Automatic line break when text overflows max_width

emgui/src/font.rs

@@ -1,5 +1,27 @@
 use rusttype::{point, Scale};
 
+use crate::math::{vec2, Vec2};
+
+pub struct TextFragment {
+    /// The start of each character, starting at zero.
+    pub x_offsets: Vec<f32>,
+    /// 0 for the first line, n * line_spacing for the rest
+    pub y_offset: f32,
+    pub text: String,
+}
+
+impl TextFragment {
+    pub fn min_x(&self) -> f32 {
+        *self.x_offsets.first().unwrap()
+    }
+
+    pub fn max_x(&self) -> f32 {
+        *self.x_offsets.last().unwrap()
+    }
+}
+
+// ----------------------------------------------------------------------------
+
 #[derive(Clone, Copy, Debug, PartialEq)]
 pub struct UvRect {
     /// X/Y offset for nice rendering
@@ -190,27 +212,109 @@ impl Font {
         }
     }
 
-    /// Returns the start (X) of each character, starting at zero, plus the total width.
+    /// Returns the a single line of characters separated into words
-    /// i.e. returns text.chars().count() + 1 numbers.
+    pub fn layout_single_line(&self, text: &str) -> Vec<TextFragment> {
-    pub fn layout_single_line(&self, text: &str) -> Vec<f32> {
         let scale = Scale::uniform(self.scale as f32);
 
-        let mut x_offsets = Vec::new();
+        let mut current_fragment = TextFragment {
+            x_offsets: vec![0.0],
+            y_offset: 0.0,
+            text: String::new(),
+        };
+        let mut all_fragments = vec![];
         let mut cursor_x = 0.0f32;
         let mut last_glyph_id = None;
+
         for c in text.chars() {
-            cursor_x = cursor_x.round();
-            x_offsets.push(cursor_x);
             if let Some(glyph) = self.glyph_info(c) {
                 if let Some(last_glyph_id) = last_glyph_id {
                     cursor_x += self.font.pair_kerning(scale, last_glyph_id, glyph.id)
                 }
                 cursor_x += glyph.advance_width;
+                cursor_x = cursor_x.round();
                 last_glyph_id = Some(glyph.id);
+
+                let is_space = glyph.uv.is_none();
+                if is_space {
+                    // TODO: also break after hyphens etc
+                    if !current_fragment.text.is_empty() {
+                        all_fragments.push(current_fragment);
+                        current_fragment = TextFragment {
+                            x_offsets: vec![cursor_x],
+                            y_offset: 0.0,
+                            text: String::new(),
+                        }
+                    }
+                } else {
+                    current_fragment.text.push(c);
+                    current_fragment.x_offsets.push(cursor_x);
+                }
+            } else {
+                // Ignore unknown glyph
             }
         }
-        x_offsets.push(cursor_x);
+
-        x_offsets
+        if !current_fragment.text.is_empty() {
+            all_fragments.push(current_fragment)
+        }
+        all_fragments
+    }
+
+    pub fn layout_single_line_max_width(&self, text: &str, max_width: f32) -> Vec<TextFragment> {
+        let mut words = self.layout_single_line(text);
+        if words.is_empty() || words.last().unwrap().max_x() <= max_width {
+            return words; // Early-out
+        }
+
+        let line_spacing = self.line_spacing();
+
+        // Break up lines:
+        let mut line_start_x = 0.0;
+        let mut cursor_y = 0.0;
+
+        for word in words.iter_mut().skip(1) {
+            if word.max_x() - line_start_x >= max_width {
+                // Time for a new line:
+                cursor_y += line_spacing;
+                line_start_x = word.min_x();
+            }
+
+            word.y_offset += cursor_y;
+            for x in &mut word.x_offsets {
+                *x -= line_start_x;
+            }
+        }
+
+        words
+    }
+
+    /// Returns each line + total bounding box size.
+    pub fn layout_multiline(&self, text: &str, max_width: f32) -> (Vec<TextFragment>, Vec2) {
+        let line_spacing = self.line_spacing();
+        let mut cursor_y = 0.0;
+        let mut text_fragments = Vec::new();
+        for line in text.split('\n') {
+            let mut line_fragments = self.layout_single_line_max_width(&line, max_width);
+            if let Some(last_word) = line_fragments.last() {
+                let line_height = last_word.y_offset + line_spacing;
+                for fragment in &mut line_fragments {
+                    fragment.y_offset += cursor_y;
+                }
+                text_fragments.append(&mut line_fragments);
+                cursor_y += line_height; // TODO: add extra spacing between paragraphs
+            } else {
+                cursor_y += line_spacing;
+            }
+            cursor_y = cursor_y.round();
+        }
+
+        let mut widest_line = 0.0;
+        for fragment in &text_fragments {
+            widest_line = fragment.max_x().max(widest_line);
+        }
+
+        let bounding_size = vec2(widest_line, cursor_y);
+        (text_fragments, bounding_size)
     }
 
     pub fn debug_print_atlas_ascii_art(&self) {

emgui/src/layout.rs

@@ -5,7 +5,7 @@ use std::{
 };
 
 use crate::{
-    font::Font,
+    font::{Font, TextFragment},
     math::*,
     types::*,
     widgets::{label, Widget},
@@ -95,18 +95,6 @@ pub struct Memory {
 
