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Constant Buffers


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#1 Gavin Williams   Members   -  Reputation: 638

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Posted 09 December 2012 - 09:38 PM

Hi,

I have always used the effects framework to manage my shaders, but I decided to introduce constant buffers, as I'm about to implement geometry instancing and I figured it would give me greater control. And also it was about time I get to know how they work. But I don't think I'm doing it right as my wall sections are just disappearing. So can anyone see what I'm doing wrong ..

So here's all the relevant code :

The CBufferStruct ...

/// <summary>
		/// CBufferStruct
		/// </summary>
		[StructLayout(LayoutKind.Sequential)]
		public struct CBufferStruct
		{
			public Matrix mWorld;
			public Matrix mView;
			public Matrix mProj;
			public static readonly int SizeInBytes = Marshal.SizeOf(typeof(CBufferStruct));
		}

Then in the Walls constructor ...

// create cBuffer
			BufferDescription bufferDescription = new BufferDescription()
			{
				BindFlags = BindFlags.ConstantBuffer,
				CpuAccessFlags = CpuAccessFlags.None,
				OptionFlags = ResourceOptionFlags.None,
				SizeInBytes = CBufferStruct.SizeInBytes,
				Usage = ResourceUsage.Default,
			};
			cBuffer = new Buffer(SlimDXGraphics.Device11,  bufferDescription);
			cBufferStruct = new CBufferStruct()
			{
				mProj = new Matrix(),
				mView = new Matrix(),
				mWorld = Matrix.Translation(new Vector3()),
				//padding = new Matrix()
			};

Then in Walls.RenderToGBuffer() ...

foreach (Chunk chunk in map.VisibleChunks)
			{
				//if (!(chunk.Coords.X == 1 && chunk.Coords.Y == 1)) // debug code to selectively render a single terrain chunk
				foreach (KeyValuePair<int, List<Point>> kVPair in chunk.wallInstanceCollectionsDictionary)
				{
					foreach (Point p in kVPair.Value)
					{
						context.InputAssembler.SetVertexBuffers(0, new VertexBufferBinding(map.wall000.VertexBuffer, VertexPCNT.SizeInBytes, 0));
						cBufferStruct.mProj = camera.ProjMatrix;
						cBufferStruct.mView = camera.ViewMatrix;
						cBufferStruct.mWorld = Matrix.Translation(new Vector3(p.X, p.Y, 0));
					  
						using (DataStream data = new DataStream(CBufferStruct.SizeInBytes, true, true))
						{
							data.Position = 0;
							data.Write(cBufferStruct);
							context.UpdateSubresource(new DataBox(0, 0, data), cBuffer, 0);
							data.Dispose();
						}
						// now bind the constant buffer to the pipeline
						context.VertexShader.SetConstantBuffer(cBuffer, 0); // not sure about this, some examples don't have it
					  
						// configure vertex shader ------------------------------------------------------------
						//effect_Walls.GetVariableByName("gWorld").AsMatrix().SetMatrix(Matrix.Translation(new Vector3(p.X, p.Y, 0)));
						//effect_Walls.GetVariableByName("gView").AsMatrix().SetMatrix(camera.ViewMatrix);
						//effect_Walls.GetVariableByName("gProj").AsMatrix().SetMatrix(camera.ProjMatrix);
						effect_Walls.GetVariableByName("gTexture").AsResource().SetResource(map.SRVWallTexture);
						// draw -------------------------------------------------------------------------------
						for (int pass = 0; pass < effectTech_Walls.Description.PassCount; ++pass)
						{
							EffectPass Pass = effectTech_Walls.GetPassByIndex(pass);
							System.Diagnostics.Debug.Assert(Pass.IsValid, "Invalid EffectPass");
							Pass.Apply(context);
							if (map.wall000.IndexCount == 0)
								context.Draw(map.wall000.VertexCount, 0);
							else
								context.DrawIndexed(map.wall000.IndexCount, 0, 0);
						};
					}
				}
			}

Edit : And here's the shader vars ...

// constant buffers need to be a multiple of 16 byte in size
cbuffer gConstantBuffer : register (b0)
{
// spacial transforms
float4x4 gWorld;
float4x4 gView;
float4x4 gProj;
// padding
//float4x4 padding;
}
Texture2D<float4> gTexture : register (t0);


Thanks for any help or comments.

