TRACKBAL.C
/*
* Trackball code:
*
* Implementation of a virtual trackball.
* Implemented by Gavin Bell, lots of ideas from Thant Tessman and
* the August '88 issue of Siggraph's "Computer Graphics," pp. 121-129.
*
* Vector manip code:
*
* Original code from:
* David M. Ciemiewicz, Mark Grossman, Henry Moreton, and Paul Haeberli
*
* Much mucking with by:
* Gavin Bell
*
* Shell hacking courtesy of:
* Reptilian Inhaleware
*/
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <windows.h>
#include <math.h>
#include <GL/gl.h>
#include <GL/glu.h>
#include <GL/glaux.h>
#include "trackbal.h"
/*
* globals
*/
static GLenum (*MouseDownFunc)(int, int, GLenum) = NULL;
static GLenum (*MouseUpFunc)(int, int, GLenum) = NULL;
static HWND ghwnd;
GLint giWidth, giHeight;
LONG glMouseDownX, glMouseDownY;
BOOL gbLeftMouse = FALSE;
BOOL gbSpinning = FALSE;
float curquat[4], lastquat[4];
/*
* This size should really be based on the distance from the center of
* rotation to the point on the object underneath the mouse. That
* point would then track the mouse as closely as possible. This is a
* simple example, though, so that is left as an Exercise for the
* Programmer.
*/
#define TRACKBALLSIZE (0.8f)
/*
* Local function prototypes (not defined in trackball.h)
*/
static float tb_project_to_sphere(float, float, float);
static void normalize_quat(float [4]);
void
trackball_Init( GLint width, GLint height )
{
ghwnd = auxGetHWND();
giWidth = width;
giHeight = height;
trackball_calc_quat( curquat, 0.0f, 0.0f, 0.0f, 0.0f );
}
void
trackball_Resize( GLint width, GLint height )
{
giWidth = width;
giHeight = height;
}
GLenum
#ifdef _USE_TK
trackball_MouseDown( int mouseX, int mouseY, GLenum button )
#else
trackball_MouseDown( AUX_EVENTREC *event)
#endif
{
SetCapture(ghwnd);
glMouseDownX = event->data[AUX_MOUSEX];
glMouseDownY = event->data[AUX_MOUSEY];
gbLeftMouse = TRUE;
return GL_TRUE;
}
GLenum
#ifdef _USE_TK
trackball_MouseUp( int mouseX, int mouseY, GLenum button )
#else
trackball_MouseUp( AUX_EVENTREC *event )
#endif
{
ReleaseCapture();
gbLeftMouse = FALSE;
return GL_TRUE;
}
/* these 4 not used yet */
void
trackball_MouseDownEvent( int mouseX, int mouseY, GLenum button )
{
}
void
trackball_MouseUpEvent( int mouseX, int mouseY, GLenum button )
{
}
void
trackball_MouseDownFunc(GLenum (*Func)(int, int, GLenum))
{
MouseDownFunc = Func;
}
void
trackball_MouseUpFunc(GLenum (*Func)(int, int, GLenum))
{
MouseUpFunc = Func;
}
void
trackball_CalcRotMatrix( GLfloat matRot[4][4] )
{
POINT pt;
if (gbLeftMouse)
{
auxGetMouseLoc( &pt.x, &pt.y );
// If mouse has moved since button was pressed, change quaternion.
