Projectile Collisions

I'm trying to do some work with projectiles and wonder if anyone else has looked into this. My collision detection seems to work okay when I'm on my own, but falls apart in the Godlands. I've run into a couple of issues so far.

1.) I receive projectiles from object IDs that have never been sent to me client (and never do). How can I track a projectile without knowing it's type from who created it? Is this why the client sometimes sends SHOOTACK with -1 Time field possibly to indicate it can't track a projectile?

2.) What sort of collision detection algorithm does the client use? Currently I'm doing a point (projectile) against an axis aligned bounding box (objects/players). I know the projectile has size though, does it treat it as a sphere or a rotated by angle rectangle?

Code:

2015-10-23 09:08:16.3406|INFO|Oryx.Utilities.Log|Proj 32 [Purple Magic] destroyed by hitting Archer - 'LostAlpha'.
2015-10-23 09:08:16.5412|INFO|Oryx.Utilities.Log|Proj 25 [Green Bolt] destroyed by hitting Trickster - 'SgtWilson'.
2015-10-23 09:08:16.6512|INFO|Oryx.Utilities.Log|Proj 36 [Grey Boomerang] destroyed by hitting Succulent Plant 1.
2015-10-23 09:08:16.8512|INFO|Oryx.Utilities.Log|Proj 41 [Grey Boomerang] destroyed by hitting Rock Grey.
2015-10-23 09:08:17.3013|INFO|Oryx.Utilities.Log|Proj 30 [Green Bolt] destroyed by hitting Knight - 'Yutil'.
2015-10-23 09:08:17.3513|INFO|Oryx.Utilities.Log|Proj 37 [Purple Magic] destroyed by hitting Trickster - 'XxXAKXxX'.
2015-10-23 09:08:17.4214|INFO|Oryx.Utilities.Log|Proj 6 [White Demon Shot] destroyed for life time over.
2015-10-23 09:08:17.5514|INFO|Oryx.Utilities.Log|Proj 120 [White Bullet] destroyed by hitting Succulent Plant 1.
2015-10-23 09:08:17.7414|INFO|Oryx.Utilities.Log|Proj 132 [White Bullet] destroyed by hitting Rock Grey.
2015-10-23 09:08:17.9225|INFO|Oryx.Utilities.Log|Proj 140 [White Bullet] destroyed by hitting Rock Grey.
2015-10-23 09:08:17.9225|INFO|Oryx.Utilities.Log|Proj 124 [White Bullet] destroyed by hitting Small Fir Tree 1.
2015-10-23 09:08:18.0060|INFO|Oryx.Utilities.Log|Proj 42 [Purple Magic] destroyed by hitting Succulent Plant 1.
2015-10-23 09:08:18.0960|INFO|Oryx.Utilities.Log|Proj 55 [Pink Bolt] destroyed by hitting Knight - 'Yutil'.
2015-10-23 09:08:18.1060|INFO|Oryx.Utilities.Log|Proj 112 [White Bullet] destroyed for life time over.
2015-10-23 09:08:18.1060|INFO|Oryx.Utilities.Log|Proj 116 [White Bullet] destroyed for life time over.
2015-10-23 09:08:18.1460|INFO|Oryx.Utilities.Log|Proj 144 [White Bullet] destroyed by hitting Rock Grey.
2015-10-23 09:08:18.1960|INFO|Oryx.Utilities.Log|Proj 9 [White Demon Shot] destroyed for life time over.
2015-10-23 09:08:18.2360|INFO|Oryx.Utilities.Log|Proj 35 [Green Bolt] destroyed by hitting Knight - 'Yutil'.
2015-10-23 09:08:18.3060|INFO|Oryx.Utilities.Log|Proj 136 [White Bullet] destroyed for life time over.
2015-10-23 09:08:18.3460|INFO|Oryx.Utilities.Log|Proj 152 [White Bullet] destroyed by hitting Rock Grey.
2015-10-23 09:08:18.3460|INFO|Oryx.Utilities.Log|Proj 212 [White Bullet] destroyed by hitting Rock Grey.
2015-10-23 09:08:18.5161|INFO|Oryx.Utilities.Log|Proj 128 [White Bullet] destroyed for life time over.
2015-10-23 09:08:18.6866|INFO|Oryx.Utilities.Log|Proj 136 [White Bullet] destroyed for life time over.
2015-10-23 09:08:18.8066|INFO|Oryx.Utilities.Log|Proj 12 [White Demon Shot] destroyed for life time over.
2015-10-23 09:08:18.8866|INFO|Oryx.Utilities.Log|Proj 40 [Green Bolt] destroyed by hitting Paladin - 'KNCHA'.

If you are worried about the size of the projectile, it doesn't change the size of the hit-box (same for any sprite). If I understood what you said at the end, then this probably isn't what you are looking for, but, the sprites for projectiles are rectangles. There is then some data that dictates what angle the sprite will be when it is created.

Sorry if I could not be of help.

Originally Posted by Invader_Zim

So all sprites have a 100 (1.0f) hitbox? A single tile?

So are projectiles treated as points, circles, or rotating rectangles when checking for collision? If you're saying their size doesn't affect it, it sounds like they're treated as points? I noticed in the XML that there's both regular shots and circles that have sizes associated with the projectile, and nothing to describe the geometry of the shape...

- - - Updated - - -

For example, we have both circles and rectangles. How are these collisions calculated?

There are both 8/8, and 16/16 sprites. From your picture, the knight is an 8x8 sprite with scale at 1. His hurt-box is either the entire 8x8 square he is made from, or since the game is capable of giving all sprites an outline, the outline could be his hurt-box. I believe it's the first option, as it's very easy to get hit from a projectile.

