I'm working on a small iPhone/iPad game with the Cocos2d framework. Basically the idea of the game is very simple, there a ball which is moving at a certain speed. The user can draw a line so that the ball bounces in the opposite direction.
Now I've already have the ball moving and the user can draw a line also. (When he draw a line it becomes a member of an array and dissapears a few seconds later.)
But the question is how to detect a collision between the ball and a line? The line doesn't need to be horizontal or vertical, it can be diagonal also. It all depends on how the user draws this line.
I've the coordinates of the line: see the answer to my previous question: CGRect with an angle
Can you guys point in me right direction?
Thanks in advance!
You can use box2d to detect collisions. Actually, if your ball and these lines will have bodies in b2World, you will be able not to check collisions by yourself. All changes, bounces, etc. physics will done for you. You will only have to synchronize object's view position (also you can synchronize angle) according to the position of it's body in physical world.
You can use the Pixel perfect collision so when ball and line collide it is not check the rect but it check the pixel collision...
in this forum you got that you want..
http://www.cocos2d-iphone.org/forum/topic/18522/page/3
Related
I have two objects: one is a ball, whose velocity is given by a vector of components velocity.x and velocity.y, such that, at every frame, the (x, y) position of the ball gets updated to (x + velocity.x, y + velocity.y); the other is a very thin horizontal rectangle that cannot move. Of course, I'd love the ball to change its trajectory whenever it hits the rectangle either from above or from below.
However, I've run into a problem I don't know how to fix: whenever the ball travels fast enough to go from one side of the rectangle to the other side in just one frame, the collision isn't detected because the ball never actually comes in contact with the rectangle. Being the rectangle very thin, the minimum velocity beyond which this behaviour occurs isn't even too high.
I know this is a problem that usually occurs when you want to keep an object inside the screen: in fact, if you just change the sign of its velocity as soon as it exits the screen, this doesn't necessarily make your object rebound off the side of the window (because it could travel so fast that a part of it gets stuck outside the edge), so you actually have to reposition it inside the window first, and then change the sign of its velocity accordingly. But I cannot use this trick here, because the behaviours of the ball on the two sides of the rectangle are supposed to be different: if the ball hits it from above, it will bounce upwards; if from below, it will bounce downwards. But when the ball manages to go past the rectangle in just one frame, how can I tell the program which side the ball should be repositioned? After all, once that frame is drawn, the program isn't able to know whether the ball came 'from the other side' of the rectangle, or if it's always been on that side.
I hope I managed to explain my problem clearly enough. What can I do to solve it?
Take the previous position of the ball and the current position of the ball, and create a line. Use that line to perform collision detection instead of the ball itself. Test for collision detection between the line and the rectangle.
This is going to be a bit more complicated than testing for collision detection between a circle and a rectangle, but googling "line rectangle collision detection" will return a ton of results. Basically you'll want to break the rectangle down into 4 lines and then check whether each line intersects your path line.
This question might help: How do you detect where two line segments intersect?
I am trying to make a pool game with C and GTK+3.0
game is top-view so there are some circles as pool balls.
I've set image to each circle with Gtk.
now somehow I want to show sphere rotation in my 2D game. I guess there is some tricks with changing the image while moving the ball but I don't know exactly what to do!
I just want my circles seems like 3D sphere when they move. have any idea?
Please try the game development subsection: https://gamedev.stackexchange.com/
If the balls have only one color, then what can convey the notion of motion is either the change of lights (better done in 3D), or the rotation of the number on the ball.
Give a look here to see what was done a few years back on the Amiga computer:
http://www.youtube.com/watch?v=zTQIPFBUFIg
A quick introduction:
We're developing a positioning system that works the following way. Our camera is situated on a robot and is pointed upwards (looking at the ceiling). On the ceiling we have something like landmarks, thanks to whom we can compute the position of the robot. It looks like this:
Our problem:
The camera is tilted a bit (0-4 degrees I think), because the surface of the robot is not perfectly even. That means, when the robot turns around but stays at the same coordinates, the camera looks at a different position on the ceiling and therefore our positioning program yields a different position of the robot, even though it only turned around and wasn't moved a bit.
