Physics.cpp

/*
	Greyout - a colourful platformer about love

	Greyout is Copyright (c)2011-2014 Janek Schäfer

	This file is part of Greyout.

	Greyout 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 3 of the License, or
	(at your option) any later version.

	Greyout 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 this program.  If not, see <http://www.gnu.org/licenses/>.

	Please direct any feedback, questions or comments to
	Janek Schäfer (foxblock), foxblock_at_gmail_dot_com
*/

#include "Physics.h"

#include "SimpleDirection.h"
#include "Colour.h"
#include "NumberUtility.h"
#include "GFX.h"
#include "Vector2di.h"

#include "BaseUnit.h"
#include "Level.h"

// you can do funky horizontal gravity, but the collision checking would need some tinkering to make it work
// it currently checks the y-directions last for a reason...
#define DEFAULT_GRAVITY Vector2df(0,1)
#define DEFAULT_MAXIMUM Vector2df(10,10) // this should be the size of a tile if that's applicable

Physics* Physics::self = 0;

Physics::Physics()
{
	gravity = DEFAULT_GRAVITY;
	maximum = DEFAULT_MAXIMUM;

	checkPointsX.push_back(diTOPLEFT);
	checkPointsX.push_back(diTOPRIGHT);
	checkPointsX.push_back(diLEFT);
	checkPointsX.push_back(diRIGHT);

	checkPointsY.push_back(diTOP);
	checkPointsY.push_back(diBOTTOMLEFT);
	checkPointsY.push_back(diBOTTOM);
	checkPointsY.push_back(diBOTTOMRIGHT);
	checkPointsY.push_back(diTOPLEFT);
	checkPointsY.push_back(diTOPRIGHT);
}

Physics::~Physics()
{
	//
}

Physics* Physics::GetSingleton()
{
	if (not self)
		self = new Physics();
	return self;
}

void Physics::reset()
{
	gravity = DEFAULT_GRAVITY;
	maximum = DEFAULT_MAXIMUM;
}

void Physics::applyPhysics(BaseUnit* const unit) const
{
	// Acceleration
	if (unit->acceleration[0].x > 0.0f)
	{
		unit->velocity.x += min(max(unit->acceleration[1].x - unit->velocity.x,0.0f),unit->acceleration[0].x);
	}
	else if (unit->acceleration[0].x < 0.0f)
	{
		unit->velocity.x += max(min(unit->acceleration[1].x - unit->velocity.x,0.0f),unit->acceleration[0].x);
	}
	if (unit->acceleration[0].y > 0.0f)
	{
		unit->velocity.y += min(max(unit->acceleration[1].y - unit->velocity.y,0.0f),unit->acceleration[0].y);
	}
	else if (unit->acceleration[0].y < 0.0f)
	{
		unit->velocity.y += max(min(unit->acceleration[1].y - unit->velocity.y,0.0f),unit->acceleration[0].y);
	}

	// Reset acceleration
	if (unit->velocity.x == unit->acceleration[1].x)
	{
		unit->acceleration[0].x = 0.0f;
		unit->acceleration[1].x = 0.0f;
	}
	if (unit->velocity.y == unit->acceleration[1].y)
	{
		unit->acceleration[0].y = 0.0f;
		unit->acceleration[1].y = 0.0f;
	}

	// Gravity
	if (not unit->flags.hasFlag(BaseUnit::ufNoGravity))
	{
		unit->velocity += gravity;
	}

	// Check for max
	if ( unit->velocity.x > maximum.x )
		unit->velocity.x = maximum.x;
	else if ( unit->velocity.x < -maximum.x )
		unit->velocity.x = -maximum.x;
	if ( unit->velocity.y > maximum.y )
		unit->velocity.y = maximum.y;
	else if ( unit->velocity.y < -maximum.y )
		unit->velocity.y = -maximum.y;
}

/** NOTICE:
New implementation, checking each direction of movement individually. This keeps
the correction of gravity induced movement separate from sideways movement
correction, which is desired in platformers. (assuming gravity in y-direction)
**/
void Physics::unitMapCollision(const Level* const level, SDL_Surface* const colImage, BaseUnit* const unit, const Vector2df& mapOffset) const
{
	/// TODO: Implement step-size and check diBOTTOMLEFT and -RIGHT in x-direction, too
	/// compare to y-correction values and step-size
	/// TODO: Take the unit's velocity into account when returning correction value, so sub-pixel movements get corrected properly

	static vector<MapCollisionEntry> collisionDir;
	collisionDir.clear();
	Vector2df correction(0,0);
	Vector2di pixelCorrection(0,0); // unit will be moved by this step until no collision occurs
	Colour colColour; // the colour taken from the collision surface at the tested point
	Vector2df pixel(0,0); // currently tested pixel

