Sources/Classes/Application/Model/OpenGL/Trackball/OpenGLTrackball.mm
//--------------------------------------------------------------------------- |
// |
// File: OpenGLTrackball.mm |
// |
// Abstract: Utility class for managing a virtual sphere's (trackball) |
// interaction with an OpenGL world. |
// |
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//--------------------------------------------------------------------------- |
//--------------------------------------------------------------------------- |
// |
// The trackball works by assuming that a sphere encloses the 3D view. You |
// roll this virtual sphere with the mouse. For example, if you click on |
// the center of the sphere and move the mouse straight to the right, you |
// roll the sphere around its Y-axis. This produces a Y-axis rotation. |
// You can click on the "edge" of the sphere and roll it around in a circle |
// to get a Z-axis rotation. |
// |
//--------------------------------------------------------------------------- |
//--------------------------------------------------------------------------- |
#import <math.h> |
#import "Vector.h" |
#import "Quaternion.h" |
//--------------------------------------------------------------------------- |
#import "OpenGLTrackball.h" |
//--------------------------------------------------------------------------- |
//--------------------------------------------------------------------------- |
#define kPi 3.1415927f // IEEE-754 single precision |
//--------------------------------------------------------------------------- |
//--------------------------------------------------------------------------- |
static const GLfloat kDeltaTolerance = 0.001; |
static const GLfloat kRadians2Degrees = 180.0f/kPi; |
static const GLfloat kDegrees2Radians = kPi/180.0f; |
//--------------------------------------------------------------------------- |
//--------------------------------------------------------------------------- |
struct OpenGLTrackballData |
{ |
GLfloat radius; |
Math::Vector3<GLfloat> center; |
Math::Vector3<GLfloat> start; |
Math::Vector3<GLfloat> end; |
}; |
typedef struct OpenGLTrackballData OpenGLTrackballData; |
//--------------------------------------------------------------------------- |
//--------------------------------------------------------------------------- |
@implementation OpenGLTrackball |
//--------------------------------------------------------------------------- |
- (id) init |
{ |
self = [super init]; |
if( self ) |
{ |
mpTrackball = (OpenGLTrackballDataRef)calloc(1, sizeof(OpenGLTrackballData)); |
if( !mpTrackball ) |
{ |
NSLog( @">> ERROR: OpenGL Trackball - Can't allocate memory for the backing store!" ); |
} // else |
} // if |
return( self ); |
} // init |
//--------------------------------------------------------------------------- |
- (void) cleanUpTrackball |
{ |
if( mpTrackball != NULL ) |
{ |
free( mpTrackball ); |
mpTrackball = NULL; |
} // if |
} // cleanUpTrackball |
//--------------------------------------------------------------------------- |
- (void) dealloc |
{ |
[self cleanUpTrackball]; |
[super dealloc]; |
} // dealloc |
//--------------------------------------------------------------------------- |
//--------------------------------------------------------------------------- |
// |
// Start up the trackball. Inputs are mouse positon and view size. |
// |
// The math behind the trackball is simple: start with a vector from the |
// first mouse-click on the sphere to the center of the 3D view. At the |
// same time, set the radius of the sphere to be the smaller dimension of |
// the 3D view. As you drag the mouse around in the 3D view, a second |
// vector is computed from the surface of the sphere to the center. The |
// axis of rotation is the cross product of these two vectors, and the |
// angle of rotation is the angle between the two vectors. |
// |
//--------------------------------------------------------------------------- |
- (void) start:(const NSPoint *)thePosition |
origin:(const NSPoint *)theOrigin |
size:(const NSSize *)theSize |
{ |
Math::Vector3<GLfloat> bounds(0.5f * theSize->width, 0.5f * theSize->height); |
Math::Vector3<GLfloat> position(thePosition->x, thePosition->y); |
Math::Vector3<GLfloat> origin(theOrigin->x, theOrigin->y); |
