Why is my OpenGL program unable to load the GLUT bitmap fonts?

问题

I want to display some simple text on the HUD of my 3D environment in OpenGL. All sources say that I should use the bitmap fonts included in GLUT, however, my program can't seem the find/load the fonts.

I have included all of the correct libraries and have double checked that the fonts.py file is definitely in the ...\Python37\...\OpenGL\GLUT\ directory, but when I type GLUT_BITMAP_TIMES_ROMAN_24 (or any of the other bitmap fonts), it is highlighted as an error in my code.

This is the function I call to display the text:

def text(self, x, y, r, g, b, text):

    glColor3f(r, g, b)

    glRasterPos2f(x, y)

    for i in range(len(text)):
        glutBitmapCharacter(GLUT_BITMAP_TIMES_ROMAN_24, text[i])

And this is how I call the function:

epoch_str = "Epoch: {0}".format(self.epoch)

self.text(x, y, 1.0, 1.0, 1.0, epoch_str)

As mentioned, the GLUT_BITMAP_TIMES_ROMAN_24 is highlighted in my IDE (PyCharm) as an error, and I get the following error if I try to run it:

C:\Users\mickp\AppData\Local\Programs\Python\Python37\python.exe C:/Users/mickp/PycharmProjects/Test/U_Matrix.py
Traceback (most recent call last):
  File "C:\Users\mickp\AppData\Local\Programs\Python\Python37\lib\site-packages\OpenGL\GLUT\special.py", line 130, in safeCall
    return function( *args, **named )
  File "C:/Users/mickp/PycharmProjects/Test/U_Matrix.py", line 142, in render
    self.text(x, y, 1.0, 1.0, 1.0, epoch_str)
  File "C:/Users/mickp/PycharmProjects/Test/U_Matrix.py", line 79, in text
    glutBitmapCharacter(GLUT_BITMAP_TIMES_ROMAN_24, text[i])
ctypes.ArgumentError: argument 2: <class 'TypeError'>: wrong type
GLUT Display callback <bound method U_MATRIX.render of <__main__.U_MATRIX object at 0x000002877FF45438>> with (),{} failed: returning None argument 2: <class 'TypeError'>: wrong type

Process finished with exit code 1

I really don't understand what the problem could be?

Edit: The above error has been fixed, it was a separate problem. The underlying problem with GLUT_BITMAP_TIMES_ROMAN_24is still there. See: IDE shows an error for GLUT_BITMAP_TIMES_ROMAN_24

Edit 2: Full Code (it's not too long):

Edit 3: Removed full code (it was too long). Adding the following fixed my problem:

# added before
glMatrixMode(GL_PROJECTION)
glPushMatrix()
glLoadIdentity()
gluOrtho2D(0.0, width, 0.0, height)
glMatrixMode(GL_MODELVIEW)
glPushMatrix()
glLoadIdentity()

# these two lines were here
epoch_str = "Epoch: {0}".format(self.epoch)
self.text(x+10, y+10, 0.0, 1.0, 0.0, epoch_str)

# added after
glMatrixMode(GL_MODELVIEW)
glPopMatrix()
glMatrixMode(GL_PROJECTION)
glPopMatrix()
glEnable(GL_TEXTURE_2D)

The text was actually just hidden as I had rendered it into the 3D environment behind an object, as opposed to in front of the 3D environment.

回答1:

The issue is not the 1st parameter GLUT_BITMAP_TIMES_ROMAN_24, but it is the 2nd parameter text[i]. The parameter to glutBitmapCharacter has to be an integral value (int), which represents the character.
The chracter has to be converted to an ordinary number (int) by ord:

glutBitmapCharacter(GLUT_BITMAP_TIMES_ROMAN_24, ord(text[i]))

for c in text:
    glutBitmapCharacter(GLUT_BITMAP_TIMES_ROMAN_24, ord(c))

If the text doesn't appear on the screen, then reset the projection and model view matrix and draw the text at position (0, 0) for debug reasons:

glMatrixMode(GL_PROJECTION)
glPushMatrix()
glLoadIdentity()

glMatrixMode(GL_MODELVIEW)
glPushMatrix()
glLoadIdentity()

self.text(0.0, 0.0, 1.0, 1.0, 1.0, epoch_str)

glMatrixMode(GL_PROJECTION)
glPopMatrix()

glMatrixMode(GL_MODELVIEW)
glPopMatrix()

来源：https://stackoverflow.com/questions/55957159/why-is-my-opengl-program-unable-to-load-the-glut-bitmap-fonts

标签

python

opengl

glut

pyopengl

opengl-compat