takes an image and crops it to f it your displays on OS X

gistfile1.txt

//
//  main.m
//  span-image-across-displays
//
//  Created by Abhi Beckert on 2013-2-19.
//  Copyright (c) 2013 Abhi Beckert. All rights reserved.
//

#import <Cocoa/Cocoa.h>

int main(int argc, const char * argv[])
{
  
  @autoreleasepool {
    
    if (argc != 2) {
      printf("Usage: span-image-across-displays example.jpg\n");
      return 0;
    }
    
    // find image
    NSURL *imgURL = [NSURL fileURLWithPath:[NSString stringWithCString:argv[1] encoding:NSUTF8StringEncoding]];
    
    // load image
    NSImage *sourceImage = [[NSImage alloc] initWithContentsOfURL:imgURL];
    NSSize sourceImageSize= sourceImage.size;
    NSLog(@"image: %@", NSStringFromSize(sourceImageSize));
    
    // load screen area
    NSRect screenArea = NSMakeRect(0, 0, 0, 0);
    for (NSScreen *screen in [NSScreen screens]) {
      NSLog(@"screen %@: %@", screen, NSStringFromRect([screen frame]));
      
      screenArea.origin.x = MIN(NSMinX(screen.frame), NSMinX(screenArea));
      screenArea.origin.y = MIN(NSMinY(screen.frame), NSMinY(screenArea));
    };
    for (NSScreen *screen in [NSScreen screens]) {
      screenArea.size.width = MAX(NSMaxX(screen.frame), NSMaxX(screenArea)) - screenArea.origin.x;
      screenArea.size.height = MAX(NSMaxY(screen.frame), NSMaxY(screenArea)) - screenArea.origin.y;
    };
    NSLog(@"screen area: %@", NSStringFromRect(screenArea));
    
    // figure out resize ratio
    float imageScale = MAX(screenArea.size.width / sourceImageSize.width, screenArea.size.height / sourceImageSize.height);
    NSLog(@"scale image by: %f", imageScale);
    
    NSPoint imageOffset = NSMakePoint(0 - roundf((roundf(sourceImageSize.width * imageScale) - screenArea.size.width) / 2), 0 - roundf((roundf(sourceImageSize.height * imageScale) - screenArea.size.height) / 2));
    NSLog(@"offset image: %@", NSStringFromPoint(imageOffset));
    
    // create image for each screen
    int counter = 0;
    for (NSScreen *screen in [NSScreen screens]) {
      counter++;
      NSURL *newImageURL = [NSURL fileURLWithPath:[NSString stringWithFormat:@"%@ %i.jpg", imgURL.path.stringByDeletingPathExtension, counter]];
      
      NSImage *newImage = [[NSImage alloc] initWithSize:screen.frame.size];
      [newImage lockFocus];
      [sourceImage drawInRect:NSMakeRect(0, 0, screen.frame.size.width, screen.frame.size.height) fromRect:NSMakeRect((0 - (imageOffset.x / imageScale)) + ((screen.frame.origin.x - screenArea.origin.x) / imageScale), (0 - (imageOffset.y / imageScale)) + ((screen.frame.origin.y - screenArea.origin.y) / imageScale), screen.frame.size.width / imageScale, screen.frame.size.height / imageScale) operation:NSCompositeCopy fraction:1.0];
      [newImage unlockFocus];
      
      [[[NSBitmapImageRep imageRepWithData:[newImage TIFFRepresentation]] representationUsingType:NSJPEGFileType properties:@{NSImageCompressionFactor: [NSNumber numberWithFloat:0.9]}] writeToURL:newImageURL atomically:YES];
      NSLog(@"wrote %@ to %@", newImage, newImageURL);
      
      [[NSWorkspace sharedWorkspace] setDesktopImageURL:newImageURL forScreen:screen options:nil error:NULL];
    }
    
  }
  return 0;
}