how to write shader

To write shaders for custom visual effects in SwiftUI, you need to use the Metal shading language. Here are the steps to get started:

1. Instantiate a Shader in SwiftUI:

   • You can instantiate a shader in SwiftUI by calling a function with its name on the shader library. You can also pass additional parameters to your shader function, such as colors, numbers, or images.
   • Example:

     let myShader = ShaderLibrary.myShaderFunction(color: .red, number: 5)
     

2. Apply the Shader to a View:

   • Use the layerEffect view modifier to apply the shader to a view. SwiftUI will call your shader function for every pixel of your view.
   • Example:

     myView.layerEffect(myShader)
     

3. Write the Shader in Metal:

   • Shaders are written in the Metal shading language, not Swift. The shader function name in the Metal file should match the invocation in the shader library.
   • Example Metal shader function:

     fragment half4 myShaderFunction(VertexOut in [[stage_in]], constant float4 &color [[buffer(0)]]) {
         // Shader code here
         return half4(color);
     }
     

4. Understand the Arguments:

   • The position argument refers to the pixel's location, and the layer argument represents your view's content. You can sample the layer to obtain its contents.
   • Example:

     fragment half4 myShaderFunction(VertexOut in [[stage_in]], constant float4 &color [[buffer(0)]]) {
         float2 pos = in.position.xy;
         // Sample the layer content
         half4 layerColor = layer.sample(pos);
         return layerColor * half4(color);
     }
     

For more detailed information, you can refer to the session Create custom visual effects with SwiftUI (20:10).

Relevant Sessions

• Create custom visual effects with SwiftUI
• Port advanced games to Apple platforms

These sessions provide comprehensive insights into writing and optimizing shaders for both SwiftUI and advanced game development on Apple platforms.