basic GL function glTranslatef don't seem to be working - c++

Question

I was following this tutorial, the triangle renders perfectly, but when I hit the Page Up key, nothing happens.
Here's my code:
// made in Visual Studio Express 2008
// OpenGL3-1.cpp : Defines the entry point for the console application.
//
#include "stdafx.h"
// if you are not using Visual Studio to compile this then remove stdafx.h
#include <stdlib.h>
#include <windows.h>
#include "glut.h"
void init(void)
{
glClearColor (0.0, 0.0, 0.0, 0.0);
glEnable(GL_DEPTH_TEST);
glShadeModel (GL_SMOOTH);
}
void display(void)
{
glClear (GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
/* Loading the Identity matrix means we reset the screen coordinate system to XYZ axis of lenght 1:
The screen starts at z=0, x=-1 to x=1 and y=-1 to y=1 */
glLoadIdentity ();
glTranslatef(0,0.0f,-6.0f);
// translate everything by 6 units in the z axis.
glBegin(GL_TRIANGLES);
glColor3f(1.0f,0.0f,0.0f);
glVertex3f( 0.0f, 1.0f, 0.0f);
glColor3f(0.0f,1.0f,0.0f); // Set The Color To Green
glVertex3f(-1.0f,-1.0f, 0.0f);
glColor3f(0.0f,0.0f,1.0f); // Set The Color To Blue
glVertex3f( 1.0f,-1.0f, 0.0f);
glEnd(); // Done Drawing A Triangle
Sleep(5);
glutSwapBuffers();
}
void reshape (int w, int h)
{
// just the window reshape function
glViewport (0, 0, (GLsizei) w, (GLsizei) h);
glMatrixMode (GL_PROJECTION);
glLoadIdentity ();
gluPerspective(60.0, (GLfloat) w/(GLfloat) h, 1.0, 20.0);
glMatrixMode (GL_MODELVIEW);
}
void keyboard(unsigned char key, int x, int y)
{
// escapes from the program if the ESC key is hit
switch (key) {
case 27:
exit(0);
break;
}
}
void keyspecial( int key, int x, int y )
{
if( key == GLUT_KEY_PAGE_UP) // Page up
{
glTranslatef(90.0,0.0,0.0);
// ...... do what ever you want to do
glutPostRedisplay(); // redraw everything to reflect the changes
}
if (key == GLUT_KEY_PAGE_DOWN)
{
// ...... do what ever you want to do
glutPostRedisplay();// redraw everything to reflect the changes
}
if (key == GLUT_KEY_HOME)
{
// ...... do what ever you want to do
glutPostRedisplay();// redraw everything to reflect the changes
}
if (key == GLUT_KEY_END)
{
// ...... do what ever you want to do
glutPostRedisplay();// redraw everything to reflect the changes
}
}
int main(int argc, char** argv)
{
glutInit(&argc, argv);
glutInitDisplayMode (GLUT_RGB | GLUT_DEPTH | GLUT_DOUBLE);
glutInitWindowSize (500, 500);
glutInitWindowPosition (100, 100);
glutCreateWindow (argv[0]);
init ();
glutDisplayFunc(display);
glutReshapeFunc(reshape);
glutKeyboardFunc(keyboard); // tell glut to call this function when the user presses a key
glutSpecialFunc(keyspecial); // tell glut to call this function when the user presses a special a key
glutMainLoop();
return 0;
}
Note:
The tutorial suggested using glTranslate(x,y,z) instead of glTranslatef(x,y,z). I assumed that was a typo since glTranslate() doesn't exist

Answer 1

You're resetting your matrix in display, so your glTranslate* from the key event handler is lost. Rethink what you're trying to achieve.

Answer 2

What you're doing in this function is not the right thing to do
void reshape (int w, int h)
{ // just the window reshape function
glViewport (0, 0, (GLsizei) w, (GLsizei) h);
glMatrixMode (GL_PROJECTION);
glLoadIdentity ();
gluPerspective(60.0, (GLfloat) w/(GLfloat) h, 1.0, 20.0);
glMatrixMode (GL_MODELVIEW);
}
Speak with me: Don't set the viewport size and projection in the reshape handler!
You always set viewport and projection together with everything else in the display handler. It's the only right place to do it.
Next, you don't "place" objects using OpenGL matrix functions. You're just manipulating the transformation matrix, which should be set according to the placement of the objects, which may be perfectly well stored as matrix but independently of OpenGL state. So your keyboard handler should set some variable, which is then used for setting the modelview matrix at the right moment.