Ticket #18720: default-zoom-offset-based-on-HiDPISupport.patch

src/org/openstreetmap/josm/gui/layer/AbstractTileSourceLayer.java

@@ -121 +121 @@
 import org.openstreetmap.josm.gui.progress.ProgressMonitor;
 import org.openstreetmap.josm.gui.util.GuiHelper;
 import org.openstreetmap.josm.tools.GBC;
+import org.openstreetmap.josm.tools.HiDPISupport;
 import org.openstreetmap.josm.tools.HttpClient;
 import org.openstreetmap.josm.tools.Logging;
 import org.openstreetmap.josm.tools.MemoryManager;
 import org.openstreetmap.josm.tools.MemoryManager.MemoryHandle;
 import org.openstreetmap.josm.tools.MemoryManager.NotEnoughMemoryException;
-import org.openstreetmap.josm.tools.PlatformManager;
 import org.openstreetmap.josm.tools.Utils;
 import org.openstreetmap.josm.tools.bugreport.BugReport;
 
@@ -168 +168 @@
     private final AttributionSupport attribution = new AttributionSupport();
 
     /**
-     * Offset between calculated zoom level and zoom level used to download and show tiles. Negative values will result in
-     * lower resolution of imagery useful in "retina" displays, positive values will result in higher resolution
+     * Offset between calculated zoom level, and zoom level used to download and show tiles. Negative values will result in
+     * lower resolution of imagery, positive values will result in higher resolution useful in "Retina" displays
      */
     public static final IntegerProperty ZOOM_OFFSET = new IntegerProperty(PREFERENCE_PREFIX + ".zoom_offset",
-            PlatformManager.getPlatform().isHighDpiDisplay() ? 2 : 0);
+            getDefaultZoomOffset(HiDPISupport.getHiDPIScale()));
+
+    /**
+     * Calculate the zoom offset for best display results, given the scaling factor of the screen (e.g. 2 for Retina displays)
+     * @param scalingFactor scaling factor of the screen
+     * @return suggested zoom offset
+     */
+    static int getDefaultZoomOffset(double scalingFactor) {
+        return (int) Math.ceil(Math.log(scalingFactor) / (Math.log(2.0) / 2.0));  // calculate logarithm on base sqrt(2), and round up
+    }
 
     /*
      *  use MemoryTileCache instead of tileLoader JCS cache, as tileLoader caches only content (byte[] of image)

src/org/openstreetmap/josm/tools/HiDPISupport.java

@@ -169 +169 @@
      * only take the default screen device into account.
      * @return the GUI scale for HiDPI mode, a value of 1.0 means standard mode.
      */
-    static double getHiDPIScale() {
+    public static double getHiDPIScale() {
         if (GraphicsEnvironment.isHeadless())
             return 1.0;
         GraphicsConfiguration gc = GraphicsEnvironment

src/org/openstreetmap/josm/tools/PlatformHook.java

@@ -136 +136 @@
                 GraphicsEnvironment.getLocalGraphicsEnvironment().getDefaultScreenDevice().isFullScreenSupported();
     }
 
-    /**
-     * Determines if the default screen is a high-dpi device such as a mac Retina display.
-     * @return {@code true} if the default screen is a high-dpi device such as a mac Retina display
-     * @since 15918
-     */
-    default boolean isHighDpiDisplay() {
-        // https://stackoverflow.com/a/49770313
-        return !GraphicsEnvironment.isHeadless() &&
-                !GraphicsEnvironment.getLocalGraphicsEnvironment().getDefaultScreenDevice().getDefaultConfiguration()
-                .getDefaultTransform().isIdentity();
-    }
-
     /**
      * Renames a file.
      * @param from Source file

test/unit/org/openstreetmap/josm/gui/layer/AbstractTileSourceLayerTest.java

@@ -204 +204 @@
     public void testTileSourceLayerPopup() {
         assertNotNull(testLayer.new TileSourceLayerPopup(100, 100));
     }
+
+    /**
+     * Test {@link AbstractTileSourceLayer#getDefaultZoomOffset}
+     */
+    @Test
+    public void testGetDefaultZoomOffset() {
+        assertEquals(-1, AbstractTileSourceLayer.getDefaultZoomOffset(0.7));
+        assertEquals(0, AbstractTileSourceLayer.getDefaultZoomOffset(0.8));
+        assertEquals(0, AbstractTileSourceLayer.getDefaultZoomOffset(1.0));
+        assertEquals(1, AbstractTileSourceLayer.getDefaultZoomOffset(1.25));
+        assertEquals(2, AbstractTileSourceLayer.getDefaultZoomOffset(1.5));
+        assertEquals(2, AbstractTileSourceLayer.getDefaultZoomOffset(2.0));
+        assertEquals(4, AbstractTileSourceLayer.getDefaultZoomOffset(3.0));
+    }
 }