How do I use metal in SwiftUI animations?

To use Metal in SwiftUI animations, you can leverage SwiftUI shaders, which are small programs that calculate various rendering effects directly on your device's GPU. These shaders are written in the Metal shading language. Here's a step-by-step guide based on the information from the WWDC sessions:

1. Create a Shader Function in Metal:

   • Write a shader function in a .metal file. This function will define the visual effect you want to achieve. For example, you might create a ripple effect that distorts the view based on touch input.
   • Example Metal shader function:

     kernel void ripple(texture2d<float, access::read> inTexture [[texture(0)]],
                        texture2d<float, access::write> outTexture [[texture(1)]],
                        constant float2 &touchPosition [[buffer(0)]],
                        constant float &time [[buffer(1)]],
                        uint2 gid [[thread_position_in_grid]]) {
         // Calculate the ripple effect based on touch position and time
         float2 uv = float2(gid) / float2(outTexture.get_width(), outTexture.get_height());
         float dist = distance(uv, touchPosition);
         float ripple = sin(dist * 10.0 - time * 5.0) * 0.1;
         float2 newUV = uv + ripple;
         outTexture.write(inTexture.sample(sampler(), newUV), gid);
     }
     

2. Instantiate the Shader in SwiftUI:

   • Use the ShaderLibrary to load your shader function and apply it to a view using the layerEffect view modifier.
   • Example SwiftUI code:

     struct RippleEffect: ViewModifier {
         var touchPosition: CGPoint
         var time: Float
     
         func body(content: Content) -> some View {
             content
                 .layerEffect(ShaderLibrary.ripple(touchPosition: touchPosition, time: time))
         }
     }
     
     struct ContentView: View {
         @State private var touchPosition: CGPoint = .zero
         @State private var time: Float = 0.0
     
         var body: some View {
             Rectangle()
                 .fill(Color.blue)
                 .modifier(RippleEffect(touchPosition: touchPosition, time: time))
                 .onTapGesture { location in
                     touchPosition = location
                     time = 0.0
                 }
                 .onAppear {
                     withAnimation(.linear(duration: 2.0).repeatForever(autoreverses: false)) {
                         time = 2.0
                     }
                 }
         }
     }
     

3. Apply the Shader to a View:

   • Use the layerEffect view modifier to apply the shader to your SwiftUI view. This will call your shader function for every pixel of the view, running the shader on the GPU for real-time performance.

For more detailed information, you can refer to the session Create custom visual effects with SwiftUI (19:02) which covers how to implement and use Metal shaders in SwiftUI.

Relevant Sessions

• Create custom visual effects with SwiftUI
• Enhance your UI animations and transitions
• What’s new in SwiftUI