react-native/Libraries/Image/RCTImageUtils.m

/**
 * Copyright (c) 2015-present, Facebook, Inc.
 * All rights reserved.
 *
 * This source code is licensed under the BSD-style license found in the
 * LICENSE file in the root directory of this source tree. An additional grant
 * of patent rights can be found in the PATENTS file in the same directory.
 */

#import "RCTImageUtils.h"

#import "RCTLog.h"

static CGFloat RCTCeilValue(CGFloat value, CGFloat scale)
{
  return ceil(value * scale) / scale;
}

static CGFloat RCTFloorValue(CGFloat value, CGFloat scale)
{
  return floor(value * scale) / scale;
}

static CGSize RCTCeilSize(CGSize size, CGFloat scale)
{
  return (CGSize){
    RCTCeilValue(size.width, scale),
    RCTCeilValue(size.height, scale)
  };
}

CGRect RCTTargetRect(CGSize sourceSize, CGSize destSize,
                     CGFloat destScale, UIViewContentMode resizeMode)
{
  if (CGSizeEqualToSize(destSize, CGSizeZero)) {
    // Assume we require the largest size available
    return (CGRect){CGPointZero, sourceSize};
  }

  CGFloat aspect = sourceSize.width / sourceSize.height;
  // If only one dimension in destSize is non-zero (for example, an Image
  // with `flex: 1` whose height is indeterminate), calculate the unknown
  // dimension based on the aspect ratio of sourceSize
  if (destSize.width == 0) {
    destSize.width = destSize.height * aspect;
  }
  if (destSize.height == 0) {
    destSize.height = destSize.width / aspect;
  }

  // Calculate target aspect ratio if needed (don't bother if resizeMode == stretch)
  CGFloat targetAspect = 0.0;
  if (resizeMode != UIViewContentModeScaleToFill) {
    targetAspect = destSize.width / destSize.height;
    if (aspect == targetAspect) {
      resizeMode = UIViewContentModeScaleToFill;
    }
  }

  switch (resizeMode) {
    case UIViewContentModeScaleToFill: // stretch

      return (CGRect){CGPointZero, RCTCeilSize(destSize, destScale)};

    case UIViewContentModeScaleAspectFit: // contain

      if (targetAspect <= aspect) { // target is taller than content

        sourceSize.width = destSize.width = destSize.width;
        sourceSize.height = sourceSize.width / aspect;

      } else { // target is wider than content

        sourceSize.height = destSize.height = destSize.height;
        sourceSize.width = sourceSize.height * aspect;
      }
      return (CGRect){CGPointZero, RCTCeilSize(sourceSize, destScale)};

    case UIViewContentModeScaleAspectFill: // cover

      if (targetAspect <= aspect) { // target is taller than content

        sourceSize.height = destSize.height = destSize.height;
        sourceSize.width = sourceSize.height * aspect;
        destSize.width = destSize.height * targetAspect;
        return (CGRect){
          {RCTFloorValue((destSize.width - sourceSize.width) / 2, destScale), 0},
          RCTCeilSize(sourceSize, destScale)
        };

      } else { // target is wider than content

        sourceSize.width = destSize.width = destSize.width;
        sourceSize.height = sourceSize.width / aspect;
        destSize.height = destSize.width / targetAspect;
        return (CGRect){
          {0, RCTFloorValue((destSize.height - sourceSize.height) / 2, destScale)},
          RCTCeilSize(sourceSize, destScale)
        };
      }

    default:

      RCTLogError(@"A resizeMode value of %zd is not supported", resizeMode);
      return (CGRect){CGPointZero, RCTCeilSize(destSize, destScale)};
  }
}

CGSize RCTTargetSize(CGSize sourceSize, CGFloat sourceScale,
                     CGSize destSize, CGFloat destScale,
                     UIViewContentMode resizeMode,
                     BOOL allowUpscaling)
{
  switch (resizeMode) {
    case UIViewContentModeScaleToFill: // stretch

      if (!allowUpscaling) {
        CGFloat scale = sourceScale / destScale;
        destSize.width = MIN(sourceSize.width * scale, destSize.width);
        destSize.height = MIN(sourceSize.height * scale, destSize.height);
      }
      return RCTCeilSize(destSize, destScale);

    default: {

      // Get target size
      CGSize size = RCTTargetRect(sourceSize, destSize, destScale, resizeMode).size;
      if (!allowUpscaling) {
        // return sourceSize if target size is larger
        if (sourceSize.width * sourceScale < size.width * destScale) {
          return sourceSize;
        }
      }
      return size;
    }
  }
}

BOOL RCTUpscalingRequired(CGSize sourceSize, CGFloat sourceScale,
                          CGSize destSize, CGFloat destScale,
                          UIViewContentMode resizeMode)
{
  if (CGSizeEqualToSize(destSize, CGSizeZero)) {
    // Assume we require the largest size available
    return YES;
  }

  // Precompensate for scale
  CGFloat scale = sourceScale / destScale;
  sourceSize.width *= scale;
  sourceSize.height *= scale;

  // Calculate aspect ratios if needed (don't bother if resizeMode == stretch)
  CGFloat aspect = 0.0, targetAspect = 0.0;
  if (resizeMode != UIViewContentModeScaleToFill) {
    aspect = sourceSize.width / sourceSize.height;
    targetAspect = destSize.width / destSize.height;
    if (aspect == targetAspect) {
      resizeMode = UIViewContentModeScaleToFill;
    }
  }

  switch (resizeMode) {
    case UIViewContentModeScaleToFill: // stretch

      return destSize.width > sourceSize.width || destSize.height > sourceSize.height;

    case UIViewContentModeScaleAspectFit: // contain

      if (targetAspect <= aspect) { // target is taller than content

        return destSize.width > sourceSize.width;

      } else { // target is wider than content

        return destSize.height > sourceSize.height;
      }

    case UIViewContentModeScaleAspectFill: // cover

      if (targetAspect <= aspect) { // target is taller than content

        return destSize.height > sourceSize.height;

      } else { // target is wider than content

        return destSize.width > sourceSize.width;
      }

    default:

      RCTLogError(@"A resizeMode value of %zd is not supported", resizeMode);
      return NO;
  }
}