Custom skin example (#462)

# Objective

This PR aims to make it a little bit easier to create player entities
with custom skins. This is common for things like NPCs.

closes #460

# Solution

- Added a new example.
- Added `skin` and `set_skin` methods to `Properties`.

crates/valence_server/src/client.rs

@@ -444,6 +444,32 @@ impl Properties {
     pub fn textures_mut(&mut self) -> Option<&mut Property> {
         self.0.iter_mut().find(|p| p.name == "textures")
     }
+
+    /// Returns the value of the "textures" property. It's a base64-encoded
+    /// JSON string that contains the skin and cape URLs.
+    pub fn skin(&self) -> Option<&str> {
+        self.textures().map(|p| p.value.as_str())
+    }
+
+    /// Sets the value of the "textures" property, or adds it if it does not
+    /// exist. Can be used for custom skins on player entities.
+    ///
+    /// `signature` is the Yggdrasil signature for the texture data. It is
+    /// required if you want the skin to show up on vanilla Notchian
+    /// clients. You can't sign skins yourself, so you'll have to get it from
+    /// Mojang.
+    pub fn set_skin(&mut self, skin: impl Into<String>, signature: impl Into<String>) {
+        if let Some(prop) = self.textures_mut() {
+            prop.value = skin.into();
+            prop.signature = Some(signature.into());
+        } else {
+            self.0.push(Property {
+                name: "textures".to_owned(),
+                value: skin.into(),
+                signature: Some(signature.into()),
+            });
+        }
+    }
 }
 
 #[derive(Clone, PartialEq, Eq, Debug)]

examples/custom_npc.rs

@@ -0,0 +1,109 @@
+use valence::entity::player::PlayerEntityBundle;
+use valence::player_list::{DisplayName, Listed, PlayerListEntryBundle};
+use valence::prelude::*;
+use valence::text::IntoText;
+
+const SPAWN_Y: i32 = 64;
+
+pub fn main() {
+    App::new()
+        .add_plugins(DefaultPlugins)
+        .add_systems(Startup, setup)
+        .add_systems(
+            Update,
+            (
+                init_clients,
+                despawn_disconnected_clients,
+                apply_custom_skin,
+            ),
+        )
+        .run();
+}
+
+fn setup(
+    mut commands: Commands,
+    server: Res<Server>,
+    dimensions: Res<DimensionTypeRegistry>,
+    biomes: Res<BiomeRegistry>,
+) {
+    let mut layer = LayerBundle::new(ident!("overworld"), &dimensions, &biomes, &server);
+
+    for z in -5..5 {
+        for x in -5..5 {
+            layer.chunk.insert_chunk([x, z], UnloadedChunk::new());
+        }
+    }
+
+    for z in -25..25 {
+        for x in -25..25 {
+            layer
+                .chunk
+                .set_block([x, SPAWN_Y, z], BlockState::GRASS_BLOCK);
+        }
+    }
+
+    let layer_id = commands.spawn(layer).id();
+
+    let npc_id = UniqueId::default();
+
+    commands.spawn(PlayerEntityBundle {
+        layer: EntityLayerId(layer_id),
+        uuid: npc_id,
+        position: Position::new((0.0, SPAWN_Y as f64 + 1.0, 6.0)),
+        look: Look::new(180.0, 0.0),
+        head_yaw: HeadYaw(180.0),
+        ..Default::default()
+    });
+
+    // In order for the player entity to be visible to other players, there must
+    // be an entry in the player list.
+    commands.spawn(PlayerListEntryBundle {
+        uuid: npc_id,
+        username: Username("Alice".into()),
+        // adjusts the appearance of the name in the player list only
+        display_name: DisplayName("Alice".color(Color::RED).into()),
+        // makes the fake player not appear in the player list
+        listed: Listed(false),
+        ..Default::default()
+    });
+}
+
+fn init_clients(
+    mut clients: Query<
+        (
+            &mut EntityLayerId,
+            &mut VisibleChunkLayer,
+            &mut VisibleEntityLayers,
+            &mut Position,
+            &mut GameMode,
+        ),
+        Added<Client>,
+    >,
+    layers: Query<Entity, (With<ChunkLayer>, With<EntityLayer>)>,
+) {
+    for (
+        mut layer_id,
+        mut visible_chunk_layer,
+        mut visible_entity_layers,
+        mut pos,
+        mut game_mode,
+    ) in &mut clients
+    {
+        let layer = layers.single();
+
+        layer_id.0 = layer;
+        visible_chunk_layer.0 = layer;
+        visible_entity_layers.0.insert(layer);
+        pos.set([0.0, 65.0, 0.0]);
+        *game_mode = GameMode::Creative;
+    }
+}
+
+fn apply_custom_skin(mut query: Query<&mut Properties, (Added<Properties>, Without<Client>)>) {
+    for mut props in query.iter_mut() {
+        props.set_skin(
+            "ewogICJ0aW1lc3RhbXAiIDogMTY5MTcwNjU3MzE1NiwKICAicHJvZmlsZUlkIiA6ICJlODgyNzRlYjNmNTE0ZDYwYmMxYWQ5NTQ4MTIxODMwMyIsCiAgInByb2ZpbGVOYW1lIiA6ICJBbmltYWxUaGVHYW1lciIsCiAgInNpZ25hdHVyZVJlcXVpcmVkIiA6IHRydWUsCiAgInRleHR1cmVzIiA6IHsKICAgICJTS0lOIiA6IHsKICAgICAgInVybCIgOiAiaHR0cDovL3RleHR1cmVzLm1pbmVjcmFmdC5uZXQvdGV4dHVyZS8xZGUyYzgzZjhmNGZiMzgwNjlmNTVmNTJlNGY4ZWU1ZjA4NjcyMjllYWQ5MWI3ZTc5ZGVmNzU0YjcwZWE5NDMzIiwKICAgICAgIm1ldGFkYXRhIiA6IHsKICAgICAgICAibW9kZWwiIDogInNsaW0iCiAgICAgIH0KICAgIH0KICB9Cn0=",
+            "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",
+        );
+    }
+}