	/// x-direction
	// check which pixels are colliding
	for (vector<SimpleDirection>::const_iterator dir = checkPointsX.begin(); dir != checkPointsX.end(); ++dir)
	{
		pixel = unit->getPixel((*dir));
		pixel.x += unit->velocity.x;
		pixel += unit->collisionInfo.positionCorrection;
		pixel = level->transformCoordinate(pixel);

		// out of bounds check
		if (pixel.x < 0 || pixel.y < 0 || pixel.x >= colImage->w || pixel.y >= colImage->h)
			continue;

		colColour = GFX::getPixel(colImage,pixel.x,pixel.y);

		if (unit->checkCollisionColour(colColour))
		{
			// we have a collision
			MapCollisionEntry entry;
			entry.dir = (*dir);
			entry.pos = pixel;
			entry.col = colColour;
			entry.correction = Vector2df(0,0);
			collisionDir.push_back(entry);
			int temp = dir->xDirection();
			// only use direction if not set before or aiming in the same direction as velocity
			if (pixelCorrection.x == 0 || NumberUtility::sign(unit->velocity.x) == temp)
				pixelCorrection.x = temp * -1;
		}
	}

	// move unit until the collision is solved (maximum by unit's velocity as we
	// are assuming the unit was in a no-collision state before)
	bool stillColliding = (!collisionDir.empty()); // don't check when there are no colliding pixels
	int correctionX = 0; // total correction to solve collision in this direction
	while (stillColliding && abs(correctionX) <= maximum.x)
	{
		correctionX += pixelCorrection.x;

		vector<MapCollisionEntry>::const_iterator entryPtr;
		for (entryPtr = collisionDir.begin(); entryPtr != collisionDir.end(); ++entryPtr)
		{
			pixel = entryPtr->pos;
			pixel.x += correctionX;
			pixel = level->transformCoordinate(pixel);
			if (pixel.x < 0 || pixel.y < 0 || pixel.x >= colImage->w || pixel.y >= colImage->h)
				continue;

			colColour = GFX::getPixel(colImage,pixel.x,pixel.y);
			if (unit->checkCollisionColour(colColour))
				break;
		}
		if (entryPtr == collisionDir.end()) // all pixel have been checked, so no new collision has been found
			stillColliding = false;
	}

	if (abs(correctionX) < maximum.x)
		correction.x = correctionX;
	unit->collisionInfo.pixels.insert(unit->collisionInfo.pixels.end(),collisionDir.begin(),collisionDir.end());


	/// y-direction
	pixelCorrection = Vector2di(0,0);
	collisionDir.clear();

	for (vector<SimpleDirection>::const_iterator dir = checkPointsY.begin(); dir != checkPointsY.end(); ++dir)
	{
		pixel = unit->getPixel((*dir));
		pixel += unit->velocity;
		pixel.x += correction.x;
		pixel += unit->collisionInfo.positionCorrection;
		pixel = level->transformCoordinate(pixel);

		if (pixel.x < 0 || pixel.y < 0 || pixel.x >= colImage->w || pixel.y >= colImage->h)
			continue;

		colColour = GFX::getPixel(colImage,pixel.x,pixel.y);

		if (unit->checkCollisionColour(colColour))
		{
			// we have a collision
			MapCollisionEntry entry;
			entry.dir = (*dir);
			entry.pos = pixel;
			entry.col = colColour;
			entry.correction = Vector2df(0,0);
			collisionDir.push_back(entry);
			int temp = dir->yDirection();
			// only use direction if not set before or aiming in the same direction as velocity
			if (pixelCorrection.y == 0 || NumberUtility::sign(unit->velocity.y) == temp)
				pixelCorrection.y = temp * -1;
		}
	}

	stillColliding = (!collisionDir.empty()); // don't check when there are no colliding pixels
	int correctionY = 0; // total correction to solve collision in this direction
	while (stillColliding && abs(correctionY) <= maximum.y)
	{
		correctionY += pixelCorrection.y;

		vector<MapCollisionEntry>::const_iterator entryPtr;
		for (entryPtr = collisionDir.begin(); entryPtr != collisionDir.end(); ++entryPtr)
		{
			pixel = entryPtr->pos;
			pixel.y += correctionY;
			pixel = level->transformCoordinate(pixel);
			if (pixel.x < 0 || pixel.y < 0 || pixel.x >= colImage->w || pixel.y >= colImage->h)
				continue;

			colColour = GFX::getPixel(colImage,pixel.x,pixel.y);
			if (unit->checkCollisionColour(colColour))
				break;
		}
		if (entryPtr == collisionDir.end()) // all pixel have been checked, so no new collision has been found
			stillColliding = false;
	}

	correction.y = correctionY;
	unit->collisionInfo.pixels.insert(unit->collisionInfo.pixels.end(),collisionDir.begin(),collisionDir.end());

	unit->collisionInfo.correction = correction;

	unit->hitMap(correction);
}

void Physics::particleMapCollision(const Level* const level, SDL_Surface* const colImage, BaseUnit* const particle) const
{
	Vector2df proPos = particle->position;
	Vector2df correction(0,0);
	Vector2di pixelCorrection(0,0);
	pixelCorrection.x = NumberUtility::sign(particle->velocity.x) * -1;
	pixelCorrection.y = NumberUtility::sign(particle->velocity.y) * -1;

