OpenGL 3D Navigation glRotatef, glTranslatef, gluLookAt EP_OpenGL_005

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Introduction

I think one of the most important steps for beginners is to learn how to create a 3D space and navigate in this space. It is especially important to know how to navigate in 3D space. It can be very confusing for beginners. This program shows how to navigate in 3D space.

Using the Code

The base code is from the redbook "OpenGL Programming Guide (Third Edition)". This is a beginner level program to show how to navigate in 3D space. It uses glRotatef(), glTranslatef() and gluLookAt() functions. I divided the 3D space with lines. The intersection of the x,y,z arises is the location (0,0,0). The doted parts of the lines are the negative sides of the axises.The z axis is not viewable, because we look at the space from (0,0,15) coordinates. I rotated the above picture so that the z axis can be seen.

• Green for x axis
• Red for y axis
• Blue for z axis
• x,X - rotates on x axis // uses glRotatef() function
• y,Y - rotates on y axis "
• z,Z - rotates on z axis "
• left_key - translates to left (x axis) // uses glTranslatef()
• right_key - translates to right (x axis) "
• up_key - translates up (y axis) "
• down_key - translates down (y axis) "
• page_up - translates on z axis (zoom in) "
• page_down - translates on z axis (zoom out) "
• j,J translates on x axis // uses glLookAt()
• k,K translates on y axis "
• l,L translates on z axis "
• b,B rotates (+/-)90 degrees on x axis
• n,N rotates (+/-)90 degrees on y axis
• m,M rotates (+/-)90 degrees on z axis
• o,O brings everything to default (starting coordinates)

Notice that glTranslatef and gluLookAt() behave the same. However, it is not exactly the same. You can figure out by using this program.

#include "stdafx.h"
#include <GL/glut.h> // Once you include glut.h (you don't need gl.h or glu.h)   


GLfloat X = 0.0f; // Translate screen to x direction (left or right)
GLfloat Y = 0.0f; // Translate screen to y direction (up or down)
GLfloat Z = 0.0f; // Translate screen to z direction (zoom in or out)
GLfloat rotX = 0.0f; // Rotate screen on x axis 
GLfloat rotY = 0.0f; // Rotate screen on y axis
GLfloat rotZ = 0.0f; // Rotate screen on z axis
GLfloat rotLx = 0.0f; // Translate screen by using the glulookAt function (left or right)
GLfloat rotLy = 0.0f; // Translate screen by using the glulookAt function (up or down)
GLfloat rotLz = 0.0f; // Translate screen by using the glulookAt function (zoom in or out)

void glDisplayLines(void); // Did declare the function 
			// so I did not have to check for order of the functions

// Initialize the OpenGL window
void init(void)
{
    glClearColor (0.0, 0.0, 0.0, 0.0); // Clear the color 
    glShadeModel (GL_FLAT); // Set the shading model to GL_FLAT
    glEnable (GL_LINE_SMOOTH);
    glHint(GL_LINE_SMOOTH_HINT, GL_NICEST); // Set Line Antialiasing
}

// Draw the lines (x,y,z)
void display(void)
{ 
    glClear (GL_COLOR_BUFFER_BIT); // Clear the Color Buffer 
    glPushMatrix(); 	// It is important to push the Matrix before calling 
			// glRotatef and glTranslatef
    glRotatef(rotX,1.0,0.0,0.0); // Rotate on x
    glRotatef(rotY,0.0,1.0,0.0); // Rotate on y
    glRotatef(rotZ,0.0,0.0,1.0); // Rotate on z
    glTranslatef(X, Y, Z); 	// Translates the screen left or right, 
			// up or down or zoom in zoom out
    // Draw the positive side of the lines x,y,z
    glBegin(GL_LINES);
    glColor3f (0.0, 1.0, 0.0); // Green for x axis
    glVertex3f(0,0,0);
    glVertex3f(10,0,0);
    glColor3f(1.0,0.0,0.0); // Red for y axis
    glVertex3f(0,0,0);
    glVertex3f(0,10,0);
    glColor3f(0.0,0.0,1.0); // Blue for z axis
    glVertex3f(0,0,0); 
    glVertex3f(0,0,10);
    glEnd();

    // Dotted lines for the negative sides of x,y,z
    glEnable(GL_LINE_STIPPLE); 	// Enable line stipple to use a 
				// dotted pattern for the lines
    glLineStipple(1, 0x0101); 	// Dotted stipple pattern for the lines
    glBegin(GL_LINES); 
    glColor3f (0.0, 1.0, 0.0); 	// Green for x axis
    glVertex3f(-10,0,0);
    glVertex3f(0,0,0);
    glColor3f(1.0,0.0,0.0); 	// Red for y axis
    glVertex3f(0,0,0);
    glVertex3f(0,-10,0);
    glColor3f(0.0,0.0,1.0); 	// Blue for z axis
    glVertex3f(0,0,0);
    glVertex3f(0,0,-10);
    glEnd();
    glDisable(GL_LINE_STIPPLE); 	// Disable the line stipple
    glPopMatrix(); 		// Don't forget to pop the Matrix
    glutSwapBuffers();
}

// This function is called whenever the window size is changed
void reshape (int w, int h)
{
    glViewport (0, 0, (GLsizei) w, (GLsizei) h); // Set the viewport
    glMatrixMode (GL_PROJECTION); 	// Set the Matrix mode
    glLoadIdentity (); 
    gluPerspective(75, (GLfloat) w /(GLfloat) h , 0.10, 100.0);
    glMatrixMode(GL_MODELVIEW);
    glLoadIdentity();
    gluLookAt (rotLx, rotLy, 15.0 + rotLz, 0.0, 0.0, 0.0, 0.0, 1.0, 0.0); 
}

