2020_11_19_physically_based_shader_development_for_unity_2017.md

Physically Based Shader Development for Unity 2017

• hlsl 从 Unity 2019.3 的 URP 开始启用（之前用的 Cg）
• 原书用的 Surface Shader，本文改写为 hlsl 版本

Chapter 1 - How Shader Development Works

What Is a Shader?

Shader Execution

• A rendered scene containing only a cube with colored vertices

• The scene's vertices and their respective data are passed to the vertex shader.
• A vertex shader is executed on each of them.
• The vertex shader produces an output data structure from each vertex.
  • Vertex contains information such as color and position of the vertex on the final image.
• Sequences of vertices are assembled into primitives, such as trianges, line, points, and others.
• The rasterizer takes a primitive and transforms it into a list of pixels.
  • For each potential pixel within that triangle, that structure's values are interpolated and passed to the pixel shader.
• The fragment shader (pixel shader) is run for any potential pixel.
  • Most lighting calculations happen here.
• If the renderer is a forward render, for every light after the first, the fragment shader will be run again, which that light's data.
• Each potential pixel (aka, fragment) is checked for whether there is another potential pixel nearer to the camera, therefore in front of the current pixel.
  • If there is, the fragment will be rejected.
• All the fragment shader light passes are blended together.
• All pixel colors are wirtten to a render target (could be the screen, or a texture, or a file, etc.)

Different Types of Shaders

• Vertex shader
• Fragment shader / Pixel shader
• Compute shader
  • computes arbitrary calculations, not necessarily rendering, e.g., physics simulation, image processing, raytracing
  • in general, any task that can be easily broken down into many independent tasks
• Unlit shader (Unity-only)
  • a shader that combines a vertex and pixel shader in one file
• Surface shader (Unity-only)
  • contains both vertex and fragment shader functionality
  • takes advantage of the ShaderLab extensions to the Cg shading language to automate some of the code that's commonly used in lighting shaders
• Image Effect shader (Unity-only)
  • used to apply effects like Blur, Bloom, Depth of Field, Color Grading, etc.
  • It is generally the last shader run on a renderer, because it's applied to a render of the geometry of the scene

Coordinate Systems

• Local (or Object) Space
  • The 3D coordinate system relative to the model being rendered
• World Space
  • The 3D coordiate system relative to the entire scene being rendered
• View (or Eye) Space
  • The 3D coordinate system relative to the viewer's point of view (the camera you're rendering from)
• Clip Space
  • A 3D coordinate system that has a range of -1.0 to 1.0
• Screen Space
  • The 2D coordinate system relative to the render target (the screen, etc.)
• Tangent Space
  • Used in Normal Mapping

Types of Light

• Point light
• Directional light
• Area light (only for baking lightmaps)

The Rendering Equation

The Behavior of Light

TODO

Bounced Light

Bouched light will keep bouncing untli the energy is completely used up. That is what GI (Global Illumination) simulates.

• Direct light
  • The light that hits a surface directly.
• Indirect light
  • The light that hits the object after bouncing off from another surface.

Direct light only

Direct and indirect light

Renderer Types

• Forward
• Deferred
• Forward+ (Tiled Forward Shading)
• URP (Universal Render Pipeline)

Shader Visual Graphs

• Unity doesn't include one
• ShaderForge, a 3rd-party implementation

Chapter 2 - Your First Unity Shader

• 场景中，创建一个 Cube
• Assets中，创建一个 Material，命名为 "RedMaterial"
• Assets中，创建一个 Unlit Shader，命名为 "RedShader"
• 将 "RedMaterial" 的 shader 设置为 "RedShader"

• 将 "RedMaterial" 从 Assets 中拖入 Cube 上，赋给它
• 此时，Cube 是白色。Inspector面板 上可看到 Materials 设置为 "RedMaterial"

• 双击 "RedShader"，可以看到原始文件内容，如下
• 把 _MainTex ("Texture", 2D) = "white" {} 改为 = "red" {} 就变红了
• 太简单了，没啥好说的

Shader "Unlit/RedShader"
{
    Properties
    {
        _MainTex ("Texture", 2D) = "white" {}
    }
    SubShader
    {
        Tags { "RenderType"="Opaque" }
        LOD 100

        Pass
        {
            CGPROGRAM
            #pragma vertex vert
            #pragma fragment frag
            // make fog work
            #pragma multi_compile_fog

            #include "UnityCG.cginc"

            struct appdata
            {
                float4 vertex : POSITION;
                float2 uv : TEXCOORD0;
            };

            struct v2f
            {
                float2 uv : TEXCOORD0;
                UNITY_FOG_COORDS(1)
                float4 vertex : SV_POSITION;
            };

            sampler2D _MainTex;
            float4 _MainTex_ST;

            v2f vert (appdata v)
            {
                v2f o;
                o.vertex = UnityObjectToClipPos(v.vertex);
                o.uv = TRANSFORM_TEX(v.uv, _MainTex);
                UNITY_TRANSFER_FOG(o,o.vertex);
                return o;
            }

            fixed4 frag (v2f i) : SV_Target
            {
                // sample the texture
                fixed4 col = tex2D(_MainTex, i.uv);
                // apply fog
                UNITY_APPLY_FOG(i.fogCoord, col);
                return col;
            }
            ENDCG
        }
    }
}

• CGPROGRAM/ENDCG - Cg Program

CGPROGRAM
v2f vert (appdata v)
{
    v2f o;
    o.vertex = UnityObjectToClipPos(v.vertex);
    o.uv = TRANSFORM_TEX(v.uv, _MainTex);
    UNITY_TRANSFER_FOG(o,o.vertex);
    return o;
}

fixed4 frag (v2f i) : SV_Target
{
    // sample the texture
    fixed4 col = tex2D(_MainTex, i.uv);
    // apply fog
    UNITY_APPLY_FOG(i.fogCoord, col);
    return col;
}
ENDCG

• HLSLPROGRAM/ENDHLSL - 2019.3 可以用 hlsl

HLSLPROGRAM
#pragma prefer_hlslcc gles
#pragma exclude_renderers d3d11_9x
#pragma target 3.5
#pragma multi_compile_fwdadd

#pragma shader_feature __ _NORMALMAP
#pragma shader_feature __ _ALPHATEST_ON

#define _TONE_MAPPING 1
#define BIOUM_ADDPASS

#pragma vertex ForwardAddVert
#pragma fragment ForwardAddFrag

#include "CharacterCommonPass.hlsl"
ENDHLSL

Chapter 3 - The Graphics Pipeline

TODO