Guide to Built-in Legacy Shaders

The shader code related to Legacy Shader is located in two folders.

• internal/chunks/legacy/
• internal/effects/legacy/

In the chunks/legacy/ folder, there are some common functions, such as decode, fog, input, output, shadows, skeletal skinning, and so on.

Both Legacy Shader and Surface Shader will call functions provided in internal/chunks/builtin/ and internal/chunks/common/.

In the effects/legacy/ folder, there are three built-in Legacy Shaders:

• standard: for standard PBR
• terrain: for terrain
• toon: for cartoon rendering

Basic Structure

The code of Legacy Shader is usually composed of several parts:

• CCEffect: Describes the techniques, passes, shader entries, rendering states, properties, etc.
• Shared UBOs: Used to define uniforms that are needed by both vs and fs together for easy access.
• Shader Body: Used to implement the shader code

The CCEffect and Shared UBOs in Legacy Shaders are consistent with that in Surface Shaders, For more details, please go to Guide to Built-in Surface Shader.

Shader Functions

For a better understanding of the rendering process, please first check to Understand the Render Flow of Forward Rendering and Deferred Rendering。

standard(PBR)

In the legacy/standard.effect file, we can see the shader code.

CCProgram standard-vs %{
    //...
    void main(){
        StandardVertInput In;
        CCVertInput(In);
        //...
        gl_Position = cc_matProj * (cc_matView * matWorld) * In.position;
    }
}%
CCProgram standard-fs %{
    //...
    void surf(out StandardSurface s){
        //s.albedo = ...
        //s.occlusion = ...
        //s.roughness = ...
        //s.metallic = ...
        //s.specularIntensity = ...
        //s.normal = ...
    }
    CC_STANDARD_SURFACE_ENTRY()
}%

You can see that in the vertex shader, the main function is directly used as the entry point, while in the fragment shader, there is only a surf function.

This is because after expanding the CC_STANDARD_SURFACE_ENTRY, it becomes the main function, and this main function will call the surf function.

terrain

The terrain uses StandardSurface as the material surface data structure and CC_STANDARD_SURFACE_ENTRY as the entry point. This indicates that the rendering process and lighting calculations of the terrain are completely the same as standard.

However, because the terrain uses a multi-textures blend, the textures used by the terrain and the code of the surf function are significantly different from the standard.

toon

In legacy/toon.effect, we can see.

CCProgram toon-vs %{
    //...
    void main(){
        StandardVertInput In;
        CCVertInput(In);
        //...
        gl_Position = cc_matProj * (cc_matView * matWorld) * In.position;
    }
}%
CCProgram toon-fs %{
    //...
    void surf(out ToonSurface s){
        //s.baseStep = ...
        //s.baseFeather = ...
        //s.shadeStep = ...
        //s.shadeFeather = ...
        //s.shadowCover = ...
    }
    void frag(){
        ToonSurface s; surf(s);
        vec4 color = CCToonShading(s);
        return CCFragOutput(color);
    }
}%

The biggest feature of toon is that it defines an additional outline pass in the CCEffect section, and the code of the outline pass is located in chunks/legacy/main-functions/outline-vs(fs).

The structure of surface material data is ToonSurface, which is different from the one used by the standard. In the frag function, you can see that the lighting calculation of the toon uses a special CCToonShading.

Moreover, toon defines its own frag entry function and does not use the CC_STANDARD_SURFACE_ENTRY macro. This means that toon does not support the deferred rendering pipeline.

shadow-caster

You can see that the standard, terrain, and toon all have code fragments related to shadows.

CCProgram shadow-caster-vs %{
    //...
}%
CCProgram shadow-caster-fs %{
    //...
}%

This set of vs/fs is used for shadow map generation. During the shadow stage, the engine rendering pipeline will search for objects which have the pass with the phase of ‘shadow-add’ to draw.