C#•15mo ago

per pixel collision

Hi, I was just curious if anyone might know how to impliment per pixel collision into a project? I'm making a game for my A level Computer Science course - it's c# Monogame. The per pixel code is in each class that needs it, but how would I go about implimenting it in the game itself, and furthermore, should I put the code in a globals class instead? Thanks for any help in advance. I've attached screenshots of my code and where it needs to be used.

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☆ nubbs ☆OP•10/28/24, 7:52 PM

to add to this, I need 3 kinds of collision responses - one for collectables, one to move the player position and one for enemies. I'll attach an image of the game to show what I mean

☆☆ nubbs ☆to add to this, I need 3 kinds of collision responses - one for collectables, on...

TheRanger•10/28/24, 8:18 PM

and you want the 3 of them to collide by pixel?

TTheRanger and you want the 3 of them to collide by pixel?

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☆ nubbs ☆OP•10/28/24, 8:24 PM

yeah, I need the three collision responses to respond to per-pixel collision detection

☆☆ nubbs ☆yeah, I need the three collision responses to respond to per-pixel collision det...

TheRanger•10/28/24, 8:26 PM

well for the enemy, first you have to check if the player's rectangle is intersecting with the enemy's rectangle

TheRanger•10/28/24, 8:27 PM

in line 199 it seems ur trying to check if the player's rectangle is intersecting with itself

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☆ nubbs ☆OP•10/28/24, 8:29 PM

yeah i think i am, i'm a bit confused on the logistics of implimenting it between multiple objects if that makes sense?

TheRanger•10/28/24, 8:32 PM

yeah i get what u mean

TheRanger•10/28/24, 8:36 PM

well first lets start with the enemy

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☆ nubbs ☆OP•10/28/24, 8:36 PM

okay one second, i

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☆ nubbs ☆OP•10/28/24, 8:36 PM

i'll take a screenshot of the enemy collision code in the class itself

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☆ nubbs ☆OP•10/28/24, 8:37 PM

i used the exact same code for the enemy as seen here

TheRanger•10/28/24, 8:39 PM

first try not to allocate a new array every time, this will affect the performance of your game

TheRanger•10/28/24, 8:40 PM

you should only allocate the array once, and add its color data

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☆ nubbs ☆OP•10/28/24, 8:40 PM

okay, so should i put the array outside of the bool method and call it in the method?

TheRanger•10/28/24, 8:42 PM

this is monogame right? the colors of the sprites are already stored when you load them

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☆ nubbs ☆OP•10/28/24, 8:43 PM

ohh okay, i didn't know that. for added context all my knowledge has come off tutorials and whatnot, we were given no beforehand knowledge of the engine. this is my first project also. so should i remove the array entirely?

TheRanger•10/28/24, 8:44 PM

yeah

TheRanger•10/28/24, 8:44 PM

what is EnemyTXTR?

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☆ nubbs ☆OP•10/28/24, 8:46 PM

its the texture for the enemy that the animation is drawn onto

TheRanger•10/28/24, 8:46 PM

is its type Texture2DTexture2D ?

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☆ nubbs ☆OP•10/28/24, 8:46 PM

yes it is

☆☆ nubbs ☆ohh okay, i didn't know that. for added context all my knowledge has come off tu...

Mango lol•10/28/24, 8:47 PM

i hear ya brother!

TheRanger•10/28/24, 8:47 PM

yeah the colors of ur enemy are already stored in that instance of a class

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☆ nubbs ☆OP•10/28/24, 8:47 PM

okay, i'll remove the colour data from the method then and try and rewrite it

TheRanger•10/28/24, 8:48 PM

u can probably access the colors directly

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☆ nubbs ☆OP•10/28/24, 8:49 PM

okay, i'll try that

TheRanger•10/28/24, 8:50 PM

hmm seems u cant do that in monogame

TheRanger•10/28/24, 8:51 PM

then have the Color[] as a field

TheRanger•10/28/24, 8:54 PM

or theres a better way

TheRanger•10/28/24, 8:54 PM

use a bool array

TheRanger•10/28/24, 8:55 PM

each Color represents 4 bytes, we dont need to store 4 bytes in every element of the array, we can store only 1 byte for every element

TheRanger•10/28/24, 8:55 PM

we can use a bool array of trues and falses

TheRanger•10/28/24, 8:56 PM

you only need to check if there's a pixel in this position of the image or not

TheRanger•10/28/24, 8:57 PM

with that way you will save alot of memory allocations for your RAM

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☆ nubbs ☆OP•10/28/24, 8:57 PM

okay thank you! i'll give that a go and see what I can do

thanks!

