fix(decorated-window-jni): apply DPI scaling to window min/max size on Windows

On non-JBR JVMs (Azul, Oracle OpenJDK), AWT's WM_GETMINMAXINFO handler
sets ptMinTrackSize in logical pixels but Windows expects physical pixels.
This causes window.minimumSize to be ignored at HiDPI scaling levels.

Intercept WM_GETMINMAXINFO in our WndProc subclass and apply MulDiv DPI
scaling, matching the fix JBR applies via ScaleUpX/Y.

Closes #102

Author: kdroidFilter

decorated-window-jni/src/main/kotlin/io/github/kdroidfilter/nucleus/window/TitleBar.Windows.kt

@@ -99,6 +99,9 @@ private fun DecoratedWindowScope.NativeWindowsTitleBar(
         }
     }
 
+    // Fix DPI scaling for min/max size on non-JBR JVMs (issue #102)
+    SyncMinMaxSizeToNative(window)
+
     val useNewFullscreenControls = modifier.hasNewFullscreenControls()
 
     // ── Fullscreen with newFullscreenControls: sliding overlay ──
@@ -238,3 +241,38 @@ private fun DecoratedWindowScope.FallbackWindowsTitleBar(
         content(currentState)
     }
 }
+
+/**
+ * Syncs [java.awt.Window.minimumSize] and [java.awt.Window.maximumSize] to the native
+ * WM_GETMINMAXINFO handler so that DPI scaling is applied correctly on non-JBR JVMs.
+ */
+@Suppress("FunctionNaming")
+@Composable
+private fun SyncMinMaxSizeToNative(window: java.awt.Window) {
+    DisposableEffect(window) {
+        val hwnd = JniWindowsWindowUtil.getHwnd(window)
+        if (hwnd != 0L) {
+            val syncSizes = {
+                val min = window.minimumSize
+                JniWindowsDecorationBridge.nativeSetMinimumSize(hwnd, min.width, min.height)
+                val max = window.maximumSize
+                val maxW = if (max.width < Short.MAX_VALUE) max.width else 0
+                val maxH = if (max.height < Short.MAX_VALUE) max.height else 0
+                JniWindowsDecorationBridge.nativeSetMaximumSize(hwnd, maxW, maxH)
+            }
+            syncSizes()
+            val propertyListener =
+                java.beans.PropertyChangeListener { evt ->
+                    if (evt.propertyName == "minimumSize" || evt.propertyName == "maximumSize") {
+                        syncSizes()
+                    }
+                }
+            window.addPropertyChangeListener(propertyListener)
+            onDispose {
+                window.removePropertyChangeListener(propertyListener)
+            }
+        } else {
+            onDispose { }
+        }
+    }
+}

decorated-window-jni/src/main/kotlin/io/github/kdroidfilter/nucleus/window/utils/windows/JniWindowsDecorationBridge.kt

@@ -73,6 +73,26 @@ internal object JniWindowsDecorationBridge {
         argb: Int,
     )
 
+    // Sets the minimum window size in logical pixels. The native
+    // WM_GETMINMAXINFO handler applies DPI scaling automatically.
+    // Pass (0, 0) to disable the override and fall back to AWT default.
+    @JvmStatic
+    external fun nativeSetMinimumSize(
+        hwnd: Long,
+        widthPx: Int,
+        heightPx: Int,
+    )
+
+    // Sets the maximum window size in logical pixels. The native
+    // WM_GETMINMAXINFO handler applies DPI scaling automatically.
+    // Pass (0, 0) to disable the override and fall back to AWT default.
+    @JvmStatic
+    external fun nativeSetMaximumSize(
+        hwnd: Long,
+        widthPx: Int,
+        heightPx: Int,
+    )
+
     // Returns debug counters as a string (temporary).
     @JvmStatic
     external fun nativeGetDebugInfo(hwnd: Long): String

decorated-window-jni/src/main/native/windows/nucleus_windows_decoration.c

@@ -93,6 +93,9 @@ typedef struct {
     LONG    savedStyle;
     LONG    savedExStyle;
     WINDOWPLACEMENT savedPlacement;
+    /* Min/max size override (logical pixels, 0 = not set) */
+    POINT   minSizePx;
+    POINT   maxSizePx;
     /* Debug counters */
     int     hitTestCount;
     int     hitTestCaption;
@@ -418,6 +421,33 @@ static LRESULT CALLBACK decorationWndProc(
         break;  /* also let original handle it */
     }
 
