core: Add methods for introspecting text metrics on an `EditText`.

core/src/avm2/globals.rs

@@ -112,6 +112,7 @@ pub struct SystemClasses<'gc> {
     pub ioerror: ClassObject<'gc>,
     pub eoferror: ClassObject<'gc>,
     pub uncaughterrorevents: ClassObject<'gc>,
+    pub textlinemetrics: ClassObject<'gc>,
 }
 
 impl<'gc> SystemClasses<'gc> {
@@ -191,6 +192,7 @@ impl<'gc> SystemClasses<'gc> {
             ioerror: object,
             eoferror: object,
             uncaughterrorevents: object,
+            textlinemetrics: object,
         }
     }
 }
@@ -730,6 +732,7 @@ fn load_playerglobal<'gc>(
             ("flash.geom", "Transform", transform),
             ("flash.geom", "ColorTransform", colortransform),
             ("flash.utils", "ByteArray", bytearray),
+            ("flash.text", "TextLineMetrics", textlinemetrics),
         ]
     );
 

core/src/display_object/edit_text.rs

@@ -19,7 +19,7 @@ use crate::display_object::{DisplayObjectBase, DisplayObjectPtr, TDisplayObject}
 use crate::drawing::Drawing;
 use crate::events::{ButtonKeyCode, ClipEvent, ClipEventResult, KeyCode};
 use crate::font::{round_down_to_pixel, Glyph, TextRenderSettings};
-use crate::html::{BoxBounds, FormatSpans, LayoutBox, LayoutContent, TextFormat};
+use crate::html::{BoxBounds, FormatSpans, LayoutBox, LayoutContent, LayoutMetrics, TextFormat};
 use crate::prelude::*;
 use crate::string::{utils as string_utils, AvmString, WStr, WString};
 use crate::tag_utils::SwfMovie;
@@ -1383,6 +1383,78 @@ impl<'gc> EditText<'gc> {
             ),
         }
     }
+
+    /// Count the number of lines in the text box's layout.
+    pub fn layout_lines(self) -> usize {
+        self.0.read().line_data.len()
+    }
+
+    /// Calculate the layout metrics for a given line.
+    ///
+    /// Returns None if the line does not exist or there is not enough data
+    /// about the line to calculate metrics with.
+    pub fn layout_metrics(self, line: usize) -> Option<LayoutMetrics> {
+        let line = self.0.read().line_data.get(line).copied()?;
+        let mut union_bounds = None;
+        let mut font = None;
+        let mut text_format = None;
+
+        let read = self.0.read();
+
+        for layout_box in read.layout.iter() {
+            if layout_box.bounds().offset_y() < line.offset
+                || layout_box.bounds().extent_y() > line.extent
+            {
+                continue;
+            }
+
+            log::error!("{:?}", layout_box);
+
+            if let Some(bounds) = &mut union_bounds {
+                *bounds += layout_box.bounds();
+            } else {
+                union_bounds = Some(layout_box.bounds());
+            }
+
+            if font.is_none() {
+                match layout_box.content() {
+                    LayoutContent::Text {
+                        font: box_font,
+                        text_format: box_text_format,
+                        ..
+                    } => {
+                        font = Some(box_font);
+                        text_format = Some(box_text_format);
+                    }
+                    LayoutContent::Bullet {
+                        font: box_font,
+                        text_format: box_text_format,
+                        ..
+                    } => {
+                        font = Some(box_font);
+                        text_format = Some(box_text_format);
+                    }
+                    LayoutContent::Drawing { .. } => {}
+                }
+            }
+        }
+
+        let union_bounds = union_bounds?;
+        let font = font?;
+        let size = Twips::from_pixels(text_format?.size?);
+        let ascent = font.get_baseline_for_height(size);
+        let descent = font.get_descent_for_height(size);
+        let leading = font.get_leading_for_height(size);
+
+        Some(LayoutMetrics {
+            ascent,
+            descent,
+            leading,
+            width: union_bounds.width(),
+            height: ascent + descent + leading,
+            x: union_bounds.offset_x() + Twips::from_pixels(EditText::INTERNAL_PADDING),
+        })
+    }
 }
 
 impl<'gc> TDisplayObject<'gc> for EditText<'gc> {

core/src/font.rs

@@ -88,7 +88,6 @@ struct FontData {
 
     /// The distance from the baseline of the font to the bottom of each glyph,
     /// in EM-square coordinates.
-    #[allow(dead_code)]
     descent: u16,
 
     /// The distance between the bottom of any one glyph and the top of
@@ -227,6 +226,13 @@ impl<'gc> Font<'gc> {
         Twips::new((self.0.ascent as f32 * scale) as i32)
     }
 
+    /// Get the descent from the baseline to the bottom of the glyph at a given height.
+    pub fn get_descent_for_height(&self, height: Twips) -> Twips {
+        let scale = height.get() as f32 / self.scale();
+
+        Twips::new((self.0.descent as f32 * scale) as i32)
+    }
+
     /// Returns whether this font contains kerning information.
     pub fn has_kerning_info(&self) -> bool {
         !self.0.kerning_pairs.is_empty()

core/src/html.rs

@@ -8,7 +8,7 @@ mod text_format;
 pub use dimensions::BoxBounds;
 pub use dimensions::Position;
 pub use dimensions::Size;
-pub use layout::{LayoutBox, LayoutContent};
+pub use layout::{LayoutBox, LayoutContent, LayoutMetrics};
 pub use text_format::{FormatSpans, TextFormat, TextSpan};
 
 #[cfg(test)]

core/src/html/layout.rs

@@ -555,7 +555,7 @@ impl<'a, 'gc> LayoutContext<'a, 'gc> {
 #[derive(Clone, Debug, Collect)]
 #[collect(no_drop)]
 pub struct LayoutBox<'gc> {
-    /// The rectangle corresponding to the outer boundaries of the
+    /// The rectangle corresponding to the outer boundaries of the content box.
     bounds: BoxBounds<Twips>,
 
     /// What content is contained by the content box.
@@ -841,3 +841,14 @@ impl<'gc> LayoutBox<'gc> {
         matches!(&self.content, LayoutContent::Bullet { .. })
     }
 }
+
+pub struct LayoutMetrics {
+    pub ascent: Twips,
+    pub descent: Twips,
+    pub leading: Twips,
+
+    pub width: Twips,
+    pub height: Twips,
+
+    pub x: Twips,
+}