Support CSS font size keywords

android/src/toga_android/fonts.py

@@ -4,6 +4,9 @@
 from android.graphics import Typeface
 from android.util import TypedValue
 from org.beeware.android import MainActivity
+from travertino.constants import (
+    FONT_SIZE_SCALE,
+)
 
 from toga.fonts import (
     _REGISTERED_FONT_CACHE,
@@ -98,6 +101,7 @@ def typeface(self, *, default=Typeface.DEFAULT):
     def size(self, *, default=None):
         """Return the font size in physical pixels."""
         context = MainActivity.singletonThis
+        base_size = 14
         if self.interface.size == SYSTEM_DEFAULT_FONT_SIZE:
             if default is None:
                 typed_array = context.obtainStyledAttributes(
@@ -106,12 +110,15 @@ def size(self, *, default=None):
                 default = typed_array.getDimension(0, 0)
                 typed_array.recycle()
             return default
-
+        elif isinstance(self.interface.size, str):
+            default = base_size * FONT_SIZE_SCALE[self.interface.size]
+            return default
         else:
             # Using SP means we follow the standard proportion between CSS pixels and
             # points by default, but respect the system text scaling setting.
-            return TypedValue.applyDimension(
+            default = TypedValue.applyDimension(
                 TypedValue.COMPLEX_UNIT_SP,
                 self.interface.size * (96 / 72),
                 context.getResources().getDisplayMetrics(),
             )
+            return default

android/tests_backend/fonts.py

@@ -6,6 +6,9 @@
 from fontTools.ttLib import TTFont
 from java import jint
 from java.lang import Integer, Long
+from travertino.constants import (
+    FONT_SIZE_SCALE,
+)
 
 from toga.fonts import (
     BOLD,
@@ -77,14 +80,20 @@ def assert_font_options(self, weight=NORMAL, style=NORMAL, variant=NORMAL):
 
     def assert_font_size(self, expected):
         if expected == SYSTEM_DEFAULT_FONT_SIZE:
-            expected = self.default_font_size * (72 / 96)
-        assert round(self.text_size) == round(
-            TypedValue.applyDimension(
+            expected = TypedValue.applyDimension(
+                TypedValue.COMPLEX_UNIT_SP,
+                self.default_font_size,
+                self.native.getResources().getDisplayMetrics(),
+            )
+        elif isinstance(expected, str):
+            expected = self.default_font_size * FONT_SIZE_SCALE[expected]
+        else:
+            expected = TypedValue.applyDimension(
                 TypedValue.COMPLEX_UNIT_SP,
                 expected * (96 / 72),
                 self.native.getResources().getDisplayMetrics(),
             )
-        )
+        assert round(self.text_size) == round(expected)
 
     def assert_font_family(self, expected):
         if not SYSTEM_FONTS:

changes/1814.misc.rst

@@ -0,0 +1 @@
+Added support for absolute CSS font size keywords in Android, Cocoa, GTK, iOS, and Windows.

cocoa/src/toga_cocoa/fonts.py

@@ -1,6 +1,9 @@
 from pathlib import Path
 
 from fontTools.ttLib import TTFont
+from travertino.constants import (
+    FONT_SIZE_SCALE,
+)
 
 from toga.fonts import (
     _REGISTERED_FONT_CACHE,
@@ -88,6 +91,9 @@ def __init__(self, interface):
 
             if self.interface.size == SYSTEM_DEFAULT_FONT_SIZE:
                 font_size = NSFont.systemFontSize
+            elif isinstance(self.interface.size, str):
+                base_size = NSFont.systemFontSize
+                font_size = base_size * FONT_SIZE_SCALE[self.interface.size]
             else:
                 # A "point" in Apple APIs is equivalent to a CSS pixel, but the Toga
                 # public API works in CSS points, which are slightly larger

cocoa/tests_backend/fonts.py

@@ -1,3 +1,7 @@
+from travertino.constants import (
+    FONT_SIZE_SCALE,
+)
+
 from toga.fonts import (
     BOLD,
     CURSIVE,
@@ -48,6 +52,9 @@ def assert_font_options(self, weight=NORMAL, style=NORMAL, variant=NORMAL):
     def assert_font_size(self, expected):
         if expected == SYSTEM_DEFAULT_FONT_SIZE:
             assert self.font.pointSize == 13
+        elif isinstance(expected, str):
+            expected_size = 13 * FONT_SIZE_SCALE[expected]
+            assert abs(self.font.pointSize - expected_size) < 0.01
         else:
             assert self.font.pointSize == expected * 96 / 72
 

core/src/toga/fonts.py

@@ -72,6 +72,8 @@ def __str__(self) -> str:
         size = (
             "default size"
             if self.size == SYSTEM_DEFAULT_FONT_SIZE
+            else f"{self.size}"
+            if isinstance(self.size, str)
             else f"{self.size}pt"
         )
         weight = f" {self.weight}" if self.weight != NORMAL else ""

