Pipeline concept of graphic technology

Pipeline： The output of each step will be used as the input of the next step , Render passes in GPU Is a parallel operation , The blue background part can be passed through shader Code control

1. Vertex Shader

Vertex transformation ; Coordinate transformation

2. Shape Assembly / Primitive Assembly

Convert vertices to primitives ( Here is the triangular surface ), And cut out the primitive data in the field of view

3. Geometry Shader

Generate other primitives by increasing or decreasing vertices

4. Rasterization / Rasterize

Rasterization is the process of transforming an entity into a two-dimensional image , Each point on the two-dimensional image contains color 、 Depth and texture data , Such a point is called pianyuan fragment

An entity will be converted to multiple slices , And type in fragment shader in

The process ：4 The vertices are rasterized to form a 10*10 Pixel graphics , be fragment shader Parallel processing 100 Time (Vertex shader parallel processing 4 Time )

5. Fragment Shader

Texture mapping of slices 、 Light calculation forms pixels

6. Test and Blend

In the end ,fragment Shader The output pixels in also need to be connected with buffer Pixel points at corresponding positions stored in （ Other objects rendered in the current frame ） Carry on all kinds of test And blending after , Form the pixels finally displayed on the screen

Stencil Test ( Template testing )：

by shader Set a reference value for the rendered pixels in Ref , Then with stencil buffer Compare the values stored in the corresponding pixel in , Render through or discard

Each pixel on the screen has a  stencil buffer value , The default is 0, Can be set to 0 - 255

Use Stencil test when , The usual practice is to use a shader to update buffer value , In passing for others shader Set up Ref From previous buffer Comparison produces various special effects

Depth Test ( Depth testing )：

By default , Compares the depth value of the current rendered pixel with Depth buffer Compare the depth values of the corresponding pixels in , If it is smaller than the value in the cache , Replace the value of the corresponding pixel in the cache with the new pixel value , After the in-depth test , The order in which objects are rendered is less important , Can be displayed normally according to the depth value

ZWrite： When on, the depth value is written to depth buffer in , Pixel if no depth value is written , It seems that there is no near and far effect

ZTest： adopt ZTest The depth value and color value can be written into the cache ( stay ZTest after , If the color value is not written to the cache , The rendered pixels will not show the color on the final screen )

Blend ( blend )：

Defines the current rendered pixel and frame cache (G buffer) Blending between rendered pixels in

Rendered pixels are ： Pixels of other objects rendered in the current frame , Like the pixels of another piece of rendered grass

grammar ：Blend SrcFactor DstFactor ( New rendered pixels * SrcFactor + There are already pixels on the screen * DstFactor)

 

other ：

G buffer There is a store of ： Template cache (stencil buffer)、 The depth of the cache (z / depth buffer)、 Color the cache (color / pixel buffer) Etc

Reference documents ：learnopengl  Nishikawa Shinji