ArcBall.h

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#pragma once
 
 
#include "gui/objects/Point.h"
#include "math/AffineMatrix.h"
#include "math/Quat.h"
 
NAMESPACE_SPH_BEGIN
 
class ArcBall {
private:
    Vector start{ NAN };
 
    Pixel size;
 
public:
    ArcBall() {
        size = Pixel(0, 0);
    }
 
    explicit ArcBall(const Pixel size)
        : size(size) {}
 
    void resize(const Pixel newSize) {
        size = newSize;
    }
 
    void click(const Pixel point) {
        start = this->mapToSphere(point);
    }
 
    AffineMatrix drag(const Pixel point, const Vector& pivot) {
        SPH_ASSERT(isReal(start));
        const Vector end = this->mapToSphere(point);
        const Vector perp = cross(start, end);
        if (getSqrLength(perp) > EPS) {
            Quat q;
            q[0] = perp[0];
            q[1] = perp[1];
            q[2] = perp[2];
            q[3] = dot(start, end);
 
            AffineMatrix result = AffineMatrix::identity();
            result.translate(pivot);
            result = result * q.convert();
            result.translate(-pivot);
            return result;
        } else {
            return AffineMatrix::identity();
        }
    }
 
private:
    Vector mapToSphere(const Pixel point) {
        // rescale to <-1, 1> and invert y
        SPH_ASSERT(size.x > 0 && size.y > 0);
        const Vector p(2.f * float(point.x) / size.x - 1.f, 1.f - 2.f * float(point.y) / size.y, 0._f);
 
        const Float lengthSqr = getSqrLength(p);
        if (lengthSqr > 1.f) {
            const Float length = sqrt(lengthSqr);
            return p / length;
        } else {
            return Vector(p[X], p[Y], sqrt(1.f - lengthSqr));
        }
    }
};
 
NAMESPACE_SPH_END