I am making a "shoot them up" game on my iPhone (with planes) and I want to detect a collision between my plane and an ennemy but without applying the physics on them.
If I juste detect the collision with a ContactListener, I can lower my plane's life but it will bounce back after the collision.
If I put my ennemies and my plane on the same fixture groupIndex, there will be no collision and I won't be able to lower my plane's life.
I have found questions like mine but still not answered. Can you help me ??
Thx
I've found the trick !
All I had to do is to set the plane's fixture as a sensor.
myPlaneFixtureDef.isSensor = YES;
Related
I'm trying to make the basic robot arm which can hit the ping pong ball using OpenCv and C++.
I managed to detect the ball and move the robot arm according to XY coordinates using inverse kinematics, but now I need to hit the ball, and that's a hard thing.
I thought that if I'll predict the trajectory of the ball, the things would be easier, but unfortunately, this part doesn't seems easy to me either.
I thought that trajectory equations would be a good way to start, so I measured the distance of the ball between 2 frames, also I found the time between those, the angle between table and ball when the ball hits the table, but I don't know how to predict the future trajectory (or how to implement in C++) and I need some help with this.
Also, if you know any way to hit the ball in 2D it would help me a lot.
Thanks!
I have some questions for correctly implementing a system that add gravity to my player while still detecting and correcting collision with the floor. I understand the basic math for the AABB and adding gravity vector to the players velocity vector then adding it to the position. For some reason when I try the player stops for the first few frames then eventually the velocity builds up to be more than the tile width and it goes through. I guess my real question is how to properly implement the gravity with the collision. Do I make gravity vector 0, 0 when it hits the floor or when I am just standing on the floor my collision detection will constantly move me out of the floor? I really don't know the flow of the logic with this situation.
Edit 1:
I am trying to make the simple engine myself to gain experience with programming. I kind of solved the one problem, I now can stop on the floor. My current logic is:
add gravity to velocity, check for collision, adjust the velocity by the offset of the collision, if any, add velocity to the position then set velocity to 0.
m_velocity += m_gravity;
glm::vec2 mtd = collideWithObject(objectVector);
m_velocity -= mtd;
m_position += m_velocity;
m_velocity.x = 0.0f;
m_velocity.y = 0.0f;
It works but I am not sure if that is the flow, I guess I just want to know what is the most common way to implement this.
For some reason when I try the player stops for the first few frames then eventually the velocity builds up to be more than the tile width and it goes through.
If you are applying physics in increments - such as once every frame - you must account for the infinite increments that exist between each of those points.
For a simple "plane collision", like your floor, don't test if your current AABB collides with the floor. Create the smallest AABB that includes your current AABB and the last AABB. If that box collides, you've collided with the plane.
as #MorphingDragon mentioned, you should consider Box2D, many games use Box2D.
For your question "Do I make gravity vector 0, 0 when it hits the floor or when I am just standing on the floor my collision detection will constantly move me out of the floor? I really don't know the flow of the logic with this situation.". I just assume you know Verlet integration, for calculate your new position, you don't need to change your gravity, [as you know, gravity is everywhere on earth, or you want to do a game in space, ;)] you just need to handle the collision detection logic as "when collision happens, just make the collision point satisfy my constraints", and your constraint should be "all point should not be placed under the floor, otherwise just move it and make it sit on the floor".
The collection detection and constraint solver theory should be very common in modern physical engine and easy to understand and implement.
Hope this help.
Thanks
An
I am building an IOS game in Cocos2d - Chipmunk - Spritebuilder. I need to make a characters orbit around around a point, and I was having quite some difficulty in implementing orbits with real physics.
So far, I have tried two methods, one is creating a distance joint from the player to the planet, and then applying a 90 degree force on the player where an angle is created between the end of the distance joint and an imaginary line drawn at a 90 angle to it. He moves around crazily and this method is not working for me.
I then tried calculating 180 points on the circumference at a radius from the planet (which is the bounds of detecting and implementing its effects on the player) - and then in a scheduled update method [character.physicsbody applyForce:nextCircumferencePoint]; This does not work, as he does not follow the path exactly and is quite far from it. I am thinking that I need to also apply a gravitational force towards the planet which would cause him to circle it. Though I don't know how to calculate that force, apply it, or if it would even help.
