//////////////////////////////////////////////////////////////////////////////////////////////////
// 
// File: pickSample.cpp
// 
// Author: Frank Luna (C) All Rights Reserved
//
// Edited by Tom Plick, 28 July 2005
//////////////////////////////////////////////////////////////////////////////////////////////////

#include "d3dUtility.h"

extern IDirect3DDevice9* Device;

//
// Functions
//
d3d::Ray CalcPickingRay(int x, int y)
{
	float px = 0.0f;
	float py = 0.0f;

	D3DVIEWPORT9 vp;
	Device->GetViewport(&vp);

	D3DXMATRIX proj;
	Device->GetTransform(D3DTS_PROJECTION, &proj);

	px = ((( 2.0f*x) / vp.Width)  - 1.0f) / proj(0, 0);
	py = (((-2.0f*y) / vp.Height) + 1.0f) / proj(1, 1);

	d3d::Ray ray;
	ray._origin    = D3DXVECTOR3(0.0f, 0.0f, 0.0f);
	ray._direction = D3DXVECTOR3(px, py, 1.0f);

	return ray;
}

void TransformRay(d3d::Ray* ray, D3DXMATRIX* T)
{
	// transform the ray's origin, w = 1.
	D3DXVec3TransformCoord(
		&ray->_origin,
		&ray->_origin,
		T);

	// transform the ray's direction, w = 0.
	D3DXVec3TransformNormal(
		&ray->_direction,
		&ray->_direction,
		T);

	// normalize the direction
	D3DXVec3Normalize(&ray->_direction, &ray->_direction);
}

bool RaySphereIntTest(d3d::Ray* ray, d3d::BoundingSphere* sphere)
{
	D3DXVECTOR3 v = ray->_origin - sphere->_center;

	float b = 2.0f * D3DXVec3Dot(&ray->_direction, &v);
	float c = D3DXVec3Dot(&v, &v) - (sphere->_radius * sphere->_radius);

	// find the discriminant
	float discriminant = (b * b) - (4.0f * c);

	// test for imaginary number
	if( discriminant < 0.0f )
		return false;

	discriminant = sqrtf(discriminant);

	float s0 = (-b + discriminant) / 2.0f;
	float s1 = (-b - discriminant) / 2.0f;

	// if a solution is >= 0, then we intersected the sphere
	if( s0 >= 0.0f || s1 >= 0.0f )
		return true;
	
	return false;
}

//
// GetRay
//
d3d::Ray GetPickingRay(LPARAM lParam)
{

		// compute the ray in view space given the clicked screen point
		d3d::Ray ray = CalcPickingRay(LOWORD(lParam), HIWORD(lParam));

		// transform the ray to world space
		D3DXMATRIX view;
		Device->GetTransform(D3DTS_VIEW, &view);

		D3DXMATRIX viewInverse;
		D3DXMatrixInverse(&viewInverse,	0, &view);

		TransformRay(&ray, &viewInverse);

		return ray;
}

char * StringifyRay(d3d::Ray ray)
{
	static char s[200];
	sprintf(s, "origin (%.2f, %.2f, %.2f);\ndirection <%.2f, %.2f, %.2f>",
		ray._origin.x,    ray._origin.y,    ray._origin.z, 
		ray._direction.x, ray._direction.y, ray._direction.z);
	return s;
}