How to blit a png image as an image overlay in PyOpenGL?

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I am making a game in PyOpenGL and want to blit some images onto the screen as some overlay (for example, the pause button). How can I do that?

I've tried using glBitmap(), but it doesn't work.

This is what I have:

pauseimg = pygame.image.load(path + "pause.png").convert_alpha()
def blit_image(x,y,w,h,img,r,g,b):
    glColor3f(r,g,b)
    glWindowPos2f(x,y)
    glBitmap(w,h,0,0,0,0,img)
blit_image(300,300,313,115,pauseimg,1,1,1)

I expected it to blit the image, but instead it threw an exception: 

Traceback (most recent call last):
  File "/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/site-packages/OpenGL/latebind.py", line 41, in __call__
    return self._finalCall( *args, **named )
TypeError: 'NoneType' object is not callable

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File ".py", line 438, in <module>
    blit_image(300,300,313,115,pauseimg,1,1,1)
  File ".py", line 135, in blit_image
    glBitmap(w,h,0,0,0,0,img)
  File "/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/site-packages/OpenGL/latebind.py", line 45, in __call__
    return self._finalCall( *args, **named )
  File "/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/site-packages/OpenGL/wrapper.py", line 675, in wrapperCall
    pyArgs = tuple( calculate_pyArgs( args ))
  File "/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/site-packages/OpenGL/wrapper.py", line 436, in calculate_pyArgs
    yield converter(args[index], self, args)
  File "/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/site-packages/OpenGL/converters.py", line 135, in __call__
    return self.function( incoming )
  File "/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/site-packages/OpenGL/arrays/arraydatatype.py", line 149, in asArray
    return cls.getHandler(value).asArray( value, typeCode or cls.typeConstant )
  File "/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/site-packages/OpenGL/arrays/arraydatatype.py", line 53, in __call__
    typ.__module__, type.__name__, repr(value)[:50]
TypeError: ('No array-type handler for type pygame.type (value: <Surface(313x114x32 SW)>) registered', <OpenGL.converters.CallFuncPyConverter object at 0x111a720b8>)```
opengl-compat pyopengl opengl pygame python
1 Answers

It is not possible to draw bitmap with the format GL_RGBA8 by glBitmap, because the buffer is treated as a buffer with format GL_COLOR_INDEX (see glTexImage2D)

See OpenGL 4.6 API Compatibility Profile Specification - 14.8 Bitmaps, page 579:

Like a polygon pattern, a bitmap is unpacked from memory according to the procedure given in section 18.1 for DrawPixels; it is as if the width and height passed to that command were equal to w and h, respectively, the type were BITMAP, and the format were COLOR_INDEX.

If you wan to draw a RGBA trexutre, then you've to create a butte array buffer. This can be achieved by NumPy:

raw_data = img.get_buffer().raw
data = numpy.fromstring(raw_data, numpy.uint8)

Create a texture object by glTexImage2D:

bitmap_tex = glGenTextures(1)
glBindTexture(GL_TEXTURE_2D, bitmap_tex)
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST)
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST)
glTexImage2D(GL_TEXTURE_2D,0,GL_RGBA,w,h,0,GL_BGRA,GL_UNSIGNED_BYTE,data)

And draw the texture by a Quads - Primitive:

glEnable(GL_TEXTURE_2D)
glBegin(GL_QUADS)
glTexCoord2f(0, 1)
glVertex2f(x, y)
glTexCoord2f(1, 1)
glVertex2f(x+w, y)
glTexCoord2f(1, 0)
glVertex2f(x+w, y+h)
glTexCoord2f(0, 0)
glVertex2f(x, y+h)
glEnd()
glDisable(GL_TEXTURE_2D)

If the texture is transparent, then you've to activate Blending.
The function can be implemented as follows:

bitmap_tex = None
def blit_image(x,y,img,r,g,b):
    global bitmap_tex

    # get texture data
    w,h = img.get_size()
    raw_data = img.get_buffer().raw
    data = numpy.fromstring(raw_data, numpy.uint8)

    # create texture object
    if bitmap_tex == None:
      bitmap_tex = glGenTextures(1)
    glBindTexture(GL_TEXTURE_2D, bitmap_tex)
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST)
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST)
    glTexImage2D(GL_TEXTURE_2D,0,GL_RGBA,w,h,0,GL_BGRA,GL_UNSIGNED_BYTE,data)

    # save and set model view and projection matrix
    glMatrixMode(GL_PROJECTION)
    glPushMatrix()
    glLoadIdentity()
    glOrtho(0, display[0], 0, display[1], -1, 1)
    glMatrixMode(GL_MODELVIEW)
    glPushMatrix()
    glLoadIdentity()

    # enable blending
    glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA)
    glEnable(GL_BLEND)

    # draw textured quad
    glColor3f(r,g,b)

    glEnable(GL_TEXTURE_2D)
    glBegin(GL_QUADS)
    glTexCoord2f(0, 1)
    glVertex2f(x, y)
    glTexCoord2f(1, 1)
    glVertex2f(x+w, y)
    glTexCoord2f(1, 0)
    glVertex2f(x+w, y+h)
    glTexCoord2f(0, 0)
    glVertex2f(x, y+h)
    glEnd()
    glDisable(GL_TEXTURE_2D)

    # restore matrices
    glMatrixMode(GL_PROJECTION)
    glPopMatrix()
    glMatrixMode(GL_MODELVIEW)
    glPopMatrix()

    # disable blending
    glDisable(GL_BLEND)

pauseimg = pygame.image.load(path + "pause.png").convert_alpha()
blit_image(300,300,pauseimg,1,1,1)
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