Fix the Minecraft window teleporting back to the center of the screen

when early load finishes

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

@@ -48,6 +48,7 @@ public class ModernFixEarlyConfig {
         this.addMixinRule("perf.biome_zoomer", true);
         this.addMixinRule("perf.compress_blockstate", false);
         this.addMixinRule("bugfix.concurrency", true);
+        this.addMixinRule("bugfix.preserve_early_window_pos", true);
         this.addMixinRule("bugfix.edge_chunk_not_saved", true);
         this.addMixinRule("bugfix.starlight_emptiness", modPresent("starlight"));
         this.addMixinRule("bugfix.packet_leak", false);

src/main/java/org/embeddedt/modernfix/mixin/bugfix/preserve_early_window_pos/WindowMixin.java

@@ -0,0 +1,68 @@
+package org.embeddedt.modernfix.mixin.bugfix.preserve_early_window_pos;
+
+import com.mojang.blaze3d.platform.Monitor;
+import com.mojang.blaze3d.platform.ScreenManager;
+import com.mojang.blaze3d.platform.Window;
+import net.minecraftforge.fml.common.ObfuscationReflectionHelper;
+import net.minecraftforge.fml.loading.progress.EarlyProgressVisualization;
+import org.lwjgl.glfw.GLFW;
+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.Redirect;
+
+import java.util.function.IntSupplier;
+import java.util.function.LongSupplier;
+import java.util.function.Supplier;
+
+@Mixin(Window.class)
+public class WindowMixin {
+    @Shadow private boolean fullscreen;
+    @Shadow private int width;
+    @Shadow private int height;
+    @Shadow private int windowedWidth;
+    @Shadow private int windowedHeight;
+    private static Class<?> VISUALIZER;
+
+    static {
+        try {
+            VISUALIZER = Class.forName("net.minecraftforge.fml.loading.progress.ClientVisualization");
+        } catch(ClassNotFoundException e) {
+            VISUALIZER = null;
+        }
+    }
+
+    private Object getEarlyProgressVisualizer() {
+        if(VISUALIZER == null || this.fullscreen)
+            return null;
+        Object o = ObfuscationReflectionHelper.getPrivateValue(EarlyProgressVisualization.class, EarlyProgressVisualization.INSTANCE, "visualization");
+        return VISUALIZER.isAssignableFrom(o.getClass()) ? o : null;
+    }
+
+    /**
+     * Return a null monitor if not in fullscreen and the visualizer is present, so that the code grabs the
+     * original X/Y position of the window.
+     */
+    @Redirect(method = "<init>", at = @At(value = "INVOKE", target = "Lcom/mojang/blaze3d/platform/ScreenManager;getMonitor(J)Lcom/mojang/blaze3d/platform/Monitor;"))
+    private Monitor getMonitor(ScreenManager manager, long id) {
+        return getEarlyProgressVisualizer() != null ? null : manager.getMonitor(id);
+    }
+
+    /**
+     * Grab the original width/height from the window and inject them into our state variables.
+     */
+    @SuppressWarnings("unchecked")
+    @Redirect(method = "<init>", at = @At(value = "INVOKE", target = "Lnet/minecraftforge/fml/loading/progress/EarlyProgressVisualization;handOffWindow(Ljava/util/function/IntSupplier;Ljava/util/function/IntSupplier;Ljava/util/function/Supplier;Ljava/util/function/LongSupplier;)J"))
+    private long performHandoff(EarlyProgressVisualization instance, IntSupplier width, IntSupplier height, Supplier<String> title, LongSupplier monitor) {
+        Object visualizer = getEarlyProgressVisualizer();
+        if(visualizer != null) {
+            long windowId = ObfuscationReflectionHelper.<Long, Object>getPrivateValue((Class<? super Object>)visualizer.getClass(), visualizer, "window");
+            int[] w = new int[1];
+            int[] h = new int[1];
+            GLFW.glfwGetWindowSize(windowId, w, h);
+            this.windowedWidth = this.width = w[0];
+            this.windowedHeight = this.height = h[0];
+        }
+        return instance.handOffWindow(width, height, title, monitor);
+    }
+}

src/main/resources/modernfix.mixins.json

@@ -78,6 +78,7 @@
     "feature.measure_time.MinecraftMixin",
     "feature.reduce_loading_screen_freezes.ModelBakeryMixin",
     "perf.skip_first_datapack_reload.MinecraftMixin",
+    "bugfix.preserve_early_window_pos.WindowMixin",
     "bugfix.concurrency.RenderTypeMixin",
     "bugfix.concurrency.MinecraftMixin",
     "bugfix.concurrency.StaticTagHelperMixin",