Speed up FontManager loading

src/main/java/org/embeddedt/modernfix/core/config/ModernFixEarlyConfig.java

@@ -89,6 +89,7 @@ public class ModernFixEarlyConfig {
         this.addMixinRule("perf.async_locator", true);
         this.addMixinRule("perf.faster_texture_stitching", true);
         this.addMixinRule("perf.faster_texture_loading", true);
+        this.addMixinRule("perf.faster_font_loading", true);
         this.addMixinRule("perf.kubejs", modPresent("kubejs"));
         this.addMixinRule("perf.faster_singleplayer_load", false);
         /* Keep this off if JEI isn't installed to prevent breaking vanilla gameplay */

src/main/java/org/embeddedt/modernfix/mixin/perf/faster_font_loading/LegacyUnicodeBitmapsProviderMixin.java

@@ -0,0 +1,64 @@
+package org.embeddedt.modernfix.mixin.perf.faster_font_loading;
+
+import com.mojang.blaze3d.platform.NativeImage;
+import net.minecraft.client.gui.font.providers.LegacyUnicodeBitmapsProvider;
+import net.minecraft.resources.ResourceLocation;
+import org.spongepowered.asm.mixin.Final;
+import org.spongepowered.asm.mixin.Mixin;
+import org.spongepowered.asm.mixin.Shadow;
+import org.spongepowered.asm.mixin.injection.At;
+import org.spongepowered.asm.mixin.injection.Inject;
+import org.spongepowered.asm.mixin.injection.Redirect;
+import org.spongepowered.asm.mixin.injection.callback.CallbackInfo;
+import org.spongepowered.asm.mixin.injection.callback.CallbackInfoReturnable;
+
+import java.io.IOException;
+import java.io.InputStream;
+import java.util.Map;
+
+/**
+ * Objective: avoid recomputing locations many times, as well as loading all the font sheets in the constructor
+ * only to do it again later.
+ */
+@Mixin(LegacyUnicodeBitmapsProvider.class)
+public abstract class LegacyUnicodeBitmapsProviderMixin {
+    @Shadow protected abstract ResourceLocation getSheetLocation(int i);
+
+    @Shadow @Final private Map<ResourceLocation, NativeImage> textures;
+    private final ResourceLocation[] glyphLocations = new ResourceLocation[256];
+
+    private ResourceLocation currentCharIdx;
+
+    @Redirect(method = "<init>", at = @At(value = "INVOKE", target = "Lnet/minecraft/client/gui/font/providers/LegacyUnicodeBitmapsProvider;getSheetLocation(I)Lnet/minecraft/resources/ResourceLocation;"))
+    private ResourceLocation storeCurrentCharIdx(LegacyUnicodeBitmapsProvider provider, int i) {
+        ResourceLocation location = getSheetLocation(i);
+        currentCharIdx = location;
+        return location;
+    }
+
+    @Redirect(method = "<init>", at = @At(value = "INVOKE", target = "Lcom/mojang/blaze3d/platform/NativeImage;read(Lcom/mojang/blaze3d/platform/NativeImage$Format;Ljava/io/InputStream;)Lcom/mojang/blaze3d/platform/NativeImage;"))
+    private NativeImage storeLoadedFontSheet(NativeImage.Format format, InputStream stream) throws IOException {
+        NativeImage image = NativeImage.read(format, stream);
+        textures.put(currentCharIdx, image);
+        return image;
+    }
+
+    @Inject(method = "<init>", at = @At("RETURN"))
+    private void clearLocation(CallbackInfo ci) {
+        currentCharIdx = null;
+    }
+
+    @Inject(method = "getSheetLocation", at = @At("HEAD"), cancellable = true)
+    private void useCachedLocation(int idx, CallbackInfoReturnable<ResourceLocation> cir) {
+        int cachedIdx = idx / 256;
+        if(cachedIdx >= 0 && cachedIdx < glyphLocations.length && glyphLocations[cachedIdx] != null)
+            cir.setReturnValue(glyphLocations[cachedIdx]);
+    }
+
+    @Inject(method = "getSheetLocation", at = @At("RETURN"))
+    private void saveCachedLocation(int idx, CallbackInfoReturnable<ResourceLocation> cir) {
+        int cachedIdx = idx / 256;
+        if(cachedIdx >= 0 && cachedIdx < glyphLocations.length)
+            glyphLocations[cachedIdx] = cir.getReturnValue();
+    }
+}

src/main/resources/modernfix.mixins.json

@@ -113,6 +113,7 @@
     "perf.cache_model_materials.MultipartMixin",
     "perf.faster_texture_stitching.StitcherMixin",
     "perf.faster_texture_loading.TextureAtlasMixin",
+    "perf.faster_font_loading.LegacyUnicodeBitmapsProviderMixin",
     "bugfix.packet_leak.ClientPlayNetHandlerMixin",
     "bugfix.packet_leak.SCustomPayloadPlayPacketMixin",
     "perf.reuse_datapacks.MinecraftMixin",