The Code So Far VII

The source code using glutPostRedisplay instead of registering an idle function. As usual check out the source code at GitHub.

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

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

// angle of rotation for the camera direction
float angle = 0.0f;

// actual vector representing the camera's direction
float lx=0.0f,lz=-1.0f, ly = 0.0f;

// XZ position of the camera
float x=0.0f, z=5.0f, y = 1.75f;

// the key states. These variables will be zero
//when no key is being presses
float deltaAngle = 0.0f;
float deltaMove = 0;
int xOrigin = -1;

// width and height of the window
int h,w;

// variables to compute frames per second
int frame;
long time, timebase;
char s[50];

// variables to hold window identifiers
int mainWindow, subWindow1,subWindow2,subWindow3;
//border between subwindows
int border = 6;

void setProjection(int w1, int h1)
{
	float ratio;
	// Prevent a divide by zero, when window is too short
	// (you cant make a window of zero width).
	ratio = 1.0f * w1 / h1;
	// Reset the coordinate system before modifying
	glMatrixMode(GL_PROJECTION);
	glLoadIdentity();

	// Set the viewport to be the entire window
        glViewport(0, 0, w1, h1);

	// Set the clipping volume
	gluPerspective(45,ratio,0.1,1000);
	glMatrixMode(GL_MODELVIEW);
}

void changeSize(int w1,int h1) {

	if(h1 == 0)
		h1 = 1;

	// we're keeping these values cause we'll need them latter
	w = w1;
	h = h1;

	// set subwindow 1 as the active window
	glutSetWindow(subWindow1);
	// resize and reposition the sub window
	glutPositionWindow(border,border);
	glutReshapeWindow(w-2*border, h/2 - border*3/2);
	setProjection(w-2*border, h/2 - border*3/2);

	// set subwindow 2 as the active window
	glutSetWindow(subWindow2);
	// resize and reposition the sub window
	glutPositionWindow(border,(h+border)/2);
	glutReshapeWindow(w/2-border*3/2, h/2 - border*3/2);
	setProjection(w/2-border*3/2,h/2 - border*3/2);

	// set subwindow 3 as the active window
	glutSetWindow(subWindow3);
	// resize and reposition the sub window
	glutPositionWindow((w+border)/2,(h+border)/2);
	glutReshapeWindow(w/2-border*3/2,h/2 - border*3/2);
	setProjection(w/2-border*3/2,h/2 - border*3/2);
}

void drawSnowMan() {

	glColor3f(1.0f, 1.0f, 1.0f);

// Draw Body
	glTranslatef(0.0f ,0.75f, 0.0f);
	glutSolidSphere(0.75f,20,20);

// Draw Head
	glTranslatef(0.0f, 1.0f, 0.0f);
	glutSolidSphere(0.25f,20,20);

// Draw Eyes
	glPushMatrix();
	glColor3f(0.0f,0.0f,0.0f);
	glTranslatef(0.05f, 0.10f, 0.18f);
	glutSolidSphere(0.05f,10,10);
	glTranslatef(-0.1f, 0.0f, 0.0f);
	glutSolidSphere(0.05f,10,10);
	glPopMatrix();

// Draw Nose
	glColor3f(1.0f, 0.5f, 0.5f);
	glRotatef(0.0f,1.0f, 0.0f, 0.0f);
	glutSolidCone(0.08f,0.5f,10,2);

	glColor3f(1.0f, 1.0f, 1.0f);

}

void renderBitmapString(
		float x,
		float y,
		float z,
		void *font,
		char *string) {

	char *c;
	glRasterPos3f(x, y,z);
	for (c=string; *c != '\0'; c++) {
		glutBitmapCharacter(font, *c);
	}
}

void restorePerspectiveProjection() {

	glMatrixMode(GL_PROJECTION);
	// restore previous projection matrix
	glPopMatrix();

	// get back to modelview mode
	glMatrixMode(GL_MODELVIEW);
}

void setOrthographicProjection() {

	// switch to projection mode
	glMatrixMode(GL_PROJECTION);

	// save previous matrix which contains the
	//settings for the perspective projection
	glPushMatrix();

	// reset matrix
	glLoadIdentity();

	// set a 2D orthographic projection
	gluOrtho2D(0, w, h, 0);

	// switch back to modelview mode
	glMatrixMode(GL_MODELVIEW);
}

void computePos(float deltaMove) {

	x += deltaMove * lx * 0.1f;
	z += deltaMove * lz * 0.1f;
}

// Common Render Items for all subwindows
void renderScene2() {

// Draw ground

	glColor3f(0.9f, 0.9f, 0.9f);
	glBegin(GL_QUADS);
		glVertex3f(-100.0f, 0.0f, -100.0f);
		glVertex3f(-100.0f, 0.0f,  100.0f);
		glVertex3f( 100.0f, 0.0f,  100.0f);
		glVertex3f( 100.0f, 0.0f, -100.0f);
	glEnd();

// Draw 36 SnowMen
	for(int i = -3; i < 3; i++)
		for(int j=-3; j < 3; j++)
		{
			glPushMatrix();
			glTranslatef(i*10.0f, 0.0f, j * 10.0f);
			drawSnowMan();
			glPopMatrix();
		}
}

// Display func for main window
void renderScene() {
	glutSetWindow(mainWindow);
	glClear(GL_COLOR_BUFFER_BIT);
	glutSwapBuffers();
}

// Display func for sub window 1
void renderScenesw1() {

	glutSetWindow(subWindow1);

	glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

	glLoadIdentity();
	gluLookAt(x, y, z,
		  x + lx,y + ly,z + lz,
		  0.0f,1.0f,0.0f);

	renderScene2();

