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How To: Instance a Geometry Shader

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Geometry shader instancing allows multiple executions of the same geometry shader to be executed per primitive. To instance a geometry shader, add an instance attribute to the main shader function and identify an instance index parameter in the shader function body.

To Instance a Geometry Shader:

  1. Add the instance attribute to the main function.

    [instance(24)]

    This defines the number of instances (a maximum of 32) to be run for each primitive.

  2. Attach the SV_GSInstanceID system value to a variable in the function parameter list that can be used to track the ID of the instance being executed.

    uint InstanceID : SV_GSInstanceID

  3. Compile and create the shader just as you would any other geometry shader.

Other details include:

  • The maximum instance count is 32.
  • The maximum vertex count is a per-instance maximum vertex count.
  • Each instance invocation (like any geometry shader invocation) increases the invocation count and generates an implicit RestartStrip().

Geometry Shader Features