Subwindow Reshape

The callback for the reshape function needs to do two things: it resizes the subwindows, and recomputes the projection matrices for each subwindow. In our case we’re not rendering any geometry in the main window, so we’ll skip recomputing the projection matrix for the main window.

First let’s introduce the functions to resize, and reposition the subwindows.

void glutPositionWindow(int x, int y);
void glutReshapeWindow(int width, int height);

Parameters:

• x,y – the top left corner of the window
• width, height – the dimensions of the window in pixels

These two function act on the current window so first we must set a particular window as being the current window. In order to do this we need to have the window identifier at hand and call glutSetWindow. The syntax is as follows:

void glutSetWindow(int windowIdentifier);

Parameters:

• windowIdentifier – the value returned when the window is created.

If we need to know which window is the current window we can use GLUTs function glutGetWindow.

int glutGetWindow();

The return value of this function is the identifier of the current window.

Before we do any calls to position and resize the window we must set each subwindow as the current window. The following piece of code provides the reshape function, in our case the function is called changeSize. As mentioned in the PREVIOUS section we have defined a callback for reshaping the window only for the main window. This is enough because by default the user can only resize the main window.

Since, in our example, the projection is similar to all subwindows we are going to define a function for this purpose, and call it for each subwindow.

int w,h, 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);
}

On the next section we’ll look at the rendering functions.