Home/ Questions/Q 7896387
In Process

The Archive Base Latest Questions

Editorial Team
  • 0
Asked: 2026-06-03T07:52:59+00:00

What’s the difference between glMatrixMode(GL_PROJECTION) and glMatrixMode(GL_MODELVIEW) ? #include <stdio.h> #include <GL/gl.h> #include <GL/glut.h>

  • 0

What’s the difference between glMatrixMode(GL_PROJECTION) and glMatrixMode(GL_MODELVIEW)?

#include <stdio.h>
#include <GL/gl.h>
#include <GL/glut.h>

#define KEY_ESCAPE 27

void display();
void keyboard(unsigned char,int,int);

int main(int argc, char **argv) {
    glutInit(&argc, argv);                                    
    glutInitDisplayMode(GLUT_RGB|GLUT_DOUBLE|GLUT_DEPTH );
    glutInitWindowSize(600,400);                  
    glutCreateWindow("Opengl Test");                              
    glutDisplayFunc(display);
    glutKeyboardFunc(keyboard);
    glutMainLoop();
    return 0;
}
void display() {
    float x,y,z;
    int i;
    x=0;
    y=-0.8;
    z=0;
    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();
    glClear(GL_COLOR_BUFFER_BIT);
    glColor3f(1,1,0);
    glBegin(GL_POINTS);
    for(i=0;i<98;i++) {
        glVertex3f(x,y,z);
        x=x+0.01;
    }
    glEnd();
    glutSwapBuffers();    
}
void keyboard(unsigned char key, int mousePositionX, int mousePositionY) {
    switch ( key ) {
        case KEY_ESCAPE:
            exit ( 0 );  
            break;      
        default:      
            break;
    }
}

Example 2:

#include <stdio.h>
#include <GL/gl.h>
#include <GL/glut.h>

#define KEY_ESCAPE 27

void display();
void keyboard(unsigned char,int,int);

int main(int argc, char **argv) {
    glutInit(&argc, argv);                                    
    glutInitDisplayMode(GLUT_RGB|GLUT_DOUBLE|GLUT_DEPTH );
    glutInitWindowSize(600,400);                  
    glutCreateWindow("Opengl Test");                              
    glutDisplayFunc(display);
    glutKeyboardFunc(keyboard);
    glutMainLoop();
    return 0;
}
void display() {
    float x,y,z;
    int i;
    x=0;
    y=-0.8;
    z=0;
    glMatrixMode(GL_MODELVIEW);
    glLoadIdentity();
    glClear(GL_COLOR_BUFFER_BIT);
    glColor3f(1,1,0);
    glBegin(GL_POINTS);
    for(i=0;i<98;i++) {
        glVertex3f(x,y,z);
        x=x+0.01;
    }
    glEnd();
    glutSwapBuffers();    
}
void keyboard(unsigned char key, int mousePositionX, int mousePositionY) {
    switch ( key ) {
        case KEY_ESCAPE:
            exit ( 0 );  
            break;      
        default:      
            break;
    }
}

For both codes, I got the same result.
Can anyone show the difference of these glMatrixMode(GL_MODELVIEW) and glMatrixMode(GL_PROJECTION)?

Share

Leave an answer

You must login to add an answer.

Need An Account,

1 Answer

  1. Editorial Team

    When you are looking at a scene, from GL point of view, you have a camera and a lens.

    ModelView is the matrix that represents your camera (position, pointing, and up vector).

    ProjectionView is the matrix that represents your camera’s lens (aperture, far-field, near-field, etc).

    See here for more info on those…

    In simple examples like yours, that doesn’t make many difference. However, in general, you need to ask OpenGL to calculate stuff by using matrix multiplications and inversions. For instance, if you want to transform a point on screen to a point of the GL coordinate system, GL will need a projection matrix and a model matrix and multiply them by a specific order. In that case, you must use them accordingly, because matrix multiplications are non-commutable.

    • 0