Fit 3d model inside a window

Question

I want to display models of different sizes fitted into a view, so that the whole model is visible inside the screen.
What is the best way to do it? I tried scaling (usi

Answer 1

Section 8.070:

The following is from a posting by Dave Shreiner on setting up a basic viewing system:

First, compute a bounding sphere for all objects in your scene. This should provide you with two bits of information: the center of the sphere (let ( c.x, c.y, c.z ) be that point) and its diameter (call it "diam").

Next, choose a value for the zNear clipping plane. General guidelines are to choose something larger than, but close to 1.0. So, let's say you set

zNear = 1.0; zFar = zNear + diam; 

Structure your matrix calls in this order (for an Orthographic projection):

GLdouble left = c.x - diam; 
GLdouble right = c.x + diam;
GLdouble bottom c.y - diam; 
GLdouble top = c.y + diam; 
glMatrixMode(GL_PROJECTION); 
glLoadIdentity(); 
glOrtho(left, right, bottom, top, zNear, zFar); 
glMatrixMode(GL_MODELVIEW); 
glLoadIdentity(); 

This approach should center your objects in the middle of the window and stretch them to fit (i.e., its assuming that you're using a window with aspect ratio = 1.0). If your window isn't square, compute left, right, bottom, and top, as above, and put in the following logic before the call to glOrtho():

GLdouble aspect = (GLdouble) windowWidth / windowHeight; 
if ( aspect < 1.0 ) { 
    // window taller than wide 
    bottom /= aspect; 
    top /= aspect; 
} else { 
    left *= aspect; 
    right *= aspect;
} 

The above code should position the objects in your scene appropriately. If you intend to manipulate (i.e. rotate, etc.), you need to add a viewing transform to it.

A typical viewing transform will go on the ModelView matrix and might look like this:

GluLookAt (0., 0., 2.*diam, c.x, c.y, c.z, 0.0, 1.0, 0.0);