I played around with it for a while, but i simply cant figure it out.
I made a tank that fires missiles, and when the missiles hit the walls, i want them to bounce off, but i want them to bounce off to the right angle.
Right now i havent got any obstacles, the missiles just bounce off when they get outside the viewportRectangle i made.
I have a suspicion that the solution im looking for is quite advanced?
Is there a relativly simple way to do
Thanks in advance :)
Not complicated at all - pseudo-code:
angleObjectHitWall = a;
bounceAngle = 180-a;
Of course this is a very simple calculation, and is totally irrelevant once you start to take into account factors such as material, gravity, walls which aren't straight, etc...
180-a will not work in all instances, unless you are merely working a bounce on a top surface when X is increasing.
One direction to head is the XNA forums or pick up XNA sample code. It is C# and it is for building games. I am not stating you want to build your games in XNA, but it is a great tool, and it is free.
This is really a physics question, so if you are not a physicist (and since you are asking this question, I'm going to take it that you are not) it will require a lot of reading and brainstorming to get it right.
I suggest reading this wikipedia entry to get the basic idea about the depth of your question.
If you only want to make it "look plausible" then I wouldn't worry about it too much and use Bill the Lizard's answer, however if you want to make it right you will have quite an adventure. Don't let this scare you tho! Good luck!
You might think that because your walls are aligned with the coordinate axes that it makes sense to write special case code (for a vertical wall, negate the x-coordinate of the velocity; for a horizontal wall, negate the y-coordinate of the velocity). However, once you've got the game working well with vertical and horizontal walls, probably the next thing you'll think is, "what about walls at arbitrary angles?" So it's worth thinking about the general case from the beginning.
In the general case, suppose your missile has velocity v and hits a wall with surface normal n.
Split v into components u perpendicular to the wall and w parallel to it.
Here u = − v (v.n / n.n) and w = v − u. ("v.n" is the dot product of the vectors v and n. See the link for an explanation of how to compute it. The dot product n.n evaluates to the square of the length of the normal vector; if you always keep your normals in the form of unit vectors then n.n = 1 and you can omit the division.)
After bouncing, the component of motion parallel to the wall is affected by friction f, and the component perpendicular to the wall is affected by elasticity, which can be given in the form of a coefficient of restitution r.
So the velocity after the collision is v' = wf − ur. In a perfectly elastic, frictionless collision, v' = w − u; that is, the motion is reflected about the normal at the point of collision, as in the diagram given in Bill's answer.
This approach works just the same in three dimensions too.
(Obviously this is a very simplified notion of bouncing; it takes no account of angular momentum or deformation. But for many kinds of video games this kind of simplification is perfectly adequate.)
As an aside to the specific physics question you are asking, I would recommend the book "Beginning Math and Physics for Game Programmers" by Wendy Stahler. I found it quite useful for my game/physics programming projects.
The code that accompanies the book is C++ but if you know C#, it would be pretty easy to make the conversion.
Have a good one!