// Developed by Neil Kemp: http://neilkemp.us
// Licensed under the MIT license: http://www.opensource.org/licenses/mit-license.php


// Convert a mouse point in window client space to world space ray position and direction
void mouse_point_to_ray(IDirect3DDevice9* device_pointer, 
						const CRect &window_client_rect, const D3DXVECTOR2 &mouse_point, 
						D3DXVECTOR3 &ray_position_out, D3DXVECTOR3 &ray_direction_out)
{
	// Assertions
	_ASSERT(device_pointer != 0);

	// Local data
	D3DXMATRIX		projection_matrix, view_matrix, inverse_view_matrix;
	D3DXVECTOR3		v;

	// Get projection and view matricies
	device_pointer->GetTransform(D3DTS_PROJECTION, &projection_matrix);
	device_pointer->GetTransform(D3DTS_VIEW, &view_matrix);

	// Inverse view matrix
	D3DXMatrixInverse(&inverse_view_matrix, 0, &view_matrix);

	// Get pick ray in screen space
	v.x	= (((2.0f * mouse_point.x) / (float)window_client_rect.Width()) - 1.0f) / projection_matrix._11;
	v.y	= -(((2.0f * mouse_point.y) / (float)window_client_rect.Height()) - 1.0f) / projection_matrix._22;	
	v.z	= 1.0f;

	// Transform screen space pick ray to world space
	ray_position_out.x		= inverse_view_matrix._41;
	ray_position_out.y		= inverse_view_matrix._42;
	ray_position_out.z		= inverse_view_matrix._43;	
	ray_direction_out.x		= v.x * inverse_view_matrix._11 + v.y * inverse_view_matrix._21 + v.z * inverse_view_matrix._31;
	ray_direction_out.y		= v.x * inverse_view_matrix._12 + v.y * inverse_view_matrix._22 + v.z * inverse_view_matrix._32;
	ray_direction_out.z		= v.x * inverse_view_matrix._13 + v.y * inverse_view_matrix._23 + v.z * inverse_view_matrix._33;
	
	// Normalize direction vector
	D3DXVec3Normalize(&ray_direction_out, &ray_direction_out);
}

/*
	Example usage:

	IDirect3DDevice9*		device;
	D3DXVECTOR3				mouse_point, ray, dir, hit, p0, p1;
	D3DXPLANE				plane;
	CRect					d3d_window_rect;

	// ... Initialize device, rect, and plane ...

	// Get ray from mouse point
	mouse_point_to_ray(device, d3d_window_rect, mouse_point, ray, dir);

	// Intersect plane with line
	p0 = ray;
	p1 = dir * 1000.0f;
	D3DXPlaneIntersectLine(&hit, &plane, &p0, &p1);

	// Can also be used with other D3D functions
	// ID3DX10Mesh::Intersect()
	// ID3DX10Mesh::IntersectSubset()
	// D3DXIntersectSubset()
	// D3DXIntersect()
	// D3DXboxBoundProbe()
	// D3DXSphereBoundProbe()
	// D3DXIntersectTri()
	// ID3DXPRTEngine::ClosestRayIntersects()
*/