0ad/source/maths/Frustum.cpp

/* Copyright (C) 2021 Wildfire Games.
 * This file is part of 0 A.D.
 *
 * 0 A.D. is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 2 of the License, or
 * (at your option) any later version.
 *
 * 0 A.D. is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with 0 A.D.  If not, see <http://www.gnu.org/licenses/>.
 */

/*
Usually associated with the camera, there are 6 planes which define the
view pyramid. But we allow more planes per frustum which may be used for
portal rendering, where a portal may have 3 or more edges.
*/

#include "precompiled.h"

#include "Frustum.h"

#include "maths/BoundingBoxAligned.h"
#include "maths/MathUtil.h"
#include "maths/Matrix3D.h"

CFrustum::CFrustum()
{
	m_NumPlanes = 0;
}

CFrustum::~CFrustum()
{
}

void CFrustum::SetNumPlanes(size_t num)
{
	m_NumPlanes = num;

	if (m_NumPlanes >= MAX_NUM_FRUSTUM_PLANES)
	{
		debug_warn(L"CFrustum::SetNumPlanes: Too many planes");
		m_NumPlanes = MAX_NUM_FRUSTUM_PLANES - 1;
	}
}

void CFrustum::AddPlane(const CPlane& plane)
{
	if (m_NumPlanes >= MAX_NUM_FRUSTUM_PLANES)
	{
		debug_warn(L"CFrustum::AddPlane: Too many planes");
		return;
	}

	m_Planes[m_NumPlanes++] = plane;
}

void CFrustum::Transform(const CMatrix3D& m)
{
	for (size_t i = 0; i < m_NumPlanes; ++i)
	{
		CVector3D n = m.Rotate(m_Planes[i].m_Norm);
		CVector3D p = m.Transform(m_Planes[i].m_Norm * -m_Planes[i].m_Dist);
		m_Planes[i].Set(n, p);
		m_Planes[i].Normalize();
	}
}

bool CFrustum::IsPointVisible(const CVector3D& point) const
{
	for (size_t i = 0; i < m_NumPlanes; ++i)
	{
		if (m_Planes[i].IsPointOnBackSide(point))
			return false;
	}

	return true;
}

bool CFrustum::DoesSegmentIntersect(const CVector3D& startRef, const CVector3D& endRef) const
{
	CVector3D start = startRef;
	CVector3D end = endRef;

	if (IsPointVisible(start) || IsPointVisible(end))
		return true;

	CVector3D intersect;
	for (size_t i = 0; i < m_NumPlanes; ++i)
	{
		if (m_Planes[i].FindLineSegIntersection(start, end, &intersect))
		{
			if (IsPointVisible(intersect))
				return true;
		}
	}
	return false;
}

bool CFrustum::IsSphereVisible(const CVector3D& center, float radius) const
{
	for (size_t i = 0; i < m_NumPlanes; ++i)
	{
		// If none of the sphere is in front of the plane, then
		// it is outside the frustum.
		if (-m_Planes[i].DistanceToPlane(center) > radius)
			return false;
	}

	return true;
}

bool CFrustum::IsBoxVisible(const CVector3D& position, const CBoundingBoxAligned& bounds) const
{
	// Basically for every plane we calculate the furthest point
	// in the box to that plane. If that point is beyond the plane
	// then the box is not visible.
	CVector3D farPoint;
	CVector3D minPoint = position + bounds[0];
	CVector3D maxPoint = position + bounds[1];

	for (size_t i = 0; i < m_NumPlanes; ++i)
	{
		farPoint.X = m_Planes[i].m_Norm.X > 0.0f ? maxPoint.X : minPoint.X;
		farPoint.Y = m_Planes[i].m_Norm.Y > 0.0f ? maxPoint.Y : minPoint.Y;
		farPoint.Z = m_Planes[i].m_Norm.Z > 0.0f ? maxPoint.Z : minPoint.Z;

		if (m_Planes[i].IsPointOnBackSide(farPoint))
			return false;
	}

	return true;
}

bool CFrustum::IsBoxVisible(const CBoundingBoxAligned& bounds) const
{
	// Same as the previous one, but with the position = (0, 0, 0).
	CVector3D farPoint;

	for (size_t i = 0; i < m_NumPlanes; ++i)
	{
		farPoint.X = m_Planes[i].m_Norm.X > 0.0f ? bounds[1].X : bounds[0].X;
		farPoint.Y = m_Planes[i].m_Norm.Y > 0.0f ? bounds[1].Y : bounds[0].Y;
		farPoint.Z = m_Planes[i].m_Norm.Z > 0.0f ? bounds[1].Z : bounds[0].Z;

		if (m_Planes[i].IsPointOnBackSide(farPoint))
			return false;
	}

	return true;
}