Pixel aligned CGFloat equality fix #128
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bryankeller
commented
Mar 30, 2024
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| func isEqual(to rhs: CGFloat, screenScale: CGFloat) -> Bool { | ||
| let lhs = alignedToPixel(forScreenWithScale: screenScale) | ||
| let rhs = rhs.alignedToPixel(forScreenWithScale: screenScale) | ||
| return lhs == rhs |
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this is the actual fix - the rest of the PR is just some minor refactoring
bryankeller
commented
Mar 30, 2024
| XCTAssert(!CGFloat(1).isEqual(to: 10, screenScale: 9)) | ||
| XCTAssert(!CGFloat(1).isEqual(to: 10, screenScale: 9)) | ||
| XCTAssert(!CGFloat(1).isEqual(to: 9, screenScale: 9)) | ||
| XCTAssert(!CGFloat(1.333).isEqual(to: 1.666, screenScale: 3)) |
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what was I thinking - of course these aren't equal. They're literally 1px apart on a 3x screen! 🤦♂️
brynbodayle
approved these changes
Mar 30, 2024
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Details
This PR corrects how we compare pixel-aligned
CGFloats. It's been wrong this whole time, and it's causing an off-by-one error on the Airbnb Messages surface.The previous implementation considered
0.66and0.84to be equal for a 3x screen, since 0.84-0.66=0.18, and 0.18 is smaller than 0.33, implying that these 2 values are within 1px of each other (0.33) on a 3x screen. This approach failed to take into account the actual rounding to valid pixel values. In reality, 0.84 and 0.66 should not be considered equal because they round to different pixels (0.66 stays at 0.66, 0.84 rounds up to 1, not down to 0.66).Related Issue
N/A
Motivation and Context
Bug fix
How Has This Been Tested
Types of changes
Checklist