core/src/toga/style/pack.py

@@ -9,6 +9,7 @@
     from travertino.colors import hsl, rgb
 
 from travertino.constants import (  # noqa: F401
+    ABSOLUTE_FONT_SIZES,
     BOLD,
     BOTTOM,
     CENTER,
@@ -233,7 +234,11 @@ class IntrinsicSize(BaseIntrinsicSize):
     font_style: str = validated_property(*FONT_STYLES, initial=NORMAL)
     font_variant: str = validated_property(*FONT_VARIANTS, initial=NORMAL)
     font_weight: str = validated_property(*FONT_WEIGHTS, initial=NORMAL)
-    font_size: int = validated_property(integer=True, initial=SYSTEM_DEFAULT_FONT_SIZE)
+    font_size: int | str = validated_property(
+        *ABSOLUTE_FONT_SIZES,
+        integer=True,
+        initial=SYSTEM_DEFAULT_FONT_SIZE,
+    )
 
     ######################################################################
     # Directional aliases
@@ -978,7 +983,10 @@ def __css__(self) -> str:
             ]
             css.append(f"font-family: {', '.join(families)};")
         if self.font_size != SYSTEM_DEFAULT_FONT_SIZE:
-            css.append(f"font-size: {self.font_size}pt;")
+            if isinstance(self.font_size, str):
+                css.append(f"font-size: {self.font_size};")
+            else:
+                css.append(f"font-size: {self.font_size}pt;")
         if self.font_weight != NORMAL:
             css.append(f"font-weight: {self.font_weight};")
         if self.font_style != NORMAL:

core/tests/style/pack/test_css.py

@@ -467,6 +467,26 @@
             "flex-direction: row; flex: 0.0 0 auto; font-size: 42pt;",
             id="font-size",
         ),
+        pytest.param(
+            Pack(font_size="small"),
+            "flex-direction: row; flex: 0.0 0 auto; font-size: small;",
+            id="font-size-small",
+        ),
+        pytest.param(
+            Pack(font_size="xx-small"),
+            "flex-direction: row; flex: 0.0 0 auto; font-size: xx-small;",
+            id="font-size-xx-small",
+        ),
+        pytest.param(
+            Pack(font_size="x-large"),
+            "flex-direction: row; flex: 0.0 0 auto; font-size: x-large;",
+            id="font-size-x-large",
+        ),
+        pytest.param(
+            Pack(font_size="large"),
+            "flex-direction: row; flex: 0.0 0 auto; font-size: large;",
+            id="font-size-large",
+        ),
         pytest.param(
             Pack(font_size=SYSTEM_DEFAULT_FONT_SIZE),
             "flex-direction: row; flex: 0.0 0 auto;",

core/tests/test_fonts.py

@@ -95,6 +95,69 @@ async def app():
             NORMAL,
             "system default size",
         ),
+        # Custom font, small size
+        (
+            "Custom Font",
+            "small",
+            NORMAL,
+            NORMAL,
+            NORMAL,
+            "Custom Font small",
+        ),
+        # System font, medium size
+        (
+            SYSTEM,
+            "medium",
+            NORMAL,
+            NORMAL,
+            NORMAL,
+            "system medium",
+        ),
+        # System font, large size
+        (
+            SYSTEM,
+            "large",
+            NORMAL,
+            NORMAL,
+            NORMAL,
+            "system large",
+        ),
+        # System font, x-small size
+        (
+            SYSTEM,
+            "x-small",
+            NORMAL,
+            NORMAL,
+            NORMAL,
+            "system x-small",
+        ),
+        # System font, xx-small size
+        (
+            SYSTEM,
+            "xx-small",
+            NORMAL,
+            NORMAL,
+            NORMAL,
+            "system xx-small",
+        ),
+        # System font, xx-large size
+        (
+            SYSTEM,
+            "xx-large",
+            NORMAL,
+            NORMAL,
+            NORMAL,
+            "system xx-large",
+        ),
+        # System font, x-large size
+        (
+            SYSTEM,
+            "x-large",
+            NORMAL,
+            NORMAL,
+            NORMAL,
+            "system x-large",
+        ),
     ],
 )
 def test_builtin_font(family, size, weight, style, variant, as_str):

docs/reference/style/pack.rst

@@ -305,12 +305,17 @@ The weight of the font to be used.
 ``font_size``
 -------------
 
-**Value:** an integer
+**Values:**
+    - ``<integer>`` (in :ref:`CSS points <css-units>`)
+    - Absolute keywords: ``xx-small`` | ``x-small`` | ``small`` | ``medium`` | ``large`` | ``x-large`` | ``xx-large``
 
 **Initial value:** ``-1``; will use the system default size. This is also stored as a
 constant named ``SYSTEM_DEFAULT_FONT_SIZE``.
 