TheRanger•10/28/24, 8:59 PM

remember, store it as a field instead of a local variable so u can only initialize it once

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☆ nubbs ☆OP•10/28/24, 9:01 PM

i will thanks so much for your help!

TheRanger•10/28/24, 9:05 PM

to greatly enhance maintability its better to encapsulate it in a class

TheRanger•10/28/24, 9:12 PM

public class TexturePixelCollision
{
  bool[] _pixels;
  int width;
  int height;
  public TexturePixelCollision(Texture2D texture)
  {
     var colors = new Color[texture.Width * texture.Height];
     texture.GetData(colors); // store the colors of the texture into this array
     _pixels = new bool[colors.Length];

     for(int i = 0; i < colors.Length; i++)
     {
        if (colors[i].A > 0)
        {
           _pixels[i] = true;
        }
     }
     width = texture.Width;
     height = texture.Height;
  }

  // methods you can put for accessing pixels
  public bool HasPixel(int x, int y)
  {
     return _pixels[y * width + x];
  }
}

public class TexturePixelCollision
{
  bool[] _pixels;
  int width;
  int height;
  public TexturePixelCollision(Texture2D texture)
  {
     var colors = new Color[texture.Width * texture.Height];
     texture.GetData(colors); // store the colors of the texture into this array
     _pixels = new bool[colors.Length];

     for(int i = 0; i < colors.Length; i++)
     {
        if (colors[i].A > 0)
        {
           _pixels[i] = true;
        }
     }
     width = texture.Width;
     height = texture.Height;
  }

  // methods you can put for accessing pixels
  public bool HasPixel(int x, int y)
  {
     return _pixels[y * width + x];
  }
}

TTheRanger ```cs public class TexturePixelCollision { bool[] _pixels; int width; int ...

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☆ nubbs ☆OP•10/28/24, 9:25 PM

this is really heplful thank you so much! I'll trace it through so i fully understand and use it as reference when i rewrite it!

TheRanger•10/28/24, 9:34 PM

for the intersection part u only need to loop on the intersecting pixels between the 2 rectangles, no need to loop on the entire pixels of an object

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☆ nubbs ☆OP•10/28/24, 9:35 PM

okay so, if i make the class static so i can acess it from anywhere, if i then feed in my objects in the gamestate class and set up what I want to happen if they return true, that should work?

TheRanger•10/28/24, 9:36 PM

what class? the one i provided?

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☆ nubbs ☆OP•10/28/24, 9:36 PM

yes that one

TheRanger•10/28/24, 9:36 PM

no? each texture has its own pixel collision

TheRanger•10/28/24, 9:36 PM

sonic has his own texture, egg pawn has its own

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☆ nubbs ☆OP•10/28/24, 9:37 PM

so should I just write what I want to happen when the rectangles collide in the classes or in the state they're used in?

TheRanger•10/28/24, 9:39 PM

what do u mean by state

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☆ nubbs ☆OP•10/28/24, 9:39 PM

hold on let me show you

TheRanger•10/28/24, 9:39 PM

does sonic have multiple textures? ie running textures, jumping texture, etc...

public class TexturePixelCollision { bool[] _pixels; int width; int height; public TexturePixelCollision(Texture2D texture) { var colors = new Color[texture.Width * texture.Height]; texture.GetData(colors); // store the colors of the texture into this array _pixels = new bool[colors.Length]; for(int i = 0; i < colors.Length; i++) { if (colors[i].A > 0) { _pixels[i] = true; } } width = texture.Width; height = texture.Height; } // methods you can put for accessing pixels public bool HasPixel(int x, int y) { return _pixels[y * width + x]; } }

per pixel collision

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