I'm just trying to program a game with Box2D/ SDL2 & C++. Unfortunately, I am not really getting on with a problem. In the game there are boxes (b2_dynamicBody) that are generated at the click of a mouse. These then fall down. The character is in the middle and when it is moved I create speed X and Y with
m_pCamera->SetLinearVelocity(b2Vec2(z.B. x = 0.0f, y = 10.0f));
I then add within the game loop to any speed of my own box the speed of the character.
ObjectIterator>SetLinearVelocity(ObjectIterator->GetLinearVelocity() + m_pCamera->GetLinearVelocity());
Unfortunately, there are always funny results and I don't know exactly where I need to look.
When I move the player the falling boxes velocity is slowing down!
Here is a source code excerpt :
for (boxit = m_pBoxList.begin(); boxit != m_pBoxList.end(); boxit++) {
if ((*boxit)->getBody()->GetType() == b2_kinematicBody) {
(*boxit)->getBody()->SetLinearVelocity(b2Vec2(0,0));
}
if((*boxit)->getBody()->GetType() == b2_dynamicBody && m_pCamera->getBody()->GetLinearVelocity().x != 0.0f) {
(*boxit)->getBody()->SetLinearVelocity(m_pCamera->getBody()->GetLinearVelocity());
}
else {
(*boxit)->getBody()->SetLinearVelocity(b2Vec2((*boxit)->getBody()->GetLinearVelocity().x + m_pCamera->getBody()->GetLinearVelocity().x, (*boxit)->getBody()->GetLinearVelocity().y + m_pCamera->getBody()->GetLinearVelocity().y));
}
(*boxit)->Update();
(*boxit)->Render();
(*boxit)->RenderOutline();
if ((*boxit)->getBody()->GetLinearVelocity().y == 0.0f) {
(*boxit)->getBody()->SetType(b2_kinematicBody);
}
}
Screenshot:
screenshot / error description
Related
Hey my player isn't falling while I'm pressing any of movement inputs while I'm falling. Just stands still and moves right or left.
Just watch the video; Video
My movement code;
if (right == true) {
p_pBody.body->SetLinearVelocity(b2Vec2(5, 0));
}
else
{
p_pBody.rect.setPosition(p_xPos * s_METPX, p_yPos * s_METPX); // Set The SFML Graphics
}
if (left == true) {
p_pBody.body->SetLinearVelocity(b2Vec2(-5, 0));
}
else
{
p_pBody.rect.setPosition(p_xPos * s_METPX, p_yPos * s_METPX); // Set The SFML Graphics
}
You're setting the vertical velocity to 0 when you're pressing right or left. That's the second coordinate of b2Vec2. If you want to have gravity, replace that zero with the vertical velocity the block has when the buttons are not being pressed.
I added touch input for my game's character. The camera moves when a player's finger is dragged across the screen. However, when the joysticks are used to move, the camera doesn't move at the same time.
When I do the same code with Blueprints the code works and the camera still moves. When I drag the touch while pressing the joystick to move, I think that there is a problem in the ETouchIndex::Type. This is because in the BP when I use the finger index given in the touch event, it works. However, when I only use touch 1 as the finger index, it does not work. I think if I put that index in my CPP code it will work too, but where can I find the finger index? Can anyone please help me?
//here's my touch code that executes every tick.
FVector2D TouchLocation;
APlayerController* ActivePlayerController = UGameplayStatics::GetPlayerController(this, 0);
ActivePlayerController->GetInputTouchState(TouchType, TouchLocation.X, TouchLocation.Y, IsTouched);
if (!IsTouched)
{
DidOnce = false;
}
if (IsTouchMoved())
{
if (!DidOnce)
{
ActivePlayerController->GetInputTouchState(TouchType, PrevX, PrevY, IsTouched);
DidOnce = true;
}
ActivePlayerController->GetInputTouchState(TouchType, X, Y, IsTouched);
float FinalRotYaw = (X - PrevX) * UGameplayStatics::GetWorldDeltaSeconds(this) * 20;
float FinalRotPitch = (Y - PrevY) * UGameplayStatics::GetWorldDeltaSeconds(this) * 20;
AddControllerYawInput(FinalRotYaw);
AddControllerPitchInput(FinalRotPitch);
ActivePlayerController->GetInputTouchState(TouchType, PrevX, PrevY, IsTouched);
}
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've successfully implemented dragging a sprite on the screen, by simply remembering touch position on touchbegan and translating sprite by currentTouchPoint - startingTouchPoint, which gives me nice dragging. But now I want to sprite track my finger instead so it also should rotate. This would give me an advantage of making user able to rotate sprite as well as drag it around with just one finger.
