Creating a slightly more advanced camera for use in OpenGL

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In this opengl camera tutorial you will learn how to incorporate
the mouse using the glut mouse functions, to move our opengl camera like in a first person shooter, along with how to implement the strafe (sideways movement) you see in these games also.

To add the strafe we use:
if (key=='d')
{
float yrotrad;
yrotrad = (yrot / 180 * 3.141592654f);
xpos += float(cos(yrotrad)) * 0.2;
zpos += float(sin(yrotrad)) * 0.2;
}

if (key=='a')
{
float yrotrad;
yrotrad = (yrot / 180 * 3.141592654f);
xpos -= float(cos(yrotrad)) * 0.2;
zpos -= float(sin(yrotrad)) * 0.2;
}

You can see that I have simply flipped the cos and sin functions
and set both the xpos and zpos to either a negative or a positive

Now the mouse is a little easier as it uses no trigonometry.

We have to add a function which I have called: mouseMovement
void mouseMovement(int x, int y) {
int diffx=x-lastx; //check the difference between the current x and the last x position
int diffy=y-lasty; //check the difference between the current y and the last y position
lastx=x; //set lastx to the current x position
lasty=y; //set lasty to the current y position
xrot += (float) diffy; //set the xrot to xrot with the addition of the difference in the y position
yrot += (float) diffx;// set the xrot to yrot with the addition of the difference in the x position
}

To get GLUT to register the mouse movements, we call the line:
glutPassiveMotionFunc(mouseMovement);
to see where the mouse is when no mouse button is pressed and call
any functions within our mouseMovement function.

And that does it...

You now know how to add a strafe movement and mouse view.
The next camera tutorial will have lean, jump and duck effects.

If you have any questions, email me at swiftless@gmail.com

#include <GL/gl.h>
#include <GL/glut.h>
#include <stdlib.h>
#include <math.h>

//angle of rotation
float xpos = 0, ypos = 0, zpos = 0, xrot = 0, yrot = 0, angle=0.0;

float lastx, lasty;

//positions of the cubes
float positionz[10];
float positionx[10];

void cubepositions (void) { //set the positions of the cubes
for (int i=0;i<10;i++)
{
positionz[i] = rand()%5 + 5;
positionx[i] = rand()%5 + 5;
}
}

//draw the cube
void cube (void) {
for (int i=0;i<10;i++)
{
glPushMatrix();
glTranslated(-positionx[i + 1] * 10, 0, -positionz[i + 1] * 10); //translate the cube
glutSolidCube(2); //draw the cube
glPopMatrix();
}
}

void init (void) {
cubepositions();
}

void enable (void) {
glEnable (GL_DEPTH_TEST); //enable the depth testing
glEnable (GL_LIGHTING); //enable the lighting
glEnable (GL_LIGHT0); //enable LIGHT0, our Diffuse Light
glShadeModel (GL_SMOOTH); //set the shader to smooth shader
}

void camera (void) {
glRotatef(xrot,1.0,0.0,0.0); //rotate our camera on teh x-axis (left and right)
glRotatef(yrot,0.0,1.0,0.0); //rotate our camera on the y-axis (up and down)
glTranslated(-xpos,-ypos,-zpos); //translate the screen to the position of our camera
}

void display (void) {
glClearColor (0.0,0.0,0.0,1.0); //clear the screen to black
glClear (GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT); //clear the color buffer and the depth buffer
glLoadIdentity();
camera();
enable();
cube(); //call the cube drawing function
glutSwapBuffers(); //swap the buffers
angle++; //increase the angle
}

void reshape (int w, int h) {
glViewport (0, 0, (GLsizei)w, (GLsizei)h); //set the viewport to the current window specifications
glMatrixMode (GL_PROJECTION); //set the matrix to projection
glLoadIdentity ();
gluPerspective (60, (GLfloat)w / (GLfloat)h, 1.0, 1000.0); //set the perspective (angle of sight, width, height, , depth)
glMatrixMode (GL_MODELVIEW); //set the matrix back to model
}

void keyboard (unsigned char key, int x, int y) {
if (key=='q')
{
xrot += 1;
if (xrot >360) xrot -= 360;
}

if (key=='z')
{
xrot -= 1;
if (xrot < -360) xrot += 360;
}

if (key=='w')
{
float xrotrad, yrotrad;
yrotrad = (yrot / 180 * 3.141592654f);
xrotrad = (xrot / 180 * 3.141592654f);
xpos += float(sin(yrotrad)) ;
zpos -= float(cos(yrotrad)) ;
ypos -= float(sin(xrotrad)) ;
}

if (key=='s')
{
float xrotrad, yrotrad;
yrotrad = (yrot / 180 * 3.141592654f);
xrotrad = (xrot / 180 * 3.141592654f);
xpos -= float(sin(yrotrad));
zpos += float(cos(yrotrad)) ;
ypos += float(sin(xrotrad));
}

if (key=='d')
{
float yrotrad;
yrotrad = (yrot / 180 * 3.141592654f);
xpos += float(cos(yrotrad)) * 0.2;
zpos += float(sin(yrotrad)) * 0.2;
}

if (key=='a')
{
float yrotrad;
yrotrad = (yrot / 180 * 3.141592654f);
xpos -= float(cos(yrotrad)) * 0.2;
zpos -= float(sin(yrotrad)) * 0.2;
}

if (key==27)
{
exit(0);
}
}

void mouseMovement(int x, int y) {
int diffx=x-lastx; //check the difference between the current x and the last x position
int diffy=y-lasty; //check the difference between the current y and the last y position
lastx=x; //set lastx to the current x position
lasty=y; //set lasty to the current y position
xrot += (float) diffy; //set the xrot to xrot with the addition of the difference in the y position
yrot += (float) diffx; //set the xrot to yrot with the addition of the difference in the x position
}

int main (int argc, char **argv) {
glutInit (&argc, argv);
glutInitDisplayMode (GLUT_DOUBLE | GLUT_DEPTH);
glutInitWindowSize (500, 500);
glutInitWindowPosition (100, 100);
glutCreateWindow ("A basic OpenGL Window");
init ();
glutDisplayFunc (display);
glutIdleFunc (display);
glutReshapeFunc (reshape);

glutPassiveMotionFunc(mouseMovement); //check for mouse movement

glutKeyboardFunc (keyboard);
glutMainLoop ();
return 0;
}

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