I'm getting my feet wet with game development by working on a platformer using Cocos2d for iPhone. I'm struggling a bit in getting collision detection running so that my character will have his jump action cancelled when he hits a platform.
I'm using a technique from this tutorial where I create a separate layer of "meta tiles". The problem is that collision detection does not occur until the character sprite is well within the collidable tile, not on top of it.
I'm using the code below to determine the tile coordinate based on my character sprite's current position:
- (CGPoint) tileCoordForPosition: (CGPoint) position {
int x = position.x / tileMap.tileSize.width;
int y = ((tileMap.mapSize.height * tileMap.tileSize.height) - position.y) / tileMap.tileSize.height;
return ccp(x, y);
}
I tried various techniques, even trying to figure out what tile was below my character using this code:
- (void) update: (ccTime) dt {
BOOL isCollision = NO;
if (firstRun) {
oldY = player.position.y;
firstRun = NO;
}
CGPoint oneTileDown = ccp(player.position.x, player.position.y / 2);
CGPoint tileCoord = [gameplayLayer tileCoordForPosition:oneTileDown];
int tileGid = [gameplayLayer.meta tileGIDAt:tileCoord];
if (tileGid) {
NSDictionary* tileProperties = [gameplayLayer.tileMap propertiesForGID:tileGid];
if (tileProperties) {
NSString* collision = [tileProperties valueForKey:#"Collidable"];
if (collision && [collision compare:#"True"] == NSOrderedSame) {
//CCLOG(#"Collision Below");
isCollision = YES;
if (player.characterState == kStateFalling) {
[player stopAllActions];
}
}
}
}
if (oldY < player.position.y) {
CCLOG(#"Character is jumping");
player.characterState = kStateJumping;
}
else if (oldY > player.position.y) {
CCLOG(#"Character is falling");
player.characterState = kStateFalling;
}
oldY = player.position.y;
}
But the same problem happens: my character jumps, lands inside of the collision tile and is stopped instead of landing on top of the tile.
Is there a better way of checking for collision in a tilemap?
I have the solution to this issue.
In the method (CGPoint) tileCoordForPosition: (CGPoint) position you have to write the following:
int x = position.x / tileMap.tileSize.width;
int y = ((tileMap.mapSize.height * tileMap.tileSize.height + player.contenSize().height / 2) - position.y) / tileMap.tileSize.height;
return ccp(x, y);
player is a sprite from which you have to add half its height.
What you need to do is use CGRectContainRect to check if the player sprite's bounding box is intersecting with and of the tiles where it shouldn't.
Related
While I found many problems that are similar too mine, none of the solutions solved my problem.
I've been experimenting with SDL2 in C++ (Visual C++) and the entity-component-system (ECS). But I just can't figure out the bug in my collision response.
So here it is: My player sometimes gets set back to its origin when it encounters something like a rock (a simple gray tile). But sometimes it goes right through and gets stuck or ends up on the other side.
I can only assume it has something to do with the data changed in between frames, so it isn't always caught. But for the life of me I can't figure it out.
Here is my rectangular detection method:
bool Collision::RectIntersect(const SDL_Rect& a, const SDL_Rect& b, SDL_Rect& intersect)
{
intersect = { 0, 0, 0, 0 };
int leftX = std::max(a.x, b.x);
int rightX = std::min(a.x + a.w, b.x + b.w);
int topY = std::max(a.y, b.y);
int bottomY = std::min(a.y + a.h, b.y + b.h);
if (leftX < rightX && topY < bottomY)
{
intersect = { leftX, topY, rightX - leftX, bottomY - topY };
return true;
}
return false;
}
Here is my snippet where my inputs are handled and subsequently any collision detections are resolved before the code actually moves anything:
void InputComponent::handleEvents(SDL_Event* e)
{
const Uint8 *keyboardState = SDL_GetKeyboardState(NULL);
if (e != nullptr)
{
/*
keyHeld: array of 4 for each direction (+/- x, +/- y (WASD))
hold value true, if pressed down, otherwise false
*/
if (keyboardState[SDL_SCANCODE_A])
{
keyHeld[0] = true;
}
else
{
keyHeld[0] = false;
}
if (keyboardState[SDL_SCANCODE_D])
{
keyHeld[1] = true;
}
else
{
keyHeld[1] = false;
}
if (keyboardState[SDL_SCANCODE_W])
{
keyHeld[2] = true;
}
else
{
keyHeld[2] = false;
}
if (keyboardState[SDL_SCANCODE_S])
{
keyHeld[3] = true;
}
else
{
keyHeld[3] = false;
}
}
/*
tmpVel: Vector to store the assumed velocity in x- and y-direction
*/
Vector2D tmpVel(0.0f, 0.0f);
// left and right (A and D)
if (keyHeld[0] && !keyHeld[1]) // left
{
tmpVel.x = -1.0f;
}
else if (!keyHeld[0] && keyHeld[1]) // right
{
tmpVel.x = 1.0f;
}
else
