On tapping on screen I`m gonna apply impulse and angular rotation to sprite to move it to the sides. But after some time OR parameters of physics body attached to sprite should go back to initial (impulse 0, angular speed = 0). What are the best ways to do that (use CCAction or on update detect parameters of physics body and change them to initial)?
If i were in your position, I would probably start a timer at the first collision of the sprite and then use a CCAction to transition to the initial state to make it look smooth. Don't know if its the best way though.
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I try to make 2D game with C++ using SFML. I have drawn sprite and now I want to make that sprite moving automatically to random direction and when it hit wall then it bounce away and change direction. I don't know how to do auto moving sprite what bounce from wall... So please help me.
sf::Sprite has a member function setPosition (float x, float y) that you can use to set the position of the sprite before it's drawn. By moving the sprite to a new position each frame you create the impression of movement, much like a cartoon. By comparing the position of the sprite with the position of other elements in your scene, like the walls, you can calculate when 2 objects hit and take appropriate action. Typically it works like this:
Reset a clock at the beginning of a new frame, you can use sf::Clock or C++'s chrono for example.
Update the position of all elements in the scene that should be moving with something like: ObjectSpeed * Previous frame time
Draw the frame
Save time elapsed for calculating the next frame
Loop
I'm working on a Little Mobile Game with Cocos2D-X and Box2D.
The Point where I got stuck is the movement of a box2d-body (the main actor) and the according Sprite. Now I want to :
move this Body with a constant velocity along the x-axis, no matter if it's rolling (it's a circleshape) upwards or downwards
keep the body nearly sticking to the ground on which it's rolling
keep the Body and the according Sprite in the Center of the Screen.
What I tried :
in the update()- method I used body->SetLinearVelocity(b2Vec2(x,y)) to higher/lower values, if the Body was passing a constant value for his velocity
I used to set very high y-Values in body->SetLinearVelocity(b2Vec2(x,y))
First tried to use CCFollow with my playerSprite, which was also Scrolling along the y-axis, as i only need to scroll along the x-axis, so I decided to move the whole layer which is containing the ambience (platforms etc.) to the left of my Screen and my Player Body & Player sprite to the right of the Screen, adjusting the speed values to Keep the Player in the Center of the Screen.
Well...
...didn't work as i wanted it to, because each time i set the velocity manually (I also tried to use body->applyLinearImpulse(...) when the Body is moving upwards just as playing around with the value of velocityIterations in world->Step(...)) there's a small delay, which pushes the player Body more or less further of the Center of the Screen.
... didn't also work as I expected it to, because I needed to adjust the x-Values, when the Body was moving upwards to Keep it not getting slowed down, this made my Body even less sticky to the ground....
... CCFollow did a good Job, except that I didn't want to scroll along the y-axis also and it Forces the overgiven sprite to start in the Center of the Screen. Moving the whole Layer even brought no good results, I have tried a Long time to adjust values of the movement Speed of the layer and the Body to Keep it negating each other, that the player stays nearly in the Center of the Screen....
So my question is :
Does anyone of you have any Kind of new Approach for me to solve this cohesive bunch of Problems ?
Cheers,
Seb
To make it easy to control the body, the main figure to which the force is applied should be round. This should be done because of the processing mechanism of collisions. More details in this article: Why does the character get stuck?.
For processing collisions with the present contour of the body you can use the additional fixtures and sensors with an id or using category and mask bits. For of constant velocity is often better to use SetLinearVelocity, because even when using impulse velocity gets lost at sharp uphill or when jumping. If you want to use the implulse to change the position of the body, then you need to use the code for the type of this:
b2Vec2 vel = m_pB2Body->GetLinearVelocity();
float desiredVel = mMoveSpeed.x; //set there your speed x value
float velChange = desiredVel - vel.x;
float impulse = m_pB2Body->GetMass() * velChange;
m_pB2Body->ApplyLinearImpulse( b2Vec2(impulse, mMoveSpeed.y), m_pB2Body->GetWorldCenter());
This will allow maintain a constant speed most of the time. Do not forget that these functions must be called every time in your game loop. You can combine these forces, depending on the situation. For example, if the at the beginning you need to make a small acceleration, it is possible to use ApplyForce to the body, and when a desired speed is to use ApplyLinearImpulse or SetLinearVelocity. How correctly to use it is described here: Moving at constant speed
If you use world with the normal gravity(b2Vec2(0, -9.81)), then it should not be a problem.
