# 第四节：游戏引擎中的渲染实现

## 渲染概述

### Challenges on Game Rendering

1. Complex render objects
2. Deal with architecture of modern computer with a complex combination of CPU and GPU
3. Commit a bullet-proof framerate, 4. 30 or 60 or 120 fps 5. HD, 1080p, 4k, 8k
4. CPU memory

### Rendering on Game Engine

A heavily optimized parctical software framework to fulfill the critical rendering requirements of games on modern hadware

### Outline of Rendering

1. Basics of Game Rendering
   * Hardware architecture
   * Render data organization
   * Visibility
2. Materials, Shaders and Lighting
   * PBR
   * Shader permutation
   * Lighting
   * Point / Directional lighting
   * IBL / Simple GI
3. Special Rendering
   * Terrain
   * Sky / Fog
   * Postprocess
4. Pipeline
   * Forward, deferred rendering forward plus
   * Real pipeline with mixed effects
   * Ring buffer and V-Sync
   * Tiled-based rendering

## 渲染系统的对象

### Building Block of Rendering

![image-20220413212212448](https://image-1253155090.cos.ap-nanjing.myqcloud.com/202308021852078.png)

![image-20220413212321697](https://image-1253155090.cos.ap-nanjing.myqcloud.com/202308021853463.png)

![image-20220413212331478](https://image-1253155090.cos.ap-nanjing.myqcloud.com/202308021854047.png)

### Computation - Texture Sampling

昂贵的三线性滤波，采样 8 个像素点，7 次滤波

1. Use tow nearest mipmap levels
2. Perform bilinear inerpolation in both mip-maps
3. Linear interpolate between the results

## GPU 架构

The dedicated hardware to solve massive jobs

### SIMD and SIMT

* SIMD 单指令多数据

![image.png](https://image-1253155090.cos.ap-nanjing.myqcloud.com/202308021903257.png)

* SIMT 单指令多线程

![image.png](https://image-1253155090.cos.ap-nanjing.myqcloud.com/202308021904181.png)

### GPU Architecture

架构和不同核心

![image-20220413212419569](https://image-1253155090.cos.ap-nanjing.myqcloud.com/202308221914508.png)

数据流动

cpu 到 gpu 的高延迟

![image-20220413212434311](https://image-1253155090.cos.ap-nanjing.myqcloud.com/202508292000758.png)

多级缓存，数据尽量要放在一起

![image-20220413212513383](https://image-1253155090.cos.ap-nanjing.myqcloud.com/202308221934117.png)

### GPU Bounds and Performance

* Memory Bounds 内存瓶颈
* ALU Bounds 计算瓶颈
* TMU (Texture Mapping Unit) Bound 纹理采样瓶颈
* BW (Bandwidth) Bound 数据传输瓶颈

![image-20220413212550528](https://image-1253155090.cos.ap-nanjing.myqcloud.com/202308221936217.png)

![image-20220413212555358](https://image-1253155090.cos.ap-nanjing.myqcloud.com/202308221936208.png)

## Renderable

可绘制的东西

* Mesh Render Component
* Building Blocks of Renderable
* Mesh Primitive
  * struct Vertex
    * position
    * color
    * normal
  * struct Triangle
    * Vertex\[3]
* Vertex and Index Buffer

  * Vertex Datda
  * Index Data

  ![image-20220413212626112](https://image-1253155090.cos.ap-nanjing.myqcloud.com/202309041706687.png)
* We Need Per-Vertex Normal
* Materials ![image-20220413212640347](https://image-1253155090.cos.ap-nanjing.myqcloud.com/202309041706166.png)
* Material Model ![image-20220413212730864](https://image-1253155090.cos.ap-nanjing.myqcloud.com/202309041706757.png)
* Various Textures in Materials
* Variety of Shaders

## Render Objects on Engine

* Coordinate System and Transformation
* Object with Many Materials
* Resource Pool
  * Use Handle to Reuse Resources

    ![image-20220413213129463](https://image-1253155090.cos.ap-nanjing.myqcloud.com/202309041722675.png)

    ![image-20220413213209476](https://image-1253155090.cos.ap-nanjing.myqcloud.com/202309041724766.png)
* Instancing 实例化，前边的都是物体绘制的定义，实际上绘制到屏幕上才是实例
* Sort by Material
* GPU Batch Rendering

  ![image-20220413213223322](https://image-1253155090.cos.ap-nanjing.myqcloud.com/202309041724775.png)

## Visibility Culling 可见性裁剪

* Culling One Object
  * View Frustum
  * Bounding Box
  * Hierarchial View Frustum Culling
  * Construction and Insertion of BVH in GameEngine
    * BVH 在动态物体多的情况下构建成本低
    * PVS (Potential Visibility Set) 对于空间上的一点关于其他物体的潜在可见性，即是否不会被其他物体遮挡
    * The Idea of Using PVS in Stand-alone Games
  * GPU Culling
    * Depth pre pass / early z 提前渲染深度到 z buffer，防止重复像素点着色

## Texture Compression

纹理压缩

* Traditional image compression like JPG and PNG
* In game texture compression
  * 需要支持随机访问
* Block Compressions
  * Common block-based compression format
  * On PC BC7 or DXTC
  * On mobile, ASTC or ETC

## Authoring Tools of Modeling

* Modeling
  * Polymodeling : MAX, MAYA, Blender 网格建模
  * Sculptiong : 雕刻
  * Scanning : 扫描
  * Procedural Modeling : 程序化生成

## Cluster-Based Mesh Pipeline

* Sculpting Tools Create Infinite Details 无数的细节
* GPU-Driven Rendering Pipeline
* Geometry Rendering Pipeline Architecture
* Programmable Mesh Pipeline
* Mesh shader, cluster base mesh

  ![image-20220413213322563](https://github.com/okzkx/Blog/blob/master/game-tech/engine/tutorials/games-104/image-20220413213322563.png)
* GPU Driven
  * 把越来越多 CPU 上的计算放到 GPU 上做

## PILOT

小引擎项目 <https://github.com/BoomingTech/Pilot>


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