Simple OpenGL (SDL) 3D FPS camera - functions.cpp

//This example program is created by thecplusplusuy for demonstration purposes. It's a simple 3D FPS camera:
//http://www.youtube.com/user/thecplusplusguy
//Free source, modify if you want, LGPL licence (I guess), I would be happy, if you would not delete the link
//so other people can see the tutorial
//this file is functions.h, it's contain the actual implementation of the 3D camera
#include "functions.h"

float camX=0.0,camY=0.0,camZ=5.0;   //current position of the camera
float camYaw=0.0;   //camera rotation in Y axis
float camPitch=0.0; //camera rotation in X axis
#ifndef M_PI    //if the pi is not defined in the cmath header file
#define M_PI 3.1415926535   //define it
#endif

void lockCamera()
{
    //set campitch between -90 and 90 and set camyaw between 0 and 360 degrees
    if(camPitch>90)
        camPitch=90;
    if(camPitch<-90)
        camPitch=-90;
    if(camYaw<0.0)
        camYaw+=360.0;
    if(camYaw>360.0)
        camYaw-=360;
}

void moveCamera(float dist,float dir)
{
    float rad=(camYaw+dir)*M_PI/180.0;  //convert the degrees into radians
    camX-=sin(rad)*dist;    //calculate the new coorinate, if you don't understand, draw a right triangle with the datas, you have
    camZ-=cos(rad)*dist;    //and try to calculate the new coorinate with trigonometric functions, that should help
}

void moveCameraUp(float dist,float dir)
{
    //the the same, only this time we calculate the y coorinate
    float rad=(camPitch+dir)*M_PI/180.0;
    camY+=sin(rad)*dist;
}

void Control(float movevel,float mousevel,bool mi)  //move and mouse sensitivity, and is the mouse inside the window?
{
    if(mi)  //if the mouse is in the screen
    {
        int MidX=320;   //middle of the screen
        int MidY=240;
        SDL_ShowCursor(SDL_DISABLE);    //we don't show the cursor
        int tmpx,tmpy;
        SDL_GetMouseState(&tmpx,&tmpy); //get the current position of the cursor
        camYaw+=mousevel*(MidX-tmpx);   //get the rotation, for example, if the mouse current position is 315, than 5*0.2, this is for Y
        camPitch+=mousevel*(MidY-tmpy); //this is for X
        lockCamera();
        SDL_WarpMouse(MidX,MidY);   //move back the cursor to the center of the screen
        Uint8* state=SDL_GetKeyState(NULL); //which key is pressed?
        if(state[SDLK_w])
        {
            if(camPitch!=90 && camPitch!=-90)   //if we are facing directly up or down, we don't go forward, it will be commented out, when there will be gravity
                moveCamera(movevel,0.0);    //move forward
            moveCameraUp(movevel,0.0);  //move up/down
        }else if(state[SDLK_s])
        {
            //same, just we use 180 degrees, so we move at the different direction (move back)
            if(camPitch!=90 && camPitch!=-90)
                moveCamera(movevel,180.0);
            moveCameraUp(movevel,180.0);
        }
        if(state[SDLK_a])   //move left
            moveCamera(movevel,90.0);
        else if(state[SDLK_d])  //move right
            moveCamera(movevel,270);
    }
    glRotatef(-camPitch,1.0,0.0,0.0);   //rotate the camera (more precisly move everything in the opposit direction)
    glRotatef(-camYaw,0.0,1.0,0.0);
}

void UpdateCamera()
{
    glTranslatef(-camX,-camY,-camZ);    //move the camera
}









//draw a cube, not related to the 3D camera
void drawCube(float size)
{
    float difamb[]={1.0,0.5,0.3,1.0};
    glBegin(GL_QUADS);
        //front face
        glMaterialfv(GL_FRONT_AND_BACK,GL_AMBIENT_AND_DIFFUSE,difamb);
        glNormal3f(0.0,0.0,1.0);
        glVertex3f(size/2,size/2,size/2);
        glVertex3f(-size/2,size/2,size/2);
        glVertex3f(-size/2,-size/2,size/2);
        glVertex3f(size/2,-size/2,size/2);

        //left face
        glNormal3f(-1.0,0.0,0.0);
        glVertex3f(-size/2,size/2,size/2);
        glVertex3f(-size/2,size/2,-size/2);
        glVertex3f(-size/2,-size/2,-size/2);
        glVertex3f(-size/2,-size/2,size/2);

        //back face
        glNormal3f(0.0,0.0,-1.0);
        glVertex3f(size/2,size/2,-size/2);
        glVertex3f(-size/2,size/2,-size/2);
        glVertex3f(-size/2,-size/2,-size/2);
        glVertex3f(size/2,-size/2,-size/2);

        //right face
        glNormal3f(1.0,0.0,0.0);
        glVertex3f(size/2,size/2,-size/2);
        glVertex3f(size/2,size/2,size/2);
        glVertex3f(size/2,-size/2,size/2);
        glVertex3f(size/2,-size/2,-size/2);

        //top face
        glNormal3f(0.0,1.0,0.0);
        glVertex3f(size/2,size/2,size/2);
        glVertex3f(-size/2,size/2,size/2);
        glVertex3f(-size/2,size/2,-size/2);
        glVertex3f(size/2,size/2,-size/2);

        //bottom face
        glNormal3f(0.0,-1.0,0.0);
        glVertex3f(size/2,-size/2,size/2);
        glVertex3f(-size/2,-size/2,size/2);
        glVertex3f(-size/2,-size/2,-size/2);
        glVertex3f(size/2,-size/2,-size/2);
    glEnd();
}