Mac Forum / Programming / Mac Programming / March 2007

Take a look at:
http://www.cocoabuilder.com/archive/message/cocoa/2003/12/3/854

Here's a working model:

#import <Cocoa/Cocoa.h>

@interface MyView : NSView {
 int width_;
 int height_;
 unsigned short *imagearray_;
 CGImageRef myCGImage_;
 CGDataProviderRef dataProvider_;
 char *p_;
}
- (char *)p;
- (char *)pBase;
- (char *)pMax;
- (void)setP:(char *)p;
@end
==================================
//
//  MyView.m
//  CGImage
//
//  Created by David Phillip Oster on 3/6/07.
//

#import "MyView.h"
#import <memory.h>
#import <string.h>

static size_t DataProviderGetBytes(void *info, void *buffer, size_t
count){
 MyView *me = (MyView *)info;
 if ([me pMax] < [me p]) {
   count = 0;
 }else if ([me pMax] < [me p]+count){
   count = [me pMax] - [me p];
 }
 memmove(buffer, [me p], count);
 [me setP:count + [me p]];
 return count;
}

static void DataProviderSkipBytes(void *info, size_t count){
 MyView *me = (MyView *)info;
 [me setP:count + [me p]];
}

static void DataProviderRewind(void *info){
 MyView *me = (MyView *)info;
 [me setP:[me pBase]];
}

static void DataProviderReleaseInfo(void *info){
}

@implementation MyView

- (id)initWithFrame:(NSRect)frame {
   self = [super initWithFrame:frame];
   if (self) {
   }
   return self;
}

- (void)awakeFromNib {
 width_ = [self frame].size.width;
 width_ = ((width_ + (16-1)) / 16) * 16;
 height_ = [self frame].size.height;

 // initialize our 2 d array of pixels.
 imagearray_ = (unsigned short *) malloc(width_*height_
*sizeof(unsigned short));
 p_ = (char *) imagearray_;
 int i, j, k;
 for(j = k = 0; j < height_;  ++j) {
   unsigned short *p = &imagearray_[j*width_];
   for(i = 0; i < width_; ++i, ++k, ++p) {
     *p = ((int)(i * (31./width_)) & 0x1F) << 1 |
       ((int)(i * (31./width_)) & 0x1F) << 6 |
       ((int)(i * (31./width_)) & 0x1F) << 11;
   }
 }
 CGDataProviderCallbacks callbacks = {
  DataProviderGetBytes,
  DataProviderSkipBytes,
  DataProviderRewind,
  DataProviderReleaseInfo
 };
 dataProvider_ = CGDataProviderCreate(self, &callbacks);
 CGColorSpaceRef colorspace = CGColorSpaceCreateDeviceRGB();
 myCGImage_ =  CGImageCreate(width_, height_, 5, 16, width_*2,
colorspace,
     kCGBitmapByteOrder32Host, dataProvider_, nil, NO,
kCGRenderingIntentDefault);
 CGColorSpaceRelease(colorspace);
}

- (void)dealloc {
 if (imagearray_) {
   free(imagearray_);
   imagearray_ = nil;
 }
 if (myCGImage_) {
   CGImageRelease(myCGImage_);
   myCGImage_ = nil;
 }
 if (dataProvider_) {
   CGDataProviderRelease(dataProvider_);
   dataProvider_ = nil;
 }
 [super dealloc];
}

- (void)drawRect:(NSRect)rect {
 CGRect cgRect = CGRectMake(rect.origin.x, rect.origin.y,
rect.size.width, rect.size.height);
 NSGraphicsContext *currentContext = [NSGraphicsContext currentContext];
 CGContextDrawImage((CGContextRef) [currentContext graphicsPort],
cgRect, myCGImage_);
}

- (char *)p {
 return p_;
}

- (char *)pBase {
 return (char *) imagearray_;
}

- (char *)pMax {
 return [self pBase] + (width_*height_ *sizeof(unsigned));
}

- (void)setP:(char *)p {
 p_ = p;
}

@end