# Blender.BGL module (OpenGL wrapper)

"""
The Blender.BGL submodule

This module wraps OpenGL constants and functions, making them available from
within Blender Python.  The complete list can be retrieved from the module
itself, by listing its contents: dir(Blender.BGL).  There are too many to be
documented here, but a simple search on the net can point to more than enough
material to teach OpenGL programming, from books to many collections of
tutorials.  The I{red book}: "OpenGL Programming Guide", is a very good
resource, even for newcomers.
@see: U{www.opengl.org}

Example::
 import Blender
 from Blender.BGL import *
 from Blender import Draw
 R = G = B = 0
 A = 1
 instructions = "Hold mouse buttons to change the background color."
 quitting = " Press ESC or q to quit."
 #
 def show_win():
  glClearColor(R,G,B,A)                # define color used to clear buffers 
  glClear(GL_COLOR_BUFFER_BIT)         # use it to clear the color buffer
  glColor3f(1,1,1)                     # change default color
  glRasterPos2i(50,100)                # move cursor to x = 50, y = 100
  Draw.Text("Testing BGL  + Draw")     # draw this text there
  glRasterPos2i(350,20)                # move cursor again
  Draw.Text(instructions + quitting)   # draw another msg
  glBegin(GL_LINE_LOOP)                # begin a vertex-data list
  glVertex2i(46,92)
  glVertex2i(120,92)
  glVertex2i(120,115)
  glVertex2i(46,115)
  glEnd()                              # close this list
  glColor3f(0.35,0.18,0.92)            # change default color again
  glBegin(GL_POLYGON)                  # another list, for a polygon
  glVertex2i(315, 292)
  glVertex2i(412, 200)
  glVertex2i(264, 256)
  glEnd()
  Draw.Redraw(1)                       # make changes visible.
 #
 def ev(evt, val):                     # this is a callback for Draw.Register()
  global R,G,B,A                       # it handles input events
  if evt == Draw.ESCKEY or evt == Draw.QKEY:
    Draw.Exit()                        # this quits the script
  elif evt == Draw.LEFTMOUSE: R = 1 - R
  elif evt == Draw.MIDDLEMOUSE: G = 1 - G
  elif evt == Draw.RIGHTMOUSE: B = 1 - B
  else:
    Draw.Register(show_win, ev, None)
 #
 Draw.Register(show_win, ev, None)     # start the main loop
"""