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glRotatef

Started by Monty Python Jul 13, 2003 at 1:52 PM 2 replies 850+ views

Original Post

Jul 13, 2003 at 1:52 PM

Can anybody spot a problem with the following code: * The quad is displayed correctly on the scene * The variable thetaQuad is definitely a float * The Python interpreter reports no errors

import sys

from OpenGL.GL import *
from OpenGL.GLU import *
from OpenGL.GLUT import *


thetaQuad = 0.1


def renderScene():
    global thetaQuad

    glClear( GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT )
    glLoadIdentity()

    glRotatef( thetaQuad, 0.0, 1.0, 0.0 )
    glBegin( GL_QUADS )
    glVertex3f( -0.5, -0.5, 0.0 )
    glVertex3f( -0.5, 0.5, 0.0 )
    glVertex3f( 0.5, 0.5, 0.0 )
    glVertex3f( 0.5, -0.5, 0.0 )
    glEnd()

    glutSwapBuffers()
    thetaQuad += 0.2


def initScene():
    glClearColor( 0.3, 0.3, 0.3, 1.0 )
    glShadeModel( GL_SMOOTH )


def idleScene():
    pass


def main():
    glutInit( sys.argv )
    glutInitDisplayMode( GLUT_RGBA | GLUT_DOUBLE )
    glutInitWindowPosition( 200, 200 )
    glutInitWindowSize( 800, 600 )
    glutCreateWindow( "OpenGL" )

    initScene()
    glutDisplayFunc( renderScene )
    glutIdleFunc( idleScene )
    glutMainLoop()


main()

Daivuk

Jul 13, 2003 at 3:00 PM

before you make glRotatef, write : glPushMatrix();
And after drawing your quads, write glPopMatrix();

If you always use that, you will never get problem with Transformation.

All transformations you make between Push and Pop will not affect the rest of the drawing.

thats the way to draw an object :

glPushMatrix();
.. Do Transformation.. (Translate, Rotate, Scale)
.. Draw Your object..
glPopMatrix();

Trienco

Jul 14, 2003 at 2:27 AM

quote:
Original post by Daivuk
before you make glRotatef, write : glPushMatrix();
And after drawing your quads, write glPopMatrix();

what for? he''s doing nothing else and pushing the identity seems quite pointless, too.

quote:

If you always use that, you will never get problem with Transformation.

and if youre always doing that without understanding why and what it does you start pushing and popping for a single triangle where its extremely useless.

btw. what exactly is the problem? if there are no errors and its displayed correctly, why looking for errors? if you DONT see anything then thats most likely because the quad is exactly around the same position as your point of view or because you never set a color. do that and for example translate it a few units along the negative z-axis before rotating. or tell us what exactly is the problem?

Fruny

Jul 14, 2003 at 4:00 AM

You need to refresh your image as an idle task.


def idleScene():
     glutPostRedisplay()

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