Edited by Gavin Williams, 09 December 2012 - 09:52 PM.


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#2 MJP   Moderators   -  Reputation: 10025

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Posted 09 December 2012 - 09:58 PM

You probably just need to transpose your matrices. By default shaders expect column-major matrices in constant buffers, which means transposing row-major matrices when setting them into a constant buffer. The effects framework does this for you, so a lot of people hit this bug when handling constant buffers themselves for the first time.

FYI, you can tell the compiler to expect row-major matrices using a compile flag. You can also mark the matrix with "row_major" in your HLSL code to do the same thing on a per-matrix basis.

#3 Gavin Williams   Members   -  Reputation: 638

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Posted 09 December 2012 - 10:27 PM

Ok, I didn't know that, thanks. So i set the compiler flag ...

ShaderBytecode shaderByteCode = ShaderBytecode.CompileFromFile(
"Walls/effect_Walls.fx",
"fx_5_0",
ShaderFlags.EnableStrictness | ShaderFlags.Debug | ShaderFlags.OptimizationLevel0 | ShaderFlags.PackMatrixRowMajor,
EffectFlags.None);

But still nothing.

Edit : I'm removing the effects framework code just to make sure it's not hiding some mismatched binding or something.

Edit 2 : Here's the updated render code, having removed the effects framework ... but still nothing :

/// <summary>
	    public void RenderToGBuffer(Viewport viewport, ICamera camera, Map map)
	    {
		    DeviceContext context = SlimDXGraphics.Device11.ImmediateContext;

		    // configure input assembler ----------------------------------------------------------
		    context.InputAssembler.InputLayout = layout;
		    context.InputAssembler.PrimitiveTopology = PrimitiveTopology.TriangleList;
		    // set the shaders
		    context.VertexShader.Set(vertexShader);
		    context.PixelShader.Set(pixelShader);

		    // configure rasterizer ---------------------------------------------------------------
		    context.Rasterizer.SetViewports(viewport);
		    context.Rasterizer.State = SlimDXGraphics.RasterState_Solid;
 
		    context.OutputMerger.BlendState = SlimDXGraphics.BlendState_Transparent;
		    foreach (Chunk chunk in map.VisibleChunks)
		    {
			    foreach (KeyValuePair<int, List<Point>> kVPair in chunk.wallInstanceCollectionsDictionary)
			    {
				    // configure input assembler specific to the wall segment shape
				    context.InputAssembler.SetVertexBuffers(0, new VertexBufferBinding(map.wall000.VertexBuffer, VertexPCNT.SizeInBytes, 0));
				   
				    foreach (Point p in kVPair.Value)
				    {
					    // set shader variables specific for each wall section (this will be unnecessary with instancing)
					    // and even without it, the view & proj matrices need only be set for the entire world view frame render pass
					    cBufferStruct.mProj = camera.ProjMatrix;
					    cBufferStruct.mView = camera.ViewMatrix;
					    cBufferStruct.mWorld = Matrix.Translation(new Vector3(p.X, p.Y, 0));
					   
					    using (DataStream data = new DataStream(CBufferStruct.SizeInBytes, true, true))
					    {
						    data.Position = 0;
						    data.Write(cBufferStruct);
						    context.UpdateSubresource(new DataBox(0, 0, data), cBuffer, 0);
						    data.Dispose();
					    }
					    // now bind the constant buffer to the pipeline
					    context.VertexShader.SetConstantBuffer(cBuffer, 0);
 
					    context.PixelShader.SetShaderResource(map.SRVWallTexture, 0);
 
					    // draw -------------------------------------------------------------------------------
					    if (map.wall000.IndexCount == 0)
						    context.Draw(map.wall000.VertexCount, 0);
					    else
						    context.DrawIndexed(map.wall000.IndexCount, 0, 0);
				    }
			    }
		    }

Edited by Gavin Williams, 09 December 2012 - 11:48 PM.


#4 Gavin Williams   Members   -  Reputation: 638

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Posted 10 December 2012 - 02:59 AM

Ok, the above code is ok. It turned out that I was passing in the wrong camera. Which seems strange because it works when i use the effects framework. I'm not sure what's going on there, but the specific problem of using the cBuffer is solved. Thanks MJP for telling me about the Matrix issue.

Edited by Gavin Williams, 10 December 2012 - 03:09 AM.





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