C# - My Collision code won't result in the player stopping in his tracks

Question

I have been working on a C# & SFML remake of one of my LWJGL engines. So far it's going great, but, when I tried to copy/convert over my collision code, things didn't go so well.

Here's my code for the player/entity class, bounding box, and the game code.

Entity:

    using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using SFML.Graphics;
using SFML.System;
using SFML.Window;

namespace FastSrc_CS.Core
{
    public class FSEntity
    {
        public Vector2f Position, Size;
        public Color EColor;

        public RectangleShape sprite;

        public BoundingBox Bounds;

        public bool canMove;
        public float VelX, VelY;

        public FSEntity()
        {

        }

        public virtual void Init(Vector2f pos, Vector2f size, Color color)
        {
            Position = pos;
            Size = size;
            EColor = color;

            sprite = new RectangleShape();
            sprite.FillColor = EColor;
            sprite.Position = Position;
            sprite.Size = Size;
            //sprite.Origin = new Vector2f(size.X / 2, size.Y / 2);

            Bounds = new BoundingBox(Position, Size);
        }

        public void SetVelX(float x)
        {
            VelX = x;
        }

        public void SetVelY(float x)
        {
            VelY = x;
        }

        public Vector2f GetOrigin()
        {
            return new Vector2f(Size.X / 2, Size.Y / 2);
        }

        public virtual void Update()
        {

        }

        public void UpdatePos()
        {
            Position.X += VelX;
            Position.Y += VelY;
            sprite.Position = Position;
            Bounds.UpdateBounds(Position, Size);
        }

        public virtual void Render(RenderWindow w)
        {
            w.Draw(sprite);
        }
    }
}

Player:

    using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using SFML.Graphics;
using SFML.System;
using SFML.Window;

namespace FastSrc_CS
{
    class Player : Core.FSEntity
    {
        public float speed = 6f;

        public override void Init(Vector2f pos, Vector2f size, Color color)
        {
            canMove = true;
            base.Init(pos, size, color);
        }

        public override void Update()
        {
            base.Update();

            Movement();

            Position.X += VelX;
            Position.Y += VelY;
            sprite.Position = Position;
            Bounds.UpdateBounds(Position, Size);
        }

        public void Movement()
        {
            if (Keyboard.IsKeyPressed(Keyboard.Key.A) && canMove == true)
            {
                SetVelX(-speed);
                SetVelY(0);
            }
            else if (Keyboard.IsKeyPressed(Keyboard.Key.D) && canMove == true)
            {
                SetVelX(speed);
                SetVelY(0);
            }
            else if (Keyboard.IsKeyPressed(Keyboard.Key.W) && canMove == true)
            {
                SetVelY(-speed);
                SetVelX(0);
            }
            else if (Keyboard.IsKeyPressed(Keyboard.Key.S) && canMove == true)
            {
                SetVelY(speed);
                SetVelX(0);
            }
            else
            {
                SetVelX(0);
                SetVelY(0);
            }
        }

        public override void Render(RenderWindow w)
        {
            base.Render(w);
        }
    }
}

Bounding Box:

    using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using SFML.Graphics;
using SFML.System;
using SFML.Window;

namespace FastSrc_CS.Core
{
    public class BoundingBox
    {
        public FloatRect Rectangle;

        public BoundingBox(Vector2f pos, Vector2f size)
        {
            Rectangle = new FloatRect(pos, size);
        }

        public bool Collide(BoundingBox b)
        {
            bool col = false;

            if (this.Rectangle.Intersects(b.Rectangle))
            {
                col = true;
            }
            else
            {
                col = false;
            }

            return col;
        }

        public void UpdateBounds(Vector2f pos, Vector2f size)
        {
            Rectangle.Width = size.X;
            Rectangle.Height = size.Y;
            Rectangle.Left = pos.X;
            Rectangle.Top = pos.Y;
        }
    }
}

