#include <GL/glut.h>

#include <iostream>

using namespace std;

static float g_theta = 30.0f;

static float g_x1 = 0;
static float g_y1 = 0;

static float g_x2 = 0;
static float g_y2 = 0;

bool g_eraseOld = false;


void Init()
{
    glMatrixMode(GL_PROJECTION);
    glOrtho(-1.0f, 1.0f, -1.0f, 1.0f, 1.0f, -10.f);

    glMatrixMode(GL_MODELVIEW);
    glLoadIdentity();

    glClearColor(1.0f, 1.0f, 1.0f, 1.0f);
}

void DrawModel()
{
    glColor3f(1, 1, 0);
    glPushMatrix();

    glBegin(GL_TRIANGLES);
    glColor3f(0.0, 0.0, 1.0);
        glVertex3f(0.0, 0.0, 0.0);
        glVertex3f(1.0, 0.0, 0.0);
        glVertex3f(0.0, 1.0, 0.0);
    glEnd();

    glPopMatrix();
}

void OnDisplay()
{
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

    DrawModel();

    glutSwapBuffers();
}

void OnReshape(int w, int h)
{
    glViewport(0, 0, w, h);
}

void OnIdle()
{
    //g_theta += 0.5f;
    //glutPostRedisplay();
}

void DrawRectangle(float x1, float y1, float x2, float y2)
{
    glPushMatrix();
        glBegin(GL_LINES);

            glVertex2f(x1, y1);
            glVertex2f(x2, y1);

            glVertex2f(x2, y1);
            glVertex2f(x2, y2);

            glVertex2f(x2, y2);
            glVertex2f(x1, y2);

            glVertex2f(x1, y2);
            glVertex2f(x1, y1);

        glEnd();
    glPopMatrix();
}

void OnMouse(int button, int state, int x, int y)
{
    g_x1 = static_cast<float>(x-250)/500.0f;
    g_y1 = static_cast<float>(500-y)/500.0f;

    if (state == 0)
    {
        glEnable(GL_COLOR_LOGIC_OP);
        glLogicOp(GL_XOR);
        glDrawBuffer(GL_FRONT);
    }
    else
    {
        glDisable(GL_COLOR_LOGIC_OP);
        glLogicOp(GL_COPY);
        glDrawBuffer(GL_BACK);
        g_eraseOld = false;
    }
}

void OnMouseMove(int x, int y)
{
    float x2 = static_cast<float>(x-250)/500.0f;
    float y2 = static_cast<float>(500 - y)/500.0f;

    //glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

    //DrawModel();

    glColor3f(1, 0, 0);

    if (g_eraseOld)
    {
        DrawRectangle(g_x1, g_y1, g_x2, g_y2);
    }

    DrawRectangle(g_x1, g_y1, x2, y2);

    g_x2 = x2;
    g_y2 = y2;
    g_eraseOld = true;

    glFlush();
}

int main(int argc, char* argv[])
{
    glutInit(&argc, argv);
    glutInitDisplayMode(GLUT_DOUBLE | GLUT_DEPTH | GLUT_RGBA);
    glutInitWindowSize(500, 500);
    glutInitWindowPosition(100, 100);
    glutCreateWindow("OpenGL Experiment for Remote Desktop");

    const char* str = reinterpret_cast<const char*>(glGetString(GL_VERSION));
    cout << "GL Version: " << str << endl;
    
    Init();

    glutDisplayFunc(OnDisplay);
    glutReshapeFunc(OnReshape);
    glutMotionFunc(OnMouseMove);
    glutMouseFunc(OnMouse);
    glutIdleFunc(OnIdle);

    glutMainLoop();

    return 0;
}