[TA frost wolf \u may- hundred people plan] 1.3 secret of texture

---

1.3 Three questions about texture

1.3.1 What is the texture ？

Any picture can be a texture ,
From the perspective of computer rendering , It is a structured storage form that can be read and written by shaders .

Textures can be more than just pictures , You can also include various settings when sampling textures .

1.3.2 Why texture is needed ？

By sacrificing geometric details , Achieve the purpose of greatly reducing the workload , It can effectively save storage space and improve reading speed .

1.3.3 Texture pipeline

The whole process of texture pipeline ：

Model space location =》
Projection function （ It is completely different from the projection in the geometric phase of the overall process of rendering the pipeline before , Pay attention to distinguish between ）=》
Texture mapping =》
Texture coordinates =》
Communication function =》
New texture coordinates =》
Texture sampling （ Avoid relying on texture reading ）=》
Texture value

Example

1.3.4 Texture sampling settings Wrap Mode

decision UV Values in [0,1] Performance beyond
OpenGL ——“ Packaging mode ” （Wrapping Model）
DirectX ——“ Texture addressing mode ”（Texture Addressing Model）

The following is a Wrap Mode Four common methods of , To solve when uv Mapping coordinates to [0,1] Extraneous problems . It is divided into ：Repeat,Mirror,Clamp,Border

1.3.5 Texture sampling settings Filter Mode

When the texture changes due to stretching, which filtering mode should be used to adjust its performance . Simply speaking ： It is used to resist the distortion caused by graphic distortion （ I summed it up myself ）.
In general , Texture filtering is accomplished through a series of specific technologies on proprietary hardware , It can also be done in software , You can also combine software and hardware .

1.3.5.1 Zoom in ：

• Nearest neighbor

  • The method of sampling the same texture element through multiple pixels , To achieve the purpose of amplification , So as to produce the phenomenon of pixelation .
  • It costs less

• Bilinear interpolation

  • Examples are as follows ：
    
    （u’,v’） The origin of ：
  1. adopt uv Coordinates get the center coordinates of the current texture ,
  2. Thus, the nearest four pixels that can wrap the current texture element position are derived ,
  3. Then the coordinates are formed based on the four points ,
  4. The position of the texture element in this coordinate system is the above （u’,v’）.
  • The bottom formula achieves the purpose of linear interpolation by adding four times of weights , The effect is four times that of the nearest neighbor .

• cubic convolution

  • Simple understanding , Do it yourself
    

• Qu’iLez Smooth linear interpolation

  • There are two common curves ：
    
    Interpolation process of smooth curve ：
    

Effect comparison diagram of four methods ：

1.3.5.2 narrow ：

• Nearest neighbor
  
• Bilinear interpolation
  • The performance is similar to that of the nearest neighbor ,2x2 The sampling method of is still not able to resist the flicker conditions listed in the above figure .
• Mipmap
  • Take the original picture as the bottom of the pyramid
  • take 2x2 Of 4 The average value of adjacent textures is used as the new texture element value of the next level
  • Repeat until the pixel size is 1x1
  • The overall data occupation is only more 1/3
  • The key is to choose the right level( important )
  • There is a question ：overblur
    • Use anisotropic filtering
    • SAT
  • （ This part needs game101 The basis of , Make up for it gkd）

Common ways of rendering optimization

• in the light of CPU： Texture atlas / Array
  • prompt CPU and GPU Parallel work
  • DrawCall It's one of them , The bottleneck lies mainly in CPU - GPU The optimization mainly starts from the bandwidth
  • Texture compression

Introduction to common textures

• Cube map CubeMap（ Commonly used for environment mapping ）
• Bump map Bump Mapping
  
• Displacement mapping Displacement Mapping
  

summary

Filter Mode With what kind of ？

1. Zoom in ：
   • Nearest neighbor ： Take values directly from a single texture element
   • Bilinear interpolation ： take 2x2 The texture element of
   • q Curve interpolation ： The effect is between bilinear interpolation and cubic convolution interpolation
   • Cubic convolution interpolation ： take 4x4 Pixels , And consider the rate of change
2. narrow ：
   • Nearest neighbor
   • Bilinear interpolation
   • mipmap（ heavy difficult Look again games101）

Texture Optimization Methods and principles ：

1. cpu Optimize , Combine with texture number , Texture collection , promote CPU performance , Reduce DrawCall
2. gpu Optimize , Using texture compression , Make effective use of limited bandwidth .