UIScale:

- allow scale factors less than 100% for system property `flatlaf.uiScale`
- no longer round scale factor of system property `flatlaf.uiScale` to 1/4
- renamed system property `flatlaf.uiDowncale.enabled` to `flatlaf.uiScale.allowScaleDown`
- round smaller scale factors to 1/10
- absolute minimum user scale factor is now 0.1

flatlaf-core/src/main/java/com/formdev/flatlaf/FlatSystemProperties.java

@@ -16,6 +16,8 @@
 
 package com.formdev.flatlaf;
 
+import com.formdev.flatlaf.util.UIScale;
+
 /**
  * Defines/documents own system properties used in FlatLaf.
  *
@@ -32,6 +34,8 @@ public interface FlatSystemProperties
 	 * To replace the Java 9+ system scale factor, use system property "sun.java2d.uiScale",
 	 * which has the same syntax as this one.
 	 * <p>
+	 * Since FlatLaf 1.1.2: Scale factors less then 100% are allowed.
+	 * <p>
 	 * <strong>Allowed Values</strong> e.g. {@code 1.5}, {@code 1.5x}, {@code 150%} or {@code 144dpi} (96dpi is 100%)<br>
 	 */
 	String UI_SCALE = "flatlaf.uiScale";
@@ -45,12 +49,15 @@ public interface FlatSystemProperties
 	String UI_SCALE_ENABLED = "flatlaf.uiScale.enabled";
 
 	/**
-	 * Specifies whether values smaller than 1.0f are allowed for the custom scale factor.
+	 * Specifies whether values smaller than 100% are allowed for the user scale factor
+	 * (see {@link UIScale#getUserScaleFactor()}).
 	 * <p>
 	 * <strong>Allowed Values</strong> {@code false} and {@code true}<br>
 	 * <strong>Default</strong> {@code false}
+	 *
+	 * @since 1.1.2
 	 */
-	String UI_DOWNSCALE_ENABLED = "flatlaf.uiDowncale.enabled";
+	String UI_SCALE_ALLOW_SCALE_DOWN = "flatlaf.uiScale.allowScaleDown";
 
 	/**
 	 * Specifies whether Ubuntu font should be used on Ubuntu Linux.

flatlaf-core/src/main/java/com/formdev/flatlaf/util/UIScale.java

@@ -180,7 +180,7 @@ public class UIScale
 		// apply custom scale factor specified in system property "flatlaf.uiScale"
 		float customScaleFactor = getCustomScaleFactor();
 		if( customScaleFactor > 0 ) {
-			setUserScaleFactor( customScaleFactor );
+			setUserScaleFactor( customScaleFactor, false );
 			return;
 		}
 
@@ -230,7 +230,7 @@ public class UIScale
 		} else
 			newScaleFactor = computeScaleFactor( font );
 
-		setUserScaleFactor( newScaleFactor );
+		setUserScaleFactor( newScaleFactor, true );
 	}
 
 	private static float computeScaleFactor( Font font ) {
@@ -258,10 +258,6 @@ public class UIScale
 		return FlatSystemProperties.getBoolean( FlatSystemProperties.UI_SCALE_ENABLED, true );
 	}
 
-        private static boolean isDownscalingEnabled() {
-		return FlatSystemProperties.getBoolean( FlatSystemProperties.UI_DOWNSCALE_ENABLED, false );
-	}
-
 	/**
 	 * Applies a custom scale factor given in system property "flatlaf.uiScale"
 	 * to the given font.
@@ -278,7 +274,7 @@ public class UIScale
 		if( scaleFactor == fontScaleFactor )
 			return font;
 
-		int newFontSize = Math.round( (font.getSize() / fontScaleFactor) * scaleFactor );
+		int newFontSize = Math.max( Math.round( (font.getSize() / fontScaleFactor) * scaleFactor ), 1 );
 		return new FontUIResource( font.deriveFont( (float) newFontSize ) );
 	}
 
@@ -326,11 +322,18 @@ public class UIScale
 	/**
 	 * Sets the user scale factor.
 	 */
-	private static void setUserScaleFactor( float scaleFactor ) {
+	private static void setUserScaleFactor( float scaleFactor, boolean normalize ) {
-		if( ( !isDownscalingEnabled() && scaleFactor <= 1f ) || scaleFactor <= 0f )
+		if( normalize ) {
-			scaleFactor = 1f;
+			if( scaleFactor < 1f ) {
-		else // round scale factor to 1/4
+				scaleFactor = FlatSystemProperties.getBoolean( FlatSystemProperties.UI_SCALE_ALLOW_SCALE_DOWN, false )
+					? Math.round( scaleFactor * 10f ) / 10f // round small scale factor to 1/10
+					: 1f;
+			} else if( scaleFactor > 1f ) // round scale factor to 1/4
 				scaleFactor = Math.round( scaleFactor * 4f ) / 4f;
+		}
+
+		// minimum scale factor
+		scaleFactor = Math.max( scaleFactor, 0.1f );
 
 		float oldScaleFactor = UIScale.scaleFactor;
 		UIScale.scaleFactor = scaleFactor;