/* Example 3.1.shading.c: OpenGL flat or smooth shading */
// by Jim X. Chen; March, 2001

#include <windows.h> 
#include <stdlib.h>
#include <stdio.h>
#include <math.h>
#include <GL/glut.h>


#define ESC 27
#define SPACE 32
int Height=600, Width=600, cnt;


static float vdata[3][3] = {
	{1.0, 0.0, 0.0}, {0.0, 1.0, 0.0}, {0.0, 0.0, 1.0}
};


void drawtriangle(float *v1, float *v2, float *v3)
{
	glBegin(GL_TRIANGLES);
		glColor3f(1,0,0);
		glVertex3fv(v1);
		glColor3f(0,1,0);
		glVertex3fv(v2);
		glColor3f(0,0,1);
		glVertex3fv(v3);
	glEnd();
}


drawColorCoord(float xlen, float ylen, float zlen)
{
	// coordinate lines
	glBegin(GL_LINES);
		glColor3f(1,1,1);
		glVertex3f(0,0,0);
		glColor3f(0,0,1);
		glVertex3f(0,0,zlen);
		glColor3f(1,1,1);
		glVertex3f(0,0,0);
		glColor3f(0,1,0);
		glVertex3f(0,ylen, 0);
		glColor3f(1,1,1);
		glVertex3f(0,0,0);
		glColor3f(1,0,0);
		glVertex3f(xlen,0,0);
	glEnd();

	// coordinate labels: X, Y, Z
	glPushMatrix();
		glColor3f(1,0,0);
		glTranslatef(xlen,0.,0.);
		glScalef(xlen/Width,xlen/Width,1);
		glutStrokeCharacter(GLUT_STROKE_ROMAN, 'X');
	glPopMatrix();
	glPushMatrix();
		glColor3f(0,1,0);
		glTranslatef(0., ylen,0.);
		glScalef(ylen/Width,ylen/Width,1);
		glutStrokeCharacter(GLUT_STROKE_ROMAN, 'Y');
	glPopMatrix();
	glPushMatrix();
		glColor3f(0,0,1);
		glTranslatef(0., 0.,zlen);
		glScalef(zlen/Width,zlen/Width,1);
		glutStrokeCharacter(GLUT_STROKE_ROMAN, 'Z');
	glPopMatrix();
}


void display(void)
{ 
	cnt++;

	glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

	// alternate between flat and smooth
	if (cnt % 50 == 0) glShadeModel(GL_SMOOTH); 
	if (cnt%100 == 0) glShadeModel(GL_FLAT); // alt. btween flat & smooth

	glPushMatrix();
		glRotatef(cnt, 1,1,1); 
		glScalef(Width/2, Width/2, Width/2);
		drawColorCoord(1., 1., 1.);
		drawtriangle(vdata[0], vdata[1], vdata[2]);
	glPopMatrix();
	glutSwapBuffers(); 
}



static void Reshape(int w, int h)
{	float zNear=w, zFar=3*w; 

    glClearColor (0.0, 0.0, 0.0, 1.0);
    glEnable(GL_DEPTH_TEST);
    glViewport (0, 0, w, h);

	// hardware set to use projection transformation matrix stack
    glMatrixMode (GL_PROJECTION);
    glLoadIdentity ();
	glOrtho(-w, w, -h, h, -zNear, zFar); 
 	// hardware set to use model transformation matrix stack
	glMatrixMode (GL_MODELVIEW);
    glLoadIdentity ();
}



static void Key(unsigned char key, int x, int y)
{ 
    switch (key) {
      case ESC:
			exit(0);
	  case SPACE: 
			glShadeModel(GL_FLAT);
			break; 
	  default: 
			glShadeModel(GL_SMOOTH);

    }

}


int main(int argc, char **argv)
{
    glutInit(&argc, argv);
 	glutInitDisplayMode(GLUT_DOUBLE);
    glutInitWindowSize(Width, Height);
    glutCreateWindow("Example: press SPACE & another key");

    glutKeyboardFunc(Key);
    glutReshapeFunc(Reshape); 
    glutDisplayFunc(display);
    glutIdleFunc(display);

    glutMainLoop();
}