I was getting unexpected results, but I've ran into this code:
http://www.freeactionscript.com/2011/01/mouse-follow-with-easing-smooth-rotation-v2/
There's a demo so you could try it on the browser.
It's pretty much the same I need except sprite should be a lot faster (near the finger all the time) and stop after reaching it's destination instead of orbiting around (while holding touch). I've tried to port it to cocos2d-x, but it doesn't work the same. Well, updatePosition() looks good, sprite is going where it should be pretty much, but updateRotation() is a total mess. It's rotating in strange directions and sometimes even makes a full very fast circle in opposite direction.
onTouchBegan:
//check if any sprite is touched and then assign it to draggedItem
onTouchMove:
_destinationX = touchPoint.x;
_destinationY = touchPoint.y;
onTouchEnd:
//make draggedItem nullptr
void CreatorScene::update(float delta){
if(draggedItem != nullptr){
updateItemPosition();
updateItemRotation();
}
}
void CreatorScene::updateItemRotation()
{
// calculate rotation
_dx = draggedItem->getPositionX() - _destinationX;
_dy = draggedItem->getPositionY() - _destinationY;
// which way to rotate
float rad = atan2(_dy, _dx);
if(_dy < 0) rad += 2 * M_PI;
float rotateTo = CC_RADIANS_TO_DEGREES(rad);
// keep rotation positive, between 0 and 360 degrees
if (rotateTo > draggedItem->getRotation() + 180) rotateTo -= 360;
if (rotateTo < draggedItem->getRotation() - 180) rotateTo += 360;
// ease rotation
_trueRotation = (rotateTo - draggedItem->getRotation()) / ROTATE_SPEED_MAX;
// update rotation
draggedItem->setRotation(draggedItem->getRotation() + _trueRotation);
}
void CreatorScene::updateItemPosition()
{
// check if mouse is down
// if (_isActive)
// {
// update destination
// _destinationX = stage.mouseX;
// _destinationY = stage.mouseY;
// update velocity
_vx += (_destinationX - draggedItem->getPositionX()) / MOVE_SPEED_MAX;
_vy += (_destinationY - draggedItem->getPositionY()) / MOVE_SPEED_MAX;
// }
// else
// {
// // when mouse is not down, update velocity half of normal speed
// _vx += (_destinationX - _player.x) / _moveSpeedMax * .25;
// _vy += (_destinationY - _player.y) / _moveSpeedMax * .25;
// }
// apply decay (drag)
_vx *= DECAY;
_vy *= DECAY;
// if close to target, slow down turn speed
if (sqrtf((_dx*_dx)+(_dy*_dy)) < 50)
{
_trueRotation *= .5;
}
// update position
draggedItem->setPosition(draggedItem->getPosition() + Point(_vx, _vy));
}
What's wrong here? How can I achieve such a smooth movement?
Edit:
Functionality that I want to exactly achieve is here:
https://www.youtube.com/watch?v=RZouMyyNGG8
You can see it on 2:10.
I am trying to create a 2D platformer (Mario-type) game and I am some having some issues with handling collisions properly. I am writing this game in C++, using SDL for input, image loading, font loading, etcetera. I am also using OpenGL via the FreeGLUT library in conjunction with SDL to display graphics.
My method of collision detection is AABB (Axis-Aligned Bounding Box), which is really all I need to start with. What I need is an easy way to both detect which side the collision occurred on and handle the collisions properly. So, basically, if the player collides with the top of the platform, reposition him to the top; if there is a collision to the sides, reposition the player back to the side of the object; if there is a collision to the bottom, reposition the player under the platform.
I have tried many different ways of doing this, such as trying to find the penetration depth and repositioning the player backwards by the penetration depth. Sadly, nothing I've tried seems to work correctly. Player movement ends up being very glitchy and repositions the player when I don't want it to. Part of the reason is probably because I feel like this is something so simple but I'm over-thinking it.
If anyone thinks they can help, please take a look at the code below and help me try to improve on this if you can. I would like to refrain from using a library to handle this (as I want to learn on my own) or the something like the SAT (Separating Axis Theorem) if at all possible. Thank you in advance for your help!
