Hi all,

I'm trying to work my way through exercising with D3D11 blending.

In this case using blending states (not directly in the shader) and without using the alpha component.

I've created the spreadsheet below to make sure I understand the equations.

My questions:

1. Do you see any issues/ errors in the sheet?

2. I have the following challenge:

- render objects to the backbuffer

- render a cylinder with an animated texture

-- the animated texture has a large part of 'black' pixels

- I want the black pixels not to be rendered using blending (keep the 'dest'/ pixels on backbuffer the same), all others I want to stay the same

(not blended/ multiplied with the pixels already on the backbuffer.

So far I've tried this:

	transparentDesc2.RenderTarget[0].BlendEnable			= true;
	transparentDesc2.RenderTarget[0].SrcBlend			= D3D11_BLEND_ZERO;
	transparentDesc2.RenderTarget[0].DestBlend			= D3D11_BLEND_INV_SRC_COLOR;
	transparentDesc2.RenderTarget[0].BlendOp			= D3D11_BLEND_OP_ADD;

	transparentDesc2.RenderTarget[0].SrcBlendAlpha			= D3D11_BLEND_ONE;
	transparentDesc2.RenderTarget[0].DestBlendAlpha			= D3D11_BLEND_ONE;
	transparentDesc2.RenderTarget[0].BlendOpAlpha			= D3D11_BLEND_OP_ADD;
	transparentDesc2.RenderTarget[0].RenderTargetWriteMask		= D3D11_COLOR_WRITE_ENABLE_ALL;

The result is that the black pixels are indeed removed, but the color of the remaining pixels in the animated textures, are (I think) multiplied by the pixels already on the backbuffer, in this case the background color (after clearing the backbuffer).

(the non-black of the texture is dark blue/ greenish)

Can someone help me in the right direction to achieve my goal?

Any input is appreciated.

Can't you just do this by discarding completely black pixels in the pixel shader? Or are you trying to do it only with blendstates for some reason?

I'm not sure blendstates allow you to express the sharp discontinuity that you want at (0x0, 0x0, 0x0) -> (0x1, 0x0, 0x0).

Fixed it, it was indeed the Z writing I needed to disable.

The result is now as aimed (although minimally different from the books example, but that's probably because of the different cylinder size, texcoords or something).

For blending src and dest I now used BLEND_ONE, combined with 'ADD'.

- render everything other then the cylinder 'normal' (Z-write enabled)

- disable Z writing through setting a depthstencil state

- render the cylinder with animated texture

- enable Z write again (Z testing and reading is left alone)