Triangle.cpp

#include <GL/glut.h>
/* Try uncommenting this include line to compile on Max OSX
#include <GLUT/glut.h>
*/

/*! GLUT display callback function */
void display(void);
/*! GLUT window reshape callback function */
void reshape(int, int);

int main(int argc, char** argv)
{
        glutInit(&argc, argv);

	/* set the window size to 512 x 512 */
	glutInitWindowSize(512, 512);

	/* set the display mode to Red, Green, Blue and Alpha
		allocate a depth buffer
		enable double buffering
	*/
	glutInitDisplayMode(GLUT_RGBA | GLUT_DEPTH | GLUT_DOUBLE);

	/* create the window (and call it Lab 1) */
	glutCreateWindow("Lab 1");

	/* set the glut display callback function
		this is the function GLUT will call every time
		the window needs to be drawn
	*/
	glutDisplayFunc(display);

	/* set the glut reshape callback function
		this is the function GLUT will call whenever
		the window is resized, including when it is
		first created
	*/
	glutReshapeFunc(reshape);

	/* set the default background color to black */
	glClearColor(0,0,0,1);

	/* enter the main event loop so that GLUT can process
		all of the window event messages
	*/
	glutMainLoop();

        return 0;
}

/*! glut display callback function.  Every time the window needs to be drawn,
	glut will call this function.  This includes when the window size
	changes, or when another window covering part of this window is
	moved so this window is uncovered.
*/
void display()
{
	/* clear the color buffer (resets everything to black) */
	glClear(GL_COLOR_BUFFER_BIT);
	
	/* set the current drawing color to red */
	glColor3f(1, 0, 0);

	/* start drawing triangles, each triangle takes 3 vertices */
	glBegin(GL_TRIANGLES);

	/* give the 3 triangle vertex coordinates 1 at a time */
	glVertex2f(10, 10);
	glVertex2f(250, 400);
	glVertex2f(400, 10);

	/* tell OpenGL we're done drawing triangles */
	glEnd();

	/* swap the back and front buffers so we can see what we just drew */
	glutSwapBuffers();
}

/*! glut reshape callback function.  GLUT calls this function whenever
	the window is resized, including the first time it is created.
	You can use variables to keep track the current window size.
*/
void reshape(int width, int height)
{
	/* tell OpenGL we want to display in a recangle that is the 
		same size as the window
	*/
	glViewport(0,0,width,height);

	/* switch to the projection matrix */
	glMatrixMode(GL_PROJECTION);

	/* clear the projection matrix */
	glLoadIdentity();

	/* set the camera view, orthographic projection in 2D */
	gluOrtho2D(0,width,0,height);

	/* switch back to the model view matrix */
	glMatrixMode(GL_MODELVIEW);
}