How can I display an array of pixels on a NSWindow? - objective-c

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

Create a new "Cocoa Application" (if you don't know how to create a cocoa application go to Cocoa Dev Center)
Subclass NSView (if you don't know how to subclass a view read section "Create the NSView Subclass")
Set your NSWindow to size 400x400 on interface builder
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

Answer 2

There's a bunch of ways to do this. One of the more straightforward is to use CGContextDrawImage. In drawRect:
CGContextRef ctx = [[NSGraphicsContext currentContext] graphicsPort];
CGDataProviderRef provider = CGDataProviderCreateWithData(nil, bitmap, bitmap_bytes, nil);
CGImageRef img = CGImageCreate(..., provider, ...);
CGDataProviderRelease(provider);
CGContextDrawImage(ctx, dstRect, img);
CGImageRelease(img);
CGImageCreate has a bunch of arguments which I've left out here, as the correct values will depend on what your bitmap format is. See the CGImage reference for details.
Note that, if your bitmap is static, it may make sense to hold on to the CGImageRef instead of disposing of it immediately. You know best how your application works, so you decide whether that makes sense.

Answer 3

I solved this problem by using an NSImageView with NSBitmapImageRep to create the image from the pixel values. There are lots of options how you create the pixel values. In my case, I used 32-bit pixels (RGBA). In this code, pixels is the giant array of pixel value. display is the outlet for the NSImageView.
NSBitmapImageRep *myBitmap;
NSImage *myImage;
unsigned char *buff[4];
unsigned char *pixels;
int width, height, rectSize;
NSRect myBounds;
myBounds = [display bounds];
width = myBounds.size.width;
height = myBounds.size.height;
rectSize = width * height;
memset(buff, 0, sizeof(buff));
pixels = malloc(rectSize * 4);
(fill in pixels array)
buff[0] = pixels;
myBitmap = [[NSBitmapImageRep alloc] initWithBitmapDataPlanes:buff
pixelsWide:width
pixelsHigh:height
bitsPerSample:8
samplesPerPixel:4
hasAlpha:YES
isPlanar:NO
colorSpaceName:NSCalibratedRGBColorSpace
bitmapFormat:0
bytesPerRow:(4 * width)
bitsPerPixel:32];
myImage = [[NSImage alloc] init];
[myImage addRepresentation:myBitmap];
[display setImage: myImage];
[myImage release];
[myBitmap release];
free(pixels);