The djinn being from a 16x16 sprite palette, also has the same hurt-box as 8x8's. This is speculation from me, as some projectiles clip through the ends of 16x16 monsters. Which is why you shoot the bottom middle of their sprite. However, monsters like that are 16x16 sprites, but their scale is multiplied to make them seem larger. I believe their hurt-box is scaled with them.

Now projectiles I believe are different, their hit-box is more likely to be their outline. Some projectiles can barely miss you, but if they were a square filling the entire 8x8 space they are cropped from, they would seem to hit you.

Purple Box - 8x8 Hurt-Box
Yellow Box - 8x8 Hit-Box
Cyan Outline - Projectiles Hit-box

This shot missed. If the cyan line would've made contact with the purple box, the shot would've hit.

Everything stated is not backed by any sources, and is speculation coming from years of experience with the game.

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Maybe I'm wrong above, perhaps the hurt-box is either an 8x8 or 16x16 square. Which is applied to any monster, however, the size tag only makes the sprite of the monster larger, and doesn't affect the hurt-box.

<size>1</size>

For me at a resolution of 1920x1080, one pixel on the sprite sheet is five pixels on the client.

The part I'm having trouble with believing is the part about the projectile. The reason why, is because in the XML data files, there's nothing there to specify the shape of the projectile - only a size. I could see it being a rotated rectangle by the angle of the projectile, but I don't see how it would know whether or not it's a rectangle, square, or a circle.

Originally Posted by Invader_Zim

For me at a resolution of 1920x1080, one pixel on the sprite sheet is five pixels on the client.

Interestingly enough, I think in the tutorial, the cannons there, seem to have a 1.0 hit radius and so does my character. Basically, if I'm on the same tile as the bullet, I get hit.

Maybe the collision detection really is that bad.... will have to do some more experiments, I can probably fake some packets with k-relay to figure it out.

I collected some images showing that being one pixel off the tile, I was not taking hits. However, I could rotate my screen to make it seem as if the projectile was moving through me.

images

Originally Posted by Invader_Zim

I collected some images showing that being one pixel off the tile, I was not taking hits. However, I could rotate my screen to make it seem as if the projectile was moving through me.

Turn shadows on, projectiles are visibly drawn half a tile above where their true position actually is. Shadow of projectile is the real position.

Okay so, earlier I wasn't thinking in three dimensions. The hit-boxes are on the ground, where the shadow of the projectile is, not the sprite. So hurt-boxes are also on the ground.

In my testing, it was impossible for me to get hit by two rows of turrets. The two shots are exactly one tile apart, so, If my player hurt-box is only one tile large, I can not be hit by both of them.

One theory I have is, hit-boxes are just single points. A dot really, and the hurt-boxes of players/enemies are just tile underneath them where their shadows are.

Only the left projectile is hitting me.

Here is something to back that up...

The inner line is where both projectiles can hit a target, called the "true range". The distance between these two shots is one tile. The size of the projectile does not change the true-range of the weapon.

Originally Posted by Invader_Zim

In my testing, it was impossible for me to get hit by two rows of turrets. The two shots are exactly one tile apart, so, If my player hurt-box is only one tile large, I can not be hit by both of them.

One theory I have is, hit-boxes are just single points. A dot really, and the hurt-boxes of players/enemies are just tile underneath them where their shadows are.

In my testing projectiles being single points and player's being 1 tile hitboxes, works like 90% of the time so seems like a very good approximation if not what the game is actually doing. Of course, my projectile math could be off causing the other 10% to fail, or I could not be accounting for projectile size correctly, or they may not be points. That's what I'm trying to figure out.

Lol, Why not just look in the client to see how its done instead of all this nonsensical theoretical bs?

Originally Posted by FainTMako

Lol, Why not just look in the client to see how its done instead of all this nonsensical theoretical bs?

Because I don't read action script disassembly so it would be slow and tedious. I was hoping someone had already done that work. I did look at projectile.class.asasm and I think I see where it calculates the path, but I didn't see where collisions were being calculated.

Use a swf deobfuscator. You are close. Try to figure out where the projectile class is being instantiated and whhere its being called. Others have done the work for you but I dont think anyone feels like releasing the code.

You can look at a client someone made called Joryx but it doesnt do collisions correctly because the guy tried to do it his own way instead of doing it how the client processes the projectiles which I assume is how the server parses them as well so its probably best to stick to the client code in terms of calculations

Originally Posted by 059

Turn shadows on, projectiles are visibly drawn half a tile above where their true position actually is. Shadow of projectile is the real position.

Interesting, I never really noticed the shadows before, but they're always a single point for all projectiles.

I'm starting to think that projectiles are treated as a point, and that a collision is simply if a projectile and an entity occupy the same tile. This is definitely what I've seen done by other people for static objects (Trees, etc), and it works 100% in my headless client, but maybe it also applies to entities too. I'll have to test it out.

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Originally Posted by FainTMako

Oh is there more you can do on top of RABDASM? Is there a particular de-obfuscator that you recommend?

Yeah I've looked at Joryx (and talked to furyhunter), he never had it fully working. I need to 100% match, or not bother at all, because when you send playerhit's that didn't happen, the server kicks you pretty fast. If I ignore player hits, I can stay connected for like ~60 or so hits. I've also looked at private server source code, which is mostly how I'm doing things, but the problem there is that private server's don't enforce the same checks, so there's really no way of telling that it actually matches with the client does.

I bought my own as3sorcerer license and dont regret it one bit.

Projectile Collisions

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