mandelbrot.m

//At the top of the file
#import "mandelbrot.cl.h"

//Inside the @autoreleasepool in int main()

//1
dispatch_queue_t dq = gcl_create_dispatch_queue(CL_DEVICE_TYPE_GPU, NULL);
if (!dq) {
    fprintf(stdout, "Unable to create a GPU-based dispatch queue.\n");
    exit(1);
}

//Output size
size_t width = 1920, height = 1080;
//Number of iterations to do
int iter = 1000;

//2
//This actually comes out as an unsigned char *, however we can cast that to an unsigned int * to get four 8-bit channels
unsigned int * pixels = (unsigned int*)malloc(width * height * sizeof(unsigned int));

//3
cl_image_format format;
format.image_channel_order = CL_RGBA;
format.image_channel_data_type = CL_UNSIGNED_INT8;

//4
cl_mem output_image = gcl_create_image(&format, width, height, 1, NULL);

dispatch_sync(dq, ^{
    //5
    cl_ndrange range = {
        2,                  // 2 dimensions for image
        {0},                // Start at the beginning of the range
        {width, height},    // Execute width * height work items
        {0}                 // And let OpenCL decide how to divide
                            // the work items into work-groups.
    };
    
    // Copy the host-side, initial pixel data to the image memory object on
    // the OpenCL device.  Here, we copy the whole image, but you could use
    // the origin and region parameters to specify an offset and sub-region
    // of the image, if you'd like.
    const size_t origin[3] = { 0, 0, 0 };
    const size_t region[3] = { width, height, 1 };
    
    //6
    //Execute the kernel
    //mandelbrot_kernel is a GCD block declared in the autogenerated mandelbrot.cl.h file
    mandelbrot_kernel(&range, output_image, (cl_float)width, (cl_float)height, iter);
    
    //7
    // Copy back results into pointer
    gcl_copy_image_to_ptr(pixels, output_image, origin, region);
});

//8
//Finally, export to disk
NSBitmapImageRep * imageRep = [[NSBitmapImageRep alloc] initWithBitmapDataPlanes:(unsigned char **)&pixels
                                                                      pixelsWide:width
                                                                      pixelsHigh:height
                                                                   bitsPerSample:8
                                                                 samplesPerPixel:4
                                                                        hasAlpha:YES
                                                                        isPlanar:NO
                                                                  colorSpaceName:NSDeviceRGBColorSpace
                                                                    bitmapFormat:NSAlphaNonpremultipliedBitmapFormat
                                                                     bytesPerRow:4 * width
                                                                    bitsPerPixel:32];
NSData * outData = [imageRep representationUsingType:NSPNGFileType properties:nil];
[outData writeToFile:[NSHomeDirectory() stringByAppendingPathComponent:@"mandelbrot.png"] atomically:YES];
 

// Clean up device-size allocations.
// Note that we use the "standard" OpenCL API here.
clReleaseMemObject(output_image);

free(pixels);