Question

Very simple question… I have an array of pixels, how do I display them on the screen?

#define WIDTH 10
#define HEIGHT 10
#define SIZE WIDTH*HEIGHT

unsigned short pixels[SIZE];

for (int i = 0; i < WIDTH; i++) {
    for (int j = 0; j < HEIGHT; j++) {
        pixels[j*HEIGHT + i] = 0xFFFF;
    }
}

That’s it… now how can I show them on the screen?

Answer 1

1. Create a new “Cocoa Application” (if you don’t know how to create a cocoa application go to Cocoa Dev Center)
2. Subclass NSView (if you don’t know how to subclass a view read section “Create the NSView Subclass”)
3. Set your NSWindow to size 400×400 on interface builder

4. Use this code in your NSView

   #import "MyView.h"
   
   @implementation MyView
   
   #define WIDTH 400
   #define HEIGHT 400
   #define SIZE (WIDTH*HEIGHT)
   #define BYTES_PER_PIXEL 2
   #define BITS_PER_COMPONENT 5
   #define BITS_PER_PIXEL 16
   
   - (id)initWithFrame:(NSRect)frame
   {
       self = [super initWithFrame:frame];
       if (self) {
           // Initialization code here.
       }
       return self;
   }
   
   - (void)drawRect:(NSRect)dirtyRect
   {
       // Get current context
       CGContextRef context = (CGContextRef)[[NSGraphicsContext currentContext] graphicsPort];
   
       // Colorspace RGB
       CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
   
       // Pixel Matrix allocation
       unsigned short *pixels = calloc(SIZE, sizeof(unsigned short));
   
       // Random pixels will give you a non-organized RAINBOW 
       for (int i = 0; i < WIDTH; i++) {
           for (int j = 0; j < HEIGHT; j++) {
               pixels[i+ j*HEIGHT] = arc4random() % USHRT_MAX;
           }
       }
   
       // Provider
       CGDataProviderRef provider = CGDataProviderCreateWithData(nil, pixels, SIZE, nil);
   
       // CGImage
       CGImageRef image = CGImageCreate(WIDTH,
                                        HEIGHT,
                                        BITS_PER_COMPONENT,
                                        BITS_PER_PIXEL,
                                        BYTES_PER_PIXEL*WIDTH,
                                        colorSpace,
                                        kCGImageAlphaNoneSkipFirst,
                                        // xRRRRRGGGGGBBBBB - 16-bits, first bit is ignored!
                                        provider,
                                        nil, //No decode
                                        NO,  //No interpolation
                                        kCGRenderingIntentDefault); // Default rendering
   
   // Draw
   CGContextDrawImage(context, self.bounds, image);
   
   // Once everything is written on screen we can release everything
   CGImageRelease(image);
   CGColorSpaceRelease(colorSpace);
   CGDataProviderRelease(provider);
   
   }
   @end