Stretch and Resize an Image Dynamically in SwiftUI with Custom Edge/Corner Manipulation Using Metal Shader

Question

I’m working on a SwiftUI project where I need to stretch and resize an image dynamically, similar to how images are manipulated in Photoshop. Specifically, I want to achieve the following functionalities, with Metal shaders used for rendering effects:

Stretching from Edge Points:

• The goal is to be able to grab and drag the edges or corners of an image (much like the interactive resizing you see in design apps like Photoshop). As the edges or corners are dragged, the image should stretch and modify its aspect ratio dynamically.
• Each corner or edge of the image should be draggable, and as I move these points (top-left, top-right, bottom-left, and bottom-right), the corresponding parts of the image should stretch in real-time.
• Example: If I grab the top-right corner of the image, only the top-right section of the image should stretch, while keeping the left side intact. The same applies to each edge and corner.

Resizing with Distortion Effects:

• I want to distort the image as it resizes, meaning the aspect ratio should not be preserved while stretching or resizing. This allows for a completely freeform stretch effect, as opposed to being constrained by the original aspect ratio.
• For instance, when dragging one of the corners, the width and height of the image can change independently, creating a stretched or distorted effect.

Real-Time Rendering:

• The stretching effect should be applied smoothly while dragging, without causing any noticeable flickering or lag. It should feel responsive and fluid as the user moves the corners or edges, similar to the interaction in graphical design tools.
• The interaction should be intuitive and easy for users to adjust the image dynamically.

Metal Shader (Mandatory):

• I will definitely be using Metal for custom rendering effects to handle the dynamic stretching and distortion of the image.
• A Metal shader is necessary to implement the image manipulation, ensuring that real-time transformation effects are applied with smoothness and performance.
• I’m particularly focused on utilizing Metal to apply these custom stretching and distortion effects, as standard SwiftUI functionality doesn’t meet the needs for freeform image manipulation.

Key Challenges:

• SwiftUI’s built-in resizable(), scaledToFit(), and scaledToFill() modifiers all enforce constraints on aspect ratio, which is not suitable for this use case since I want freeform stretching without maintaining the aspect ratio.
• The ability to drag and stretch specific parts of the image (corners or edges) in real-time is crucial, and SwiftUI lacks built-in support for this.
• Custom image distortion and applying smooth, real-time transformations are key requirements that need to be implemented in a fluid and efficient way, and this is where Metal shaders will be essential.

What I’ve Tried:

• I’ve experimented with SwiftUI’s resizable() modifier, but it’s not flexible enough for this use case as it enforces aspect ratio constraints.
• I’ve looked into using GeometryReader to capture drag gestures on specific points (edges or corners), but I’m not sure how to bind these gestures to the image transformation dynamically in a way that also handles distortion.
• Metal shaders will be used to implement the image manipulation and distortion, but I’m unsure about the specifics of integrating Metal into SwiftUI for this purpose.

Desired Outcome:

• The image should be able to stretch and distort freely when dragging any corner or edge, without preserving the aspect ratio. The transformation should happen in real-time while dragging, with smooth, fluid rendering and no lag or flickering.
• Metal shaders should be used for custom image rendering effects to achieve smooth real-time stretching and distortion.

Example Image (Illustration of Desired Outcome): To illustrate, here is an example showing how the image should behave when dragged from the edges or corners:

This image should be manipulated dynamically as described, with each edge or corner draggable, causing the image to stretch from that specific point.

Any insights, examples, or guidance on how to implement this feature using SwiftUI and Metal shaders would be greatly appreciated!