mouse picking in OpenGL - opengl.cpp

#include <iostream>
#include <SDL/SDL.h>
#include <GL/gl.h>
#include <GL/glu.h>
#include <vector>
#include "camera.h"
#include "vector3d.h"


GLUquadric* quad;   //this one for drawing spheres, because I don't use objloader now, to load something
float zpos=-3.0;    //light's z position
camera cam;

struct sphere{
    vector3d center;
    float rad;  //radius
    int r,g,b;  //color for picking
    bool selected;  //true if it's selected
    sphere(const vector3d& c,float ra,int cr,int cg,int cb) : center(c),rad(ra),r(cr),g(cg),b(cb),selected(false) {};
};
std::vector<sphere> spheres;
int selected=-1;    //-1==nothing selected yet

//generate unique colors, like:
//0 0 0
//0 0 1
//...
//0 0 255
//0 1 0
//...
//max 256*256*256
int nextColor(int &r,int& g,int& b)
{
    //be careful, the background clear color should be unique (for me it's not, because it's 0,0,255
    b++;
    if(b>255)
    {
        b=0;
        g++;
        if(g>255)
        {
            g=0;
            r++;
            if(r>255)
            {
                std::cout << "error too many item" << std::endl;
                r=255;
            }
        }
    }
}

void init()
{
    glClearColor(0,0,1,1);
    glMatrixMode(GL_PROJECTION);
        glLoadIdentity();
        gluPerspective(50,640.0/480.0,0.1,1000);
    glMatrixMode(GL_MODELVIEW);
    quad=gluNewQuadric();   //init the quadric, so we can draw spheres
    gluQuadricNormals(quad,GLU_SMOOTH); //generate smooth normal vector for the sphere
    glEnable(GL_LIGHTING);
    glEnable(GL_LIGHT0);
    float spec[]={1.0,1.0,1.0,1.0};
    glLightfv(GL_LIGHT0,GL_SPECULAR,spec);
    glEnable(GL_CULL_FACE); //gluSphere has a hole in it without this call
    glEnable(GL_DEPTH_TEST);
    glInitNames();
    int curr=0,curg=0,curb=0;
    //generate 100 random spheres
    for(int i=0;i<100;i++)
    {
        spheres.push_back(sphere(vector3d(rand()%100-50,rand()%100-50,-(rand()%200+50)),rand()%20,curr,curg,curb));
        nextColor(curr,curg,curb);  //with unique color
    }
}


//draw the scene normally
void display()
{
    glClear(GL_COLOR_BUFFER_BIT|GL_DEPTH_BUFFER_BIT);
    glLoadIdentity();
    float pos[]={1.0,1.0,zpos,0.0};
    cam.Control();
    cam.UpdateCamera();
    glLightfv(GL_LIGHT0,GL_POSITION,pos);
    for(int i=0;i<100;i++)
    {
            glPushMatrix();
                glTranslatef(spheres[i].center.x,spheres[i].center.y,spheres[i].center.z);
                if(spheres[i].selected)
                {
                    glDisable(GL_LIGHTING);
                    glColor3f(1.0,0.0,0.0);
                }else
                {
                    glEnable(GL_LIGHTING);
                }
            //  glColor3f(spheres[i].r/255.0,spheres[i].g/255.0,spheres[i].b/255.0);
                gluSphere(quad,spheres[i].rad,100,100); //generate a sphere, lower the 100,100 parameter, to get lower resolution
                //but better performance, you may want to store all of the spheres previously, in display lists/VBO's, so you don't
                //have to generate it in runtime
            glPopMatrix();
    }


}

//if mouse is pressed at x,y coordinates
void selection(int x,int y)
{
    glDisable(GL_LIGHTING); //we don't need lighting
    //glViewport(x,480-y,1,1);  //you need to change the projection as well
    glClear(GL_COLOR_BUFFER_BIT|GL_DEPTH_BUFFER_BIT);   //clear the screen
    //draw everything to the screen
    for(int i=0;i<100;i++)
    {
        glPushMatrix();
            glTranslatef(spheres[i].center.x,spheres[i].center.y,spheres[i].center.z);
            glColor3f(spheres[i].r/255.0,spheres[i].g/255.0,spheres[i].b/255.0);    //use the unique color for every sphere
            gluSphere(quad,spheres[i].rad,100,100);
        glPopMatrix();
    }

        glFlush();  //might be important, in order, for the drawing to finish, alternatively glFinish(), to ensure that
        unsigned char rgb[3];
        //and read the current color (where the cursor is), without lighting or texturing, just the original color
        glReadPixels(x,480-y,1,1,GL_RGB,GL_UNSIGNED_BYTE,rgb);
        bool change=false;
        //find the sphere with that color, and that sphere is selected
        for(int i=0;i<100;i++)
        {
            if(spheres[i].r==rgb[0] && spheres[i].g==rgb[1] && spheres[i].b==rgb[2])
            {
                selected=i;
                change=true;
                spheres[i].selected=true;
            }else
                spheres[i].selected=false;
        }
        if(!change)
            selected=-1;
        glEnable(GL_LIGHTING);
    //  glViewport(0,0,640,480);

}

int main()
{
    SDL_Init(SDL_INIT_EVERYTHING);
    SDL_SetVideoMode(640,480,32,SDL_OPENGL);
    bool running=true;
    SDL_Event event;
    Uint32 start;
    init();
    int numframes=0;
    Uint32 lastTime=SDL_GetTicks();
    while(running)
    {
        start=SDL_GetTicks();
        while(SDL_PollEvent(&event))
        {
            switch(event.type)
            {
                case SDL_QUIT:
                    running=false;
                    break;
                case SDL_KEYDOWN:
                    switch(event.key.keysym.sym)
                    {
                        case SDLK_ESCAPE:
                            running=false;
                            break;
                        case SDLK_UP:
                            zpos+=1.0;
                            break;
                        case SDLK_DOWN:
                            zpos-=1.0;
                            break;
                        case SDLK_RETURN:
                            cam.mouseIn(true);
                            break;
                        case SDLK_BACKSPACE:
                            cam.mouseIn(false);
                            SDL_ShowCursor(SDL_ENABLE);
                            break;
                        //you can use similar approach, to move the sphere
                        case SDLK_a:
                            spheres[selected].center.x-=0.1;
                            break;
                        case SDLK_s:
                            spheres[selected].center.y-=0.1;
                            break;
                        //more case statement
                    }
                    break;
                case SDL_MOUSEBUTTONDOWN:
                    selection(event.button.x,event.button.y);   //if clicked
                    break;
                case SDL_MOUSEMOTION:
                //  selection(event.motion.x,event.motion.y);   //slow down a lot, display lists/VBO could help, to not generate sphere again every frame
                    break;
            }
        }
        display();
        SDL_GL_SwapBuffers();
        numframes++;
        //write out the FPS just for curiosity
        if(SDL_GetTicks()-lastTime>=1000)
        {
            std::cout << (float)numframes/((float)(SDL_GetTicks()-lastTime)/1000) << " FPS" << std::endl;
            numframes=0;
            lastTime=SDL_GetTicks();
        }
//      if(1000.0/30>(SDL_GetTicks()-start))
//          SDL_Delay(1000.0/30-(SDL_GetTicks()-start));
    }
    gluDeleteQuadric(quad); //delete the quadric (which draws the sphere)
    SDL_Quit();
}