How to create custom modal transition animations in swiftui?

To create custom modal transition animations in SwiftUI, you can define a custom transition by creating a new struct that conforms to the Transition protocol. Here's a brief overview of how you can achieve this:

1. Define a Custom Transition: Create a new struct for your custom transition. For example, you might call it Twirl.

2. Conform to the Transition Protocol: Implement the transition protocol, which requires a body function. This function takes content and phase parameters.

3. Use the Phase Parameter: The phase parameter helps determine if a view is currently being shown. You can use this to conditionally style your view. For instance, you might want the view to be at full scale when shown and at half scale when not.

4. Apply the Custom Transition: Attach your custom transition to your view to see the result.

Here's a snippet from the session "Create custom visual effects with SwiftUI" that discusses creating a custom transition:

In order to create a custom transition, I'll create a new struct. I'll call it twirl. This will conform to the transition protocol. The transition body function takes a content and phase parameter. The content parameter works the same as what I shared for the scroll views. As a placeholder for the content I want to transition, I can use the phase value to check if a view is currently being shown and use that to conditionally style my view for scale, I'd like it to be at full scale when it's shown and at half the scale when it's not. For opacity, I'd like my element to toggle between fully visible and hidden. I can attach my custom transition to my view and check out the result.

For more detailed guidance, you can refer to the session Create custom visual effects with SwiftUI (10:13).