Player Tracked by Turret

[MJRNightmare]

Hi all,

great forum, SGDK rocks!

Ah the challenges of being a noob! I'm trying to get my turret to track me, like it is watching me until I'm close enough for it to fire. ie: if player1 is left and higher than the turret point UpLeft etc...  automatically changing states based on the player location. I tried with rules like if Player X< Turret X, changeState left. Am I banging my head against the wall trying to do it with rules? I get it to work for left, UpLeft, right and UpRight, but adding Y just locks the state to the Up, since player is usually higher than the turrets Y and there is no rule for inbetween angles. I used PushTowardCategory, that made my cannon balls heat seaking missles. Woohoo!

I see atan seems to be the way to figure out the right angle/radian. Is there a built in function or do I have to write one? If I have to write a rule/function, should I do export as something like CustomTurret.cs with my current rule, then replace it function using atan. My math isn't great so go easy on me!

Also is c# Express the way to go as far as editing .cs files? I see you can open projects in Express, can you compile them as well? Any special setup required?

Newest Noob - MJRNightmare! Thx

[TheLaw]

Hey, MJRNightmare:
   I just wanted to welcome you to the forums. Glad to see you're getting a good start. I'm sure someone more qualified than myself will be along to answer your questions shortly.

Meantime I can throw $.02 in on:

Also is c# Express the way to go as far as editing .cs files? I see you can open projects in Express, can you compile them as well? Any special setup required?

Unless you really plan to grab sgdk by the horns and write some heavy custom code, you'll probably not need to be concerned about using c# express. (IMHO).  ...But c# express does offer a very powerful code editor for anyone doing alot of coding. Also, one of the main reasons to use c# express may be to have a debugger.  There should not be any special setup required. Just install c# express and double click the .csproj file.

I'm sure there's more to the story, but that's a quick two cents for ya!
Good Luck!

[bluemonkmn]

Glad to see you joining us in the forums!

I'm trying to get my turret to track me, like it is watching me until I'm close enough for it to fire.
...
I see atan seems to be the way to figure out the right angle/radian. Is there a built in function or do I have to write one?

You may be able use existing rules like this on the turret sprite:
1) Re-configure the sprite states so that the first state is Right (not Up), and the subsequent states step counter-clockwise.
2) Use the PushTowardCategory rule to push the turret toward the player (if you don't include a rule for actually moving the sprite, it will stay put)
3) Use GetPolarStateByVector to switch the sprite into the state appropriate to the direction it was pushed.  StateCount should be 8, and "Output to" should be set to "state", which will set the sprite's current state to the calculated state number.
(I think you'll also have to change some of the other rules that determine which way the shot is fired because they expect clockwise states.

If I have to write a rule/function, should I do export as something like CustomTurret.cs with my current rule, then replace it function using atan. My math isn't great so go easy on me!

You don't have to export/convert anything, but if you have some rules that you want to convert to code, you can use the "Convert to Function" command in the "Sprite Definition" menu.  That will help you set up a file within the project whose functions the rule editor will see as rules.  But really all you need is to create any .cs file in the project that implements functions on class SpriteBase or class GeneralRules (or your specific sprite), and provides a description like the existing functions in SpriteBase.cs do.  (Using the "partial" keywoard, you can add functions to any class in a separate file.)  Then you'll see your functions show up in the list of available rule functions while designing your sprite.  SGDK2 won't even know the difference.

You should be aware of a couple things related to converting rules to code:
1. You can't reverse the process (you can't convert the code back into rules automatically.  You'd have to re-create the rules.)
2. The generated rule functions will be applied to the specific sprite from which they were created.  You may be able to use the same rules on other sprites by changing the generated code to refer to partial class "SpriteBase" instead of "Turret", for example.  But by default the generated code is specific to the sprite type on which it was based.

Also is c# Express the way to go as far as editing .cs files? I see you can open projects in Express, can you compile them as well? Any special setup required?

You can usually edit .cs code within the SGDK2 IDE, but it's not quite as nice as the full-blown C# Express IDE.  If you use the C# Express IDE, be aware that editing code in the C# Express IDE does not update the project.  You'll have to copy/paste the updated code into the SGDK2 IDE because all project data is embedded in the SGDK2 file.  The external files used by the C# Express project are generated from the SGDK2 file for your own use in debugging or whatever else you want to do, but are no longer integrated with the project.