// Compute the center of a view. |
mpTrackball->center = origin + bounds; |
// Compute the starting vector from the sphere surface to its center. |
mpTrackball->start = position - mpTrackball->center; |
if( bounds.x > bounds.y ) |
{ |
mpTrackball->radius = bounds.y; |
} // if |
else |
{ |
mpTrackball->radius = bounds.x; |
} // else |
mpTrackball->start.z = mpTrackball->start.bound( mpTrackball->radius ); |
} // start |
//--------------------------------------------------------------------------- |
// |
// Calculate rotation based on current mouse position. Output is the |
// rotation angle. |
// |
//--------------------------------------------------------------------------- |
- (void) roll:(const NSPoint *)thePosition |
to:(GLfloat *)theRotation |
{ |
Math::Vector3<GLfloat> position(thePosition->x, thePosition->y); |
mpTrackball->end = position - mpTrackball->center; |
// Has there been a change in the (x,y) componets of our 3-vector? |
Math::Vector3<GLfloat> d = Math::diff(mpTrackball->end, mpTrackball->start); |
if( ( d.x >= kDeltaTolerance ) && ( d.y >= kDeltaTolerance ) ) |
{ |
// There has been sufficent amount of change in our |
// 3-vector to warrant continuing further. |
GLfloat A = 0.0f; // sin( angle ) |
GLfloat B = 0.0f; // cos( angle ) |
GLfloat c = 0.0f; |
GLfloat ls = 0.0f; |
GLfloat le = 0.0f; |
GLfloat lr = 0.0f; |
// Compute the end-vector from the surface of the sphere to its center. |
mpTrackball->end.z = mpTrackball->end.bound( mpTrackball->radius ); |
// ls = 1 / || s || |
ls = 1.0f / Math::norm(mpTrackball->start); |
// le = 1 / || e || |
le = 1.0f / Math::norm(mpTrackball->end); |
// c = s * e; interior product |
c = mpTrackball->start * mpTrackball->end; |
// B = cos(a) = (s . e) / (||s|| ||e||) |
B = ls * le * c; |
// r = s ^ e; exterior product |
Math::Vector3<GLfloat> r = mpTrackball->start ^ mpTrackball->end; |
// lr = || r || = ||(s ^ e)|| |
lr = Math::norm(r); |
// A = sin(a) = ||(s ^ e)|| / (||s|| ||e||) |
A = ls * le * lr; |
// Normalize the rotation axis. |
lr = 1.0f / lr; |
// GL rotations are in degrees. |
// Use atan for a better angle. Note that when using acos or asin, |
// you only get half the possible angles, and you can end up with |
// rotations that flip around and near the poles. |
theRotation[0] = kRadians2Degrees * atan2f( A, B ); |
theRotation[1] = lr * r.x; |
theRotation[2] = lr * r.y; |
theRotation[3] = lr * r.z; |
// returns rotation |
} // if |
} // rollTo |
//--------------------------------------------------------------------------- |
// |
// Determine C = A . B |
// |
// (1) In quaternions: let P <- B, and Q <- A. |
// (2) Compute the Hamilton product, R = P ^ Q. |
// (3) Then, C = R if R is not an identity rotation. |
// |
//--------------------------------------------------------------------------- |
- (void) add:(const GLfloat *)A |
to:(GLfloat *)B |
{ |
Math::Quaternion<GLfloat> P(B); |
Math::Quaternion<GLfloat> Q(A); |
// Avoid floating point errors by renormalizing quaternions |
// if it was necessary |
P = Math::norml(P); |
Q = Math::norml(Q); |
// Compute the Hamilton product |
Math::Quaternion<GLfloat> R = P ^ Q; |
// Check for identity rotation. |
// An identity rotation is expressed as rotation by 0 |
// about any axis. The "angle" term in a quaternion |
// is really the cosine of the half-angle. So, if the |
// cosine of the half-angle is one (or, 1.0 within our |
// tolerance), then you have an identity rotation. |
if( __builtin_fabsf( R.t - 1.0f ) < 1.0e-7 ) |
{ |
// Encountered an identity rotation. |
B[0] = 1.0f; |
B[1] = 0.0f; |
B[2] = 0.0f; |
B[3] = 0.0f; |
} // if |
else |
{ |
// Encountered a non-identity rotation, hence, the |
// cosine of the half-angle is non-zero, which implies |
// that the sine of the angle is also non-zero. As a |
// result, it is safe to divide by sine of the angle |
// theta. |
// Turn the quaternion back into an {angle, {axis}} rotation. |
R.toRotation(B); |
} // else |
} // add |
//--------------------------------------------------------------------------- |
@end |
//--------------------------------------------------------------------------- |
//--------------------------------------------------------------------------- |
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