One of the things that gives GPUs their significant performance advantages over CPUs is that GPUs are able to perform many more computations in parallel. For conditional branches, the command can be broken down into the math that computes the condition (executed on the math unit), followed by the command processor reading the result of the condition and picking the next command to execute based on that. If that command is a branch operation, it is the command processor that figures out where to branch to, to pick which command to execute next. The command processor is responsible for reading a command and telling the mathematical unit what to do, then reading the next command. Let us hypothetically divide up a computational unit of a CPU or GPU into a command processor and mathematical unit (note that this division isn't really true, but it is useful for this discussion). Compute shader invocations within a work group have some limited intercommunication functionality.
These instances however cannot write data (in any way, whether fragment shader outputs, Image Load Store or anything else). It may be executed more than this, as "helper" fragment shader instances may be used by the implementation. Fragment Shaders: Once per Fragment generated by the rasterizer.Geometry shader instancing allows the GS to be invoked multiple times for each input primitive. Geometry Shaders: Once per primitive reaching this stage.
#What is shader model 3.0 Patch
The minimum number of TES invocations is once per unique vertex in the patch the maximum is one for each vertex for each primitive generated by a patch. A unique vertex in the patch may be processed more than once. Tessellation Evaluation Shaders: Approximately once per vertex in the tessellation of the abstract patch.Invocations operating on the same input patch can intercommunicate though their output variables. Tessellation Control Shaders: Precisely once per output vertex per patch.This may be less than once per vertex if indexed rendering is used, due to the Post Transform Cache, but it will be at least once for each unique set of vertex attributes. Vertex Shaders: Approximately once per input vertex in the vertex stream.Exactly how many invocations execute for most shader stages depends on the amount of stuff being rendered and the nature of that shader stage. With a rare few exceptions, shader stage invocations cannot interact with one another. Each shader stage defines the frequency at which it executes.Įach execution of a shader stage within a Rendering Command is called an "invocation".
#What is shader model 3.0 code
The programmable portions of the Rendering Pipeline will execute the shader code stored in the currently used program(s).Įach shader stage that has code executes one or more times, based on exactly what is rendering. When a drawing command is executed, the currently bound Program Object, or Program Pipeline Object, will be used in the rendering operation. So while program objects can contain multiple stages, shader objects only contain code for a single stage. As such, shader objects are built for a specific shader stage. While shader stages do use the same language, each stage has a separate set of inputs and outputs, as well as built-in variables. A program pipeline object can combine programs that contain individual shader stages into a whole pipeline. (requires GL 4.3 or ARB_compute_shader)Ī program object can combine multiple shader stages (built from shader objects) into a single, linked whole. (requires GL 4.0 or ARB_tessellation_shader) Tessellation Control and Evaluation Shaders: GL_TESS_CONTROL_SHADER and GL_TESS_EVALUATION_SHADER.The OpenGL rendering pipeline defines the following shader stages, with their enumerator name: Shaders are written in the OpenGL Shading Language. Each stage has a set of inputs and outputs, which are passed from prior stages and on to subsequent stages (whether programmable or not). Each of these sections, or stages, represents a particular type of programmable processing. The rendering pipeline defines certain sections to be programmable.