A third method which would never work, but was used for testing was to set his position to the next circumference point. He does orbit, but any collision won't work (such as if a piece of space junk goes in his way.) He will simply be positioned right over any other object. This world great if you don't need collisions, are writing your own physics engine. This is not a polished way of doing things, so will avoid it.
Please correct anything I have already done and tell me how it would work, or shed light on other options and how to implement them.
Check out my answer here. It's for box2d, but you can do it with Chipmunk. If bodyA position will change, orbit will be same. You just need to change speed of body movement for your needs, just increase smoothness and slow down your update method.
I'm currently making a 2D pool game where i have to use real physics simulation. I have done the circle collision and elastic collision so far, But I want a formula which can find the collision response velocity, which differs when a ball collides with other at different points thanks in advance.
There are many approaches, but if you can afford to make the balls overlap a bit (that is, to make part of the ball "enter" the other) you can turn it into a spring-damper system and solve with Hooke's law.
Since Hooke's law give you the force, you need to integrate it to find the momentum. Momentum divided by mass is the velocity you're looking for.
Take a look at this excellent intro of spring physics for game development (that also has a link for his intro on numerical integration).
edit: if you're looking for a practical solution I suggest the Box2D physics engine.
Pool collision can be considered as elastic collision throughout the board, with friction slowing down its movement.
Don;t think the collision response in terms of angles to the circle. Using vectors will ease the problem.
The circle-circle collision velocity response is easy:
1. When collision is detected
2. FInd the normal velocity of the balls acting toward the other ball.
3. Interchange the Normal velocity between the two balls
4. Resolve the velocity in x and y direction
A very helpful webiste to find the velocity response in terms of vectors: http://archive.ncsa.illinois.edu/Classes/MATH198/townsend/math.html
I have a simple question about a game I am making using box2D and cocos2D. I started using the physics engine yesterday so I am rather inexperienced with its usage and capabilities. My game involves rolling a ball around the screen using the accelerometer. I want to add holes to the ground that if the ball rolls into, it will then require a greater acceleration via the accelerometer to escape the hole pocket. I've toyed with friction, linear damping, modifying the accelerometer's gravity vector, and tried adding attractive forces but I haven't had too much success and some of it doesn't really simulate well what I want happening. Basically I just want to create some sensors and give them the properties of a small pocket a ball can fall in to. Any tips and advice is much appreciated. Thanks
I suggest you to use Level Helper . Its an awesome tool to create physic based games.
You can find it here
You could take the y position of the ball every frame and if it is below a certain threshold, then it is in a hole. Based off on this, if the ball is in a hole, reduce the sensitivity. When the ball exits the hole, put the sensitivity back to normal.
As for creating the holes, use Vertex Helper to create bodies that will correspond to your sprites.
If you need more explanation, feel free to ask.
Elaborated:
Now, basically in the picture, I am depicting what I tried to describe earlier. All you really have to do is to change the tilt sensitivity if the player's Y position is below a certain point. I just used 50 as an example.
Some pseudocode:
- (void)update:(ccTime)dt
{
if (player.position.y >= 50) { //If the player's y position is above or equal to 50
if (sensitivity != normalSensitivity) { //We don't need to set it every frame, so lets check
sensitivity = normalSensitivity;
}
}
if (player.position.y < 50) { //If player's position is below our threshold of 50
if (sensitivity != limitedSensitivity) { //Check so we don't set the sensitivity every frame
sensitivity = limitedSensitivity;
}
}
}
Now, as far as Vertex Helper is concerned, it is an open source tool (I believe) that helps you define vertices for custom shapes that can then be copied and pasted directly into your box2d or chipmunk cocos2d project. It can be fond here.
I suggest googling around for tutorials on how this is used. It is very simple, but you may need a quick reference to get you started.
Finally, something to remember, is that box2d can only work with convex shapes, not concave.
A convex shape is a shape where in is impossible to draw a line from any vertex to another without passing through the shape itself. Basically something that has no indentations in it.
I hope this helped. I'm not sure I can elaborate anymore than I have, but if you have more specific questions, feel free to ask.