{
tmpVel.x = 0.0f; // left and right cancel each other out
}
// up and down (W and S)
if (keyHeld[2] && !keyHeld[3]) // up
{
tmpVel.y = -1.0f;
}
else if (!keyHeld[2] && keyHeld[3]) // down
{
tmpVel.y = 1.0f;
}
else
{
tmpVel.y = 0.0f; // up and down cancel each other out
}
/*
check for collision with presumed direction according to tmpVel
*/
SDL_Rect intersection;
// get current player position
SDL_Rect movedPlayer = entity->getComponent<CollisionComponent>().getCollider();
// add trajectory of theoretical movement
movedPlayer.x += static_cast<int>(tmpVel.x * vel_->getSpeed());
movedPlayer.y += static_cast<int>(tmpVel.y * vel_->getSpeed());
bool hasCollided = false;
// collect all collidable objects
for (auto& c : manager_->getGroup(GroupLabel::GR_COLLIDERS))
{
// check player against each collidable tile
//if (SDL_IntersectRect(&movedPlayer, &c->getComponent<CollisionComponent>().getCollider(), &intersection))
if (Collision::RectIntersect(movedPlayer, c->getComponent<CollisionComponent>().getCollider(), intersection))
{
// collision on x-axis
if (intersection.w > 0)
{
// set velocity on x-axis to 0
vel_->setVelocityX(0.0f);
// reset player position back according to width of intersected rectangle
pos_->setPosX(pos_->getPos().x + (static_cast<float>(intersection.w) * (-tmpVel.x)));
}
// collision on y-axis
if (intersection.h > 0)
{
// set velocity on y-axis to 0
vel_->setVelocityY(0.0f);
// reset player position back according to height of intersected rectangle
pos_->setPosY(pos_->getPos().y + (static_cast<float>(intersection.h) * (-tmpVel.y)));
}
hasCollided = true;
}
}
if (!hasCollided)
{
vel_->setVelocity(tmpVel);
}
}
Can anybody put me in the right direction?
What happens when the right edge of the player exactly equals the left edge of the rock? It looks like the collision is not detected, since the test is for (leftX < rightX). So the velocity is updated and the player is moved by the velocity. (It's odd that you simply update the velocity and later move the player instead of just moving them to the new already calculated position.) If you change the check to (leftX <= rightX), does the problem persist?
As far as I can see there are two things wrong with your collision detection. The first is that you're testing (leftX < rightX && topY < bottomY) when you should be testing (leftX <= rightX && topY <= bottomY). If you fix this your code will work in most situations.
The second problem you've got, which may not become apparent straight away, is that your are performing collision detection for discreet points in time. If your player has a large enough velocity vector you may end up with this situation:
Update 1: Player is in front of wall travelling towards it. AABB test shows no collision.
Update 2: Player is behind wall travelling away from it. AABB test shows no collision.
Your AABB test is correct and yet the player has passed through the wall. The naive approach to fixing this is to test more often (update 1.5 may have shown a collision), or to limit player velocity. Both approaches will require a lot of fine tuning especially if you're dealing with objects that can move at different speeds and walls with differing thickness.
A more robust approach is to take account of velocity in your test. Since you know the velocity of your AABB you can project this shape along its velocity vector. If you do this for both AABBs you'll end up with two elongated shapes which you can test against each other. If they overlap then you know that their paths cross and that there may be a collision.
Of course, knowing that there might be a collision is not hugely helpful. The problem is one AABB may be moving very slowly and the other very quickly so even though they both pass through the same space (their elongated shapes intersect) they don't pass through it at the same time.
Figuring out whether they both pass through the same space at the same time is hard, so instead we cheat. If you subtract the velocity of B from the velocity of A and then use this modified velocity to project the elongated shape of A, you can effectively treat B as a stationary object and still get the correct result. Knowing this, your test is now "does B overlap the elongated shape of A?". This is just a simple AABB vs Ngon problem.
While the above will give you a boolean as to whether two moving AABBs collide it will not tell you when they collide which is also useful for calculating things like rebounds.
I would very much recommend the book Real Time Collision Detection by Christer Ericson which is pretty much the go to book on collision detection for any aspiring game developer.