if (pt.x != glMouseDownX || pt.y != glMouseDownY)
{
#if 1
/* negate all params for proper operation with glTranslate(-z)
*/
trackball_calc_quat(lastquat,
-(2.0f * ( giWidth - glMouseDownX ) / giWidth - 1.0f),
-(2.0f * glMouseDownY / giHeight - 1.0f),
-(2.0f * ( giWidth - pt.x ) / giWidth - 1.0f),
-(2.0f * pt.y / giHeight - 1.0f)
);
#else
// now out-of-date
trackball_calc_quat(lastquat,
2.0f * ( Width - glMouseDownX ) / Width - 1.0f,
2.0f * glMouseDownY / Height - 1.0f,
2.0f * ( Width - pt.x ) / Width - 1.0f,
2.0f * pt.y / Height - 1.0f );
#endif
gbSpinning = TRUE;
}
else
gbSpinning = FALSE;
glMouseDownX = pt.x;
glMouseDownY = pt.y;
}
if (gbSpinning)
trackball_add_quats(lastquat, curquat, curquat);
trackball_build_rotmatrix(matRot, curquat);
}
void
vzero(float *v)
{
v[0] = 0.0f;
v[1] = 0.0f;
v[2] = 0.0f;
}
void
vset(float *v, float x, float y, float z)
{
v[0] = x;
v[1] = y;
v[2] = z;
}
void
vsub(const float *src1, const float *src2, float *dst)
{
dst[0] = src1[0] - src2[0];
dst[1] = src1[1] - src2[1];
dst[2] = src1[2] - src2[2];
}
void
vcopy(const float *v1, float *v2)
{
register int i;
for (i = 0 ; i < 3 ; i++)
v2[i] = v1[i];
}
void
vcross(const float *v1, const float *v2, float *cross)
{
float temp[3];
temp[0] = (v1[1] * v2[2]) - (v1[2] * v2[1]);
temp[1] = (v1[2] * v2[0]) - (v1[0] * v2[2]);
temp[2] = (v1[0] * v2[1]) - (v1[1] * v2[0]);
vcopy(temp, cross);
}
float
vlength(const float *v)
{
return (float) sqrt(v[0] * v[0] + v[1] * v[1] + v[2] * v[2]);
}
void
vscale(float *v, float div)
{
v[0] *= div;
v[1] *= div;
v[2] *= div;
}
void
vnormal(float *v)
{
vscale(v,1.0f/vlength(v));
}
float
vdot(const float *v1, const float *v2)
{
return v1[0]*v2[0] + v1[1]*v2[1] + v1[2]*v2[2];
}
void
vadd(const float *src1, const float *src2, float *dst)
{
dst[0] = src1[0] + src2[0];
dst[1] = src1[1] + src2[1];
dst[2] = src1[2] + src2[2];
}
/*
* Ok, simulate a track-ball. Project the points onto the virtual
* trackball, then figure out the axis of rotation, which is the cross
* product of P1 P2 and O P1 (O is the center of the ball, 0,0,0)
* Note: This is a deformed trackball-- is a trackball in the center,
* but is deformed into a hyperbolic sheet of rotation away from the
* center. This particular function was chosen after trying out
* several variations.
*
* It is assumed that the arguments to this routine are in the range
* (-1.0 ... 1.0)
*/
void
trackball_calc_quat(float q[4], float p1x, float p1y, float p2x, float p2y)
{
float a[3]; /* Axis of rotation */
float phi; /* how much to rotate about axis */
float p1[3], p2[3], d[3];
float t;
if (p1x == p2x && p1y == p2y) {
/* Zero rotation */
vzero(q);
q[3] = 1.0f;
return;
}
/*
* First, figure out z-coordinates for projection of P1 and P2 to
* deformed sphere
*/
vset(p1,p1x,p1y,tb_project_to_sphere(TRACKBALLSIZE,p1x,p1y));
vset(p2,p2x,p2y,tb_project_to_sphere(TRACKBALLSIZE,p2x,p2y));
/*
* Now, we want the cross product of P1 and P2
*/
vcross(p2,p1,a);
/*
* Figure out how much to rotate around that axis.
*/
vsub(p1,p2,d);
t = vlength(d) / (2.0f*TRACKBALLSIZE);
/*
* Avoid problems with out-of-control values...
*/
if (t > 1.0f) t = 1.0f;
if (t < -1.0f) t = -1.0f;
phi = 2.0f * (float) asin(t);
trackball_axis_to_quat(a,phi,q);
}
/*
* Given an axis and angle, compute quaternion.
