Size LabPBR maps from the texture budget

LabPBR normal and specular maps had a fixed 64 MiB budget, so with about
1300 block layers they always loaded at 64 px, however high
textureBudgetMiB was set. They now get a quarter of the current budget:
the default budget keeps the old 64 MiB, and 1536 MiB gives 256 px maps.

Co-Authored-By: Claude Opus 5.5 <[email protected]>
Claude-Session: https://claude.ai/code/session_01XnU6QPo9BpqkYWfY6y5Nwu

crates/horizon-client-render/src/sprites.rs

@@ -144,8 +144,15 @@ pub fn set_labpbr_maps(on: bool) {
 pub fn labpbr_maps() -> bool {
     LABPBR_MAPS.load(std::sync::atomic::Ordering::Relaxed)
 }
-/// Budget for either complete normal or specular image set.
-const MAX_MAP_BYTES: u64 = DEFAULT_TEXTURE_BUDGET / 4;
+/// Budget for either complete normal or specular image set: a quarter of the block textures'
+/// budget, so raising `textureBudgetMiB` sharpens a pack's LabPBR maps along with its colours.
+fn map_bytes(texture_budget: u64) -> u64 {
+    texture_budget / 4
+}
+/// [`map_bytes`] for the budget the next resource load keeps to.
+fn max_map_bytes() -> u64 {
+    map_bytes(TEXTURE_BUDGET.load(std::sync::atomic::Ordering::Relaxed))
+}
 /// Fewer layers than any game has (vanilla's are about 1300): what a map is kept at while
 /// loading assumes at least these many share the array.
 const LAYERS_AT_LEAST: u64 = 1024;
@@ -275,7 +282,7 @@ impl Sprites {
         self.specular.clear();
         let largest_map = self.pbr.iter().flatten().flatten().map(|m| m.0).max();
         self.pbr_size = largest_map.map_or(SPRITE_SIZE, |l| {
-            side_within(l.min(size), layers, MAX_MAP_BYTES)
+            side_within(l.min(size), layers, max_map_bytes())
         });
         if largest_map.is_some() {
             let pbr_size = self.pbr_size;
@@ -783,7 +790,7 @@ fn pbr_map(
         return None;
     }
     let side = w.max(h);
-    let output_side = side_within(side, LAYERS_AT_LEAST, MAX_MAP_BYTES).min(side);
+    let output_side = side_within(side, LAYERS_AT_LEAST, max_map_bytes()).min(side);
     let frames = (0..columns * rows)
         .map(|index| {
             let (x, y) = (index % columns * w, index / columns * h);
@@ -856,6 +863,12 @@ mod tests {
         assert_eq!(side_within(512, 1300, 1), SPRITE_SIZE);
     }
     #[test]
+    fn labpbr_maps_follow_the_texture_budget() {
+        // 1300 layers of 1024 px maps: 64 px at the default budget, 256 px at 1536 MiB.
+        assert_eq!(side_within(1024, 1300, map_bytes(DEFAULT_TEXTURE_BUDGET)), 64);
+        assert_eq!(side_within(1024, 1300, map_bytes(1536 << 20)), 256);
+    }
+    #[test]
     fn a_labpbr_map_selects_whole_texels_and_missing_layers_get_defaults() {
         // Selecting a texel preserves encoded channels, including categorical values.
         let frame = [