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Glitchless smooth window resizing in Metal
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MetalTest2.xcodeproj Metal Layer view plus other improvements Jun 20, 2019
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Metal Window Resizing Test Project

The goal of this project was to figure out a way to do glitchless smooth window resizing with Metal, I succeeded. MTKView has a problem where the redrawing is not synchronized with the window resize so it draws stretched frames, but there's a way to use CAMetalLayer to make it work.

This project draws views with a triangle with two vertices at fixed offsets from the left edge, and one vertex at a fixed offset from the right edge. It has three implementations that are displayed stacked vertically in the following order:

  1. MTKView. Which is supposed to be the easy view. Apple's Hello Triangle example uses this, and suffers terrible resize juddering. Code is in MetalView.swift.
  2. NSView. This is a benchmark implementation that draws the triangle with Core Graphics, it works perfectly. Code is in CocoaView.swift.
  3. CAMetalLayer. Implemented according to the top answer from this Stack Overflow question. Using just the Stack Overflow answer works better than MTKView but still glitches occasionally. It's also necessary to use presentsWithTransaction and follow the recommendations in the docs for that option regarding waitUntilScheduled, that delivers completely glitch-free results. Code is in MetalLayerView.swift.


Triangles are stacked in the order listed above, watch the top vertex of the top triangle:

Screen Recording

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