Add configurable tab width (DirectWrite and Pango)

piet-cairo/src/text.rs

@@ -7,7 +7,7 @@ use std::rc::Rc;
 
 use glib::translate::{from_glib_full, ToGlibPtr};
 
-use pango::{AttrList, FontMapExt};
+use pango::{AttrList, FontMapExt, TabAlign, TabArray};
 use pango_sys::pango_attr_insert_hyphens_new;
 use pangocairo::FontMap;
 
@@ -49,9 +49,12 @@ pub struct CairoTextLayout {
 
 pub struct CairoTextLayoutBuilder {
     text: Rc<dyn TextStorage>,
+
     defaults: util::LayoutDefaults,
     attributes: Vec<AttributeWithRange>,
     last_range_start_pos: usize,
+
+    tab_width: Option<f64>,
     width_constraint: f64,
     pango_layout: PangoLayout,
 }
@@ -193,6 +196,7 @@ impl Text for CairoText {
             defaults: util::LayoutDefaults::default(),
             attributes: Vec::new(),
             last_range_start_pos: 0,
+            tab_width: None,
             width_constraint: f64::INFINITY,
             pango_layout,
         }
@@ -213,6 +217,11 @@ impl TextLayoutBuilder for CairoTextLayoutBuilder {
         self
     }
 
+    fn tab_width(mut self, width: f64) -> Self {
+        self.tab_width = Some(width);
+        self
+    }
+
     fn alignment(self, alignment: TextAlignment) -> Self {
         /*
          * NOTE: Pango has `auto_dir` enabled by default. This means that
@@ -277,6 +286,13 @@ impl TextLayoutBuilder for CairoTextLayoutBuilder {
     }
 
     fn build(self) -> Result<Self::Out, Error> {
+        if let Some(tab_width) = self.tab_width {
+            let tab_width = (tab_width * PANGO_SCALE) as i32;
+            let mut array = TabArray::new(1, false);
+            array.set_tab(0, TabAlign::Left, tab_width);
+            self.pango_layout.set_tabs(Some(&array));
+        }
+
         let pango_attributes = AttrList::new();
         let add_attribute = |attribute| {
             if let Some(attribute) = attribute {

piet-coregraphics/src/text.rs

@@ -514,6 +514,10 @@ impl TextLayoutBuilder for CoreGraphicsTextLayoutBuilder {
         self
     }
 
+    fn tab_width(self, _width: f64) -> Self {
+        self
+    }
+
     fn alignment(mut self, alignment: piet::TextAlignment) -> Self {
         self.alignment = alignment;
         self

piet-direct2d/src/dwrite.rs

@@ -341,6 +341,12 @@ impl TextLayout {
         }
     }
 
+    pub(crate) fn set_incremental_tab_stop(&self, distance: f32) {
+        unsafe {
+            self.0.SetIncrementalTabStop(distance);
+        }
+    }
+
     /// Set the weight for a range of this layout. `start` and `len` are in utf16.
     pub(crate) fn set_weight(&mut self, range: Utf16Range, weight: FontWeight) {
         let weight = weight.to_raw() as DWRITE_FONT_WEIGHT;

piet-direct2d/src/text.rs

@@ -84,6 +84,7 @@ pub struct D2DTextLayout {
 pub struct D2DTextLayoutBuilder {
     text: Rc<dyn TextStorage>,
     layout: Result<dwrite::TextLayout, Error>,
+    tab_width: Option<f32>,
     len_utf16: usize,
     loaded_fonts: D2DLoadedFonts,
     default_font: FontFamily,
@@ -161,6 +162,7 @@ impl Text for D2DText {
         D2DTextLayoutBuilder {
             layout,
             text,
+            tab_width: None,
             len_utf16: wide_str.len(),
             colors: Vec::new(),
             loaded_fonts: self.loaded_fonts.clone(),
@@ -186,6 +188,11 @@ impl TextLayoutBuilder for D2DTextLayoutBuilder {
         self
     }
 
+    fn tab_width(mut self, width: f64) -> Self {
+        self.tab_width = Some(width as f32);
+        self
+    }
+
     fn alignment(mut self, alignment: TextAlignment) -> Self {
         if let Ok(layout) = self.layout.as_mut() {
             layout.set_alignment(alignment);
@@ -229,6 +236,10 @@ impl TextLayoutBuilder for D2DTextLayoutBuilder {
         let (default_line_height, default_baseline) = self.get_default_line_height_and_baseline();
         let layout = self.layout?;
 
+        if let Some(tab_width) = self.tab_width {
+            layout.set_incremental_tab_stop(tab_width);
+        }
+
         let mut layout = D2DTextLayout {
             text: self.text,
             colors: self.colors.into(),

piet-svg/src/text.rs

@@ -47,6 +47,10 @@ impl piet::TextLayoutBuilder for TextLayoutBuilder {
         self
     }
 
+    fn tab_width(self, _width: f64) -> Self {
+        self
+    }
+
     fn alignment(self, _alignment: piet::TextAlignment) -> Self {
         self
     }

piet-web/src/text.rs

@@ -144,6 +144,10 @@ impl TextLayoutBuilder for WebTextLayoutBuilder {
         self
     }
 
+    fn tab_width(self, _width: f64) -> Self {
+        self
+    }
+
     fn alignment(self, _alignment: piet::TextAlignment) -> Self {
         web_sys::console::log_1(&"TextLayout alignment unsupported on web".into());
         self

piet/src/null_renderer.rs

@@ -157,6 +157,10 @@ impl TextLayoutBuilder for NullTextLayoutBuilder {
         self
     }
 
+    fn tab_width(self, _width: f64) -> Self {
+        self
+    }
+
     fn alignment(self, _alignment: crate::TextAlignment) -> Self {
         self
     }

piet/src/text.rs

@@ -175,6 +175,12 @@ pub trait TextLayoutBuilder: Sized {
     /// default behaviour.
     fn max_width(self, width: f64) -> Self;
 
+    /// Set the base tabulator width.
+    ///
+    /// The width specified here controls the max width for tab characters
+    /// in the final layout.
+    fn tab_width(self, width: f64) -> Self;
+
     /// Set the [`TextAlignment`] to be used for this layout.
     ///
     /// [`TextAlignment`]: enum.TextAlignment.html