+# This file is part of NIT ( http://www.nitlanguage.org ).
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+# http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+# Abstract font drawing services, implemented by `bmfont` and `tileset`
+module font
+
+import flat
+
+# Abstract font, drawn by a `TextSprites`
+abstract class Font
+
+ # Line spacing modifier for `pld` and `plu`
+ #
+ # This value acts as multiplier to the standard line height.
+ # Defaults to 0.4, so a `pld` moves chars down by about half a line.
+ var partial_line_mod: Numeric = 0.4 is writable
+
+ # Backend writing service, clients should use `TextSprites.text=`
+ protected fun write_into(text_sprites: TextSprites, text: Text) is abstract
+end
+
+# Manage a set of sprites to display some text
+class TextSprites
+
+ # Font used to draw text
+ var font: Font
+
+ # Top left of the first character in UI coordinates
+ var anchor: Point3d[Float]
+
+ # Last set of sprites generated to display `text=`
+ var sprites = new Array[Sprite]
+
+ # Sprite set where to put created sprites
+ #
+ # Defaults to `app::ui_sprites`, but it could also be set to a
+ # `app::sprites` or a custom collection.
+ var target_sprite_set: Set[Sprite] = app.ui_sprites is lazy, writable
+
+ private var cached_text: nullable Text = ""
+
+ # Last text drawn
+ fun text: nullable Text do return cached_text
+
+ # Update the text displayed by inserting new sprites into `app.ui_sprites`
+ #
+ # Does not redraw if `text` has not changed.
+ fun text=(text: nullable Text)
+ is autoinit do
+ # Don't redraw if text hasn't changed
+ if text == cached_text then return
+ cached_text = text
+
+ # Clean up last used sprites
+ for s in sprites do if target_sprite_set.has(s) then target_sprite_set.remove s
+ sprites.clear
+
+ if text == null then return
+
+ font.write_into(self, text)
+
+ # Register sprites to be drawn by `app.ui_camera`
+ target_sprite_set.add_all sprites
+ end
+end
+
+# Partial line forward (U+008B)
+fun pld: Char do return '\8b'
+
+# Partial line backward (U+008C)
+fun plu: Char do return '\8c'