Losing my alpha channel somewhere !

Gavin Williams · 2012-01-24T14:06:48

I'm trying to render a quad (with character sprite from a spritesheet) over the top of my terrain. But I seem to be losing my alpha data, I'm saving my 32bit bitmap out of photoshop, and I've checked that the alpha channel is still there using Pixelformer (which shows alpha clearly) Here's the shader code that should demonstrate the alpha channel : float4 finalColor = gSpriteSheet.Sample(PointSampler, input.texcoord); // ------------------------------------------------------------------------ // final composition // ------------------------------------------------------------------------ return float4(finalColor.a,0,0,1); But all I get is red ! What could I be doing wrong ? Here's my rendertarget construction : // create DirectX11 device CreateDevice11(form, out swapChain, out device11); // create depth buffer CreateDepthBuffer(form.ClientSize.Width, form.ClientSize.Height); // create a view of our render target, which is the backbuffer of the swap chain we just created RenderTargetView renderTarget; using (Resource resource = Resource.FromSwapChain<Texture2D>(swapChain, 0)) renderTarget = new RenderTargetView(device11, resource); // setting a viewport is required if you want to actually see anything var context = device11.ImmediateContext; //var viewport = new Viewport(0.0f, 0.0f, form.ClientSize.Width, form.ClientSize.Height); context.OutputMerger.SetTargets(renderTarget); and here's my device/swapchain construction : private static Result CreateDevice11(RenderForm form, out SwapChain swapChain, out Device device11) { var description = new SwapChainDescription() { BufferCount = 2, Usage = Usage.RenderTargetOutput, OutputHandle = form.Handle, IsWindowed = true, ModeDescription = new ModeDescription(0, 0, new Rational(60, 1), Format.R8G8B8A8_UNorm), SampleDescription = new SampleDescription(1, 0), Flags = SwapChainFlags.AllowModeSwitch, SwapEffect = SwapEffect.Discard }; return SlimDX.Direct3D11.Device.CreateWithSwapChain(adapter1, DeviceCreationFlags.Debug, description, out device11, out swapChain); }

Graphics and GPU Programming Programming

Started by Gavin Williams January 24, 2012 03:25 AM

10 comments, last by Postie 12 years, 3 months ago

Gavin Williams

986

Author

January 24, 2012 11:48 AM

Thank you kauna, It took me no time to test alpha blending with a texture in dds format. I never knew about that exporter. So very helpful.

Postie

1,559

January 24, 2012 02:06 PM

Sounds like you've solved your problem already by switching to the dds format, but thought I'd mention I had exactly the same problem with png's output from Photoshop losing their Alpha Channel. It looks as though Photoshop converts the png to use pre-multiplied alpha when loading the file. The thing is, the png I was editing was originally exported from Illustrator, another Adobe product, and guess what... It writes the alpha channel in the png properly. Bizarre huh? Not sure why those two products are inconsistent.

I discovered a plugin for Photoshop called SuperPNG which fixes the problem. To load the png, you select "Open As" and then pick the super png format, and the alpha channel is properly imported as a separate channel.

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Losing my alpha channel somewhere !

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Losing my alpha channel somewhere !

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