The following is a code snippet from the CD-ROM which accompanies the book. It tests a moving AABB against another moving AABB and also provides a time of first contact.
// Intersect AABBs ‘a’ and ‘b’ moving with constant velocities va and vb.
// On intersection, return time of first and last contact in tfirst and tlast
int IntersectMovingAABBAABB(AABB a, AABB b, Vector va, Vector vb, float &tfirst, float &tlast)
{
// Exit early if ‘a’ and ‘b’ initially overlapping
if (TestAABBAABB(a, b)) {
tfirst = tlast = 0.0f;
return 1;
}
// Use relative velocity; effectively treating ’a’ as stationary
Vector v = vb - va;
// Initialize times of first and last contact
tfirst = 0.0f;
tlast = 1.0f;
// For each axis, determine times of first and last contact, if any
for (int i = 0; i < 3; i++) {
if (v[i] < 0.0f) {
if (b.max[i] < a.min[i]) return 0;
// Nonintersecting and moving apart
if (a.max[i] < b.min[i]) tfirst = Max((a.max[i] - b.min[i]) / v[i], tfirst);
if (b.max[i] > a.min[i]) tlast = Min((a.min[i] - b.max[i]) / v[i], tlast);
}
if (v[i] > 0.0f) {
if (b.min[i] > a.max[i]) return 0;
// Nonintersecting and moving apart
if (b.max[i] < a.min[i]) tfirst = Max((a.min[i] - b.max[i]) / v[i], tfirst);
if (a.max[i] > b.min[i]) tlast = Min((a.max[i] - b.min[i]) / v[i], tlast);
}
// No overlap possible if time of first contact occurs after time of last contact
if (tfirst > tlast) return 0;
}
return 1;
}
The following attribution is required by Elsevier's Software License Agreement:
“from Real-Time Collision Detection by Christer Ericson, published by Morgan Kaufmann Publishers, © 2005 Elsevier Inc”
I am working with the flappy bird demo trying different things just to get to "know each other".
Going through the demo, I've managed to change the direction of the game to vertical scroll moving upwards.
Having reversed the CGFloat to negative values makes my obstacles move upward but once they are out of bounds they do not re-spawn.
If I change the values for a downward scroll they re-spawn as per the update method.
Can someone explain to me what I'm doing wrong with the x to y conversion? Why is the bottom recognized and the top of my screen not?
Thanks in advance
#import "MainScene.h"
static const CGFloat scrollSpeed = -280.f; //upwards
static const CGFloat firstObstaclePosition = -568.f;
static const CGFloat distanceBetweenObstacles = 80;
#implementation MainScene {
CCSprite *_hero;
CCPhysicsNode *_physicsNode;
NSMutableArray *_obstacles;
}
- (void)spawnNewObstacle {
CCNode *previousObstacle = [_obstacles lastObject];
CGFloat previousObstacleYPosition = previousObstacle.position.y;
if (!previousObstacle) {
// this is the first obstacle
previousObstacleYPosition = firstObstaclePosition;
}
CCNode *obstacle = [CCBReader load:#"Obstacle"];
obstacle.position = ccp(0, previousObstacleYPosition + distanceBetweenObstacles);
[_physicsNode addChild:obstacle];
[_obstacles addObject:obstacle];
}
- (void)update:(CCTime)delta {
_hero.position = ccp(_hero.position.x, _hero.position.y + delta * scrollSpeed);//move on Y axis
_physicsNode.position = ccp(_physicsNode.position.x, _physicsNode.position.y - (scrollSpeed *delta));//scroll in Y axis
//spawn more
NSMutableArray *offScreenObstacles = nil;
for (CCNode *obstacle in _obstacles) {
CGPoint obstacleWorldPosition = [_physicsNode convertToWorldSpace:obstacle.position];
CGPoint obstacleScreenPosition = [self convertToNodeSpace:obstacleWorldPosition];
if (obstacleScreenPosition.y < -obstacle.contentSize.height) {
if (!offScreenObstacles) {
offScreenObstacles = [NSMutableArray array];
}
[offScreenObstacles addObject:obstacle];
}
}
for (CCNode *obstacleToRemove in offScreenObstacles) {
[obstacleToRemove removeFromParent];
[_obstacles removeObject:obstacleToRemove];
// for each removed obstacle, add a new one
[self spawnNewObstacle];
}
}
- (void)didLoadFromCCB {
self.userInteractionEnabled = TRUE;
_obstacles = [NSMutableArray array];
[self spawnNewObstacle];
[self spawnNewObstacle];
[self spawnNewObstacle];
}
- (void)touchBegan:(UITouch *)touch withEvent:(UIEvent *)event {
}
#end
I've attached the _physicsNode screenshot from SB.
