Graphics rendering pipeline

Several render stages of the graphics rendering pipeline ：

The first part of the graphics rendering pipeline is Vertex shader (Vertex Shader), It takes a single vertex as input . The main purpose of vertex shaders is to transform 3D The coordinates change to another 3D coordinate （ It will be explained later ）, At the same time, vertex shaders allow us to do some basic processing of vertex attributes .

Primitive Assembly (Primitive Assembly) Phase takes all vertices output by the vertex shader as input （ If it is GL_POINTS, So it's a vertex ）, And all the points are assembled into the shape of the specified element ; The example in this section is a triangle .

The output of the element assembly phase is passed to the geometry shader (Geometry Shader). Geometry shaders take a set of vertices in the form of primitives as input , It can construct new... By generating new vertices （ Or something else ） Elements to create other shapes . In the example , It makes another triangle .

Geometry shaders The output of the is passed into the rasterization phase (Rasterization Stage), Here it maps the primitives to the corresponding pixels on the final screen , Generate for Fragment Shader (Fragment Shader) The fragments used (Fragment). Clipping is performed before the fragment shader runs (Clipping). Clipping discards all pixels beyond your view , To improve the efficiency of execution .

OpenGL One of the clips in is OpenGL All the data needed to render a pixel .

Fragment Shader The main purpose of is to calculate the final color of a pixel , This is all OpenGL Where high-level effects come from . Usually , Fragment shaders contain 3D Scene data （ Like light 、 shadow 、 The color of light and so on ）, This data can be used to calculate the final pixel color .

After all corresponding color values are determined , The final object will be passed to the last stage , We call it Alpha Testing and mixing (Blending) Stage . This stage detects the corresponding depth of the fragment （ And template (Stencil)） value （ The back can speak ）, Use them to determine whether the pixel is in front of or behind other objects , Decide whether you should discard . This stage will also check alpha value （alpha Value defines the transparency of an object ） And mix the objects (Blend). therefore , Even if the color output of a pixel is calculated in the clip shader , When rendering multiple triangles, the final pixel color may also be completely different .