annotation: TEXT/MTEXT store the model height of their default scale

Annotative text in DWG/DXF holds the model height of its default
(native) scale representation; other scales draw it at the ratio of the
two. OCS read the stored value as paper height and multiplied it by the
annotation scale again, so text from AutoCAD came out far too small
(#1734), and annotative text OCS wrote came out too small in AutoCAD.

- Rendering uses the active/native context ratio (1 when the object has
  no representation for the displayed scale).
- TEXT with an annotative style asks for the paper height, stores the
  model height of the creation scale and gets that context; MTEXT
  starts from the model height; ANNOUPDATE converts a fixed style
  height the same way.
- Properties: the Height row of annotative TEXT and MTEXT is the paper
  height at the displayed scale, with the model height beside it, and
  an edit converts back. MTEXT shows Annotative when it has contexts.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

src/scene/annotative.rs

@@ -722,18 +722,12 @@ pub fn effective_annotation_scale_for(
     if !context_annotative && (text_like || !style_annotative) {
         return 1.0;
     }
-    // Annotative TEXT/MTEXT store their paper text height as the base value.
-    // `fallback` is the absolute paper-to-model multiplier for the active
-    // annotation scale and already includes the drawing's INSUNITS conversion.
-    //
-    // Example for a metre drawing with 2 mm paper text:
-    //   1:1   -> 2 * 0.001 = 0.002 m
-    //   1:100 -> 2 * 0.100 = 0.200 m
-    //
-    // Using active/native here would only produce 1 / 100 and would lose the
-    // millimetre-to-metre conversion entirely.
+    // Annotative TEXT/MTEXT store the model height of their default (native)
+    // scale representation; another scale draws it at the ratio of the two.
+    // A scale the object has no representation for shows the stored one.
     if matches!(entity, EntityType::Text(_) | EntityType::MText(_)) {
-        return fallback;
+        return text_context_ratio(doc, entity.common().handle, scale_handle)
+            .map_or(1.0, |ratio| ratio as f32);
     }
     if matches!(
         entity,
@@ -750,41 +744,39 @@ pub fn effective_annotation_scale_for(
         return fallback;
     }
 
-    let Some(coll_h) = annotation_scales_dict(doc, entity.common().handle) else {
-        return fallback;
-    };
-    let Some(coll) = as_dict(doc, coll_h) else {
-        return fallback;
-    };
+    text_context_ratio(doc, entity.common().handle, scale_handle)
+        .map_or(fallback, |ratio| ratio as f32)
+}
 
-    let active = active_object_context_for_scale(doc, entity.common().handle, scale_handle);
+/// How much larger the representation at `scale_handle` (the displayed scale
+/// when `None`) draws than the object's default representation: the ratio of
+/// their model-per-paper factors. `None` when either is missing.
+pub fn text_context_ratio(
+    doc: &CadDocument,
+    handle: Handle,
+    scale_handle: Option<Handle>,
+) -> Option<f64> {
+    let coll = as_dict(doc, annotation_scales_dict(doc, handle)?)?;
+    let active = active_object_context_for_scale(doc, handle, scale_handle)?;
     let native = coll
         .entries
         .iter()
         .find_map(|(_, leaf_h)| match doc.objects.get(leaf_h) {
             Some(ObjectType::ObjectContextData(leaf)) if leaf.is_default => Some(leaf),
             _ => None,
-        });
-    let (Some(active), Some(native)) = (active, native) else {
-        return fallback;
-    };
+        })?;
     let (Some(ObjectType::Scale(active_scale)), Some(ObjectType::Scale(native_scale))) = (
         doc.objects.get(&active.scale),
         doc.objects.get(&native.scale),
     ) else {
-        return fallback;
+        return None;
     };
-
     let native_factor = native_scale.inverse_factor();
     if native_factor.abs() <= 1.0e-12 {
-        return fallback;
+        return None;
     }
     let relative = active_scale.inverse_factor() / native_factor;
-    if relative.is_finite() && relative > 0.0 {
-        relative as f32
-    } else {
-        fallback
-    }
+    (relative.is_finite() && relative > 0.0).then_some(relative)
 }
 
