// Alexandri Zavodny
// CSE 40166: Computer Graphics, Fall 2010
// Example 7: Arcball Camera around a teapot


#include <math.h>
#include <stdio.h>
#include <stdlib.h>

#ifdef __APPLE__
#include <GLUT/glut.h>
#else
#include <GL/glut.h>
#endif

// GLOBAL VARIABLES ////////////////////////////////////////////////////////////

static size_t windowWidth = 640;
static size_t windowHeight = 480;
static float aspectRatio;

GLint leftMouseButton, rightMouseButton;    //status of the mouse buttons
int mouseX = 0, mouseY = 0;                 //last known X and Y of the mouse

float cameraTheta, cameraPhi, cameraRadius; //camera position in spherical coordinates
float x, y, z;                              //camera position in cartesian coordinates


// recomputeOrientation() //////////////////////////////////////////////////////
//
// This function updates the camera's position in cartesian coordinates based 
//  on its position in spherical coordinates. Should be called every time 
//  cameraTheta, cameraPhi, or cameraRadius is updated. 
//
////////////////////////////////////////////////////////////////////////////////
void recomputeOrientation()
{
    x = cameraRadius * sinf(cameraTheta)*sinf(cameraPhi);
    z = cameraRadius * -cosf(cameraTheta)*sinf(cameraPhi);
    y = cameraRadius * -cosf(cameraPhi);
    glutPostRedisplay();
}

// resizeWindow() //////////////////////////////////////////////////////////////
//
//  GLUT callback for window resizing. Resets GL_PROJECTION matrix and viewport.
//
////////////////////////////////////////////////////////////////////////////////
void resizeWindow(int w, int h)
{
    aspectRatio = w / (float)h;

    windowWidth = w;
    windowHeight = h;

    //update the viewport to fill the window
    glViewport(0, 0, w, h);

    //update the projection matrix with the new window properties
    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();
    gluPerspective(45.0,aspectRatio,0.1,100000);
}



// mouseCallback() /////////////////////////////////////////////////////////////
//
//  GLUT callback for mouse clicks. We save the state of the mouse button
//      when this is called so that we can check the status of the mouse
//      buttons inside the motion callback (whether they are up or down).
//
////////////////////////////////////////////////////////////////////////////////
void mouseCallback(int button, int state, int thisX, int thisY)
{
    //update the left and right mouse button states, if applicable
    if(button == GLUT_LEFT_BUTTON)
        leftMouseButton = state;
    else if(button == GLUT_RIGHT_BUTTON)
        rightMouseButton = state;
    
    //and update the last seen X and Y coordinates of the mouse
    mouseX = thisX;
    mouseY = thisY;
}

// mouseMotion() ///////////////////////////////////////////////////////////////
//
//  GLUT callback for mouse movement. We update cameraPhi, cameraTheta, and/or
//      cameraRadius based on how much the user has moved the mouse in the
//      X or Y directions (in screen space) and whether they have held down
//      the left or right mouse buttons. If the user hasn't held down any
//      buttons, the function just updates the last seen mouse X and Y coords.
//
////////////////////////////////////////////////////////////////////////////////
void mouseMotion(int x, int y)
{
    if(leftMouseButton == GLUT_DOWN)
    {
        cameraTheta += (x - mouseX)*0.005;
        cameraPhi   += (y - mouseY)*0.005;

        // make sure that phi stays within the range (0, M_PI)
        if(cameraPhi <= 0)
            cameraPhi = 0+0.001;
        if(cameraPhi >= M_PI)
            cameraPhi = M_PI-0.001;
        
        
        recomputeOrientation();     //update camera (x,y,z) based on (radius,theta,phi)
    } else if(rightMouseButton == GLUT_DOWN) {
        double totalChangeSq = (x - mouseX) + (y - mouseY);
        
        cameraRadius += totalChangeSq*0.01;
        
        //limit the camera radius to some reasonable values so the user can't get lost
        if(cameraRadius < 2.0) 
            cameraRadius = 2.0;
        if(cameraRadius > 10.0) 
            cameraRadius = 10.0;

        recomputeOrientation();     //update camera (x,y,z) based on (radius,theta,phi)
    }
    mouseX = x;
    mouseY = y;
}



// initScene() /////////////////////////////////////////////////////////////////
//
//  A basic scene initialization function; should be called once after the
//      OpenGL context has been created. Doesn't need to be called further.
//
////////////////////////////////////////////////////////////////////////////////
void initScene() 
{
    glEnable(GL_DEPTH_TEST);

    float lightCol[4] = { 1, 1, 1, 1};
    float ambientCol[4] = {0.3, 0.3, 0.3, 1.0};
    float lPosition[4] = { 10, 10, 10, 1 };
    glLightfv(GL_LIGHT0,GL_POSITION,lPosition);
    glLightfv(GL_LIGHT0,GL_DIFFUSE,lightCol);
    glLightfv(GL_LIGHT0, GL_AMBIENT, ambientCol);
    glEnable(GL_LIGHTING);
    glEnable(GL_LIGHT0);


    glShadeModel(GL_SMOOTH);
    //glShadeModel(GL_FLAT);
}

// renderScene() ///////////////////////////////////////////////////////////////
//
//  GLUT callback for scene rendering. Sets up the modelview matrix, renders
//      a teapot to the back buffer, and switches the back buffer with the
//      front buffer (what the user sees).
//
////////////////////////////////////////////////////////////////////////////////
void renderScene(void) 
{
    //update the modelview matrix based on the camera's position
    glMatrixMode(GL_MODELVIEW);         //make sure we aren't changing the projection matrix!
    glLoadIdentity();
    gluLookAt(x, y, z,                  //camera is located at (x,y,z)
                0, 0, 0,                //camera is looking at (0,0,0)
                0.0f,1.0f,0.0f);        //up vector is (0,1,0) (positive Y)

    //clear the render buffer
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

    //see documentation for glutSolidTeapot; glutSolidTeapot must be called with a different winding set.
    //there is a known 'bug' that results in the winding of the teapot to be backwards.
    glFrontFace(GL_CW);
    glutSolidTeapot(1.0f);
    glFrontFace(GL_CCW);

    //push the back buffer to the screen
    glutSwapBuffers();
}


// normalKeys() ////////////////////////////////////////////////////////////////
//
//  GLUT keyboard callback.
//
////////////////////////////////////////////////////////////////////////////////
void normalKeys(unsigned char key, int x, int y) 
{
    if(key == 'q' || key == 'Q')
        exit(0);
}




// main() //////////////////////////////////////////////////////////////////////
//
//  Program entry point. Does not process command line arguments.
//
////////////////////////////////////////////////////////////////////////////////
int main(int argc, char **argv)
{
    //create a double-buffered GLUT window at (50,50) with predefined windowsize
    glutInit(&argc, argv);
    glutInitDisplayMode(GLUT_DEPTH | GLUT_DOUBLE | GLUT_RGBA);
    glutInitWindowPosition(50,50);
    glutInitWindowSize(windowWidth,windowHeight);
    glutCreateWindow("it's teatime");

    //give the camera a 'pretty' starting point!
    cameraRadius = 7.0f;
    cameraTheta = 2.80;
    cameraPhi = 2.0;
    recomputeOrientation();

    //register callback functions...
    glutKeyboardFunc(normalKeys);
    glutDisplayFunc(renderScene);
    glutReshapeFunc(resizeWindow);
    glutMouseFunc(mouseCallback);
    glutMotionFunc(mouseMotion);

    //do some basic OpenGL setup
    initScene();

    //and enter the GLUT loop, never to exit.
    glutMainLoop();

    return(0);
}