Tip jar: your first Server Object

note

Server Objects run on ck-exec.

This page builds the village square's tip jar. Every villager can drop a coin in, and everyone sees the same running total. The total is worth keeping on the server, so nobody can tip a thousand coins from a modified client. You use only the editor and Blueprints; the one piece of code is a few lines of Rust that you paste.

Before you start you need:

• a project with the Crowdy SDK, on the Dev backend, where your players can sign in (see Player sign-in);
• Crowdy Studio signed in to your app, for the Deploy step (see Server Compute).

Make the Server Object

1. In the Content Browser, click Add, then Crowdy.
2. Pick Server Object. The new asset is named CSO_NewServerObject.
3. Rename it CSO_TipJar and double-click it. The asset editor opens.
4. In the Variables section of the Server Object panel, click +.
5. In Details, set Variable Name to Total.
6. Leave its type on Integer and its Default Value on 0.
7. Leave the eye at the end of the Total row open, so it is Visible to Players.
8. In the Functions section, click +.
9. In Details, set Name to Tip.
10. Leave Callable By on Players.
11. In the Inputs header, click +, and rename the new NewParam to Amount. Leave it an Integer.
12. In the Outputs header, click +, and rename the new NewParam to Total. Leave it an Integer.
13. Select Type Settings, the first row of the Server Object panel.
14. In Details, set Type Name to tip_jar, or click Use tip_jar beside it.
15. Click Save.

The panel now shows the variable Total with an open eye, and the function Tip with (Amount) returns Total beside it. The definition asset page explains every setting.

Write what Tip does

1. In the asset editor's toolbar, click Generate. It writes the server code under Server/tip_jar/ in your project.

2. Open the Server Code tab. It shows logic.rs, where Tip refuses with "not written yet".

3. Click in the code, press Ctrl+A to select it all, and paste this over it:

   use crate::*;
   use ckx_sdk::prelude::*;
   
   impl Functions for TipJarState {
       fn tip(&mut self, _ctx: &Ctx, _call: &Call<'_>, params: TipParams) -> Result<TipReply> {
           if params.Amount < 1 || params.Amount > 100 {
               return Err(Error::new("a tip is 1 to 100 coins"));
           }
           self.Total = self.Total.saturating_add(params.Amount);
           Ok(TipReply { Total: self.Total })
       }
   }

4. Click Save on the tab.

Tip adds the amount to Total and answers with the new total. It refuses a tip of 0 or of a thousand, and the server checks that, not the game. Write its server logic says what each line does.

Put it on the server

1. In the asset editor's toolbar, click Deploy. It sends every Server Object type in the project, and asks first.
2. Read the dialog, which should say it adds tip_jar, and click Yes.
3. Wait for the status line to say "Deployed as version" and a number.

Deploy builds the code on the server and makes it live for your app at once. If it fails, the build output opens, usually with a mistake in the pasted code. The Server Compute page has the rest.

Make the actor

1. In the Content Browser, click Add, then Blueprint Class, then Actor.
2. Name it BP_TipJar and double-click it.
3. In the Components panel, click Add and choose Crowdy Server Object.
4. With the component selected, in Details, under Server Object, set Definition to CSO_TipJar.
5. Leave Instance Mode on Instance Id.
6. Set Instance Id to lobby.

Every BP_TipJar with the Instance Id lobby, on every player's machine, now shares one tip jar. A different id is a different jar.

Show the total

1. Open the Event Graph.
2. Right-click in the graph, type Total, and choose On Total Changed (CSO_TipJar) under Server Objects.
3. Drag from Event BeginPlay's execution pin to the Bind pin of the new node.
4. Drag from the node's Changed pin, type Print String and choose it.
5. Drag from the Total pin of the node to In String of Print String. The editor adds the conversion from Integer to String.

Loading Blueprint...

Event BeginPlay, On Total Changed, Print StringDownload .txt

Pan a Blueprint figure with the right mouse button. Press Copy nodes, then Ctrl+V in your own event graph.

The node runs Changed once as soon as the jar is ready, with the current total, and again after every change. You wired Bind once and there is nothing to unbind.

Tip from the keyboard

1. Click Class Defaults in the toolbar.
2. In Details, under Input, set Auto Receive Input to Player 0, so this actor hears the local player's keys.
3. Back in the Event Graph, right-click, type T, and choose the T key event under Input, Keyboard Events.
4. Drag from its Pressed pin, type Tip, and choose Call Tip (CSO_TipJar).
5. Set its Amount pin to 1.
6. Drag from On Success, type Print String, and choose it.
7. Drag from the Total output pin of Call Tip to its In String.
8. Click the small arrow at the bottom of Call Tip to show its Reason pin. Drag from On Failed, add another Print String, and drag Reason to its In String.
9. Click Compile, then Save.

Loading Blueprint...

T, Call Tip (Amount 1), Print String on On Success and On FailedDownload .txt

Neither node needs a Target wired: they use this actor's own component. On Success runs when the server has added the coin, with the new total. On Failed runs with the reason if the server refused, or could not be reached. The Blueprint page says what Outcome and Retryable tell you.

Play it with two players

1. Drag BP_TipJar from the Content Browser into your level.
2. Open the dropdown beside the Play button, choose Advanced Settings, and under Multiplayer Options set Number of Players to 2.
3. Click Play. Both windows are players of your app, so each has to be signed in the way your game signs players in.
4. Watch the two screens. Each prints the jar's total, 0 the first time, as soon as the jar is ready.
5. Click in one window and press T.
6. The window you pressed in prints 1 twice, once from On Success and once from Changed. The other window prints 1 once, from Changed.
7. Press T in the other window, and both print 2.

Both windows read the one jar on the server, and On Total Changed told each of them. The total is not kept anywhere in your Blueprint; the server holds it.

Where to go next

• Next: a shared boss. Many players hit one boss, the server refuses hits while it is defeated and brings it back on a timer, and you switch the type off and on from Server Compute to watch everyone recover.
• Make a second variable, such as LastTipper as a String, keep its eye open, and use On LastTipper Changed the same way. Add it to logic.rs and Deploy again. After any change to the asset, Generate and Deploy again; see After you change the definition.
• Let only a leader call a function, with Callable By set to Leader: Access, members and timers.
• If the whole game should share one jar, with no Instance Id to choose, tick Only One Instance in the asset: Only One Instance.
• For a widget that shows the total with no actor, use Find By Asset: Where the object comes from.