+    /* -------------------------------------------------------------- */
+    /*  WM_GETMINMAXINFO: fix DPI scaling for min/max size.            */
+    /*  Standard OpenJDK stores logical pixels in ptMinTrackSize but  */
+    /*  Windows expects physical pixels. JBR applies ScaleUpX/Y;      */
+    /*  we replicate that fix here so it works on all JVMs.            */
+    /* -------------------------------------------------------------- */
+    case WM_GETMINMAXINFO: {
+        /* Let AWT process first (sets unscaled values) */
+        LRESULT result = CallWindowProcW(state->originalWndProc,
+                                          hwnd, msg, wParam, lParam);
+        LPMINMAXINFO lpmmi = (LPMINMAXINFO)lParam;
+        UINT dpi = getDpi(hwnd);
+
+        /* Override with DPI-scaled values if set */
+        if (state->minSizePx.x > 0 || state->minSizePx.y > 0) {
+            lpmmi->ptMinTrackSize.x = MulDiv(state->minSizePx.x, dpi, 96);
+            lpmmi->ptMinTrackSize.y = MulDiv(state->minSizePx.y, dpi, 96);
+        }
+        if (state->maxSizePx.x > 0 || state->maxSizePx.y > 0) {
+            if (state->maxSizePx.x > 0)
+                lpmmi->ptMaxTrackSize.x = MulDiv(state->maxSizePx.x, dpi, 96);
+            if (state->maxSizePx.y > 0)
+                lpmmi->ptMaxTrackSize.y = MulDiv(state->maxSizePx.y, dpi, 96);
+        }
+        return result;
+    }
+
     /* -------------------------------------------------------------- */
     /*  WM_SYSCOMMAND: block state-changing commands while fullscreen  */
     /*  to prevent native/Kotlin state desync. The application must   */
@@ -1032,3 +1062,43 @@ Java_io_github_kdroidfilter_nucleus_window_utils_windows_JniWindowsDecorationBri
     }
     return (*env)->NewStringUTF(env, buf);
 }
+
+/* -------------------------------------------------------------- */
+/*  nativeSetMinimumSize(long hwnd, int widthPx, int heightPx)     */
+/*  Stores the minimum window size in logical pixels. The          */
+/*  WM_GETMINMAXINFO handler applies DPI scaling automatically.    */
+/*  Pass (0, 0) to disable the override and fall back to AWT.      */
+/* -------------------------------------------------------------- */
+JNIEXPORT void JNICALL
+Java_io_github_kdroidfilter_nucleus_window_utils_windows_JniWindowsDecorationBridge_nativeSetMinimumSize(
+    JNIEnv *env, jclass clazz, jlong hwndLong, jint widthPx, jint heightPx)
+{
+    HWND hwnd = (HWND)(uintptr_t)hwndLong;
+    if (!hwnd) return;
+
+    DecoState *state = getState(hwnd);
+    if (!state) return;
+
+    state->minSizePx.x = (LONG)widthPx;
+    state->minSizePx.y = (LONG)heightPx;
+}
+
+/* -------------------------------------------------------------- */
+/*  nativeSetMaximumSize(long hwnd, int widthPx, int heightPx)     */
+/*  Stores the maximum window size in logical pixels. The          */
+/*  WM_GETMINMAXINFO handler applies DPI scaling automatically.    */
+/*  Pass (0, 0) to disable the override and fall back to AWT.      */
+/* -------------------------------------------------------------- */
+JNIEXPORT void JNICALL
+Java_io_github_kdroidfilter_nucleus_window_utils_windows_JniWindowsDecorationBridge_nativeSetMaximumSize(
+    JNIEnv *env, jclass clazz, jlong hwndLong, jint widthPx, jint heightPx)
+{
+    HWND hwnd = (HWND)(uintptr_t)hwndLong;
+    if (!hwnd) return;
+
+    DecoState *state = getState(hwnd);
+    if (!state) return;
+
+    state->maxSizePx.x = (LONG)widthPx;
+    state->maxSizePx.y = (LONG)heightPx;
+}