[MJRNightmare]

Thanks for the help/replies bluemonkmn and TheLaw,

I'm going to try it out right after this post. I had tried with GetPolarStatByVector, since it sounded just like an automated version of using atan2, but I had the output going to wrong place, a counter (to use later) I think, not"state". Makes sense to me now.

On a side note making the projectiles aim via pushtowardscat is awesome. Then I added a rule once moving to continue in the same direction so it's not a heat seeking missile anymore. My heat seeking missiles are glad the cannon balls aren't infringing on their turf now.

OK, so c# nice but not a must. Off to turret making town...

Cheers guys!

[MJRNightmare]

Back from Turret town!

I was stumped for 2 days, almost gave on the turret tracking dream. Then I decide to add movebyvelocity to see what the turret would do once in motion. It worked perfectly except for the fact it was following me. So I added a rule to reset pixelX and pixelY. Voila turrets that watch your every move. As GetPolarStateByVector describes, you have to setup the first state in the sprite as right, each subsequent state counter clockwise. The order in the sprite state window matters! 8 states or 72. Right 1st, DonwRight at the bottom of the list.

Then it was time to Fire! Well the cannon balls only went right??? So I set the cannon balls up like the turret with some minor differences. You don't need to reset pixel X and Y since we want them to move. They also needed 8 states, even though they were all the same frame, to fire in the 8 different directions. Didn't make sense to me at the time, but if you used the missiles from the 3D space ship demo, you'd would want the missiles pointing in the same direction as the turret barrel. Then I used PolarAccelerate after the initial PushtowardsCategory, to stop the cannon ball from following the player and continue on straight path.

Once that was all done, I decide to add a second turret and realized, my hard coded X and Y would be a problem, so I changed the rule to get the original pixelX and Y before any other rule and copy it to a parameter, then pass it back just after GetPolarStateByVector rule. Now they are self contained. You can add as many turrets(sprites) as you want, just include them in the Manage Cannon Plan firing sequence.

Then I was on a mission... again... I added the explosions on contact, destroy breakables, collision test with player and health counter. Almost feels like a game! AWESOME and Onwards!!!

Bluemonkmn, can a post the turret test project somewhere? It's about 700KB.

Cheers

[bluemonkmn]

You could submit it as a sample project in the project listing at http://sgdk2.enigmadream.com/

I will have to try implementing this myself.  I don't know why it wouldn't have worked without allowing the turret to move.  It would certainly be simpler if you didn't have to reset the X and Y.  I will let you know if I discover anything interesting.

[bluemonkmn]

I tried it (in my own project) and I think I figured out the problem.  I was seeing some very interesting strange behavior.  The cannon was following (pointing at) me, but with a very delayed reaction.  I was quite puzzled for a moment, and then it occurred to me.  The velocity must have been building up over time so after repeatedly being pushed toward the player for hundreds of frames, the sprite had acquired a huge velocity, and then when the player moved, it took some time for the velocity to adjust sufficiently to point in a new direction.  To resolve the problem, I simply added a rule before the PushTowardCategory rule to limit the velocity.  So here is my final list of rules:
1. LimitVelocity: Maximum = 5
2. PushTowardCategory: Target = (Player category); Index = -1; Force = 50
3. GetPolarStateByVector: FirstState = Right; StateCount = 8; Output to = state
4. If Fire (imported from sprite template)
5. If animating (imported from sprite template)

Now it follows me immediately.  Interesting effect though -- if you want a delayed reaction you could increase the velocity limit.  500 seems to result in a reasonable delay.

[bluemonkmn]

I just tried the project you submitted.  I noticed that sometimes (rarely) the ship would go through solid tiles.  I think it's because you have a rule that can affect velocity between ReactToSolid and Move.  Move should generally be immediately after ReactToSolid to prioritize the avoidance of obstacles above everything else.  ReactToSolid adjusts the velocity very specifically so that when you move with that specific velocity you will be avoiding solids.  But if inertia affects your velocity before you actually move, you can't count on that any more.  For example, if you are moving up and right on a diagonal, and the bottom right corner of the ship just barely manages to avoid the corner of a solid tile, it's possible ReactToSolid won't need to adjust your velocity, but then if your inertia slows your ship down slightly, the bottom right corner of your ship might not quite clear that tile after all.  Then part of your ship ends up inside the tile and now suddenly you're able to move through a solid tile.

[Jam0864]

The delay would be a nice touch actually, of course not for all cannons but perhaps certain types with a faster fire rate, to create inaccuracies.

