If you want to know more about geometry shaders, I recommend you read the following book. This is done as follows: glProgramParameteri(programName,GL_GEOMETRY_OUTPUT_TYPE,intvalue) Finally, you must also provide the primitive type that will be generated by the geometry shader. Where intvalue can be any of the following values: This is done as follows: glProgramParameteri(programName,GL_GEOMETRY_INPUT_TYPE,intvalue) Provide information about the primitive type that will be sent to the geometry shader. Where intvalue is the number of vertices. This is done as follows: glProgramParameteri(programName,GL_GEOMETRY_VERTICES_OUT,intvalue) by MargraveUnreal Show more Last Updated: Applications: UE 5. Provide the number of vertices the geometry shader will be producing. In this tutorial Ill show how to use displacement or height maps with tessellation using Nanite meshes, a new feature available in Unreal engine since version 5.3. This function sets various parameters concerning the operation of the geometry shader. Such OpenGL API function is glProgramParameteri(). OpenGL APIĪside from the GLSL layout statements, you can also use OpenGL API functions to inform the geometry shader what type of topology to receive or generate. Where topology must be one of the following:Īnd num is the maximum number of vertices this shader will emit. Output topology layout( topology, max_vertices=num ) out This is done by using the following GLSL statement as shown in listing 2: Listing 2. The geometry shader must also be inform of the topology to generate. Where the input topology must be one of the following: For example, the code in listing 1 informs the shader what topology is receiving: Listing 1. The GLSL Layout statements informs the geometry shader the incoming/outgoing primitive topology. This information can be supplied to the shader either in the shader program or through the OpenGL API. Informing the Geometry Shader about topologyĪ geometry shader needs to be told what topology to expect and it needs to be told what topology to generate. For example, points can generate triangles, triangles can generate triangle strips.įigure 2 illustrates the operations that geometry shaders can do. There is no correlation between the input topologies and the output topologies. In the same manner, geometry shaders can only generate a limited number of topologies such as: Geometry shaders can accept limited topologies. Geometry Shaders have limited access to the surrounding vertex information.Geometry Shaders have a limit to the number of new vertices they can create.The geometry shader, although able to generate new geometry, are not intended to provide Level Of Detail (LOD) capability. The geometry shader receive its input from the Vertex/Tessellation shaders and provides its output to the rasterizer. Unlike a Vertex or Fragment shader, a geometry shader can create new geometry.
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