It looks like your obstacles will be spawning fine if they are a short, constant height, and the distance between them value is large enough. It may be better to incorporate the height of the obstacles to get a more meaningful value of the distance variable. Just a thought.
The line -
obstacle.position = ccp(0, previousObstacleYPosition + distanceBetweenObstacles);
Could be -
obstacle.position = ccp(0, previousObstacleYPosition + distanceBetweenObstacles + previousObstacle.contentSize.height);
As for the problem of the vertical scrolling working downwards and not upwards I believe it is due to this line:
if (obstacleScreenPosition.y < -obstacle.contentSize.height) {
Since this line is responsible for determining when an obstacle is off the screen it has an effect on the spawning of the next obstacle. It makes sense why this line works for downwards scrolling but needs to be changed for upwards scrolling.
Try:
if (obstacleScreenPosition.y > (_physicsNode.contentSize.height + obstacle.contentSize.height)) {
You may or may not need the size of the obstacle depending on where it is anchored.
I hope this works, Good luck.
I have a box2d object that is being moved down the screen via gravity
int32 velocityIterations = 6;
int32 positionIterations = 2;
self.world->Step(dt, velocityIterations, positionIterations);
self.world->ClearForces();
for(b2Body *b = self.world->GetBodyList(); b; b=b->GetNext()) {
if (b->GetUserData() != NULL) {
id object = (id)b->GetUserData();
if([object isKindOfClass:[FallingObject class]])
{
CCSprite *sprite = (CCSprite *)b->GetUserData();
sprite.position = CGPointMake(b->GetPosition().x * PTM_RATIO, b->GetPosition().y * PTM_RATIO);
sprite.rotation = -1 * CC_RADIANS_TO_DEGREES(b->GetAngle());
}
}
}
When the user moves their finger across the screen either left or right i want to move the box2d object left or right while the object is still moving down the screen.
Can anyone suggest the best way to do this. I have tried applying linear velocity but it just seems to shoot of screen.
Any suggestions
Thanks
There some ways to do this, and you need to try the best for your case.
You can apply forces, impulse, or change the body velocity manually just for X parameter:
// x axis force
b2Vec2 xAxisForce = b2Vec2(10, 0);
// Try one of these
b->ApplyForce(xAxisForce, b->GetWorldCenter());
b->ApplyForceToCenter(xAxisForce);
b->ApplyLinearImpulse(xAxisForce, b->GetWorldCenter());
// Or change the body velocity manually
b->SetLinearVelocity(b2Vec2(10, b->GetLinearVelocity().y));
I need to have the Cocos2d camera follow a sprite (attached to a Box2D body) that the user is touching on the screen. As the user is dragging the player around, I need it to be able to go to other parts of the world. This has to be through touch, and not automatic scrolling.
I tried several approaches based on tutorials but nothing seem to address this issue. For example the solution offered here Move CCCamera with the ccTouchesMoved method? (cocos2d,iphone) by #Michael Fredrickson has the entire layer move, but when it moves, the sprites / bodies on the screen have unmatched coordinations and when I test to see if they're touched, the if(fixture->TestPoint(locationWorld)) fails.
I also looked at the tutorials here http://www.learn-cocos2d.com/2012/12/ways-scrolling-cocos2d-explained/ but this also isn't what I'm looking for.
Any help would be greatly appreciated.
