I have an arrow sprite, and it is for aiming purposes in my Cocos2d game. Therefore, I want it to point to where the user touches the screen. How do I program the rotation of the sprite so it will rotate to the user's touch location? Thanks!
These tutorials may be helpful:
http://www.learn-cocos2d.com/knowledge-base/cocos2d-iphone-faq/learn-cocos2d-public-content/manual/cocos2d-general/14826-how-to-rotate-a-sprite-in-a-circular-motion/
http://www.raywenderlich.com/2343/how-to-drag-and-drop-sprites-with-cocos2d
Also, this question is asked (with code) and answered (with more code) here: Rotating Sprite with Touch - Cocos2d
I haven't actually done this before, but I have adapted some of my code (that makes a enemy ship face the player ship) to what you need. Hopefully this is correct.
//rotate to face the touch
CGPoint diff = ccpSub(sprite.position, touch.position);
float angleRadians = atanf((float)diff.y / (float)diff.x);
float angleOffset = CC_DEGREES_TO_RADIANS(90);
if(diff.x < 0)
{
angleRadians += angleOffset;
}
else
{
angleRadians -= angleOffset;
}
PengOne's answer (cool name BTW) was great though and I am voting it up because you should make use of it.
Related
I'm having difficulty getting the Chipmunk physics engine to do what I want. The only solution that appears to work requires some heavy vector math. Before diving into that rabbit hole for the other components of my game, I was hoping someone could fill me in on a better way to go about this. The desired gameplay is as follows:
A character moves around a finite space in a top-down view
Movement is always a constant velocity in whatever direction the character faces
The player taps on the screen, which causes the character to 'turn' towards the touched location
The basic idea is like driving a car. You cannot immediately turn around, but instead must first perform a u-turn. That car must also maintain a constant speed. How might I do this? Bonus question: how can you override whatever method chipmunk calls to update a body's position, and is this a good idea?
There is this tutorial on how to do top down controls using specially configure joints:
http://chipmunk-physics.net/tutorials/ChipmunkTileDemo/
It's based on Chipmunk Pro, but the stuff about controlling the character is easily adapted to vanilla Chipmunk. The "Tank" demo that comes with the non-Pro Chipmunk source implements pretty much the same thing if you want to see some C code for it.
You basically want to rotate the orientation of the player more gradual. You could do this at a constant rate, so when you tap the screen it will start rotating at a constant rate until it has reached the right orientation. This would give a circular turn circle. This will however affect your position, so you would have to keep turning until you would be on a collision course with the position you tapped.
The path you would travel would be similar to that of the game Achtung die kurve.
So you would have to save the location and orientation of the player (x, y and phi coordinates). And to determine whether to stop turning you could do something like this:
dx = playerx - tapx;
dy = playery - tapy;
targetAngle = atan2(dy,dx);
if (phi > targetAngle)
{
if (phi - targetAngle > PI) omega = rotate;
else omega = -rotate;
}
else if (phi < targetAngle)
{
if (targetAngle - phi > PI) omega = -rotate;
else omega = rotate;
}
else omega = 0;
For the past days, I've been trying to make a ping pong like game. I have 2 paddles and a ball. All dynamic sprites. Everything's been working well except for one issue I'm having. The ball tends to bounce on the same angle at some point. So there would be times when the player can simply move the paddle on a specific part and the game can go on for a while or might be forever, since the ball doesn't change its angular velocity regardless of which part of the paddle it hits. I'm using a combination of linear and angular velocity to keep the ball moving like so:
if(_isPaused == FALSE)
{
_world->Step(dt, 10, 10);
for(b2Body *b = _world->GetBodyList(); b; b=b->GetNext()) {
if (b->GetUserData() != NULL) {
CCSprite *sprite = (CCSprite *)b->GetUserData();
if(sprite.tag == 2)
{
b2Vec2 dir = b->GetLinearVelocity();
dir.Normalize();
float currentSpeed = dir.Length();
int maxSpeed = 60;
float accelerate = vel;
if(currentSpeed <= maxSpeed)
{
b->SetLinearVelocity(accelerate * dir);
}
sprite.position = ccp(b->GetPosition().x * PTM_RATIO,
b->GetPosition().y * PTM_RATIO);
sprite.rotation = -1 * CC_RADIANS_TO_DEGREES(b->GetAngle());
//Keep sprite from bouncing in a straight angle
b->SetAngularVelocity(_body->GetAngle());
}}}
So my question is, how can I manipulate the angular velocity to keep the ball bouncing on different angles everytime it collides with my paddle? I'm thinking something like getting the current angular velocity then multiplying it with some value but I'm not sure if that's the right way to approach the issue I'm having. Any suggestions or ideas would be greatly appreciated. Thanks in advanced.