	// display fps in the top window
 	frame++;

	time=glutGet(GLUT_ELAPSED_TIME);
	if (time - timebase > 1000) {
		sprintf(s,"Lighthouse3D - FPS:%4.2f",
			frame*1000.0/(time-timebase));
		timebase = time;
		frame = 0;
	}

	setOrthographicProjection();

	glPushMatrix();
	glLoadIdentity();
	renderBitmapString(5,30,0,GLUT_BITMAP_HELVETICA_12,s);
	glPopMatrix();

	restorePerspectiveProjection();

	glutSwapBuffers();
}

// Display func for sub window 2
void renderScenesw2() {

	glutSetWindow(subWindow2);

	glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

	glLoadIdentity();
	gluLookAt(x, y+15, z,
		  x ,y - 1,z,
		  lx,0,lz);

	// Draw red cone at the location of the main camera
	glPushMatrix();
	glColor3f(1.0,0.0,0.0);
	glTranslatef(x,y,z);
	glRotatef(180-(angle+deltaAngle)*180.0/3.14,0.0,1.0,0.0);
	glutSolidCone(0.2,0.8f,4,4);
	glPopMatrix();

	renderScene2();

	glutSwapBuffers();
}

// Display func for sub window 3
void renderScenesw3() {

	glutSetWindow(subWindow3);

	glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

	glLoadIdentity();
	gluLookAt(x-lz*10 , y, z+lx*10,
		  x ,y ,z ,
		  0.0f,1.0f,0.0f);

	// Draw red cone at the location of the main camera
	glPushMatrix();
	glColor3f(1.0,0.0,0.0);
	glTranslatef(x,y,z);
	glRotatef(180-(angle+deltaAngle)*180.0/3.14,0.0,1.0,0.0);
	glutSolidCone(0.2,0.8f,4,4);
	glPopMatrix();

	renderScene2();

	glutSwapBuffers();
}

// Global render func
void renderSceneAll() {

	// check for keyboard movement
	if (deltaMove) {
		computePos(deltaMove);
		glutSetWindow(mainWindow);
		glutPostRedisplay();
	}

	renderScene();
	renderScenesw1();
	renderScenesw2();
	renderScenesw3();
}

// -----------------------------------
//             KEYBOARD
// -----------------------------------

void processNormalKeys(unsigned char key, int xx, int yy) {

	if (key == 27) {
		glutDestroyWindow(mainWindow);
		exit(0);
	}
}

void pressKey(int key, int xx, int yy) {

	switch (key) {
		case GLUT_KEY_UP : deltaMove = 0.5f; break;
		case GLUT_KEY_DOWN : deltaMove = -0.5f; break;
	}
	glutSetWindow(mainWindow);
	glutPostRedisplay();

}

void releaseKey(int key, int x, int y) {

	switch (key) {
		case GLUT_KEY_UP :
		case GLUT_KEY_DOWN : deltaMove = 0;break;
	}
}

// -----------------------------------
//             MOUSE
// -----------------------------------

void mouseMove(int x, int y) {

	// this will only be true when the left button is down
	if (xOrigin >= 0) {

		// update deltaAngle
		deltaAngle = (x - xOrigin) * 0.001f;

		// update camera's direction
		lx = sin(angle + deltaAngle);
		lz = -cos(angle + deltaAngle);

		glutSetWindow(mainWindow);
		glutPostRedisplay();
	}
}

void mouseButton(int button, int state, int x, int y) {

	// only start motion if the left button is pressed
	if (button == GLUT_LEFT_BUTTON) {

		// when the button is released
		if (state == GLUT_UP) {
			angle += deltaAngle;
			deltaAngle = 0.0f;
			xOrigin = -1;
		}
		else  {// state = GLUT_DOWN
			xOrigin = x;

		}
	}
}

// -----------------------------------
//             MAIN and INIT
// -----------------------------------

void init() {

	glClearColor(0.0, 0.0, 0.0, 0.0);
	glEnable(GL_DEPTH_TEST);
	glEnable(GL_CULL_FACE);

	// register callbacks
	glutIgnoreKeyRepeat(1);
	glutKeyboardFunc(processNormalKeys);
	glutSpecialFunc(pressKey);
	glutSpecialUpFunc(releaseKey);
	glutMouseFunc(mouseButton);
	glutMotionFunc(mouseMove);
}

int main(int argc, char **argv) {

	// init GLUT and create main window
	glutInit(&argc, argv);
	glutInitDisplayMode(GLUT_DEPTH | GLUT_DOUBLE | GLUT_RGBA);
	glutInitWindowPosition(100,100);
	glutInitWindowSize(800,800);
	mainWindow = glutCreateWindow("Lighthouse3D - GLUT Tutorial");

	// callbacks for main window
	glutDisplayFunc(renderSceneAll);
	glutReshapeFunc(changeSize);

	// Removing the idle function to save CPU and GPU
	//glutIdleFunc(renderSceneAll);
	init();

	// sub windows
	subWindow1 = glutCreateSubWindow(mainWindow, border,border,w-2*border, h/2 - border*3/2);
	glutDisplayFunc(renderScenesw1);
	init();

	subWindow2 = glutCreateSubWindow(mainWindow, border,(h+border)/2,w/2-border*3/2, h/2 - border*3/2);
	glutDisplayFunc(renderScenesw2);
	init();

	subWindow3 = glutCreateSubWindow(mainWindow, (w+border)/2,(h+border)/2,w/2-border*3/2,h/2 - border*3/2);
	glutDisplayFunc(renderScenesw3);
	init();

	// enter GLUT event processing cycle
	glutMainLoop();
	
	return 1;
}