fix: correct macOS OpenGL reduced resolution (#566)

Author: FlashyReese

common/src/main/java/me/flashyreese/mods/sodiumextra/client/util/MacReducedResolution.java

@@ -4,6 +4,15 @@
 import net.minecraft.util.Util;
 
 public final class MacReducedResolution {
+    /*
+     * This branch only has the OpenGL presentation path. On macOS, the reduced
+     * resolution option is handled by GLFW_COCOA_RETINA_FRAMEBUFFER=false, which
+     * gives Minecraft a logical-size drawable. Halving Window.framebufferWidth
+     * and Window.framebufferHeight after that makes a 1440p Retina setup render
+     * as 720p, so Window's framebuffer fields must not be reduced again.
+     */
+    private static boolean openGlBackend;
+
     public static boolean isEnabled() {
         return Util.getPlatform() == Util.OS.OSX && SodiumExtraClientMod.options().extraSettings.reduceResolutionOnMac;
     }
@@ -12,7 +21,20 @@ public static int reduce(int value) {
         return Math.max(1, value / 2);
     }
 
+    public static void useOpenGlBackend() {
+        openGlBackend = true;
+    }
+
+    public static boolean shouldReduceFramebuffer() {
+        return isEnabled() && !openGlBackend;
+    }
+
+    public static boolean shouldUseWindowSizeForInitialFramebuffer() {
+        return isEnabled() && openGlBackend;
+    }
+
     public static boolean shouldScalePresentation(int sourceWidth, int sourceHeight, int targetWidth, int targetHeight) {
+        // Fallback for any path where the render target and presentation target still disagree.
         return isEnabled() && (sourceWidth < targetWidth || sourceHeight < targetHeight);
     }
 }

common/src/main/java/me/flashyreese/mods/sodiumextra/mixin/reduce_resolution_on_mac/MixinWindow.java

@@ -23,6 +23,12 @@
  */
 @Mixin(Window.class)
 public class MixinWindow {
+    @Shadow
+    private int width;
+
+    @Shadow
+    private int height;
+
     @Shadow
     private int framebufferWidth;
 
@@ -32,6 +38,7 @@ public class MixinWindow {
     @Redirect(at = @At(value = "INVOKE", target = "Lorg/lwjgl/glfw/GLFW;glfwDefaultWindowHints()V"), method = "<init>", remap = false)
     private void onDefaultWindowHints() {
         GLFW.glfwDefaultWindowHints();
+        MacReducedResolution.useOpenGlBackend();
 
         if (MacReducedResolution.isEnabled()) {
             GLFW.glfwWindowHint(GLFW.GLFW_COCOA_RETINA_FRAMEBUFFER, GLFW.GLFW_FALSE);
@@ -40,21 +47,45 @@ private void onDefaultWindowHints() {
 
     @Inject(at = @At(value = "RETURN"), method = "refreshFramebufferSize")
     private void afterUpdateFrameBufferSize(CallbackInfo ci) {
-        this.scaleFramebufferSize();
+        this.scaleInitialFramebufferSize();
     }
 
     @Inject(method = "onFramebufferResize", at = @At(value = "FIELD", target = "Lcom/mojang/blaze3d/platform/Window;framebufferHeight:I", opcode = Opcodes.PUTFIELD, shift = At.Shift.AFTER))
     private void afterFramebufferResize(long handle, int newWidth, int newHeight, CallbackInfo ci) {
         this.scaleFramebufferSize();
     }
 
+    @Unique
+    private void scaleInitialFramebufferSize() {
+        /*
+         * OpenGL only: the Cocoa non-Retina window hint gives us the correct
+         * reduced drawable, but the first refreshFramebufferSize() during startup
+         * can leave Minecraft's Window framebuffer fields at the Retina backing
+         * size. A manual resize fixes it through the normal callback path; pinning
+         * the initial values to the logical window size avoids the startup-only
+         * stretched/offset GUI without changing resize behavior.
+         */
+        if (MacReducedResolution.shouldUseWindowSizeForInitialFramebuffer()) {
+            this.framebufferWidth = Math.max(1, this.width);
+            this.framebufferHeight = Math.max(1, this.height);
+            return;
+        }
+
+        this.scaleFramebufferSize();
+    }
+
     @Unique
     private void scaleFramebufferSize() {
-        if (!MacReducedResolution.isEnabled()) {
+        /*
+         * Do not halve on the OpenGL backend. GLFW already returned the reduced
+         * drawable after GLFW_COCOA_RETINA_FRAMEBUFFER=false, and a second halving
+         * was confirmed on 26.2 to render 1440p as 720p.
+         */
+        if (!MacReducedResolution.shouldReduceFramebuffer()) {
             return;
         }
 
-        framebufferWidth = MacReducedResolution.reduce(framebufferWidth);
-        framebufferHeight = MacReducedResolution.reduce(framebufferHeight);
+        this.framebufferWidth = MacReducedResolution.reduce(this.framebufferWidth);
+        this.framebufferHeight = MacReducedResolution.reduce(this.framebufferHeight);
     }
 }