对象列表上的XNA碰撞检测

Question

I'm trying to detect collision on a list of enemy objects, however it's only working on the last created object. I've tried both :

for (int i = 0; i < enemies.Count; i++)
{
    if (IntersectsPixel(player.rectangle, player.textureData, enemies[i].rectangle, enemies[i].textureData))
    {
        touched = true;
    }
    else
    {
        touched = false;
    }
}

And :

foreach (Enemy enemy in enemies)
{
    if (IntersectsPixel(player.rectangle, player.textureData, enemy.rectangle, enemy.textureData))
    {
        touched = true;
    }
    else
    {
        touched = false;
    }
}

Both of which I'm putting in the Update method. The enemies are created every few seconds so i know the detection works, but once the next one appears, the last one stops working...

Answer 1

you check last item only, you must break loop, when IntersectsPixel true and process the object

for (int i = 0; i < enemies.Count; i++)
{
    if (IntersectsPixel(player.rectangle, player.textureData, enemies[i].rectangle, enemies[i].textureData))
    {
        touched = true;
        break;
    }
}

or use linq to collect all thus objects:

var resTrue = enemies.Where(x=>x.IntersectsPixel(player.rectangle, player.textureData, enemies[i].rectangle, enemies[i].textureData)).ToList();
var resFalse = enemies.Where(x=>!x.IntersectsPixel(player.rectangle, player.textureData, enemies[i].rectangle, enemies[i].textureData)).ToList();

Answer 2

Why don't you implement a property bool Touched in class Enemy ?

That way, you could change your code like this:

if (/*check for collision*/)
    enemy.Touched = true;

Better yet, instead of Touched , implement a method OnTouched(/*arguments*/) , so you can do this:

if (/*check for collision*/)
    enemy.OnTouched(/*arguments*/); // Which would perform any and all necessary actions on the touched object