetTextureStageState(i, D3DTSS_ALPHAARG2, D3DTA_CURRENT );

Can this be combined? I want to be able to alpha test and alpha blend at the same time! I''m completely flabbergasted by the DX7 Help, which is not quite clear about all the different possibilities. Any help would be greatly appreciated! Marc

Endurion

Apr 27, 2004 at 7:39 AM

Should do the trick:


m_d3ddevice->SetTextureStageState(i, D3DTSS_ALPHAOP,   D3DTOP_MODULATE);  
m_d3ddevice->SetTextureStageState(i, D3DTSS_ALPHAARG1, D3DTA_TEXTURE);
m_d3ddevice->SetTextureStageState(i, D3DTSS_ALPHAARG2, D3DTA_DIFFUSE);

Might do this as well:


m_d3ddevice->SetTextureStageState( 0, D3DTSS_COLOROP, D3DTOP_MODULATE );
m_d3ddevice->SetTextureStageState( 0, D3DTSS_COLORARG1, D3DTA_DIFFUSE );
m_d3ddevice->SetTextureStageState( 0, D3DTSS_COLORARG2, D3DTA_TEXTURE );

[edit: Show indexed sample code - get f***ed over with boldness, Want boldness, nought]

[edited by - Endurion on April 27, 2004 8:40:31 AM]

Marc aka Foddex

Apr 27, 2004 at 7:43 AM

Damn, I said it didn't work, but I was kinda blind. It works just fine

Thanks a lot!!

[edited by - Marc aka Foddex on April 27, 2004 9:00:15 AM]

DrunkenHyena

Apr 28, 2004 at 10:42 AM

quote:

I ask this, because I''ve found out that the following piece of code sets up the the ALPHAOP stuff for proper alpha blending:
m_d3ddevice->SetTextureStageState(i, D3DTSS_ALPHAOP, D3DTOP_SELECTARG1); m_d3ddevice->SetTextureStageState(i, D3DTSS_ALPHAARG1, D3DTA_DIFFUSE);
But the code for proper alpha testing is:
m_d3ddevice->SetTextureStageState(i, D3DTSS_ALPHAOP, D3DTOP_SELECTARG1 ); m_d3ddevice->SetTextureStageState(i, D3DTSS_ALPHAARG1, D3DTA_TEXTURE ); m_d3ddevice->SetTextureStageState(i, D3DTSS_ALPHAARG2, D3DTA_CURRENT );

This is wrong. ALPHAOP determines where the alpha comes from, the renderstates say how it is used.

The first one sets the alpha to come from the DIFFUSE colour only. The second says the final alpha is the modulation of the texture alpha and the Current (lighting if lighting is on, otherwise DIFFUSE) colour.

Stay Casual,

Ken
Drunken Hyena

Marc aka Foddex

Apr 28, 2004 at 12:34 PM

DrunkenHyena, thanks for the explanation

I''m not familiar with any such functionality in OpenGL, so I was kinda wondering what it did

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