arcball.c

Go to the documentation of this file.

/*************************************************************************************/
/*************************************************************************************/
 
#include <glcomp/glcompdefs.h>
#define ARCBALL_C
#include "smyrnadefs.h"
#include "arcball.h"
 
static void setBounds(ArcBall_t *a, float NewWidth, float NewHeight) {
    assert((NewWidth > 1.0f) && (NewHeight > 1.0f));
    //Set adjustment factor for width/height
    a->AdjustWidth = 1.0f / ((NewWidth - 1.0f) * 0.5f);
    a->AdjustHeight = 1.0f / ((NewHeight - 1.0f) * 0.5f);
}
 
static void mapToSphere(ArcBall_t * a, const Point2fT * NewPt,
                        Vector3fT * NewVec)
{
    Point2fT TempPt;
 
    //Copy paramter into temp point
    TempPt = *NewPt;
 
    //Adjust point coords and scale down to range of [-1 ... 1]
    TempPt.s.X = (TempPt.s.X * a->AdjustWidth) - 1.0f;
    TempPt.s.Y = 1.0f - (TempPt.s.Y * a->AdjustHeight);
 
    //Compute the square of the length of the vector to the point from the center
    float length = TempPt.s.X * TempPt.s.X + TempPt.s.Y * TempPt.s.Y;
 
    //If the point is mapped outside of the sphere... (length > radius squared)
    if (length > 1.0f) {
 
        //Compute a normalizing factor (radius / sqrt(length))
        float norm = 1.0f / FuncSqrt(length);
 
        //Return the "normalized" vector, a point on the sphere
        NewVec->s.X = TempPt.s.X * norm;
        NewVec->s.Y = TempPt.s.Y * norm;
        NewVec->s.Z = 0.0f;
    } else                      //Else it's on the inside
    {
        //Return a vector to a point mapped inside the sphere sqrt(radius squared - length)
        NewVec->s.X = TempPt.s.X;
        NewVec->s.Y = TempPt.s.Y;
        NewVec->s.Z = FuncSqrt(1.0f - length);
    }
}
 
static Matrix4fT Transform = { {1.0f, 0.0f, 0.0f, 0.0f, // NEW: Final Transform
                                0.0f, 1.0f, 0.0f, 0.0f,
                                0.0f, 0.0f, 1.0f, 0.0f,
                                0.0f, 0.0f, 0.0f, 1.0f}
};
 
static Matrix3fT LastRot = { {1.0f, 0.0f, 0.0f, // NEW: Last Rotation
                              0.0f, 1.0f, 0.0f,
                              0.0f, 0.0f, 1.0f}
};
 
static Matrix3fT ThisRot = { {1.0f, 0.0f, 0.0f, // NEW: This Rotation
                              0.0f, 1.0f, 0.0f,
                              0.0f, 0.0f, 1.0f}
};
 
//Create/Destroy
void init_arcBall(ArcBall_t *a, float NewWidth, float NewHeight) {
    a->Transform = Transform;
    a->LastRot = LastRot;
    a->ThisRot = ThisRot;
    //Clear initial values
    a->StVec.s.X =
        a->StVec.s.Y =
        a->StVec.s.Z = a->EnVec.s.X = a->EnVec.s.Y = a->EnVec.s.Z = 0.0f;
 
    //Set initial bounds
    setBounds(a, NewWidth, NewHeight);
 
    a->isClicked = 0;
    a->isRClicked = 0;
    a->isDragging = 0;
}
 
//Mouse down
static void click(ArcBall_t * a, const Point2fT * NewPt)
{
    //Map the point to the sphere
    mapToSphere(a, NewPt, &a->StVec);
}
 
//Mouse drag, calculate rotation
static void drag(ArcBall_t * a, const Point2fT * NewPt, Quat4fT * NewRot)
{
    //Map the point to the sphere
    mapToSphere(a, NewPt, &a->EnVec);
 
    //Return the quaternion equivalent to the rotation
    if (NewRot) {
        Vector3fT Perp;
 
        //Compute the vector perpendicular to the begin and end vectors
        Vector3fCross(&Perp, &a->StVec, &a->EnVec);
 
        //Compute the length of the perpendicular vector
        if (Vector3fLength(&Perp) > Epsilon)    //if its non-zero
        {
            //We're ok, so return the perpendicular vector as the transform after all
            NewRot->s.X = Perp.s.X;
            NewRot->s.Y = Perp.s.Y;
            NewRot->s.Z = Perp.s.Z;
            //In the quaternion values, w is cosine (theta / 2), where theta is rotation angle
            NewRot->s.W = Vector3fDot(&a->StVec, &a->EnVec);
        } else                  //if its zero
        {
            //The begin and end vectors coincide, so return an identity transform
            NewRot->s.X = NewRot->s.Y = NewRot->s.Z = NewRot->s.W = 0.0f;
        }
    }
}
 
void arcmouseClick(void)
{
    view->arcball->isDragging = 1;      // Prepare For Dragging
    view->arcball->LastRot = view->arcball->ThisRot;    // Set Last Static Rotation To Last Dynamic One
    click(view->arcball, &view->arcball->MousePt);
 
}
 
void arcmouseDrag(void)
{
    Quat4fT ThisQuat;
    drag(view->arcball, &view->arcball->MousePt, &ThisQuat);
    Matrix3fSetRotationFromQuat4f(&view->arcball->ThisRot, &ThisQuat);  // Convert Quaternion Into Matrix3fT
    Matrix3fMulMatrix3f(&view->arcball->ThisRot, &view->arcball->LastRot);      // Accumulate Last Rotation Into This One
    Matrix4fSetRotationFromMatrix3f(&view->arcball->Transform, &view->arcball->ThisRot);        // Set Our Final Transform's Rotation From This One
 
}