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Windows Phone 8: Additive blending

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First of all, some key info:

  • Platform: Windows Phone 8
  • API: DirectX 11
  • Language: C++/CX

I've created a 2D project for Windows Phone 8, which uses DDS textures with 8-bit alpha. I'm having issues getting additive blending working correctly. 


The textures have had PreMultipliedAlpha applied.


I've tried various combinations of settings for the BlendState, this is what I'm using currently:


blendDescription.AlphaToCoverageEnable = false;
blendDescription.RenderTarget[0].BlendEnable = true;
blendDescription.RenderTarget[0].SrcBlend = D3D11_BLEND_ONE;
blendDescription.RenderTarget[0].DestBlend = D3D11_BLEND_ONE;
blendDescription.RenderTarget[0].BlendOp = D3D11_BLEND_OP_ADD;
blendDescription.RenderTarget[0].SrcBlendAlpha = D3D11_BLEND_ONE;
blendDescription.RenderTarget[0].DestBlendAlpha = D3D11_BLEND_ONE;
blendDescription.RenderTarget[0].BlendOpAlpha = D3D11_BLEND_OP_ADD;


The results i'm seeing are as follows:

  • The textures are being alpha blended correctly, but i'm not seeing an additive colour effect.
  • If I try DDS 1 textures (1 bit alpha) these work perfectly fine, but obviously 1 bit alpha is very limited.

Can anyone suggest what I might be doing wrong here?





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Hm... This is what I do for my additive blending with my particles, but it's based on alpha, I'm not sure if it will help you.


	blendStateDescription.RenderTarget[0].BlendEnable = TRUE;
	blendStateDescription.RenderTarget[0].SrcBlend = D3D11_BLEND_SRC_ALPHA;
	blendStateDescription.RenderTarget[0].DestBlend = D3D11_BLEND_ONE;
	blendStateDescription.RenderTarget[0].BlendOp = D3D11_BLEND_OP_ADD;
	blendStateDescription.RenderTarget[0].SrcBlendAlpha = D3D11_BLEND_ONE;
	blendStateDescription.RenderTarget[0].DestBlendAlpha = D3D11_BLEND_ZERO;
	blendStateDescription.RenderTarget[0].BlendOpAlpha = D3D11_BLEND_OP_ADD;
	blendStateDescription.RenderTarget[0].RenderTargetWriteMask = D3D11_COLOR_WRITE_ENABLE_ALL;
	D3DDEVICE->CreateBlendState(&blendStateDescription, &mBlendingState);



And I'm not using premultiplied alpha, but I suppose you have nothing to lose to try it haha.

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Thanks, SeaBolt


This is actually one of the combinations I have tried based on forum posts I found.


Unfortunately It appears to have no effect.



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More info that may be relevant: I'm using DirectXTK's SpriteBatch framework, and i'm also rendering to deferred contexts (but all the particles i'm trying to blend are using the same context).

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