The way I see it, you have two options:
Check the location of a collision. If it's close to the top/bottom edge of the paddle, deflect the outgoing velocity by an angular amount proportional to the surface "curvature" at that point. Of course, this is cheating, but if the artwork and code are in agreement, it looks correct. And graphics is "the art of cheating without getting caught".
You could take into account the current velocity of the paddle as well as that of the ball. Eg: if the ball is moving downwards and to the right, and the paddle is moving down, then you can compute the outgoing direction using conservation of linear momentum. Just make sure you restrict the paddle's change in momentum along the horizontal axis to be zero.
Finally, you could combine the above techniques, but now you'd have to use accurate collision detection (not the hack I described in (1) above).
Hope that helps!
A few pointers, you should use SetLinearVelocity() and SetAngularVelocity() rarely. Each alters a property of the body definition, which could make you run into problems later on when things get more complex. It would be better to use ApplyForceToCenter() or ApplyLinearImpulse() in the place of SetLinearVelocity() as these two are much more versatile functions and are a bit more coder-friendly. In my opinion, I don't think you should use b->SetAngularVelocity(_body->GetAngle()); If you wanted to change the angular velocity each time it collided, you could, in your beginContact method, write that every time the body collides with the paddle body, a random angular impulse is applied to the ball, using ApplyAngularImpulse().Hope that helps.
I try to detect collision between two sprite.
if(CGRectIntersectsRect([SpriteA BoundingBox], [SpriteB boundingBox]))
But when i Rotate any sprite than collision detection is not perfect..
I know to use pixel perfect Collision but i have no idea about it.
Please anyone help me for how to detect collision, Give me any block of code if any.
You can use box2d to make it detect all collisions for you
In two ways you can do.
Use box2D body for your sprite. Example: CLICK HERE
Use CGMutablePathRef, and use CGPathContainsPoint() instead of CGRectIntersectsRect.
Example: CLICK HERE
You can also refere the Ray Wenderlich Tutorial for the detection of the Collision between any 2 Box2D bodies.
it's possible! try with CGPath.
I had the same problem. I've resolved with this tutorial: http://bobueland.com/cocos2d/2011/the-magic-of-cgpaths/
for rotate the path try this method, it rotated the path round the center of the boudingBox:
-(CGPathRef) rotateCGPath:(CGPathRef)path corner:(CGFloat)radians
{
CGRect bounds = CGPathGetBoundingBox(path);
CGPoint center = CGPointMake(CGRectGetMidX(bounds), CGRectGetMidY(bounds));
CGAffineTransform transf = CGAffineTransformIdentity;
transf = CGAffineTransformTranslate(transf, center.x, center.y);
transf = CGAffineTransformRotate(transf, -radians);
transf = CGAffineTransformTranslate(transf, -center.x, -center.y);
return CGPathCreateCopyByTransformingPath(path, &transf);
}
after this you detect the collision simple with:
if (CGPathContainsPoint(Collisionpath, NULL, collisionPoint, NO))
{ //is inside the path }
good luck!
I have a maze game that using cocos2d
I have one main sprite that can save "friend" sprite
Once "friend" sprite collide with main sprite, the "friend" sprite will follow main sprite everywhere.
Now I dont know how to make "friend" sprite follow main sprite with static distance and smooth movement.
I mean if main sprite going up, "friend" will be at behind the main sprite.
If main sprite going left, "friend" sprite will be at right of main sprite.
Please help me and share me some code...