// This function is used for the navigation keys
void keyboard (unsigned char key, int x, int y)
{
switch (key) {   // x,X,y,Y,z,Z uses the glRotatef() function
    case 'x': // Rotates screen on x axis 
    rotX -= 0.5f;
    break;
    case 'X': // Opposite way 
    rotX += 0.5f;
    break;
    case 'y': // Rotates screen on y axis
    rotY -= 0.5f;
    break;
    case 'Y': // Opposite way
    rotY += 0.5f; 
    break; 
    case 'z': // Rotates screen on z axis
    rotZ -= 0.5f;
    break;
    case 'Z': // Opposite way
    rotZ += 0.5f;
    break;
    // j,J,k,K,l,L uses the gluLookAt function for navigation
    case 'j':
    rotLx -= 0.2f; 
    glMatrixMode(GL_MODELVIEW);
    glLoadIdentity();
    gluLookAt (rotLx, rotLy, 15.0 + rotLz, 0.0, 0.0, 0.0, 0.0, 1.0, 0.0);
    break;
    case 'J':
    rotLx += 0.2f;
    glMatrixMode(GL_MODELVIEW);
    glLoadIdentity();
    gluLookAt (rotLx, rotLy, 15.0 + rotLz, 0.0, 0.0, 0.0, 0.0, 1.0, 0.0);
    break; 
    case 'k':
    rotLy -= 0.2f;
    glMatrixMode(GL_MODELVIEW);
    glLoadIdentity();
    gluLookAt (rotLx, rotLy, 15.0 + rotLz, 0.0, 0.0, 0.0, 0.0, 1.0, 0.0);
    break;
    case 'K':
    rotLy += 0.2f;
    glMatrixMode(GL_MODELVIEW);
    glLoadIdentity();
    gluLookAt (rotLx, rotLy, 15.0 + rotLz, 0.0, 0.0, 0.0, 0.0, 1.0, 0.0);
    break;
    case 'l': 	// It has a special case when the rotLZ becomes 
		// less than -15 the screen is viewed from the opposite side
    // therefore this if statement below does not allow rotLz be less than -15
    if(rotLz + 14 >= 0)
    rotLz -= 0.2f;           
    glMatrixMode(GL_MODELVIEW);    
    glLoadIdentity();  
    gluLookAt (rotLx, rotLy, 15.0 + rotLz, 0.0, 0.0, 0.0, 0.
    break;
    case 'L':
    rotLz += 0.2f;
    glMatrixMode(GL_MODELVIEW);
    glLoadIdentity();
    gluLookAt (rotLx, rotLy, 15.0 + rotLz, 0.0, 0.0, 0.0, 0.0, 1.0, 0.0);
    break;
    case 'b': // Rotates on x axis by -90 degree
    rotX -= 90.0f;
    break;
    case 'B': // Rotates on y axis by 90 degree
    rotX += 90.0f; 
    break;
    case 'n': // Rotates on y axis by -90 degree
    rotY -= 90.0f;
    break;
    case 'N': // Rotates on y axis by 90 degree
    rotY += 90.0f;
    break;
    case 'm': // Rotates on z axis by -90 degree
    rotZ -= 90.0f; 
    break;
    case 'M': // Rotates on z axis by 90 degree
    rotZ += 90.0f;
    break;
    case 'o': // Default, resets the translations vies from starting view
    case 'O': 
    X = Y = 0.0f;
    Z = 0.0f;
    rotX = 0.0f;
    rotY = 0.0f;
    rotZ = 0.0f;
    rotLx = 0.0f;
    rotLy = 0.0f;
    rotLz = 0.0f;
    glMatrixMode(GL_MODELVIEW);
    glLoadIdentity();
    gluLookAt(rotLx, rotLy, 15.0f + rotLz, 0.0f, 0.0f, 0.0f, 0.0f, 1.0f, 0.0f);  
    break;
}
    glutPostRedisplay(); // Redraw the scene
}

// called on special key pressed
void specialKey(int key, int x, int y) { 

// The keys below are using the gluLookAt() function for navigation
// Check which key is pressed

switch(key) {
    case GLUT_KEY_LEFT : // Rotate on x axis
    X -= 0.1f;
    break;
    case GLUT_KEY_RIGHT : // Rotate on x axis (opposite)
    X += 0.1f;
    break;
    case GLUT_KEY_UP : // Rotate on y axis 
    Y += 0.1f;
    break;
    case GLUT_KEY_DOWN : // Rotate on y axis (opposite)
    Y -= 0.1f;
    break; 
    case GLUT_KEY_PAGE_UP: // Rotate on z axis
    Z -= 0.1f;
    break;
    case GLUT_KEY_PAGE_DOWN:// Rotate on z axis (opposite)
    Z += 0.1f;
    break;
}
    glutPostRedisplay(); // Redraw the scene
}

// Main entry point of the program
int main(int argc, char** argv)
{
    glutInit(&argc, argv);
    glutInitDisplayMode (GLUT_DOUBLE | GLUT_RGB); 	// Setup display mode to 
						// double buffer and RGB color
    glutInitWindowSize (600,600); // Set the screen size
    glutCreateWindow("OpenGL 3D Navigation Program"); 
    init ();
    glutReshapeFunc(reshape); 
    glutDisplayFunc(display); 
    glutKeyboardFunc(keyboard); // set window's key callback 
    glutSpecialFunc(specialKey); // set window's to specialKey callback
    glutMainLoop();

    return 0;
}