Game:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using FastSrc_CS.Core;
using SFML.Graphics;
using SFML.System;
using SFML.Window;

namespace FastSrc_CS
{
    public class Game : FSGame
    {
        Player p = new Player();
        Wall w = new Wall();

        public override void Init()
        {
            p.Init(new Vector2f(400, 300), new Vector2f(32, 32), Color.Red);
            w.Init(new Vector2f(100, 100), new Vector2f(32, 32), Color.Blue);

            Entities.Add(p);
            Entities.Add(w);
        }

        public override void Update()
        {
            Console.WriteLine(p.Position.X);

            //COLLISION CODE FOR WALLS
            if (p.Bounds.Collide(w.Bounds))
            {
                //Right Collision
                if (p.VelX > 0)
                {
                    Console.WriteLine("Right Collision");
                    p.canMove = false;
                    p.Position.X = w.Position.X - 32;
                    p.SetVelX(0);
                }
                else if (p.VelX < 0)
                {
                    Console.WriteLine("Left Collision");
                    p.canMove = false;
                    p.Position.X = w.Position.X + 32;
                    p.SetVelX(0);
                }

                if (p.VelX == 0)
                {
                    p.canMove = true;
                }
            }

            Entities.ForEach(k => k.Update());
        }

        public override void Render(RenderWindow w)
        {
            Entities.ForEach(k => k.Render(w));
        }
    }
}

The issue lies within the "game" class in this region:

        //COLLISION CODE FOR WALLS
        if (p.Bounds.Collide(w.Bounds))
        {
            //Right Collision
            if (p.VelX > 0)
            {
                Console.WriteLine("Right Collision");
                p.canMove = false;
                p.Position.X = w.Position.X - 32;
                p.SetVelX(0);
            }
            else if (p.VelX < 0)
            {
                Console.WriteLine("Left Collision");
                p.canMove = false;
                p.Position.X = w.Position.X + 32;
                p.SetVelX(0);
            }

            if (p.VelX == 0)
            {
                p.canMove = true;
            }
        }

When I run this, the player will stop moving, but he will be slightly implanted into the wall. I know what you're thinking, "move the if statement that make p.canMove = true outside of the collision's if statement." I have tried this, and it results in the player bouncing back-and-forth with the cube. I have tried different methods to the point where I thought about leaving this code out. I decided to revert back to Stack Overflow to see if someone could help me out. Thanks in advance.

tobahhh · Accepted Answer · 2018-04-05T03:09:04.113

I don't think the problem with your code is your engine at all - given the result and, after scanning the code, it seems to be fine. Since your player clips into the wall, the hard-coded value of 32 for both your player and your wall, chances are, is incorrect. Try this:

        if (p.VelX > 0)
        {
            Console.WriteLine("Right Collision");
            p.canMove = false;
            //move the right of our player to the left of the wall by setting
            //his x to the wall's x minus his width.
            p.Position.X = w.Position.X - p.Size.Width;
            p.SetVelX(0);
        }
        else if (p.VelX < 0)
        {
            Console.WriteLine("Left Collision");
            p.canMove = false;
            //Move the left of our player to the right of the wall, or
            //the wall's x plus the wall's width
            p.Position.X = w.Position.X + w.Size.Width;
            p.SetVelX(0);
         }

I hope this helped.

EDIT

Actually, I think I found another problem. When you change the player’s position after moving his X after collision detection, you forget to call the UpdatePos() method. Thus, you are moving his position but not his actual rectangle, which may be causing an error. Rather, after you move his x, immediately call UpdatePos()

While you did show me that it was smarter to use the players size rather than hard code it, the result is still the same. I'm honestly not sure how to fix my issue. — VocableAce, Apr 05 '18 at 02:21
Okay, after reading this, I realized what you were saying. After I move the position, i should call `UpdatePos()`. Well I did so, and It works like a charm. Thank you so much. — VocableAce, Apr 08 '18 at 19:35

C# - My Collision code won't result in the player stopping in his tracks

1 Answers1