Ok, i have implemented my basic collision detection system that i posted about here and it works ok. But i discovered that there is one annoying problem. When the player hits a wall they stop (duh!) which means setting their x velocity is set to 0, even if the left or right key is still held down. So if the wall is small enough to jump over and the player jumps then they won't continue to move forward over the wall. I'm not sure at this point whether that behaviour is what i want. It is somewhat realistic because it will mean that the player has to take a run-up to do the jump, but on the other hand it will be really annoying because you won't be able to run fast accross a level/map jumping over things and stuff. You will have to stop at every little bump and make sure you get the jump right. This will really destroy the fast paced feel that i want my game to have. So what are your thoughts on this and does anyone have a solution? I was thinking i could just keep another variable for x & y velocity which is what gets set when the left/right key is pressed. But that would be tightly coupled to the player so it's not the best O-O solution.

what does your collision code look like? Can you post a little about your movement too. In theory if you have Collision is true then velocity = 0; once you jump high enough you should no longer have collision and be able to press the right key to make the x axis increase.

Quote:Original post by wicked357
In theory if you have Collision is true then velocity = 0; once you jump high enough you should no longer have collision and be able to press the right key to make the x axis increase.

Yes, that's true. But because i only set velocity on key down then the player would have to press the left/right key again once they clear the wall. Do you understand what i mean? I have the key repeat rate set to 0 (i'm using SDL) so a key down event is only generated the first time the key is pressed down. That's the best way to do it isn't it.

Quote:Original post by gapern
You also don't need to set velocity to 0 on a collision. If the sprite overlaps with a wall just bump him backwards

Well that's what i thought too but think about what will happen with gravity. If velocity is not set to 0 then it will keep getting acceleration added to it so then if the player walks off a ledge they will fall with the current velocity.

You can check out my other post (in the link) to see some of my code but i will upload the most recent collision code to my website here.

So are you saying that i should only keep the x velocity the same on a collision and set the y velocity to 0? I would prefer not to do such a "hack" because i don't want to code for such specialised cases. I am planning on having wind that will affect the trajectory of missiles. And i will implement it simply as a small x component of gravity. Well what if i want the wind really strong, strong enough to push the players horizontally. Now that will be the same case as what i described but for x velocity.

Quote:Original post by Vorpy
Zeroing out the velocity when hitting the wall is fine, but since the key is still being held down, they should get their velocity back in the next frame.

Yeah, but how exactly would i go about doing that? I am doing physics and collision detection in my PhysicsObject class which i want completely separate from my Player class. The Player just inherits from PhysicsObject in order to have physical behaviour (i'm not sure if it's the best design but i like it). So i want a solution that's better than just storing some variable in PhysicsObject which says "has the player started walking left/right?" because not all PhysicsObjects are players. I want the solution to work for all game objects. Of course, if there is no other solution then i guess i will have to go for a hack but there must be a better way.

@gapern: Sorry if i didn't explained things better but you have to understand that i am trying not to think of the problem in general (i.e. for both x and y axis) even though i have used a specific case (moving horizontally and jumping). So you see, i don't want to code for just this case of jumping and moving forward because the physics should apply to all cases on both axis.

Input, your player, collision, and physics are all entirely separate.
There is no reason why constantly adding a forward impulse to your player while the key is down would cause these things to merge.

If these things are working together (while staying separate) then it means you already have something at a higher level binding them together. Normally it is your state class.

Your game class is responsible for updating the time and input once per frame.
A state class running under the game class is responsible for distributing that input in a state-specific way. Your state class already knows what input, players, collisions, and physics are since it is binding them together.


Every frame, if the key is still down, you apply a forward impulse to the player from the state class. The input class does not know it is being applied to a player; it does not know what a player is.
The physics system does not know how the impulse was applied; it does not know what input is nor what a player is.

So there is no reason for your concerns regarding getting messy dependences and letting objects know about each other who shouldn’t; that will not happen.


L. Spiro