react-native-image-resizer/ios/RCTImageResizer/ImageHelpers.m

/*
 File: ImageHelpers.m

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#include "ImageHelpers.h"

const CGBitmapInfo kDefaultCGBitmapInfo	= (kCGImageAlphaPremultipliedFirst | kCGBitmapByteOrder32Host);
const CGBitmapInfo kDefaultCGBitmapInfoNoAlpha	= (kCGImageAlphaNoneSkipFirst | kCGBitmapByteOrder32Host);

CGColorSpaceRef	GetDeviceRGBColorSpace() {
    static CGColorSpaceRef	deviceRGBSpace	= NULL;
    if( deviceRGBSpace == NULL )
        deviceRGBSpace	= CGColorSpaceCreateDeviceRGB();
    return deviceRGBSpace;
}

float GetScaleForProportionalResize( CGSize theSize, CGSize intoSize, bool onlyScaleDown, bool maximize )
{
    float	sx = theSize.width;
    float	sy = theSize.height;
    float	dx = intoSize.width;
    float	dy = intoSize.height;
    float	scale	= 1;

    if( sx != 0 && sy != 0 )
    {
        dx	= dx / sx;
        dy	= dy / sy;

        // if maximize is true, take LARGER of the scales, else smaller
        if( maximize )		scale	= (dx > dy)	? dx : dy;
        else				scale	= (dx < dy)	? dx : dy;

        if( scale > 1 && onlyScaleDown )	// reset scale
            scale	= 1;
    }
    else
    {
        scale	 = 0;
    }
    return scale;
}

CGContextRef CreateCGBitmapContextForWidthAndHeight( unsigned int width, unsigned int height,
                                                    CGColorSpaceRef optionalColorSpace, CGBitmapInfo optionalInfo )
{
    CGColorSpaceRef	colorSpace	= (optionalColorSpace == NULL) ? GetDeviceRGBColorSpace() : optionalColorSpace;
    CGBitmapInfo	alphaInfo	= ( (int32_t)optionalInfo < 0 ) ? kDefaultCGBitmapInfo : optionalInfo;
    return CGBitmapContextCreate( NULL, width, height, 8, 0, colorSpace, alphaInfo );
}

CGImageRef CreateCGImageFromUIImageScaled( UIImage* image, float scaleFactor )
{
    CGImageRef			newImage		= NULL;
    CGContextRef		bmContext		= NULL;
    BOOL				mustTransform	= YES;
    CGAffineTransform	transform		= CGAffineTransformIdentity;
    UIImageOrientation	orientation		= image.imageOrientation;

    CGImageRef			srcCGImage		= CGImageRetain( image.CGImage );

    size_t width	= CGImageGetWidth(srcCGImage) * scaleFactor;
    size_t height	= CGImageGetHeight(srcCGImage) * scaleFactor;

    // These Orientations are rotated 0 or 180 degrees, so they retain the width/height of the image
    if( (orientation == UIImageOrientationUp) || (orientation == UIImageOrientationDown) || (orientation == UIImageOrientationUpMirrored) || (orientation == UIImageOrientationDownMirrored)  )
    {
        bmContext	= CreateCGBitmapContextForWidthAndHeight( width, height, NULL, kDefaultCGBitmapInfo );
    }
    else	// The other Orientations are rotated ±90 degrees, so they swap width & height.
    {
        bmContext	= CreateCGBitmapContextForWidthAndHeight( height, width, NULL, kDefaultCGBitmapInfo );
    }

    //CGContextSetInterpolationQuality( bmContext, kCGInterpolationLow );
    CGContextSetBlendMode( bmContext, kCGBlendModeCopy );	// we just want to copy the data

    switch(orientation)
    {
        case UIImageOrientationDown:		// 0th row is at the bottom, and 0th column is on the right - Rotate 180 degrees
            transform	= CGAffineTransformMake(-1.0, 0.0, 0.0, -1.0, width, height);
            break;

        case UIImageOrientationLeft:		// 0th row is on the left, and 0th column is the bottom - Rotate -90 degrees
            transform	= CGAffineTransformMake(0.0, 1.0, -1.0, 0.0, height, 0.0);
            break;

        case UIImageOrientationRight:		// 0th row is on the right, and 0th column is the top - Rotate 90 degrees
            transform	= CGAffineTransformMake(0.0, -1.0, 1.0, 0.0, 0.0, width);
            break;

        case UIImageOrientationUpMirrored:	// 0th row is at the top, and 0th column is on the right - Flip Horizontal
            transform	= CGAffineTransformMake(-1.0, 0.0, 0.0, 1.0, width, 0.0);
            break;

        case UIImageOrientationDownMirrored:	// 0th row is at the bottom, and 0th column is on the left - Flip Vertical
            transform	= CGAffineTransformMake(1.0, 0.0, 0, -1.0, 0.0, height);
            break;

        case UIImageOrientationLeftMirrored:	// 0th row is on the left, and 0th column is the top - Rotate -90 degrees and Flip Vertical
            transform	= CGAffineTransformMake(0.0, -1.0, -1.0, 0.0, height, width);
            break;

        case UIImageOrientationRightMirrored:	// 0th row is on the right, and 0th column is the bottom - Rotate 90 degrees and Flip Vertical
            transform	= CGAffineTransformMake(0.0, 1.0, 1.0, 0.0, 0.0, 0.0);
            break;

        default:
            mustTransform	= NO;
            break;
    }

    if( mustTransform )	CGContextConcatCTM( bmContext, transform );

    CGContextDrawImage( bmContext, CGRectMake(0.0, 0.0, width, height), srcCGImage );
    CGImageRelease( srcCGImage );
    newImage = CGBitmapContextCreateImage( bmContext );
    CFRelease( bmContext );

    return newImage;
}

@implementation UIImage (scale)

-(UIImage*) scaleToSize:(CGSize)toSize
{
    UIImage	*scaledImg	= nil;
    float	scale		= GetScaleForProportionalResize( self.size, toSize, false, false );
    CGImageRef cgImage	= CreateCGImageFromUIImageScaled( self, scale );

    if( cgImage )
    {
        scaledImg	= [UIImage imageWithCGImage:cgImage];	// autoreleased
        CGImageRelease( cgImage );
    }
    return scaledImg;
}

@end