/*//////////////////////////////////////////////////////////////////////////////
//
// Copyright (C) 2000 Microsoft Corporation. All Rights Reserved.
//
//////////////////////////////////////////////////////////////////////////////*/

/*
 * Simple arcball rotation control using quaternions
 * Peter-Pike Sloan
 */
//  Rewritten to use D3DX types. --- Jed Lengyel

#include "GTArcBall.h"


// constructors - default makes most sense, SetWindow is what's important.

GTArcBall::GTArcBall()
{
	Reset();
}

GTArcBall::GTArcBall(int x, int y)
	: m_pCenter((float)x,(float)y,0.0f)
{
	Reset();
}

GTArcBall::GTArcBall(D3DXVECTOR3 center)
{
	m_pCenter = center;
	Reset();
}

void GTArcBall::Reset()
{
	D3DXQuaternionIdentity(&m_qNow);
	m_bDrag = false;
}

void GTArcBall::SetWindow(int w, int h, float r)
{
	m_iWidth = w; m_iHeight = h; m_fRadius = r; // set win info
	m_pCenter = D3DXVECTOR3(w/2.f,h/2.f,0.0f); // set center
}

void GTArcBall::BeginDrag(int x, int y)
{
	m_qDown = m_qNow;
	m_bDrag = true;
	m_vDown = ScreenToVector(x,y);
}

void GTArcBall::EndDrag()
{
	m_bDrag = false;
}

void GTArcBall::Mouse(int x, int y)
{
	if (m_bDrag) { // ignore it if you aren't dragging
		m_vCur = ScreenToVector(x,y);
		Update(); // always build m_qNow
	}
}

void GTArcBall::GetMatrix(D3DXMATRIX *pmat)
{
	D3DXMatrixRotationQuaternion(pmat, &m_qNow);
}

D3DXVECTOR3 GTArcBall::ScreenToVector(int ix, int iy)
{
	float x, y, z;
	
	x = (ix - m_pCenter.x)/(m_iWidth*m_fRadius*0.5f); // scales to screen
#if 1
	y = (m_pCenter.y - iy)/(m_iHeight*m_fRadius*0.5f); // invert Y coordinate
#else
	y = (iy - m_pCenter.y)/(m_iHeight*m_fRadius*0.5f);
#endif

	float mag = x*x + y*y;
	if (mag > 1.f) {
		float scale = 1.f/sqrtf(mag);
		x *= scale;
		y *= scale;
		z = 0.0;
	} else {
		z = sqrtf(1.f-mag);
	}

	return D3DXVECTOR3(-x, -y, z); //-x and -y : hack so that the rotation is 
                                 //in the way we wait
}

void GTArcBall::Update()
{
	if (m_bDrag)
	{
		// recompute m_qNow
		D3DXQUATERNION qAxisToAxis;
		D3DXQuaternionAxisToAxis(&qAxisToAxis, &m_vDown, &m_vCur);
		m_qNow = m_qDown;
		m_qNow *= qAxisToAxis;
	}
}