	// x
	bool colliding = true;
	Colour temp;
	if (pixelCorrection.x != 0)
	{
		proPos.x += particle->velocity.x;
		while (colliding && (abs(correction.x) < abs(particle->velocity.x)))
		{
			if (proPos.x + correction.x < 0 || proPos.y < 0 || proPos.x + correction.x >= colImage->w || proPos.y >= colImage->h)
				break;

			temp = GFX::getPixel(colImage,proPos.x + correction.x, proPos.y);

			if (particle->checkCollisionColour(temp)) // collision
			{
				correction.x += pixelCorrection.x;
			}
			else
			{
				colliding = false;
			}
		}
		proPos.x -= particle->velocity.x;
	}
	// y
	if (pixelCorrection.y != 0)
	{
		proPos.y += particle->velocity.y;
		colliding = true;
		while (colliding && (abs(correction.y) < abs(particle->velocity.y)))
		{
			if (proPos.x < 0 || proPos.y + correction.y < 0 || proPos.x >= colImage->w || proPos.y + correction.y >= colImage->h)
				break;

			temp = GFX::getPixel(colImage,proPos.x, proPos.y + correction.y);

			if (particle->checkCollisionColour(temp)) // collision
			{
				correction.y += pixelCorrection.y;
			}
			else
			{
				colliding = false;
			}
		}
	}

	particle->hitMap(correction);
}


/** NOTICE:
The following implementation checks both directions at once instead of one after
another. This, of course, is more accurate, probably a tad faster and has less
quirks and assumptions than the above implementation (and also leads to less copy-pasted
code). BUT on the other hand does not work that well for platformer-type games or
at least not in this, simple implementation.
There are some (different) quirks which I would have to work around and therefore
decided to scrap it. (for example, you "stick" to surfaces)
The code is preserved though and fully functionable, so just replace the above
function with the one below to see how this changes things.
Feel free to use for anything or ask me questions about it (as it is not as well
commented as the above function).
**/
/// TODO: Implement latest changes (the function is not up-to-date)
/*
void Physics::unitMapCollision(SDL_Surface* const colImage, BaseUnit* const unit, const Vector2df& mapOffset) const
{
	Vector2df correction(0,0);
	Vector2di pixelCorrection(0,0); // unit will be moved in this steps until no collision occurs

	/// clear data of previous check
	unit->collisionInfo.clear();

	/// Determine colliding pixels
	// diLEFT to diBOTTOMRIGHT
	for (int dir = 1; dir <= 8; ++dir)
	{
		// current collision pixel
		Vector2df pixel = unit->getPixel(dir) + unit->velocity;
		// pixelCorrection for this pixel (e.g. diTOPLEFT would be corrected to the bottom-right)
		Vector2df temp = SimpleDirection(dir).vectorDirection() * (-1.0f);

		if (pixel.x < 0 || pixel.y < 0 || pixel.x > GFX::getXResolution() || pixel.y > GFX::getYResolution())
			continue;

		Colour colColour = GFX::getPixel(colImage,pixel.x,pixel.y);

		if (unit->checkCollisionColour(colColour))
		{
			// we have a collision
			CollisionEntry entry;
			entry.dir = dir;
			entry.pixel = pixel;
			entry.col = colColour;
			entry.correction = Vector2df(0,0);
			unit->collisionInfo.entries.push_back(entry);
			// only use direction if not set before or aiming in the same direction as velocity
			if (temp.x != 0 && (pixelCorrection.x == 0 || NumberUtility::sign(unit->velocity.x)*-1 == temp.x))
				pixelCorrection.x = temp.x;
			if (temp.y != 0 && (pixelCorrection.y == 0 || NumberUtility::sign(unit->velocity.y)*-1 == temp.y))
				pixelCorrection.y = temp.y;
		}
	}