[MJRNightmare]

Thanks for the feedback guys! I'll make the changes to the cannon and ship. There is a simple timer, it goes off when you cross into the plan, then resets once you are out. I did that just to see the plan was going on and off as entered or left the rectangle. If you are in the plan, they all fire simultaneously at 60. I was more focused on getting the tracking working than looks or playability. Actually I want to make a series of different turrets, plasma, laser, guided etc... Once I get there I'll start adding the subtleties.

The ship going through solids stumped me as well. Good to know now I can squash that issue.

I just made my own cannon graphics with Sketchup, looks great and moves perfectly, but the cannonball is drawing on top of the cannon. Is there a way to set the priority programmatically on dynamic sprites? I tried SelectLastCreatedSprite from the cannon just after the cannon ball is created, then setTargetParam "Priority" lower than the cannon, but still showing up on top. Is there a way to control the priority on the dynamic sprites?

Cheers

[Vincent]

Hi MJRNightmare, 

Unfortunately, the dynamic sprites always have a higher priority than the "static" sprites.  It works like a stack (or an array).
When you launch the layer all the static sprites are entered into the array following their priority.
Example: [0 Ship, 1 Cannon]
Then when you spawn projectiles, they are added at the end of the array.
Example [0 Ship, 1 Cannon, 2 Bullet, 3 Bullet].

Unfortunately, setting the priority at runtime won't alter the array.
When the layer is drawn, the program goes through the list and paints the sprites one after the other:
first the ship, then the cannon, then the first bullet and finally the last bullet.  So the last elements in the array show on top.

There are some work around.  You could make the bullets as static sprites.  Place a couple of them, on the layer, but deactivate them.  When the cannon shoot, activate a bullet, place it in front of the cannon and then make it move.  That is the easiest way to do it I think, but you have to manage a couple of these bullets on each layer.

Another solution is to manage the array of sprites yourself.  But you must not be afraid of coding a new functionality.  I did it in the Taekwon-do remake demo.  You can download it in the project repository if you want to try.  It manages the array but not to achieve exactly what you want.  It is still a good starting point though.

Good luck!

[MJRNightmare]

Hi Vincent,

I love all this head banging prevention from the forum. It's so easy to get bent on finding a solution, only to find out one doesn't exist or you are looking in the wrong direction for the solution. I was thinking maybe make a couple blank frames in the cannon ball animation(so far I haven't got the timing right) or doing an offset or last thought, redraw a dynamic turret on top of the old turret after firing. I'll take a look at you game, nothing like learning from example.

Thanks

[bluemonkmn]

My suggestion is to add a few de-activated cannon balls to the layer and then activate them in the appropriate position when you need to shoot a cannon ball (this was one of Vincent's suggestions).  Originally this was going to be the only way to deal with sprites (so there are a couple functions designed to help with this, I think), but then I realized that it would be a hassle to add inactive sprites on every map where you wanted to use them, especially if you wanted to allow a lot of dynamically created sprites.  So I introduced dynamic sprites.  If you have a lot of maps and want to allow a lot of cannon balls on each map, maybe this isn't the best solution for you, but if you only need a few, it might be OK.  Alternately, you could make some sort of explosion sprite on top of the area where the cannon ball is created that covers up both the ball and the cannon so you can't see which is in front.  Cannons do kind of explode when firing.

[Vincent]

I've another idea that could solve the problem of the cannonball showing on top of the cannon.

Add a TestCollisionMask (or TestCollisionRect) rule on the cannonball.  Set the TestCollision with a sprite category which contains only the cannon. 
When the TestCollision returns something else than -1, then you know that the cannonball and the cannon are over one another.  When this happens, set the ModulateAlpha of the cannonball to 0, so it is invisible. 

When the TestCollision returns -1 then you know they are not over one another, so you set the ModulateAlpha level of the cannonball to 255, it is now visible.

This way, you don't have to manage the array of sprites yourself and you can still use dynamic sprites and don't bother with placing cannonballs on each layer where there is a cannon.  It makes a lot of TestCollisions to handle for the program but unless you have tons of cannonballs existing at the same time, you should be fine.

Anyway, it's worth giving it a try I think!

[bluemonkmn]

Another possibility that durnurd and I arrived at over the weekend is for you to add a function to SpriteCollection.cs in the project's code that looks very much like AddSprite, but instead of appending a sprite to the end of the list, it inserts it at the beginning of the range of dynamic sprites.  This may be what Vincent was talking about earlier with editing code.  It should be relatively simple, though.  I just haven't tried it myself.