void world1Level1CollisionDetection()
{
for(int i; i < blocks; i++)
{
if (de2dCheckCollision(ball,block[i],0.0f,0.0f)==true)
{
de2dObj ballPrev;
ballPrev.coords[0] = ball.coords[0];
ballPrev.coords[1] = ball.coords[1];
ballPrev.coords[2] = ball.coords[2];
ballPrev.coords[3] = ball.coords[3];
ballPrev.coords[0] -= ball.xspeed;
ballPrev.coords[1] -= ball.yspeed;
ballPrev.coords[2] -= ball.xspeed;
ballPrev.coords[3] -= ball.yspeed;
int up = 0;
int left = 0;
int right = 0;
int down = 0;
if (ballPrev.coords[0] < block[i].coords[0] && ballPrev.coords[2] < block[i].coords[0] && (((ball.coords[1] < block[i].coords[1]) || (ball.coords[3] < ball.coords[1])) || ((ball.coords[1] < block[i].coords[3]) || ball.coords[3] < block[i].coords[3])))
{
left = 1;
}
if (ballPrev.coords[0] > block[i].coords[2] && ballPrev.coords[2] > block[i].coords[2] && (((ball.coords[1] < block[i].coords[1]) || (ball.coords[3] < ball.coords[1])) || ((ball.coords[1] < block[i].coords[3]) || (ball.coords[3] < block[i].coords[3]))))
{
right = 1;
}
if(ballPrev.coords[1] < block[i].coords[1] && block[i].coords[1] < ballPrev.coords[3] && ballPrev.coords[3] < block[i].coords[3])
{
up = 1;
}
if(block[i].coords[1] < ballPrev.coords[1] && ballPrev.coords[1] < block[i].coords[3] && block[i].coords[3] < ballPrev.coords[3])
{
down = 1;
}
cout << left << ", " << right << ", " << up << ", " << down << ", " << endl;
if (left == 1)
{
ball.coords[0] = block[i].coords[0] - 18.0f;
ball.coords[2] = block[i].coords[0] - 2.0f;
}
else if (right == 1)
{
ball.coords[0] = block[i].coords[2] + 2.0f;
ball.coords[2] = block[i].coords[2] + 18.0f;
}
else if (down == 1)
{
ball.coords[1] = block[i].coords[3] + 4.0f;
ball.coords[3] = block[i].coords[3] + 20.0f;
}
else if (up == 1)
{
ball.yspeed = 0.0f;
ball.gravity = 0.0f;
ball.coords[1] = block[i].coords[1] - 17.0f;
ball.coords[3] = block[i].coords[1] - 1.0f;
}
}
if (de2dCheckCollision(ball,block[i],0.0f,0.0f)==false)
{
ball.gravity = -0.5f;
}
}
}
To explain what some of this code means:
The blocks variable is basically an integer that is storing the amount of blocks, or platforms. I am checking all of the blocks using a for loop, and the number that the loop is currently on is represented by integer i.
The coordinate system might seem a little weird, so that's worth explaining.
coords[0] represents the x position (left) of the object (where it starts on the x axis).
coords[1] represents the y position (top) of the object (where it starts on the y axis).
coords[2] represents the width of the object plus coords[0] (right).
coords[3] represents the height of the object plus coords[1] (bottom).
de2dCheckCollision performs an AABB collision detection.
Up is negative y and down is positive y, as it is in most games.
Hopefully I have provided enough information for someone to help me successfully. If there is something I left out that might be crucial, let me know and I'll provide the necessary information. Finally, for anyone who can help, providing code would be very helpful and much appreciated.
Thank you again for your help!
Edit 2: I have updated my code with a new algorithm that checks where the ball was previously before collision. Corner cases work on that single platform correctly now, and when I have a wall of objects, I can slide against it correctly now. The only remaining problem is that there is a small jittering effect that happens when I am on the ground, where the ball is constantly going up and down as if it is being pulled by gravity and then the ball falls back into the object again.
Edit: Here is a URL to an image trying to show the kinds of problems I am having:
http://img8.imageshack.us/img8/4603/collisionproblem.png
In case the explanation in the picture doesn't make too much sense, the ball cannot move left past the corner of an object unless I jump over it. However, the ball can move right, but it gets repositioned to the right of the object while moving, which is not needed. This creates a skipping movement essentially, where it appears as the the ball is skipping over half of the object or so when I move right. If this doesn't make sense, please ask me and I'll try to clarify more.
One problem with your code is that you only detect situations like this:
If the circle happens to be fully inside the block, you don't reposition at all. And that's a problem.
You're trying to think about your simulation as if it were continuous, but keep in mind it's discrete. In general, if you only look at the current state of the ball, you really cannot know which side it collided with. Look at these two possibilities:
The first solution that comes to mind is to look at the last position of the ball as well; more precisely, look at the delta vector. See if the delta vector intersects a wall. If it does, reposition in an axis-aligned direction towards the wall intersected by the delta vector.
Edit: When I said "delta vector", I forgot that you're moving a square and not a single point. So, if you just look at the delta vector of the top-left corner, that's not going to be enough because it may not detect that part of the ball entered a block. Instead, you can look at the delta vectors of all 4 corners.