Resizable Rendering

Guidance for keeping custom rendering surfaces — Metal views, video layers, maps, charts, canvases, web views, PDF viewers — correct while their window resizes live and moves between screens with different display scales.

When to Use

Use this skill when:

• MTKView or CAMetalLayer content stretches, blurs, or letterboxes when the window resizes
• Deciding what to recompute in drawableSizeWillChange (projection, viewport, render targets)
• Keeping frame rate up while the user drags the window edge (live-resize throttling)
• A video layer, camera preview, map overlay, chart, Canvas, web view, or PDFView misbehaves at new window sizes
• Thumbnails or pre-rendered images come out blurry after moving to another screen (Mirroring, external display)
• Auditing rendering code that reads a size once and caches it

Example Prompts

• "My MTKView content stretches when the iPad window resizes"
• "When do I update CAMetalLayer drawableSize?"
• "How do I keep my Metal app responsive while the window is being resized?"
• "My cached thumbnails are blurry in iPhone Mirroring"
• "My web view layout breaks at narrow window widths"

What This Skill Provides

• The sizing rule – size from the surface, scale from the traits, re-derive both on change
• Metal patterns – drawableSizeWillChange recompute/reallocate discipline with live-resize throttling, and manual CAMetalLayer.drawableSize/contentsScale ownership
• Per-surface table – what video layers, maps, Swift Charts, Canvas, WKWebView, PDFView, SpriteKit, and SceneKit each need (usually one property or nothing)
• Scale-keyed caching – keying raster caches by size and displayScale, with UIKit and SwiftUI invalidation hooks

Related

• Metal Migration – MTKView setup, pipelines, and shader work this skill builds on
• UIKit Modernization – the scene-geometry side: what changed at iOS 27, isInteractivelyResizing, screen-vs-trait migration
• SwiftUI Layout – layout-level adaptation; this skill covers the pixel level
• Display Performance – frame pacing and ProMotion once the surface sizes correctly