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Improve RCTImageView resizing logic

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Summary: @​public

It's less important to reload for downscaling than upscaling, so increase the threshold in that direction. Also, this now considers each dimension separately, and a big enough change either way should result in a reload.

Finally, this considers both the current image size and the inflight target size, so we don't reload if either is already good.

Reviewed By: @tadeuzagallo

Differential Revision: D2470911
This commit is contained in:
Justin Spahr-Summers
2015-09-23 07:30:37 -07:00
committed by facebook-github-bot-8
parent de85bcab0b
commit bcd2ef5dfc
1 changed files with 29 additions and 10 deletions
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39
Libraries/Image/RCTImageView.m
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@@ -18,6 +18,21 @@
#import "UIView+React.h"
/**
* Determines whether an image of `currentSize` should be reloaded for display
* at `idealSize`.
*/
static BOOL RCTShouldReloadImageForSizeChange(CGSize currentSize, CGSize idealSize) {
static const CGFloat upscaleThreshold = 1.2;
static const CGFloat downscaleThreshold = 0.5;
CGFloat widthMultiplier = idealSize.width / currentSize.width;
CGFloat heightMultiplier = idealSize.height / currentSize.height;
return widthMultiplier > upscaleThreshold || widthMultiplier < downscaleThreshold ||
heightMultiplier > upscaleThreshold || heightMultiplier < downscaleThreshold;
}
@interface RCTImageView ()
@property (nonatomic, copy) RCTDirectEventBlock onLoadStart;
@@ -146,8 +161,7 @@ RCT_NOT_IMPLEMENTED(- (instancetype)init)
{
[self cancelImageLoad];
if (_src && !CGSizeEqualToSize(self.frame.size, CGSizeZero)) {
if (_src && self.frame.size.width > 0 && self.frame.size.height > 0) {
if (_onLoadStart) {
_onLoadStart(nil);
}
@@ -199,15 +213,20 @@ RCT_NOT_IMPLEMENTED(- (instancetype)init)
_targetSize = frame.size;
[self reloadImage];
} else if ([RCTImageView srcNeedsReload:_src]) {
CGSize idealSize = RCTTargetSize(self.image.size, self.image.scale, frame.size,
RCTScreenScale(), self.contentMode, YES);
CGFloat widthChangeFraction = ABS(_targetSize.width - idealSize.width) / _targetSize.width;
CGFloat heightChangeFraction = ABS(_targetSize.height - idealSize.height) / _targetSize.height;
CGSize imageSize = self.image.size;
CGSize idealSize = RCTTargetSize(imageSize, self.image.scale, frame.size, RCTScreenScale(), self.contentMode, YES);
// If the combined change is more than 20%, reload the asset in case there is a better size.
if (widthChangeFraction + heightChangeFraction > 0.2) {
_targetSize = idealSize;
[self reloadImage];
if (RCTShouldReloadImageForSizeChange(imageSize, idealSize)) {
if (RCTShouldReloadImageForSizeChange(_targetSize, idealSize)) {
// If the existing image or an image being loaded are not the right size, reload the asset in case there is a
// better size available.
_targetSize = idealSize;
[self reloadImage];
}
} else {
// Our existing image is good enough.
[self cancelImageLoad];
_targetSize = imageSize;
}
}
}