 // ----------------------------------------------------------------------------
 
-pub struct TextFragment {
-    /// The start of each character, starting at zero.
-    x_offsets: Vec<f32>,
-    /// 0 for the first line, n * line_spacing for the rest
-    y_offset: f32,
-    text: String,
-}
-
-pub type TextFragments = Vec<TextFragment>;
-
-// ----------------------------------------------------------------------------
-
 #[derive(Clone, Copy, Debug, PartialEq)]
 pub enum Direction {
     Horizontal,
@@ -220,7 +208,7 @@ where
         dir: Direction::Vertical,
         cursor: window_pos + window_padding,
         bounding_size: vec2(0.0, 0.0),
-        available_space: vec2(400.0, std::f32::INFINITY), // TODO
+        available_space: vec2(400.0, std::f32::INFINITY), // TODO: popup/tooltip width
     };
 
     add_contents(&mut popup_region);
@@ -283,6 +271,14 @@ impl Region {
         self.cursor
     }
 
+    pub fn font(&self) -> &Font {
+        &*self.data.font
+    }
+
+    pub fn width(&self) -> f32 {
+        self.available_space.x
+    }
+
     // ------------------------------------------------------------------------
     // Sub-regions:
 
@@ -297,7 +293,7 @@ impl Region {
         );
         let text: String = text.into();
         let id = self.make_child_id(&text);
-        let (text, text_size) = self.layout_text(&text);
+        let (text, text_size) = self.font().layout_multiline(&text, self.width());
         let text_cursor = self.cursor + self.options().button_padding;
         let (rect, interact) = self.reserve_space(
             vec2(
@@ -434,7 +430,6 @@ impl Region {
 
     // ------------------------------------------------------------------------
 
-    // TODO: Return a Rect
     pub fn reserve_space(
         &mut self,
         size: Vec2,
@@ -499,28 +494,6 @@ impl Region {
         })
     }
 
-    // TODO: move this function to Font
-    pub fn layout_text(&self, text: &str) -> (TextFragments, Vec2) {
-        let line_spacing = self.data.font.line_spacing();
-        let mut cursor_y = 0.0;
-        let mut max_width = 0.0;
-        let mut text_fragments = Vec::new();
-        for line in text.split('\n') {
-            let x_offsets = self.data.font.layout_single_line(&line);
-            let line_width = *x_offsets.last().unwrap();
-            text_fragments.push(TextFragment {
-                x_offsets,
-                y_offset: cursor_y,
-                text: line.into(),
-            });
-
-            cursor_y += line_spacing;
-            max_width = line_width.max(max_width);
-        }
-        let bounding_size = vec2(max_width, cursor_y);
-        (text_fragments, bounding_size)
-    }
-
     pub fn add_text(&mut self, pos: Vec2, text: Vec<TextFragment>) {
         for fragment in text {
             self.add_graphic(GuiCmd::Text {

emgui/src/widgets.rs

@@ -29,7 +29,7 @@ pub fn label<S: Into<String>>(text: S) -> Label {
 
 impl Widget for Label {
     fn add_to(self, region: &mut Region) -> GuiResponse {
-        let (text, text_size) = region.layout_text(&self.text);
+        let (text, text_size) = region.font().layout_multiline(&self.text, region.width());
         region.add_text(region.cursor(), text);
         let (_, interact) = region.reserve_space(text_size, None);
         region.response(interact)
@@ -51,7 +51,7 @@ impl Button {
 impl Widget for Button {
     fn add_to(self, region: &mut Region) -> GuiResponse {
         let id = region.make_child_id(&self.text);
-        let (text, text_size) = region.layout_text(&self.text);
+        let (text, text_size) = region.font().layout_multiline(&self.text, region.width());
         let text_cursor = region.cursor() + region.options().button_padding;
         let (rect, interact) =
             region.reserve_space(text_size + 2.0 * region.options().button_padding, Some(id));
@@ -81,7 +81,7 @@ impl<'a> Checkbox<'a> {
 impl<'a> Widget for Checkbox<'a> {
     fn add_to(self, region: &mut Region) -> GuiResponse {
         let id = region.make_child_id(&self.text);
-        let (text, text_size) = region.layout_text(&self.text);
+        let (text, text_size) = region.font().layout_multiline(&self.text, region.width());
         let text_cursor = region.cursor()
             + region.options().button_padding
             + vec2(region.options().start_icon_width, 0.0);
@@ -129,7 +129,7 @@ pub fn radio<S: Into<String>>(checked: bool, text: S) -> RadioButton {
 impl Widget for RadioButton {
     fn add_to(self, region: &mut Region) -> GuiResponse {
         let id = region.make_child_id(&self.text);
-        let (text, text_size) = region.layout_text(&self.text);
+        let (text, text_size) = region.font().layout_multiline(&self.text, region.width());
         let text_cursor = region.cursor()
             + region.options().button_padding
             + vec2(region.options().start_icon_width, 0.0);
@@ -196,7 +196,7 @@ impl<'a> Widget for Slider<'a> {
             naked.text = None;
 
             if text_on_top {
-                let (text, text_size) = region.layout_text(&full_text);
+                let (text, text_size) = region.font().layout_multiline(&full_text, region.width());
                 region.add_text(region.cursor(), text);
                 region.reserve_space_inner(text_size);
                 naked.add_to(region)