	/// Calculate correction by moving unit back pixel per pixel
	Vector2df unitVel = unit->velocity;
	bool stillColliding = true;
	while (stillColliding)
	{
		// only correct current movement
		if (unitVel.x ==  0)
			pixelCorrection.x = 0;
		if (unitVel.y == 0)
			pixelCorrection.y = 0;
		if (pixelCorrection.x == 0 && pixelCorrection.y == 0)
		{
			// usually this should not happen as it means there already has been
			// an unsolved collision on the last iteration, but better check for
			// it anyway to prevent an infinite loop
			break;
		}
		unitVel += pixelCorrection;

		vector<CollisionEntry>::const_iterator entryPtr;
		for (entryPtr = unit->collisionInfo.entries.begin(); entryPtr != unit->collisionInfo.entries.end(); ++entryPtr)
		{
			Vector2df pixel = entryPtr->pixel + unitVel - unit->velocity; // unitVel - unitVelocity = pixelCorrection * iteration
			if (pixel.x < 0 || pixel.y < 0 || pixel.x > GFX::getXResolution() || pixel.y > GFX::getYResolution())
				continue;

			Colour colColour = GFX::getPixel(colImage,pixel.x,pixel.y);
			// if unit is still colliding break here and go into next iteration
			if (unit->checkCollisionColour(colColour))
				break;
		}
		if (entryPtr == unit->collisionInfo.entries.end()) // all pixel have been checked, so no new collision has been found
			stillColliding = false;
	}
	correction = unitVel - unit->velocity;

	unit->collisionInfo.correction = correction;

	unit->hitMap();
}
*/


void Physics::playerUnitCollision(const Level* const level, BaseUnit* const player, BaseUnit* const unit) const
{
	/// TODO: Optimize this and remove redundant stuff (aka this is a mess!)
	Vector2df proPosPlayer(player->position + player->velocity);
	Vector2df proPosUnit(unit->position + unit->velocity);
	Vector2df playerSize(player->getSize());
	Vector2df unitSize(unit->getSize());
	float xPos = max(proPosPlayer.x, proPosUnit.x);
	float yPos = max(proPosPlayer.y, proPosUnit.y);
	float xPosMax = min(proPosPlayer.x + playerSize.x, proPosUnit.x + unitSize.x);
	float yPosMax = min(proPosPlayer.y + playerSize.y, proPosUnit.y + unitSize.y);
	if (xPosMax > xPos && yPosMax > yPos)
	{
		float diffX = xPosMax - xPos;
		float diffY = yPosMax - yPos;
		SimpleDirection dir;
		if (player->position.x < unit->position.x)
			dir = diLEFT;
		else
			dir = diRIGHT;
		UnitCollisionEntry temp = {dir,Vector2df(diffX,diffY),player};
		unit->collisionInfo.units.push_back(temp);
		UnitCollisionEntry temp2 = {-dir,Vector2df(diffX,diffY),unit};
		player->collisionInfo.units.push_back(temp2);
		return;
	}

	Vector2df pos2p = level->boundsCheck(player);
	Vector2df pos2u = level->boundsCheck(unit);
	if (pos2p != player->position || pos2u != unit->position)
	{
		proPosPlayer = pos2p + player->velocity;
		proPosUnit = pos2u + unit->velocity;
		xPos = max(proPosPlayer.x, proPosUnit.x);
		yPos = max(proPosPlayer.y, proPosUnit.y);
		xPosMax = min(proPosPlayer.x + playerSize.x, proPosUnit.x + unitSize.x);
		yPosMax = min(proPosPlayer.y + playerSize.y, proPosUnit.y + unitSize.y);
		if (xPosMax > xPos && yPosMax > yPos)
		{
			float diffX = xPosMax - xPos;
			float diffY = yPosMax - yPos;
			SimpleDirection dir;
			if (pos2p.x < pos2u.x)
				dir = diLEFT;
			else
				dir = diRIGHT;
			UnitCollisionEntry temp = {dir,Vector2df(diffX,diffY),player};
			unit->collisionInfo.units.push_back(temp);
			UnitCollisionEntry temp2 = {-dir,Vector2df(diffX,diffY),unit};
			player->collisionInfo.units.push_back(temp2);
		}
	}
}

bool Physics::checkUnitCollision(const Level* const level, const BaseUnit* const unitA, const BaseUnit* const unitB) const
{
	SDL_Rect rectA = unitA->getRect();
	SDL_Rect rectB = unitB->getRect();
	if (rectCheck(rectA,rectB))
		return true;

	// check warped position
	Vector2df posA2 = level->boundsCheck(unitA);
	Vector2df posB2 = level->boundsCheck(unitB);
	if (posA2 != unitA->position || posB2 != unitB->position)
	{
		rectA.x = posA2.x;
		rectA.y = posA2.y;
		rectB.x = posB2.x;
		rectB.y = posB2.y;
		if (rectCheck(rectA,rectB))
			return true;
	}
	return false;
}

///

bool Physics::rectCheck(const SDL_Rect& rectA, const SDL_Rect& rectB) const
{
	if (((rectB.x - rectA.x) < rectA.w && (rectA.x - rectB.x) < rectB.w) &&
			((rectB.y - rectA.y) < rectA.h && (rectA.y - rectB.y) < rectB.h))
		return true;
	return false;
}