[ta- frost wolf \u may- hundred people plan] 1.1 rendering pipeline

【TA_ Frost Wolf _may《 Hundred people plan 》】1.1 Rendering pipeline

As the title , This is frost wolf _may《 Hundred people plan 》 A record of learning , Clear direction , Start studying hard .

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1.1.1 Application stage

Prepare basic scene data

The basic data include ：

• Scene object data
  • Object transformation data ： Location 、 rotate 、 The zoom
  • Object grid data ： Vertex Position 、uv Mapping
• Camera data
  • Location 、 Direction 、 Near and far clipping plane
  • orthogonal / perspective （FOV）
  • Viewport scale / Size, etc
• Light source shadow data （ There are many contents in this part , Shadow related knowledge is not understood ）
  • Type of light source ： Directional light 、 Spot light 、 Spotlight
  • Other parameters of the light source ： Location 、 Direction 、 Angle, etc.
• And other global data

Acceleration algorithm

Coarse grained culling
Those outside the scene can be eliminated , Those blocked by objects in front can also be eliminated .

The basic operations include ：

• collision detection
• Acceleration algorithm
• Occlusion culling
• Other algorithms

Visible scene object clipping algorithms are ：

• Octree
• BSP Trees
• K-D Trees
• BVH

Set render state

Prepare rendering parameters
The basic operations include ：

• Draw settings （ Different objects may have different shader（ Shaders ） To render ）
• Draw order （ for example ： Render from near to far or from far to near , The rendering order of opacity and translucency is determined ）
• Render Target （ Destination settings for rendering results （ RenderTexture or FrameBuffer））
• Rendering mode （ Imaging rendering or Deferred Shading ）

call DrawCall

Output rendered primitives to video memory
The data to be used include ：

• Vertex data
• Other data

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1.1.2 Geometric stage

Vertex Shader

The overall process is as shown in the figure ：

Model transformation , View transformation , Projection transformation consists of MVP（Model、View、Projection） matrix .

Surface subdivision

The overall process is as shown in the figure ：

Geometric coloring （ Element based operations ）

The overall process is as shown in the figure ：

Projection

Different projections have different characteristics , Use perspective division to process , It is divided into orthogonal projection and perspective projection .

In perspective projection , Object's w The value increases with distance from the camera , Coordinate points （xyz） By dividing by w To get the result coordinates of perspective , So as to achieve the purpose of perspective imaging .

Orthogonal projection w The value is always 1, It may be more similar to 2D imaging .
This step is NDC 了 .

tailoring

Remove targets and vertices outside the field of view .
The cutting diagram is as follows ：

Add ： The equipment coordinate system is openGL and D3D It's different in ：

• opnGL in ,xyz All three dimensions are -1 ~ 1
• D3D in ,xy by -1 ~ 1,z by 0 ~ 1

Screen mapping

Map the position in the standard coordinate system to the screen coordinate system .

It is also important to note that , The origin position of the screen coordinate system is openGL and D3D There are also differences in ：

• openGL The screen origin is at the bottom left
• D3D The screen origin is at the top left

1.1.3 Grating stage

Triangle settings

After knowing the vertex information of triangle or line , You want to know which pixels this primitive covers , It is necessary to obtain its boundary information . The process of calculating boundary information is called triangle setting . Triangle information contains line information , The following content only discusses the case of triangles .

Triangle traversal

Through the edge information of the triangle , Using interpolation algorithm , Assign values to all pieces inside the triangle .

Be careful , The boxes in the above figure represent slices, not pixels , Because in the same pixel position on the screen , There may be different pieces corresponding to multiple triangles .

Anti-Aliasing

many-ways ：

• SSAA（ Enlarge the rendering resolution n times , Again buffer Take the next sample ）
• MSAA
  • Only this method operates in the rasterization stage
  • Set multiple sub sampling points for each pixel
  • Then the coverage test and occlusion test are carried out for each sub sampling point
    • Coverage test is to judge whether the sub sampling point is in the triangle
    • Occlusion test is to compare the sub sampling point with the data in the depth cache , See if you can pass
  • The sub sampling points passing the above test belong to the triangle
  • In the following triangle coloring , Scale shading by sub sample points belonging to triangles （ This sentence needs further understanding ）

1.1.4 Slice by slice operation

Chip coloring

Color blending

Including a variety of testing links ：

• Transparency test
  
• Depth testing 、 Template testing
  
  The purpose and significance of the template test here are not well understood , You can learn more about .

blend

Combine all kinds of information （ Including color 、Alpha、 Depth, etc ）, Mix the final color . There are many ways to mix ： superposition …

Overall process summary