I can't make working keyCallback function in OpenGL and glfw - opengl

Question

import glfw
from OpenGL.GL import *
import numpy as np
currentMode = GL_LINE_LOOP
def render(currentMode):
def key_callback(window, key, scancode, action, mods):
if key==glfw.KEY_1:
if action==glfw.PRESS:
currentMode = GL_POINTS
elif key==glfw.KEY_2:
if action==glfw.PRESS:
currentMode = GL_LINES
elif key==glfw.KEY_3:
if action==glfw.PRESS:
currentMode = GL_LINE_STRIP
while not glfw.window_should_close(window):
glfw.poll_events()
render(currentMode)
glfw.swap_buffers(window)
print(currentMode)
glfw.terminate()
I try to change primitive type to use render function's parameter.
But, It doesn't work.
What should I do?

Answer 1

You missed the global statement in key_callback:
def key_callback(window, key, scancode, action, mods):
global currentMode # <--- THIS IS MISSING
if key==glfw.KEY_1:
if action==glfw.PRESS:
currentMode = GL_POINTS
# [...]
The variable currentMode exists twice. It is a variable in global namespace, and local variable in the scope of the function key_callback. Use the global statement to interpreted currentMode as global and to write to the global variable currentMode with key_callback.
Of course the same applies to the main function, too:
def main():
global currentMode
# [...]
Furthermore you have to clear the framebuffer in render:
def render(currentMode):
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT)
See the example:
import glfw
from OpenGL.GL import *
import numpy as np
def render(currentMode):
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT)
glLoadIdentity()
print(currentMode)
glBegin(currentMode)
#Draw Something
glVertex2f(-0.5, -0.5)
glVertex2f(0.5, 0.5)
glVertex2f(-0.5, 0.5)
glEnd()
def key_callback(window, key, scancode, action, mods):
global currentMode
if key==glfw.KEY_1:
if action==glfw.PRESS:
currentMode = GL_POINTS
elif key==glfw.KEY_2:
if action==glfw.PRESS:
currentMode = GL_LINES
elif key==glfw.KEY_3:
if action==glfw.PRESS:
currentMode = GL_LINE_STRIP
def main():
global currentMode
if not glfw.init():
return
window = glfw.create_window(480, 480, "Test", None, None)
if not window:
glfw.terminate()
return
glfw.make_context_current(window)
glfw.set_key_callback(window, key_callback)
glfw.swap_interval(1)
while not glfw.window_should_close(window):
glfw.poll_events()
render(currentMode)
glfw.swap_buffers(window)
glfw.terminate()
if __name__ == "__main__":
currentMode = GL_LINE_LOOP
main()