I answer for this question here: Cocos2D-x - Issues when with using CCFollow. I use this code, it may be useful to you:
CCPoint position = ccpClamp(playerPosition, mLeftBounds, mRightBounds);
CCPoint diff = ccpSub(mWorldScrollBound, mGameNode->convertToWorldSpace(position));
CCPoint newGameNodePosition = ccpAdd(mGameNode->getPosition(), mGameNode->getParent()->convertToNodeSpace(diff));
mGameNode->setPosition(newGameNodePosition);
P.S. If you are new to box2d, it is advisable to read all the articles iforce2d(tuts), they are among the best in the network, as well as his Box2D Editor - RUBE. At one time they really helped me.
I do not know if this is possible but I have an idea:
Keep the circle at a fixed position and move the background relatively. For example, during the course of the game, if the circle has a velocity of 5 towards left then keep circle fixed and move screen with velocity 5 towards right. If circle has 5 velocity towards left and screen has 3 velocity towards right, then keep circle fixed and move screen with 8 velocity towards left and so on. This should allow you to fix the circle at the center of the screen.
Another method would be to translate the entire screen along with the ball. Make everything on the screen an object that can have a velocity. And the x-component of the velocity of the ball (circle) should be the velocity of all other objects. This way, whenever the circle moves, all the other objects will try and keep up with it.
Im using Level Helper and SpriteHelper to create my sprites, images, levels and more importantly animations and physics.
Note, by physics i mean the debugdraw you can see on the simulator that is used for collision detection.
I created a swimmer and added physics to this. Done the code so the physics follows the swimmer around the pool as they move. I have now come to animate the swimmer, make the legs kick etc. Now when i load my game and only the first sprite of the animation is the outline for the physics. So i can see the legs kicking on the swimmer but the debugdraw mesh of the physics doesn't animate as well. Now this is not really a problem until for example my swimmer loses their legs (weird game i know). I change the animation to now a swimmer with no legs but again the physics mesh still shows the legs. So any collisions with stuff still happens where the legs were but they shouldnt. This make sense?
Is there a way to update the physics on the new animation or do i need to remove my whole swimmer and draw a new one?
Any help at all would be great. Thanks
This makes sense, since your sprite uses the same box2d mesh in both states. If you want to have a different collision behavior after altering your Sprite, you should assign another (smaller) mesh body.
Note that even in cocos2d side, your sprite still has the same container box with the new animation.
In order to keep using the SpriteHelper functionality you might want to create 2 different sprite-body sets: one with the full body, then after the "accident" replace it with the legless sprite.
Now, gameplay-wise, my opinion is that there shouldn't be any collision for the legs anyway. since they are moving, players will not find it weird to have them not colliding. You could use a mesh body with no legs and use it for both sprites. Except if you want to have different collisions as a gameplay feature (Like giving the player the choice to cut his legs in order to fit in a smaller cave etc)
i am trying to understand how to implement the physics of sprite when it hit a wall.
lets say i have a wall, and a sprite is is hitting the wall with velocity and gravity using box2d(cocos2d), what is the simplest way to apply a physics of what happen next to the hit, regrading the velocity,gravity,angle of collision, etc ? contact listener ? do i have to calculate what happen next by my self and apply a new speed and force to the body ??
or box2d does it for me ?
any direction would be great.
thanx.
box2d calculates everthing for you. You don't have to worry about what happens after two bodies collide.
If your body hits ground it will bounce as its natural response. You dont have to apply a new force opposite to the gravity. All calculations are done by box2d physics engine. Physics engines are made for that.
In addition to this, if you want you can apply your own forces or impulses like below. It is up to you.
b2Vec2 force = b2Vec2(100, 200);
yourBody->ApplyLinearImpulse(force, yourBodyDefinition.position);
How does one run an animation or a series of pngs(e.g. 4 pngs) on a CCSprite?
Constantly make the CCSprites image be this animation series?
Also, how does one rotate a CCSprite's orientation? e.g. 45 degrees rotation to the left or right
Thanks
Yes, you want to update the sprite's source every so often according to a timer.
For rotating, check out this tutorial: http://www.raywenderlich.com/692/rotating-turrets