Basic OpenGL reshape function question...

Member

Posts: 321
Joined: 2004.10

Post: #1

Mar 24, 2011 — 03:03 PM

Code:

void reshape1(int width, int height)

{

   glViewport(0, 0, width, height);

   glMatrixMode(GL_PROJECTION);

   glLoadIdentity();

        [b]gluPerspective(); or glFrustrum(); or glOrtho();[/b]

   glGetDoublev(GL_PROJECTION_MATRIX, projection);

   glMatrixMode(GL_MODELVIEW);

   glLoadIdentity();

   gluLookAt(lookat[0].value, lookat[1].value, lookat[2].value,

                      lookat[3].value, lookat[4].value, lookat[5].value,

                      lookat[6].value, lookat[7].value, lookat[8].value);

   glGetDoublev(GL_MODELVIEW_MATRIX, modelview);

   glClearColor(0.0, 0.0, 0.0, 0.0);

}

void reshape2(int width, int height)

{

   same as above: glViewport(), glMatrixMode, glLoadIdentity

       [b]gluPerspective(60.0, (GLfloat)width/height, 1.0, 256.0);[/b]

    glMatrixMode(GL_MODELVIEW);

    glLoadIdentity();

    glTranslatef(0.0, 0.0, -5.0);

    glRotatef(-45.0, 0.0, 1.0, 0.0);

    glClearColor(0.0, 0.0, 0.0, 0.0);

  }

This is Nate Robin's code from his projection tutorial and I'm wondering why the reshape1 function has the glGetDoublev(GL_PROJECTION_MATRIX, projection); statement whereas reshape2 does not? And I'm correct in saying that the reshape2 function doesn't have a gluLookAt() function because it uses all default values?

Thanks in advance.

OneSadCookie

Luminary

Posts: 5,131
Joined: 2002.04

Post: #2

Mar 24, 2011 — 03:26 PM

Presumably he gets the projection matrix because he wants it later. You shouldn't call glGet. He has to because he's writing an odd tutorial app

Ingemar

Member

Posts: 260
Joined: 2005.05

Post: #3

Mar 30, 2011 — 07:05 AM

(Mar 24, 2011 03:03 PM)WhatMeWorry Wrote: And I'm correct in saying that the reshape2 function doesn't have a gluLookAt() function because it uses all default values?

You can always replace gluLookAt with translations and rotations. gluLookAt simply packages the information in terms of camera position and direction.

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