May 06, 2010

hi, i make macintosh software.

Few weeks ago I finished my first Mac application — Saucejas.app. It is small (about 1000 lines of code) app which renders pretty image and video slideshow to secondary display using CoreAnimation.

Application itself doesn’t have notably pretty UI or implementation. It was written basically in one day for use in Saucejas show as a informative & mood-setting background. Here is video featuring Saucejas and previous version of app in background which I wrote earlier in Processing.

Nevertheless it was a really good exercise for me and here are few things I’ve learned:

General tips

Use Bindings — they’re great!
Objective-C is not Java (I’m still primary a Java person), do not try to organize code in Java style
Xcode plist editor is not the easiest to use tool for NSArray of NSDictionaries of 2-3 key-value pairs — consider different format for large lists or create custom editor for plist

Scaling NSImage (proportionally)

NSSize SCProportionalSizeForTargetSize(NSSize size, NSSize target) {
   if(NSEqualSizes(size, target)) {
      return size;
   }

   float widthFactor  = target.width  / size.width;
   float heightFactor = target.height / size.height;

   float scalingFactor;

   if (widthFactor < heightFactor) {
      scalingFactor = widthFactor;
   } else {
      scalingFactor = heightFactor;
   }

   return NSMakeSize(size.width  * scalingFactor, size.height * scalingFactor);
}

@implementation NSImage (SCAdditions)

  - (NSImage *)imageByScalingProportionallyToSize:(NSSize)target
  {
     NSSize size = self.size;

     NSSize proportionalSize = SCProportionalSizeForTargetSize(size, target);
     NSImage *scaledImage = [[NSImage alloc] initWithSize:proportionalSize];
     [scaledImage setCacheMode:NSImageCacheNever];

     [scaledImage lockFocus];
     [[NSGraphicsContext currentContext] setImageInterpolation:NSImageInterpolationHigh];
     [self drawInRect:NSMakeRect(.0f, .0f, proportionalSize.width, proportionalSize.height) 
             fromRect:NSMakeRect(.0f, .0f, size.width, size.height) 
            operation:NSCompositeSourceOver 
             fraction:1.0f];
     [scaledImage unlockFocus];

     return [scaledImage autorelease];
  }

@end

Drawing to NSImage can also be done in background thread
Cache mode must be NSImageCacheNever otherwise all scaled NSImages are cached
Set graphics context interpolation mode to High for better results

h2. Disabling screensaver

// Periodically called by NSTimer
- (void)disableScreenSaverTimerDidUpdate:(NSTimer *)timer
{
   UpdateSystemActivity(OverallAct);
}

Getting all connected displays

#import <IOKit/graphics/IOGraphicsLib.h>
  
@implementation SCDisplay

+ (NSArray *)displays
{
   NSMutableArray *displays = [NSMutableArray array];
   
   CGDirectDisplayID *onlineDisplays = malloc(
      sizeof(CGDirectDisplayID) * 
      kSCMaxDisplayCount);

   CGDisplayCount displayCount;
   CGDisplayErr listErr = CGGetActiveDisplayList(kSCMaxDisplayCount, 
                                                 onlineDisplays, 
                                                 &displayCount);

   if(listErr == kCGErrorSuccess) {
      for(int i=0; i<displayCount; i++) {
         CGDirectDisplayID displayId = onlineDisplays[i];

         CGRect bounds = CGDisplayBounds(displayId);
         
         NSString *name = nil;
         io_service_t port = CGDisplayIOServicePort(displayId);
         
         CFDictionaryRef infoRef = IODisplayCreateInfoDictionary(port, 
                                   kIODisplayOnlyPreferredName);
         
         if(infoRef != NULL) {
            CFDictionaryRef productNameDictionaryRef = CFDictionaryGetValue(infoRef, 
                                                       CFSTR(kDisplayProductName));
            if(productNameDictionaryRef != NULL) {
               CFIndex count = CFDictionaryGetCount(productNameDictionaryRef);
               if(count > 0) {
                  const void **values = (const void **)malloc (sizeof(void *) * count);
                  CFDictionaryGetKeysAndValues(productNameDictionaryRef, NULL, values);
                  
                  CFTypeRef nameRef = (CFTypeRef)values[0];
                  name = [NSString stringWithString:(NSString *)nameRef];
                  
                  free(values);
               }
            }
            CFRelease(infoRef);
         }
         
         if(!name) {
            name = @"Unknown";
         }
         
         SCDisplay *display = [[SCDisplay alloc] initWithDirectDisplayId:displayId 
                                                                  bounds:bounds 
                                                                    name:name];
         [displays addObject:display];
         [display release];
      }
   } else {
      NSLog(@"%@ %s • CGGetOnlineDisplayList failed: %u", [self className], _cmd, listErr);
   }
   free(onlineDisplays);
   
   return displays;
}

@end

Capturing and releasing a display

// CGDirectDisplayID displayId_; from CGGetActiveDisplayList

// Caputure
CGDisplayErr captureErr = CGDisplayCapture(self.displayId);
if(captureErr == kCGErrorSuccess) {
   self.captured = YES;
} else {
   NSLog(@"%@ %s • CGDisplayCapture failed: %u", [self className], _cmd, captureErr);
}

// Release
CGDisplayErr err = CGDisplayRelease(self.displayId);
if(err == kCGErrorSuccess) {
   self.captured = NO;
   released = YES;
} else {
   NSLog(@"%@ %s • CGDisplayRelease failed: %u", [self className], _cmd, err);
}

Full-screen `NSWindow` on captured display

CGFloat mainDisplayHeight = [[NSScreen mainScreen] frame].size.height;
CGRect displayBounds = self.display.bounds; // from CGDisplayBounds

// secondary displays are "below" main screen
NSRect rect = NSMakeRect(displayBounds.origin.x, 
                         mainDisplayHeight - displayBounds.size.height, 
                         displayBounds.size.width, 
                         displayBounds.size.height);

NSWindow *window = [[NSWindow alloc] initWithContentRect:rect
                                               styleMask:NSBorderlessWindowMask
                                                 backing:NSBackingStoreBuffered
                                                   defer:NO];

[window setLevel:CGShieldingWindowLevel()];

See -[NSScreen frame] & -[NSScreen visibleFrame] maybe they calculate correct rect for window
To get NSScreen from displayId I assume -[NSScreen deviceDescription] can be used