Part of the Khronos Group

The Industry's Foundation for High Performance Graphics

from games to virtual reality, mobile phones to supercomputers

Results 1 to 3 of 3

Thread: Problems with glDrawPixels and numpy arrays with pyOpenGl

  1. #1
    Newbie Newbie
    Join Date
    May 2015

    Problems with glDrawPixels and numpy arrays with pyOpenGl

    I'm trying to visualize mandelbrot set using numpy and OpenGL. However I have problems in drawing code, that is glDrawPixels.

    When I draw using glDrawPixels I get something black and all messed up, but when using slower method of glBegin & glEnd I get the correct result. Code:

    Code :
    #!/usr/bin/env python3  
    from OpenGL.GL import *
    from OpenGL.GLU import *
    from OpenGL.GLUT import *
    from pylab import *
    from numpy import *
    from time import clock
    w,h = 800,600
    eps = 2
    max_iter = 16
    u = (-1.5, 0.5)
    v = (-1,1)
    colorsMap = array([0x8B0000FF, 0xA52A2AFF, 0xB22222FF, 0xDC143CFF, 0xFF0000FF, 0xFF6347FF, 0xFF7F50FF, 0xCD5C5CFF, 0xF08080FF, 0xE9967AFF, 0xFA8072FF, 0xFFA07AFF, 0xFF4500FF, 0xFF8C00FF, 0xFFA500FF, 0xFFD700FF, 0xB8860BFF, 0xDAA520FF, 0xEEE8AAFF, 0xBDB76BFF, 0xF0E68CFF, 0x808000FF, 0xFFFF00FF, 0x9ACD32FF, 0x556B2FFF, 0x6B8E23FF, 0x7CFC00FF, 0x7FFF00FF, 0xADFF2FFF, 0x006400FF, 0x008000FF, 0x228B22FF, 0x00FF00FF, 0x32CD32FF, 0x90EE90FF, 0x98FB98FF, 0x8FBC8FFF, 0x00FA9AFF, 0x00FF7FFF, 0x2E8B57FF, 0x66CDAAFF, 0x3CB371FF, 0x20B2AAFF, 0x2F4F4FFF, 0x008080FF, 0x008B8BFF, 0x00FFFFFF, 0x00FFFFFF, 0xE0FFFFFF, 0x00CED1FF, 0x40E0D0FF, 0x48D1CCFF, 0xAFEEEEFF, 0x7FFFD4FF, 0xB0E0E6FF, 0x5F9EA0FF, 0x4682B4FF, 0x6495EDFF, 0x00BFFFFF, 0x1E90FFFF, 0xADD8E6FF, 0x87CEEBFF, 0x87CEFAFF, 0x191970FF, 0x000080FF, 0x00008BFF, 0x0000CDFF, 0x0000FFFF, 0x4169E1FF, 0x8A2BE2FF, 0x4B0082FF, 0x483D8BFF, 0x6A5ACDFF, 0x7B68EEFF, 0x9370DBFF, 0x8B008BFF, 0x9400D3FF, 0x9932CCFF, 0xBA55D3FF, 0x800080FF, 0xD8BFD8FF, 0xDDA0DDFF, 0xEE82EEFF, 0xFF00FFFF, 0xDA70D6FF, 0xC71585FF, 0xDB7093FF, 0xFF1493FF, 0xFF69B4FF, 0xFFB6C1FF, 0xFFC0CBFF, 0xFAEBD7FF, 0xF5F5DCFF, 0xFFE4C4FF, 0xFFEBCDFF, 0xF5DEB3FF, 0xFFF8DCFF, 0xFFFACDFF, 0xFAFAD2FF, 0xFFFFE0FF, 0x8B4513FF, 0xA0522DFF, 0xD2691EFF, 0xCD853FFF, 0xF4A460FF, 0xDEB887FF, 0xD2B48CFF, 0xBC8F8FFF, 0xFFE4B5FF, 0xFFDEADFF, 0xFFDAB9FF, 0xFFE4E1FF, 0xFFF0F5FF, 0xFAF0E6FF, 0xFDF5E6FF, 0xFFEFD5FF, 0xFFF5EEFF, 0xF5FFFAFF, 0x708090FF, 0x778899FF, 0xB0C4DEFF, 0xE6E6FAFF, 0xFFFAF0FF, 0xF0F8FFFF, 0xF8F8FFFF, 0xF0FFF0FF, 0xFFFFF0FF, 0xF0FFFFFF, 0xFFFAFAFF], dtype=uint32)
    def draw():
        t = clock()
        print("Being calculation")
        x = linspace(u[0], u[1], w)
        y = linspace(v[0], v[1], h)
        a, b = meshgrid(x,y)
        M = (a + 1j*b).T
        Alive = ones((w,h), dtype=bool)
        ### Mandelbrot | Julia picker
        ## Mandelbrot
        # C = M.copy()
        ## Julia
        C = (0.32 + 0.043j) * ones(M.shape, dtype=complex128) 
        ### End picker
        esc = max_iter * ones((w,h), dtype=int32)
        for k in range(max_iter):
            M[Alive] = square(M[Alive]) + C[Alive]
            MD = real(M)**2 + imag(M)**2
            esc[logical_and(Alive, MD > eps*eps)] = k
            Alive = MD <= eps*eps
        cmap = zeros((w,h), dtype=uint32)
        for k in range(max_iter):
            cmap[esc == k] = colorsMap[k]
        print("Finish Calculation: {:.2f}".format(clock() - t))
        t = clock()
        print("Begin Drawing")
        if False: #Change for effect
            glDrawPixels(w, h, GL_RGBA, GL_UNSIGNED_INT_8_8_8_8,
            #Primite drawing numpy array
            def transform(cl):
                r = ((cl >> 24) & 0xFF) / 256.0
                b = ((cl >> 16) & 0xFF) / 256.0
                g = ((cl >>  8) & 0xFF) / 256.0
                return (r,b,g)
            for y in range(0,h):
                for x in range(0,w):
        print("Finish drawing:     {:.2f}".format(clock() - t))
    def idle():
    def reshape(width, height):
        global w,h
        w,h =width, height
        glViewport(0, 0, width, height)
        gluOrtho2D(0, width, height, 0)
        glClearColor( 1., 1., 1., 0.)
        glClear( GL_COLOR_BUFFER_BIT )
        glColor3f(0., 0., 0.)
    glutInitDisplayMode(GLUT_SINGLE | GLUT_RGB)

  2. #2
    Senior Member OpenGL Guru
    Join Date
    Jun 2013
    Quote Originally Posted by lpp___ View Post
    When I draw using glDrawPixels I get something black and all messed up, but when using slower method of glBegin & glEnd I get the correct result.
    There are two issues with your code. First, the glDrawPixels() version doesn't call glFlush(), which may result in the call not executing. Second, glDrawPixels() expects the data in row-major ("raster scan") order, whereas your array is in column-major order. Use np.ascontiguousarray(cmap.transpose()) instead of just cmap (or, preferably, change the shape of cmap from (w,h) to (h,w)).

  3. #3
    Newbie Newbie
    Join Date
    May 2015
    Thank you, this solved the problem.

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts