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dupeguru-cocoa/cocoalib/NSImageAdditions.m

114 lines
3.9 KiB
Objective-C

// Created by Scott Stevenson on 9/28/07.
//
// Personal site: http://theocacao.com/
// Post for this sample: http://theocacao.com/document.page/497
//
// The code in this project is intended to be used as a learning
// tool for Cocoa programmers. You may freely use the code in
// your own programs, but please do not use the code as-is in
// other tutorials.
#import "NSImageAdditions.h"
@implementation NSImage (Extras)
- (NSImage*)imageByScalingProportionallyToSize:(NSSize)targetSize
{
NSImage* sourceImage = self;
NSImage* newImage = nil;
if ([sourceImage isValid])
{
NSSize imageSize = [sourceImage size];
CGFloat width = imageSize.width;
CGFloat height = imageSize.height;
CGFloat targetWidth = targetSize.width;
CGFloat targetHeight = targetSize.height;
// scaleFactor will be the fraction that we'll
// use to adjust the size. For example, if we shrink
// an image by half, scaleFactor will be 0.5. the
// scaledWidth and scaledHeight will be the original,
// multiplied by the scaleFactor.
//
// IMPORTANT: the "targetHeight" is the size of the space
// we're drawing into. The "scaledHeight" is the height that
// the image actually is drawn at, once we take into
// account the ideal of maintaining proportions
CGFloat scaleFactor = 0.0;
CGFloat scaledWidth = targetWidth;
CGFloat scaledHeight = targetHeight;
NSPoint thumbnailPoint = NSMakePoint(0,0);
// since not all images are square, we want to scale
// proportionately. To do this, we find the longest
// edge and use that as a guide.
if ( NSEqualSizes( imageSize, targetSize ) == NO )
{
// use the longeset edge as a guide. if the
// image is wider than tall, we'll figure out
// the scale factor by dividing it by the
// intended width. Otherwise, we'll use the
// height.
CGFloat widthFactor = targetWidth / width;
CGFloat heightFactor = targetHeight / height;
if ( widthFactor < heightFactor )
scaleFactor = widthFactor;
else
scaleFactor = heightFactor;
// ex: 500 * 0.5 = 250 (newWidth)
scaledWidth = width * scaleFactor;
scaledHeight = height * scaleFactor;
// center the thumbnail in the frame. if
// wider than tall, we need to adjust the
// vertical drawing point (y axis)
if ( widthFactor < heightFactor )
thumbnailPoint.y = (targetHeight - scaledHeight) * 0.5;
else if ( widthFactor > heightFactor )
thumbnailPoint.x = (targetWidth - scaledWidth) * 0.5;
}
// create a new image to draw into
newImage = [[NSImage alloc] initWithSize:targetSize];
// once focus is locked, all drawing goes into this NSImage instance
// directly, not to the screen. It also receives its own graphics
// context.
//
// Also, keep in mind that we're doing this in a background thread.
// You only want to draw to the screen in the main thread, but
// drawing to an offscreen image is (apparently) okay.
[newImage lockFocus];
NSRect thumbnailRect;
thumbnailRect.origin = thumbnailPoint;
thumbnailRect.size.width = scaledWidth;
thumbnailRect.size.height = scaledHeight;
[sourceImage drawInRect: thumbnailRect
fromRect: NSZeroRect
operation: NSCompositeSourceOver
fraction: 1.0];
[newImage unlockFocus];
}
return [newImage autorelease];
}
@end