You can implement the following behaviour by using the position of your main sprite as the target for the friend sprite. This would involve implementing separation (maintaining a min distance), cohesion (maintaining max distance) and easing (to make the movement smooth).
The exact algorithms (and some more) are detailed in a wonderful behavior animation paper by Craig Reynolds. There are also videos of the individual features and example source code (in C++).
The algorithm you need (it is a combination of multiple simpler ones) is Leader following
EDIT : I have found two straightforward implementations of the algorithms mentioned in the paper with viewable source code here and here. You will need to slightly recombine them from flocking (which is mostly following a centroid) to following a single leader. The language is Processing, resembling java-like pseudcode, so I hope the comprehension should be no problem. The C++ sourcecode I mentioned earlier is also downloadable but does not explicitly feature leader following.
I am not aware of any cocos2d implementations out there.
I have a simple solution kind of working fine. Follow the cocos2d document getting started lesson 2, Your first game. After implement the touch event. Use the following code to set seeker1 to follow cocosGuy:
- (void) nextFrame:(ccTime)dt {
float dx = cocosGuy.position.x - seeker1.position.x;
float dy = cocosGuy.position.y - seeker1.position.y;
float d = sqrt(dx*dx + dy*dy);
float v = 100;
if (d > 1) {
seeker1.position = ccp( seeker1.position.x + dx/d * v *dt,
seeker1.position.y + dy/d * v *dt);
} else {
seeker1.position = ccp(cocosGuy.position.x, cocosGuy.position.y);
}
}
The idea is at every step, the follower just need to move towards the leader at a certain speed. The direction towards the leader can be calculated by shown in the code.
It seems that this is quite a common question, but I can't find a person with my same circumstances. The closest seems to be: OpenGL: scale then translate? and how?.
The problem I'd really like some help with is to do with moving around while zoomed into (and out of) a 2d scene using OpenGl. The code for zooming out is pretty simple:
void RefMapGLScene::zoomOut(){
currentScale = currentScale-zoomFactor;
double xAdjust = (((get_width())*zoomFactor/2));
double yAdjust = ((get_height()*zoomFactor/2));
zoomTranslateX -= xAdjust;
zoomTranslateY -= yAdjust;
}
The code for zooming in is basically the same (add the zoomFactor to currentScale, and increment zoomTranslateX and Y).
The code for rending everything is also simple:
glPushMatrix();
glTranslated(-zoomTranslateX, -zoomTranslateY, 0);
glScaled(currentScale, currentScale, 1);
glTranslated(totalMovedX, totalMovedY, 0);
graph->draw();
glPopMatrix();
Essentially, zoomTranslate stores an adjustment needed to make the screen move a little towards the middle when zooming. I don't do anything nice like move to where the mouse is pointing, I just move to the middle (ie, to the right and up/down depending on your co-ordinate system). TotalMovedX and Y store the mouse movement as follows:
if (parent->rightButtonDown){
totalMovedX += (-(mousex-curx))/currentScale;
totalMovedY += (-(mousey-cury))/currentScale;
}
Dragging while not zoomed in or out works great. Zooming works great. Dragging while zoomed in/out does not work great :) Essentially, when zoomed in, the canvas moves a lot slower than the mouse. The opposite for when zoomed out.
I've tried everything I can think of, and have read a lot of this site about people with similar issues. I also tried reimplementing my code using glOrtho to handle the zooms, but ended up facing other problems, so came back to this way. Could anybody please suggest how I handle these dragging events?
The order of operations matter. Operations on matrices are applied in the reverse order in which you multiplied the matrices. In your case you apply the canvas movement before the scaling, so your mouse drag is also zoomed.
Change your code to this:
glPushMatrix();
glTranslated(-zoomTranslateX, -zoomTranslateY, 0);
glTranslated(totalMovedX, totalMovedY, 0);
glScaled(currentScale, currentScale, 1);
graph->draw();
glPopMatrix();
Also after changing that order you don't have to scale your mouse moves, so you can omit that division by currentScale
if (parent->rightButtonDown){
totalMovedX += (-(mousex-curx));
totalMovedY += (-(mousey-cury));
}