Non-programmable states

In the previous manual we learned how to create GPU programs and bind them into pipeline states. However, GPU programs alone aren't enough to fully define rendering behavior. When creating a GpuGraphicsPipelineState you can also provide it with a set of non-programmable states that control the fixed parts of the GPU pipeline - namely rasterization, depth/stencil operations, and blending.

GpuGraphicsPipelineStateCreateInformation createInformation;
// Bind GPU programs
createInformation.RasterizerState = ...;
createInformation.DepthStencilState = ...;
createInformation.BlendState = ...;

SPtr<GpuGraphicsPipelineState> graphicsPipeline = device->CreateGpuGraphicsPipelineState(createInformation);

There are three non-programmable state descriptors in total:

• RasterizerStateInformation
• DepthStencilStateInformation
• BlendStateInformation

If using Banshee Shading Language you can specify these states directly in a BSL file and should have no need to create them manually.

Rasterizer state

Rasterizer state allows you to control how are 3D polygons, lines or points converted to 2D pixels. You can create it by filling out the RasterizerStateInformation structure and assigning it to a pipeline state descriptor.

// Draw wireframe geometry with no backface culling
GpuGraphicsPipelineStateCreateInformation createInformation;
createInformation.RasterizerState.PolygonMode = PM_WIREFRAME; // Draw wireframe instead of solid
createInformation.RasterizerState.CullMode = CULL_NONE; // Disable backface culling

SPtr<GpuGraphicsPipelineState> graphicsPipeline = device->CreateGpuGraphicsPipelineState(createInformation);

Depth-stencil state

Depth-stencil state allows you to control how are depth and/or stencil buffers modified during rendering. You can create it by filling out the DepthStencilStateInformation structure and assigning it to a pipeline state descriptor.

// Draw with no depth testing or writing, and with a stencil operation that writes 1 for each sample written
GpuGraphicsPipelineStateCreateInformation createInformation;
createInformation.DepthStencilState.DepthReadEnable = false; // Don't test against current contents of depth buffer
createInformation.DepthStencilState.DepthWriteEnable = false; // Don't make any changes to depth buffer
createInformation.DepthStencilState.StencilEnable = true; // Enable stencil operations
createInformation.DepthStencilState.FrontStencilPassOp = SOP_INCREMENT; // Increment by one whenever a front-face stencil operation passes
createInformation.DepthStencilState.FrontStencilComparisonFunc = CMPF_ALWAYS_PASS; // Always pass the stencil operation

SPtr<GpuGraphicsPipelineState> graphicsPipeline = device->CreateGpuGraphicsPipelineState(createInformation);

Blend state

Blend state allows to you to control how is a rendered pixel blended with any previously rendered pixels. You can create it by filling out the BlendStateInformation structure and assigning it to a pipeline state descriptor. Most of blend state options can be controlled individually for up to 8 render targets.

// Set up blending (e.g. for transparent rendering) for the first render target
GpuGraphicsPipelineStateCreateInformation createInformation;
createInformation.BlendState.RenderTargets[0].BlendEnable = true; // Enable blending
createInformation.BlendState.RenderTargets[0].ColorSourceFactor = BF_SOURCE_ALPHA; // Use the current alpha value to blend the source (new value)
createInformation.BlendState.RenderTargets[0].ColorDestinationFactor = BF_INV_SOURCE_ALPHA; // Use the inverse of the current alpha value to blend the destination (stored value)
createInformation.BlendState.RenderTargets[0].ColorBlendOperation = BO_ADD; // Add the source and destination together

SPtr<GpuGraphicsPipelineState> graphicsPipeline = device->CreateGpuGraphicsPipelineState(createInformation);