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[Issue 838] Update ASCeilPixelValue and ASRoundPixelValue #864

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Mar 31, 2018
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[Issue 838] Update ASCeilPixelValue and ASRoundPixelValue #864

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[Issue 838] Update ASCeilPixelValue and ASRoundPixelValue
rcancro Mar 29, 2018
2acffde
addressed comments on the pr
rcancro Mar 30, 2018
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22 changes: 20 additions & 2 deletions Source/Private/ASInternalHelpers.m
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Original file line number Diff line number Diff line change
Expand Up @@ -193,16 +193,34 @@ CGSize ASCeilSizeValues(CGSize s)
return CGSizeMake(ASCeilPixelValue(s.width), ASCeilPixelValue(s.height));
}

// With 3x devices layouts will often to compute to pixel bounds but
// include garbage values beyond the precision of a float/double.
// This garbage can result in a pixel value being rounded up when it isn't
// necessary.
//
// For example, imagine a layout that comes back with a height of 100.666666666669
// for a 3x device:
// 100.666666666669 * 3 = 302.00000000000699
// ceil(302.00000000000699) = 303
//
// If we use FLT_EPSILON to get rid of the garbage at the end of the value,
// things work as expected:
// (100.666666666669 - FLT_EPSILON) * 3 = 301.99999964237912
// ceil(301.99999964237912) = 302
//
// For even more conversation around this, see:
// https://github.com/TextureGroup/Texture/issues/838
CGFloat ASCeilPixelValue(CGFloat f)
{
CGFloat scale = ASScreenScale();
return ceil(f * scale) / scale;
return ceil((f - FLT_EPSILON) * scale) / scale;
}

// See ASCeilPixelValue for an explanation of (f - FLT_EPSILON)
CGFloat ASRoundPixelValue(CGFloat f)
{
CGFloat scale = ASScreenScale();
return round(f * scale) / scale;
return round((f - FLT_EPSILON) * scale) / scale;
}

@implementation NSIndexPath (ASInverseComparison)
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