WithStatementAndOpenGl

(I think you should bring this up in the OpenGl community; if the with-statement supports the usage I don't see why not. GvR)

(Doing so. -- Andrew Dalke)

OpenGL programmers have complained about using Python because the code indentation doesn't follow the display tree. For an example pulled from one of my (Andrew Dalke) projects

 glBegin(GL_QUAD_STRIP)
 glColor3f(1.0,1.0,1.0) #corner 1
 glNormal3f(0.57735027, 0.57735027, 0.57735027)
 glVertex3f(0.5, 0.5, 0.5)
 glColor3f(1.0,0.0,1.0) #corner 2
 glNormal3f(0.57735027, -0.57735027, 0.57735027)
 glVertex3f(0.5, -0.5, 0.5)
 ...
 glEnd()

Some people write this as some variant of

 glBegin(GL_QUAD_STRIP)
 if 1:
 glColor3f(1.0,1.0,1.0) #corner 1
 glNormal3f(0.57735027, 0.57735027, 0.57735027)
 glVertex3f(0.5, 0.5, 0.5)
 glColor3f(1.0,0.0,1.0) #corner 2
 glNormal3f(0.57735027, -0.57735027, 0.57735027)
 glVertex3f(0.5, -0.5, 0.5)
 ...
 glEnd()

and sometimes using try/finally so that errors don't cause the gl state to become corrupted.

Would an appropriate use of this proposal be to allow

 with QUAD_STRIP:
 glColor3f(1.0,1.0,1.0) #corner 1
 glNormal3f(0.57735027, 0.57735027, 0.57735027)
 glVertex3f(0.5, 0.5, 0.5)
 glColor3f(1.0,0.0,1.0) #corner 2
 glNormal3f(0.57735027, -0.57735027, 0.57735027)
 glVertex3f(0.5, -0.5, 0.5)
 ....

where there are a bunch of small classes for each of the possible glBegins, such as

class QUAD_STRIP:
 @staticmethod
 def __enter__():
 glBegin(GL_QUAD_STRIP)
 @staticmethod
 def __exit__(*args):
 glEnd()

If so, I rather like that ability as it makes the graphics programmer's intent clearer and prevents problems balancing glBegin and glEnd - even in the face of code errors in the actual code block! -- Andrew Dalke

I'm (Andrew Dalke) often one to resist change to Python. The WithStatement is a counter-example. I really like how it cleans up some OpenGL programming. Consider this example from OpenGLContext's indexlineset.py

 dl = displaylist.DisplayList()
 ...
 # compile the color-friendly ILS
 dl.start()
 try:
 glEnable( GL_COLOR_MATERIAL )
 for polyline, color in zip(indices, colorIndices):
 if type(color) == int:
 glColor3d( *colors[color] )
 glBegin( GL_LINE_STRIP )
 try:
 for i in polyline:
 glVertex3f(*points[i])
 finally:
 glEnd()
 else:
 glBegin( GL_LINE_STRIP )
 try:
 for i,c in zip(polyline, color):
 glColor3d( *colors[c] )
 glVertex3f(*points[i])
 finally:
 glEnd()
 glDisable( GL_COLOR_MATERIAL )
 finally:
 dl.end()

Assuming a few minor helper classes and a couple of new __enter__/__exit__ methods and it can be rewritten using 'with' statements like this:

 dl = displaylist.DisplayList()
 ...
 with dl:
 with GLEnable( GL_COLOR_MATERIAL ):
 for polyline, color in zip(indices, colorIndices):
 if type(color) == int:
 glColor3d( *colors[color] )
 with GLGeometry( GL_LINE_STRIP ):
 for i in polyline:
 glVertex3f(*points[i])
 else:
 with GLBegin( GL_LINE_STRIP ):
 for i,c in zip(polyline, color):
 glColor3d( *colors[c] )
 glVertex3f(*points[i])

Shorter, cleaner, less error-prone, easier to read and maintain. +1 from me! -- Andrew Dalke