EDIT:
I'm accepting Liolik's answer below because it put me on the right track. The last piece of the puzzle, though, is to make the value received from the getPoint method an instance variable, and deduce it from locationWorld which I'm doing the TestPoint against. Like this:
UITouch *myTouch = [touches anyObject];
CGPoint location = [myTouch locationInView:[myTouch view]];
location = [[CCDirector sharedDirector] convertToGL:location];
b2Vec2 locationWorld = b2Vec2(location.x/PTM_RATIO, location.y/PTM_RATIO);
b2Vec2 diff = b2Vec2(difference.x, difference.y);
for (b2Body* b = _world->GetBodyList(); b; b = b->GetNext()) {
b2Fixture* f = b->GetFixtureList();
while(f != NULL) {
if(f->TestPoint(locationWorld-diff)) {
b2MouseJointDef def;
def.bodyA = _groundBody;
def.bodyB = b;
def.target = locationWorld-diff;
def.maxForce = 9999999.0f * b->GetMass();
_mouseJoint = (b2MouseJoint*)_world->CreateJoint(&def);
b->SetAwake(true);
}
f = f->GetNext();
}
}
in update function :
CGPoint direction = [self getPoint:myBody->GetPosition()];
[self setPosition:direction];
- (CGPoint)getPoint:(b2Vec2)vec
{
CGSize screen = [[CCDirector sharedDirector] winSize];
float x = vec.x * PTM_RATIO;
float y = vec.y * PTM_RATIO;
x = MAX(x, screen.width/2);
y = MAX(y, screen.height/2);
float _x = area.width - (screen.width/2);
float _y = area.height - (screen.height/2);
x = MIN(x, _x);
y = MIN(y, _y);
CGPoint goodPoint = ccp(x,y);
CGPoint centerOfScreen = ccp(screen.width/2, screen.height/2);
CGPoint difference = ccpSub(centerOfScreen, goodPoint);
return difference;
}
So if i understand correctly, when the sprite is inside of the middle of the screen, the background is stationary and the sprite follows your finger, but when you scroll toward the edge, the camera starts to pan?
I had something roughly similar in my game Star Digger where there's a ship in the middle of the screen on its own layer that has to fly around the world, and had the same problem when the ship fired bullets into the main world layer.
heres what I did:
float thresholdMinX = winSize*1/3;
float thresholdMaxX = winSize*2/3;
if(touch.x > thresholdMaxX) //scrolling right
{
self.x += touch.x - thresholdMaxX;
}
else if(touchX < thresholdMinX)
{
self.x += thresholdMinX - touchX;
}
else
{
sprite.position = touch;
}
CGPoint spritePointInWorld = ccp(sprite.x - self.x, sprite.y - self.y);
then every time you calculate collisions, you need to recompute the sprites "actual" position in the world, which is its screen position minus the worlds offset, instead of the sprites screen position.
I am working on a hockey game and I am implementing Single Player mode. I am trying to move the "computer's" paddle in offense mode (move towards the ball). I am using CoCos2d and Box2d. I am moving the paddle using MouseJoints. The problem is the Paddle doesnt move at all!
tick is called in init method
[self schedule:#selector(tick:)];
...
- (void)tick:(ccTime) dt
{
_world->Step(dt, 10, 10);
CCSprite *computer_paddle;
CCSprite *ball;
b2Body *computer_paddle_b2Body;
float32 direction;
b2Vec2 velocity;
for(b2Body *b = _world->GetBodyList(); b; b=b->GetNext()) {
if (b->GetUserData() != NULL) {
CCSprite *sprite = (CCSprite *)b->GetUserData();
if (sprite.tag == 1) { //ball
ball = sprite;
static int maxSpeed = 10;
velocity = b->GetLinearVelocity();
float32 speed = velocity.Length();
direction = velocity.y;
if (speed > maxSpeed) {
b->SetLinearDamping(0.5);
} else if (speed < maxSpeed) {
b->SetLinearDamping(0.0);
}
}
if (sprite.tag == 3){ // paddle
computer_paddle = sprite;
computer_paddle_b2Body = b;
}
// update sprite position
sprite.position = ccp(b->GetPosition().x * PTM_RATIO,b->GetPosition().y * PTM_RATIO);
sprite.rotation = -1 * CC_RADIANS_TO_DEGREES(b->GetAngle());
}
}
// update the computer paddle in single player moving it towards the ball using MouseJoint
//move towards the ball
b2Vec2 b2Position = b2Vec2(ball.position.x/PTM_RATIO,ball.position.y/PTM_RATIO);
b2MouseJointDef md1;
md1.bodyA = _groundBody;
md1.bodyB = computer_paddle_b2Body;
md1.target = b2Position;
md1.collideConnected = true;
md1.maxForce = 9999.0 * computer_paddle_b2Body->GetMass();
_mouseJoint = (b2MouseJoint *)_world->CreateJoint(&md1);
computer_paddle_b2Body->SetAwake(true);
Check whether:
a) the body is sleeping
b) the body is a static body
If it is sleeping and you have no other bodies, disable sleeping entirely. Otherwise disable sleeping of the body: body->SetSleepingAllowed(NO)
Note: this is according to Box2D 2.2.1 API Reference which isn't the default in cocos2d 1.0 yet, so the function may be different in your Box2D version.
Also check that your body is dynamic by looking up the b2BodyDef's type member and, if necessary, set it to be dynamic (see the b2BodyType enumeration). I'm not sure what the default is, it should be dynamic but this may depend on the Box2D version.