core: Always enable kerning for device fonts

core/src/font.rs

@@ -411,6 +411,10 @@ pub enum FontType {
 }
 
 impl FontType {
+    pub fn is_device(self) -> bool {
+        self == Self::Device
+    }
+
     pub fn is_embedded(self) -> bool {
         self != Self::Device
     }
@@ -744,15 +748,16 @@ pub trait FontLike<'gc> {
         // TODO [KJ] I'm not sure whether we should iterate over characters here or over code units.
         //   I suspect Flash Player does not support full UTF-16 when displaying and laying out text.
         let mut char_indices = text.char_indices().peekable();
-        let has_kerning_info = self.has_kerning_info();
+        let kerning_enabled =
+            self.has_kerning_info() && (self.font_type().is_device() || params.kerning);
         let mut x = Twips::ZERO;
         while let Some((pos, c)) = char_indices.next() {
             let c = c.unwrap_or(char::REPLACEMENT_CHARACTER);
             if let Some(render_data) = self.get_glyph_render_data(c) {
                 let glyph = render_data.glyph;
                 let scale = params.height.get() as f32 / render_data.font.scale();
                 let mut advance = glyph.advance();
-                if has_kerning_info && params.kerning {
+                if kerning_enabled {
                     let next_char = char_indices.peek().cloned().unwrap_or((0, Ok('\0'))).1;
                     let next_char = next_char.unwrap_or(char::REPLACEMENT_CHARACTER);
                     advance += self.get_kerning_offset(c, next_char);

tests/tests/swfs/fonts/device_font_kerning/Test.as

@@ -0,0 +1,39 @@
+package {
+import flash.display.*;
+import flash.text.*;
+
+[SWF(width="100", height="50")]
+public class Test extends Sprite {
+    [Embed(source="TestFont.ttf", fontName="TestFont", embedAsCFF="false", unicodeRange="U+0061-U+0064")]
+    private var TestFont:Class;
+
+    public function Test() {
+        stage.scaleMode = "noScale";
+
+        addTextField(0, 0, false);
+        addTextField(0, 25, true);
+    }
+
+    private function addTextField(x:Number, y:Number, kerning:Boolean):void {
+        var field:TextField = new TextField();
+        field.type = "input";
+        field.width = 100;
+        field.x = x;
+        field.height = 25;
+        field.y = y;
+        field.border = true;
+
+        var tf:TextFormat = new TextFormat("TestFont", 10);
+        tf.kerning = kerning;
+        field.defaultTextFormat = tf;
+
+        field.text = "abcd";
+
+        var lm = field.getLineMetrics(0);
+        trace("LM width: " + lm.width);
+        trace("width: " + field.textWidth);
+
+        addChild(field);
+    }
+}
+}

tests/tests/swfs/fonts/device_font_kerning/TestFont.sfd

@@ -0,0 +1,126 @@
+SplineFontDB: 3.2
+FontName: TestFont
+FullName: TestFont
+FamilyName: TestFont
+Weight: Regular
+Copyright: Copyright (c) 2025, Kamil Jarosz
+UComments: "2024-7-24: Created with FontForge (http://fontforge.org)"
+Version: 001.000
+ItalicAngle: 0
+UnderlinePosition: -76
+UnderlineWidth: 38
+Ascent: 800
+Descent: 200
+InvalidEm: 0
+LayerCount: 2
+Layer: 0 0 "Back" 1
+Layer: 1 0 "Fore" 0
+XUID: [1021 253 198287149 6396829]
+StyleMap: 0x0000
+FSType: 0
+OS2Version: 0
+OS2_WeightWidthSlopeOnly: 0
+OS2_UseTypoMetrics: 1
+CreationTime: 1721856925
+ModificationTime: 1763285453
+PfmFamily: 17
+TTFWeight: 400
+TTFWidth: 5
+LineGap: 100
+VLineGap: 0
+OS2TypoAscent: 0
+OS2TypoAOffset: 1
+OS2TypoDescent: 0
+OS2TypoDOffset: 1
+OS2TypoLinegap: 100
+OS2WinAscent: 0
+OS2WinAOffset: 1
+OS2WinDescent: 0
+OS2WinDOffset: 1
+HheadAscent: 0
+HheadAOffset: 1
+HheadDescent: 0
+HheadDOffset: 1
+OS2Vendor: 'PfEd'
+Lookup: 258 0 0 "'kern' Horizontal Kerning in Latin lookup 0" { "'kern' Horizontal Kerning in Latin lookup 0-1" [150,15,0] } ['kern' ('latn' <'dflt' > ) ]
+MarkAttachClasses: 1
+DEI: 91125
+Encoding: ISO8859-1
+UnicodeInterp: none
+NameList: AGL For New Fonts
+DisplaySize: -48
+AntiAlias: 1
+FitToEm: 0
+WinInfo: 0 30 10
+BeginPrivate: 0
+EndPrivate
+BeginChars: 256 4
+
+StartChar: a
+Encoding: 97 97 0
+Width: 1000
+Flags: W
+HStem: 0 800<0 1000>
+LayerCount: 2
+Fore
+SplineSet
+0 800 m 1
+ 1000 800 l 5
+ 1000 0 l 5
+ 0 0 l 1
+ 0 800 l 1
+EndSplineSet
+Kerns2: 2 1000 "'kern' Horizontal Kerning in Latin lookup 0-1"
+EndChar
+
+StartChar: c
+Encoding: 99 99 1
+Width: 1000
+Flags: W
+HStem: 0 800<0 1000>
+LayerCount: 2
+Fore
+SplineSet
+0 800 m 1
+ 1000 800 l 5
+ 1000 0 l 5
+ 0 0 l 1
+ 0 800 l 1
+EndSplineSet
+Kerns2: 3 500 "'kern' Horizontal Kerning in Latin lookup 0-1"
+EndChar
+
+StartChar: b
+Encoding: 98 98 2
+Width: 1000
+Flags: W
+HStem: 0 800<0 1000>
+LayerCount: 2
+Fore
+SplineSet
+0 800 m 1
+ 1000 800 l 5
+ 1000 0 l 5
+ 0 0 l 1
+ 0 800 l 1
+EndSplineSet
+Kerns2: 1 -500 "'kern' Horizontal Kerning in Latin lookup 0-1"
+EndChar
+
+StartChar: d
+Encoding: 100 100 3
+Width: 1000
+Flags: W
+HStem: 0 800<0 1000>
+LayerCount: 2
+Fore
+SplineSet
+0 800 m 1
+ 1000 800 l 5
+ 1000 0 l 5
+ 0 0 l 1
+ 0 800 l 1
+EndSplineSet
+EndChar
+EndChars
+EndSplineFont

tests/tests/swfs/fonts/device_font_kerning/output.txt

@@ -0,0 +1,4 @@
+LM width: 50
+width: 50
+LM width: 50
+width: 50

tests/tests/swfs/fonts/device_font_kerning/test.toml

@@ -0,0 +1,11 @@
+num_ticks = 1
+
+[image_comparisons.output]
+tolerance = 0
+
+[player_options]
+with_renderer = { optional = false, sample_count = 4 }
+
+[fonts.a]
+family = "TestFont"
+path = "TestFont.ttf"