Java game collision detection

Update the following part of the code as indicated by the highlighted line:. Next we'll check the value of each brick's status property in the drawBricks function before drawing it — if status is 1 , then draw it, but if it's 0 , then it was hit by the ball and we don't want it on the screen anymore. Update your drawBricks function as follows:. Now we need to involve the brick status property in the collisionDetection function: if the brick is active its status is 1 we will check whether the collision happens; if a collision does occur we'll set the status of the given brick to 0 so it won't be painted on the screen.

Update your collisionDetection function as indicated below:. The last thing to do is to add a call to the collisionDetection function to our main draw function. Add the following line to the draw function, just below the drawPaddle call:. Well, lets take a look at 2 circles colliding and see what we can tell:. If you look at this image you can see the radius of circle 1 the red line and the radius of circle2 the blue line when both circle touch create a line between the centers of both circles.

Any further apart and they would not be touching and any closer and they would be inside each other. This works for any angle too. So now we know if the distance between the circles is smaller than the combined radius of both circles then the circles are colliding.

So how do we work out the distance between the 2 circles? If we draw a line on the x axis from 1 circle to the other and one on the y axis we get this:. Oh look, a triangle…. Now we have a right angled triangle we can use Pythagorean theorem to work out the distance. The code for this is:. We now have the distance between the 2 circles. To make this more useful we can put it all in one method so all we have to do is ask is circle1 touching circle 2 and that is done with this method.

A rectangle in computing usually refers to a shape with 4 corners and 2 parallel sides and is a common shape for use in collision detection due to its simplicity to make and detect collisions with.

So how do we check if 2 rectangles are colliding? Lets take a look at two rectangles about to collide:. Here you can see 2 rectangles that have not collided yet. You can see by the dotted lines that neither the bottom nor right edge fall inside the other rectangle.

This says the rectangle is not colliding. Now you can see that one side of each rectangle is inside the other and this means.. A collision has happened and both sides of each rectangle are inside the other rectangle. First, we must find out where the sides of the rectangle are and we do that using the width, height and position of the rectangle. In our example we will be using the position as the bottom left corner but you could use the center of the rectangle with a little extra math.

So first we need to get the position of all sides:. Now we can tell when 2 sides are inside another rectangle we just need to combine them in a single function we can call whenever we need to:. So we covered circles and rectangles but how about polygons.

From this image you can see that if a convex polygon is colliding then at least 1 of the corners vertices is inside the other polygon. So if we check to see if a corner point is inside the other polygon we know they are colliding There are some edge cases where the points do not fall within the other polygon however this is not covered in this guide as it is only an introduction to collision detection.

So how do we check if a point is inside a polygon? We simply draw a line from the point to somewhere external to the polygon. In the image above you can see we have drawn 3 dashed lines. Find the middle point of your character sprite. Heres my code for this: if isKeyPressed KeyEvent. Sign up or log in Sign up using Google. Sign up using Facebook. Sign up using Email and Password. Post as a guest Name. Email Required, but never shown.

The Overflow Blog. Podcast Making Agile work for data science. Stack Gives Back Featured on Meta. New post summary designs on greatest hits now, everywhere else eventually. Visit chat. Related Hot Network Questions. Question feed. Stack Overflow works best with JavaScript enabled. Accept all cookies Customize settings. The game is finished if the list is empty. If it is not empty, we go trough the list and move all its items.

The destroyed aliens are removed from the list. The checkCollisions method checks for possible collisions. First, we check if the craft object collides with any of the alien objects. We get the rectangles of the objects with the getBounds method. The intersects method checks if the two rectangles intersect. Contents Previous Next Collision detection last modified July 20, In this part of the Java 2D games tutorial we will talk about collision detection.