 fn text_horizontal(value: i16) -> codec::entities::TextHorizontalAlignment {
@@ -1864,6 +1856,7 @@ pub fn update_entity_from_annotation_style(
     doc: &mut CadDocument,
     handle: Handle,
     current_scale: Option<Handle>,
+    paper_to_model: f64,
 ) -> bool {
     enum StyleUpdate {
         Text { annotative: bool, height: f64 },
@@ -1943,19 +1936,10 @@ pub fn update_entity_from_annotation_style(
         return false;
     };
 
+    let mut style_height = None;
     let annotative = match update {
         StyleUpdate::Text { annotative, height } => {
-            if height > 0.0 {
-                if let Some(entity) = doc.get_entity_mut(handle) {
-                    match entity {
-                        EntityType::Text(text) => text.height = height,
-                        EntityType::MText(text) => text.height = height,
-                        EntityType::AttributeEntity(attribute) => attribute.height = height,
-                        EntityType::AttributeDefinition(attribute) => attribute.height = height,
-                        _ => {}
-                    }
-                }
-            }
+            style_height = (height > 0.0).then_some(height);
             annotative
         }
         StyleUpdate::Dimension { annotative } => annotative,
@@ -1972,6 +1956,27 @@ pub fn update_entity_from_annotation_style(
             create_annotation_context(doc, handle, scale);
         }
     }
+    if let Some(mut height) = style_height {
+        // An annotative style's height is on paper; the entity stores the
+        // model height of its default representation.
+        let text = matches!(
+            doc.get_entity(handle),
+            Some(EntityType::Text(_) | EntityType::MText(_))
+        );
+        if annotative && text {
+            let ratio = text_context_ratio(doc, handle, current_scale).unwrap_or(1.0);
+            height *= paper_to_model / ratio;
+        }
+        if let Some(entity) = doc.get_entity_mut(handle) {
+            match entity {
+                EntityType::Text(text) => text.height = height,
+                EntityType::MText(text) => text.height = height,
+                EntityType::AttributeEntity(attribute) => attribute.height = height,
+                EntityType::AttributeDefinition(attribute) => attribute.height = height,
+                _ => {}
+            }
+        }
+    }
     true
 }
 

src/scene/mod.rs

@@ -6176,6 +6176,31 @@ impl Scene {
         added
     }
 
+    /// For an annotative TEXT/MTEXT, its stored height per unit of paper text
+    /// height at the displayed scale (the stored height is the model height
+    /// of its default representation). `None` for anything else.
+    pub(crate) fn annotative_text_height_factor(&self, handle: Handle) -> Option<f64> {
+        let entity = self.document.get_entity(handle)?;
+        if !matches!(entity, EntityType::Text(_) | EntityType::MText(_))
+            || !crate::scene::annotative::is_annotative(&self.document, entity)
+        {
+            return None;
+        }
+        let scale = self.displayed_annotation_scale_handle();
+        let model_per_paper = scale
+            .and_then(|scale| match self.document.objects.get(&scale) {
+                Some(ObjectType::Scale(scale)) => {
+                    Some(scale.inverse_factor() / self.annotation_scale_unit_factor())
+                }
+                _ => None,
+            })
+            .unwrap_or(self.annotation_scale as f64);
+        let ratio =
+            crate::scene::annotative::text_context_ratio(&self.document, handle, scale)
+                .unwrap_or(1.0);
+        Some(model_per_paper / ratio)
+    }
+
     pub(crate) fn displayed_annotation_scale_handle(&self) -> Option<Handle> {
         if self.current_layout == "Model" {
             return self.scale_object_handle(&self.document.header.current_annotation_scale);