Our current (hardcoded) solution:
We've taken some test photos from the camera, turning it around the lens axis. From the pictures we've deduced that it's tilted ca. 4 degrees in the "up direction" of the picture. Using some simple geometrical transformations we've managed to reduce the tilt effect and find the real camera position. On the following pictures the grey dot marks the center of the picture, the black dot is the real place on the ceiling under which the camera is situated. The black dot was transformed from the grey dot (its position was computed correcting the grey dot position). As you can easily notice, the grey dots form a circle on the ceiling and the black dot is the center of this circle.
The problem with our solution:
Our approach is completely unportable. If we moved the camera to a new robot, the angle and direction of tilt would have to be completely recalibrated. Therefore we wanted to leave the calibration phase to the user, that would demand takings some pictures, assessing the tilt parameters by him and then setting them in the program. My question to you is: can you think of any better (more automatic) solution to computing the tilt parameters or correcting the tilt on the pictures?
Nice work. To have an automatic calibration is a nice challenge.
An idea would be to use the parallel lines from the roof tiles:
If the camera is perfectly level, then all lines will be parallel in the picture too.
If the camera is tilted, then all lines will be secant (they intersect in the vanishing point).
Now, this is probably very hard to implement. With the camera you're using, distortion needs to be corrected first so that lines are indeed straight.
Your practical approach is probably simpler and more robust. As you describe it, it seems it can be automated to become user friendly. Make the robot turn on itself and identify pragmatically which point remains at the same place in the picture.
I'm currently drawing a 3D solar system and I'm trying to draw the path of the orbits of the planets. The calculated data is correct in 3D space but when I go towards Pluto, the orbit line shakes all over the place until the camera has come to a complete stop. I don't think this is unique to this particular planet but given the distance the camera has to travel I think its more visible at this range.
I suspect its something to do with the frustum but I've been plugging values into each of the components and I can't seem to find a solution. To see anything I'm having to use very small numbers (E-5 magnitude) for the planet and nearby orbit points but then up to E+2 magnitude for the further regions (maybe I need to draw it twice with different frustums?)
Any help greatly appreciated...
Thanks all for answering but my solution to this was to draw it with the same matrices that were drawing the planet since it wasn't bouncing around as well. So the solution really is to code better really, sorry.
I'm looking to create a jog wheel in an iPhone / iPad application. I know that you can subclass UIGestureRecognizer to write your own recognizers. Does anyone know how (mainly the maths behind it) to create one that would detect a circular movement, perhaps in combination with a pan gesture?
Thanks
this question isn't easy. I spend some time thinking of a possible solution:
I think what you need are some key properties you have to set:
The center of the circular movement (in this case no problem, because you know the center of the jog wheel)
A corridor in which the movement should happen.
so you need the inner radius and the outer radius.
Now you have something like this (unfortunately I haven't got enough reputation so only the link: http://img17.imageshack.us/img17/4416/bildschirmfoto20100721u.png
Now the maths behind this starts:
First of all you arrange the corridor in four quarters:
From 0° to 90°
From 90° to 180°
From 180° to 270°
From 270° to 360°
For each quarter you have to figure out when the finger is moving (let's say that the 0°-line is from the center point straight to the top):
if the finger is in the first quarter you know if the x changes to the left that the rotation must be anti-clockwise. If the x changes to the right the rotation must be clockwise.
Apply this logic for all quarters. Now you know if the jog wheel is moved clockwise or anti-clockwise. You have to make sure, that the finger is never leaving the corridor (if you test this logic and the movement stops because of leaving the corridor, make the corridor bigger - Thanks to CrystalSkull for his comment: Use 44px as a minimum width for the corridor to apply to the Human Interface Guidelines).
Sumary
So now you can conclude that you need a center point and a corridor the finger can move in.
You have to figure out in which quarter the finger is in and find out (using the x-value) if the rotation is clockwise or anti-clockwise.
I hope this helps you a little bit.