:orphan:

mandel_ocl
----------


Calculate Mandelbrot set using OpenCL


.. code-block:: python
    
    
    
    import pyopencl as cl
    from timeit import default_timer as timer
    
    import numpy as np
    import gr
    
    
    platform = cl.get_platforms()
    gpu_devices = platform[0].get_devices(device_type=cl.device_type.GPU)
    
    info_value = gpu_devices[0].get_info(getattr(cl.device_info, 'EXTENSIONS'))
    if not 'cl_khr_fp64' in info_value:
      print("GPU has no support for double floating-point precision")
      exit(-1)
    
    ctx = cl.Context(devices=gpu_devices)
    queue = cl.CommandQueue(ctx)
    
    prg = cl.Program(ctx, """
    #pragma OPENCL EXTENSION cl_khr_byte_addressable_store : enable
    __kernel void mandelbrot(__global double2 *q, __global ushort *output,
                             double const min_x, double const max_x,
                             double const min_y, double const max_y,
                             ushort const width, ushort const height,
                             ushort const iters)
    {
        int ci = 0, inc = 1;
        int gid = get_global_id(0);
        double nreal, real = 0;
        double imag = 0;
    
        q[gid].x = min_x + (gid % width) * (max_x - min_x) / width;
        q[gid].y = min_y + (gid / width) * (max_y - min_y) / height;
    
        output[gid] = iters;
    
        for (int curiter = 0; curiter < iters; curiter++) {
            nreal = real * real - imag * imag + q[gid].x;
            imag = 2 * real * imag + q[gid].y;
            real = nreal;
    
            if (real * real + imag * imag >= 4) {
                output[gid] = ci;
                return;
            }
            ci += inc;
            if (ci == 0 || ci == 255)
                inc = -inc;
        }
    }
    """).build()
    
    
    def calc_fractal(q, min_x, max_x, min_y, max_y, width, height, iters):
        global ctx, queue, prg
    
        output = np.empty(q.shape, dtype=np.uint16)
    
        mf = cl.mem_flags
        q_opencl = cl.Buffer(ctx, mf.READ_ONLY | mf.COPY_HOST_PTR, hostbuf=q)
        output_opencl = cl.Buffer(ctx, mf.WRITE_ONLY, output.nbytes)
    
        prg.mandelbrot(queue, output.shape, None, q_opencl, output_opencl,
                       np.double(min_x), np.double(max_x),
                       np.double(min_y), np.double(max_y),
                       np.uint16(width), np.uint16(height), np.uint16(iters))
    
        cl.enqueue_copy(queue, output, output_opencl).wait()
    
        return output
    
    
    def create_fractal(min_x, max_x, min_y, max_y, width, height, iters):
        q = np.zeros(width * height).astype(np.complex128)
    
        output = calc_fractal(q, min_x, max_x, min_y, max_y, width, height, iters)
    
        return output
    
    
    x = -0.9223327810370947027656057193752719757635
    y = 0.3102598350874576432708737495917724836010
    
    f = 0.5
    for i in range(200):
        start = timer()
        pixels = create_fractal(x-f, x+f, y-f, y+f, 500, 500, 400)
        dt = timer() - start
    
        print("Mandelbrot created in %f s" % dt)
        ca = 1000.0 + pixels.ravel()
    
        gr.clearws()
        gr.setviewport(0, 1, 0, 1)
        gr.setcolormap(13)
        gr.cellarray(0, 1, 0, 1, 500, 500, ca)
        gr.updatews()
    
        f *= 0.9