Custom Collisions

Newbie & Debugging Questions
#1

for the longest time I have been using just rectangles to handle collision, and I was happy with that but I wanted to branch out in to something more complex with polygons using slick2d as the base system.

after some working with it I realized how easy is was compared to what I was doing before, but I ran into a problem. What I want is the ability to slide up slopes with little to no customization of the engine to handle certain shapes.

this is the basis of what I have so far

Entity.class

package Pheniox.Entity;

import java.util.ArrayList;

import org.newdawn.slick.GameContainer;
import org.newdawn.slick.Graphics;
import org.newdawn.slick.geom.Shape;
import org.newdawn.slick.geom.Vector2f;
import org.newdawn.slick.state.StateBasedGame;

import Pheniox.World.World;

public abstract class Entity {
	protected Vector2f position = new Vector2f(0,0);
	protected Vector2f velocity = new Vector2f(0,0);
	protected World world;
	public boolean removed = false;
	private Object entities;
	
	//collision booleans
	protected boolean collideTop,collideLeft, collideBottom,collideRight;
	
	//constructors

	public Entity(float x, float y){
		position.x = x;
		position.y = y;
	}
	
	public void init(World world){
		this.world = world;
		init();
	}
	//removes the player from the world
	public void remove(){
		removed = true;
	}
	
	//Movement methods
	public void move(Vector2f vel, int delta){
		move(vel.x, vel.y, delta);
	}
	//takes 2 floats and moves
	public void move(float xa, float ya, int delta){
		if(xa != 0 && ya != 0){
			move(xa, 0,delta);
			move(0,ya,delta);
			return;
		}
		
		boolean canPass = true;
		
		collideTop = false;
		collideLeft = false;
		collideBottom = false;
		collideRight = false;
		
		
		ArrayList<Entity> entities = world.getEntities();
		
		for(Entity e: entities){
			if(e != this){
				if(this.getCollisionBox(xa * delta, ya * delta).intersects(e.getCollisionBox(e.velocity.x * delta,e.velocity.y * delta))){
					canPass = false;
				
			
		}
		if(xa > 0 && !canPass){
			collideLeft = true;
		}
		if(xa < 0 && !canPass){
			collideRight = true;
		}
		if(ya > 0 && !canPass){
			collideBottom = true;
		}
		if(ya < 0 && !canPass){
			collideTop = true;
		}
	}
}
		
		
		
		if(canPass){
		this.position.x += delta * xa;
		this.position.y += delta * ya;
		}
		
	}
	//render methods
	public void render(GameContainer gc, Graphics g){
		renderEntity(gc,g);
	}
	//update methods
	public void update(GameContainer gc, StateBasedGame sbg , int delta){
		move(velocity.x,velocity.y,delta);
		updateEntity(gc,sbg,delta);
	}
	
	//abstract classes
	public abstract void init();
	public abstract void renderEntity(GameContainer gc,Graphics g);
	public abstract void updateEntity(GameContainer gc, StateBasedGame sbg, int delta);
	public abstract Shape getCollisionBox(float xa, float ya);
}

the collision box shape is declared in “getCollisionBox(float xa, float ya)”
when being extends by other classes

basicaly what I want is say in a 2d platformer the ability to go up slopes, and I want it to just inheret to the entity class and not have certain cases that make it happen.

any help would be appreciated.

#2

Ok first off I’d recommend not creating that list of entities every single time you call the move method. Its going to create unnecessary slow downs since you have to create the object every single time.

For your slope problem, I’d recommend just getting the theta of the slope using the cosine if its a right triangle, and then using that angle and the opposite side of the triangle to see how much you need to rotate the entity for it to look realistic. Now, I’ve never actually tried this so i have no idea if that would work.

For none right triangle slopes, I have no idea but maybe you should use pixel perfect collision. Maybe it would work.