*/
void
trackball_axis_to_quat(float a[3], float phi, float q[4])
{
vnormal(a);
vcopy(a,q);
vscale(q,(float) sin(phi/2.0f));
q[3] = (float) cos(phi/2.0f);
}
/*
* Project an x,y pair onto a sphere of radius r OR a hyperbolic sheet
* if we are away from the center of the sphere.
*/
static float
tb_project_to_sphere(float r, float x, float y)
{
float d, t, z;
d = (float) sqrt(x*x + y*y);
if (d < r * 0.70710678118654752440f) { /* Inside sphere */
z = (float) sqrt(r*r - d*d);
} else { /* On hyperbola */
t = r / 1.41421356237309504880f;
z = t*t / d;
}
return z;
}
/*
* Given two rotations, e1 and e2, expressed as quaternion rotations,
* figure out the equivalent single rotation and stuff it into dest.
*
* This routine also normalizes the result every RENORMCOUNT times it is
* called, to keep error from creeping in.
*
* NOTE: This routine is written so that q1 or q2 may be the same
* as dest (or each other).
*/
#define RENORMCOUNT 97
void
trackball_add_quats(float q1[4], float q2[4], float dest[4])
{
static int count=0;
float t1[4], t2[4], t3[4];
float tf[4];
vcopy(q1,t1);
vscale(t1,q2[3]);
vcopy(q2,t2);
vscale(t2,q1[3]);
vcross(q2,q1,t3);
vadd(t1,t2,tf);
vadd(t3,tf,tf);
tf[3] = q1[3] * q2[3] - vdot(q1,q2);
dest[0] = tf[0];
dest[1] = tf[1];
dest[2] = tf[2];
dest[3] = tf[3];
if (++count > RENORMCOUNT) {
count = 0;
normalize_quat(dest);
}
}
/*
* Quaternions always obey: a^2 + b^2 + c^2 + d^2 = 1.0
* If they don't add up to 1.0, dividing by their magnitued will
* renormalize them.
*
* Note: See the following for more information on quaternions:
*
* - Shoemake, K., Animating rotation with quaternion curves, Computer
* Graphics 19, No 3 (Proc. SIGGRAPH'85), 245-254, 1985.
* - Pletinckx, D., Quaternion calculus as a basic tool in computer
* graphics, The Visual Computer 5, 2-13, 1989.
*/
static void
normalize_quat(float q[4])
{
int i;
float mag;
mag = (q[0]*q[0] + q[1]*q[1] + q[2]*q[2] + q[3]*q[3]);
for (i = 0; i < 4; i++) q[i] /= mag;
}
/*
* Build a rotation matrix, given a quaternion rotation.
*
*/
void
trackball_build_rotmatrix(float m[4][4], float q[4])
{
m[0][0] = 1.0f - 2.0f * (q[1] * q[1] + q[2] * q[2]);
m[0][1] = 2.0f * (q[0] * q[1] - q[2] * q[3]);
m[0][2] = 2.0f * (q[2] * q[0] + q[1] * q[3]);
m[0][3] = 0.0f;
m[1][0] = 2.0f * (q[0] * q[1] + q[2] * q[3]);
m[1][1]= 1.0f - 2.0f * (q[2] * q[2] + q[0] * q[0]);
m[1][2] = 2.0f * (q[1] * q[2] - q[0] * q[3]);
m[1][3] = 0.0f;
m[2][0] = 2.0f * (q[2] * q[0] - q[1] * q[3]);
m[2][1] = 2.0f * (q[1] * q[2] + q[0] * q[3]);
m[2][2] = 1.0f - 2.0f * (q[1] * q[1] + q[0] * q[0]);
m[2][3] = 0.0f;
m[3][0] = 0.0f;
m[3][1] = 0.0f;
m[3][2] = 0.0f;
m[3][3] = 1.0f;
}