-The size of the font to be used, in :ref:`CSS points <css-units>`.
+The size of the font to be used. Can be specified in the following ways:
+
+* An integer value in :ref:`CSS points <css-units>`
+* An absolute size keyword, which sets the size relative to the system's base font size
 
 The relationship between Pack and CSS
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

gtk/src/toga_gtk/fonts.py

@@ -1,6 +1,10 @@
 from pathlib import Path
 from warnings import warn
 
+from travertino.constants import (
+    ABSOLUTE_FONT_SIZES,
+)
+
 from toga.fonts import (
     _REGISTERED_FONT_CACHE,
     BOLD,
@@ -76,8 +80,12 @@ def __init__(self, interface):
 
             font.set_family(family)
 
-            # If this is a non-default font size, set the font size
-            if self.interface.size != SYSTEM_DEFAULT_FONT_SIZE:
+            # Default font as well as values in absolute and relative font
+            # size are handled by Pango. Otherwise set font size manually.
+            if (
+                self.interface.size != SYSTEM_DEFAULT_FONT_SIZE
+                and self.interface.size not in ABSOLUTE_FONT_SIZES
+            ):
                 font.set_size(self.interface.size * Pango.SCALE)
 
             # Set font style

gtk/src/toga_gtk/libs/styles.py

@@ -1,3 +1,7 @@
+from travertino.constants import (
+    ABSOLUTE_FONT_SIZES,
+)
+
 from toga.colors import TRANSPARENT
 from toga.fonts import SYSTEM_DEFAULT_FONT_SIZE
 
@@ -61,7 +65,10 @@ def get_font_css(value):
         "font-family": f"{value.family!r}",
     }
 
-    if value.size != SYSTEM_DEFAULT_FONT_SIZE:
+    # If value is an absolute or relative keyword, use those to set size instead
+    if value.size in ABSOLUTE_FONT_SIZES:
+        style["font-size"] = f"{value.size}"
+    elif value.size != SYSTEM_DEFAULT_FONT_SIZE:
         style["font-size"] = f"{value.size}pt"
 
     return style

gtk/tests_backend/fonts.py

@@ -1,3 +1,8 @@
+from travertino.constants import (
+    ABSOLUTE_FONT_SIZES,
+    FONT_SIZE_SCALE,
+)
+
 from toga.fonts import (
     BOLD,
     ITALIC,
@@ -29,6 +34,9 @@ def assert_font_size(self, expected):
             assert expected == SYSTEM_DEFAULT_FONT_SIZE
         elif expected == SYSTEM_DEFAULT_FONT_SIZE:
             assert 8 < int(self.font.get_size() / Pango.SCALE) < 18
+        elif expected in ABSOLUTE_FONT_SIZES:
+            scale = FONT_SIZE_SCALE[expected]
+            assert 8 * scale < int(self.font.get_size() / Pango.SCALE) < 18 * scale
         else:
             assert int(self.font.get_size() / Pango.SCALE) == expected
 

iOS/src/toga_iOS/fonts.py

@@ -1,6 +1,9 @@
 from pathlib import Path
 
 from fontTools.ttLib import TTFont
+from travertino.constants import (
+    FONT_SIZE_SCALE,
+)
 
 from toga.fonts import (
     _REGISTERED_FONT_CACHE,
@@ -88,6 +91,8 @@ def __init__(self, interface):
 
             if self.interface.size == SYSTEM_DEFAULT_FONT_SIZE:
                 size = UIFont.labelFontSize
+            elif isinstance(self.interface.size, str):
+                size = UIFont.labelFontSize * FONT_SIZE_SCALE[self.interface.size]
             else:
                 # A "point" in Apple APIs is equivalent to a CSS pixel, but the Toga
                 # public API works in CSS points, which are slightly larger

iOS/tests_backend/fonts.py

@@ -1,3 +1,7 @@
+from travertino.constants import (
+    FONT_SIZE_SCALE,
+)
+
 from toga.fonts import (
     BOLD,
     CURSIVE,
@@ -51,6 +55,9 @@ def assert_font_options(self, weight=NORMAL, style=NORMAL, variant=NORMAL):
     def assert_font_size(self, expected):
         if expected == SYSTEM_DEFAULT_FONT_SIZE:
             assert self.font.pointSize == 17
+        elif isinstance(expected, str):
+            expected_size = 17 * FONT_SIZE_SCALE[expected]
+            assert abs(self.font.pointSize - expected_size) < 0.01
         else:
             assert self.font.pointSize == expected * 96 / 72
 

testbed/tests/test_fonts.py

@@ -1,6 +1,9 @@
 from importlib import import_module
 
 import pytest
+from travertino.constants import (
+    ABSOLUTE_FONT_SIZES,
+)
 
 import toga
 from toga.fonts import (
@@ -88,7 +91,11 @@ async def test_use_first_valid_font(
 async def test_font_options(widget: toga.Label, font_probe):
     """Every combination of weight, style and variant can be used on a font."""
     for font_family in SYSTEM_DEFAULT_FONTS:
-        for font_size in [20, SYSTEM_DEFAULT_FONT_SIZE]:
+        for font_size in [
+            20,
+            SYSTEM_DEFAULT_FONT_SIZE,
+            *ABSOLUTE_FONT_SIZES,
+        ]:
             for font_weight in FONT_WEIGHTS:
                 for font_style in FONT_STYLES:
                     for font_variant in FONT_VARIANTS: