fix: caret scroll on text overflows (#19)

Author: antouhou

Cargo.lock

@@ -1,6 +1,6 @@
 [package]
 name = "protextinator"
-version = "0.5.0"
+version = "0.5.1"
 edition = "2021"
 description = "Text management, made simple"
 keywords = ["text", "rendering", "gui", "graphics", "image"]

Cargo.toml

@@ -27,7 +27,7 @@ pub(crate) fn vertical_offset(
     }
 }
 
-/// Ensures the caret is vertically visible by adjusting buffer scroll using DEVICE pixels.
+/// Ensures the caret is vertically visible by adjusting the buffer scroll using DEVICE pixels.
 /// Returns caret top-left in LOGICAL pixels relative to the viewport.
 pub(crate) fn adjust_vertical_scroll_to_make_caret_visible(
     buffer: &mut Buffer,
@@ -37,15 +37,21 @@ pub(crate) fn adjust_vertical_scroll_to_make_caret_visible(
     style: &TextStyle,
     scale_factor: f32,
 ) -> Option<Point> {
-    let mut editor = Editor::new(&mut *buffer);
-    editor.set_cursor(current_char_byte_cursor.cursor);
-
-    let caret_position = editor.cursor_position();
+    let mut caret_position =
+        cursor_position_with_trailing_space_fallback(&mut *buffer, current_char_byte_cursor);
+
+    if caret_position.is_none() {
+        let mut editor = Editor::new(&mut *buffer);
+        editor.set_cursor(current_char_byte_cursor.cursor);
+        editor.shape_as_needed(font_system, false);
+        caret_position =
+            cursor_position_with_trailing_space_fallback(&mut *buffer, current_char_byte_cursor);
+    }
 
     match caret_position {
         Some(position) => {
-            // caret position from cosmic_text is in DEVICE pixels
-            let mut caret_top_left_corner = Point::from(position);
+            // caret position is in DEVICE pixels
+            let mut caret_top_left_corner = position;
             let mut scroll = buffer.scroll();
             let scale = scale_factor.max(0.01);
             let line_height_device = style.line_height_pt() * scale;
@@ -68,38 +74,63 @@ pub(crate) fn adjust_vertical_scroll_to_make_caret_visible(
                 caret_top_left_corner.y / scale,
             ))
         }
-        None => {
-            // Caret is not visible, we need to shape the text and move the scroll
-            editor.shape_as_needed(font_system, false);
-
-            // TODO: Let's keep it the code below for a little while, it might be useful in the
-            //  future.
-
-            // If it's not visible, and the scroll is already at the top, that means that we're
-            //  at the end of the text, and we need to scroll to the bottom to avoid jumping to
-            //  the top of the text.
-            // if style.vertical_alignment == VerticalTextAlignment::End {
-            //     editor.with_buffer_mut(|buffer| {
-            //         let mut scroll = buffer.scroll();
-            //         if scroll.vertical == 0.0 && buffer_inner_dimensions.y < text_area_size.y {
-            //             let vertical_scroll_to_align_text = calculate_vertical_offset(
-            //                 style,
-            //                 text_area_size,
-            //                 buffer_inner_dimensions,
-            //             );
-            //             scroll.vertical = vertical_scroll_to_align_text;
-            //             buffer.set_scroll(scroll);
-            //         }
-            //     });
-            // }
-            // Return caret position in LOGICAL pixels
-            editor.cursor_position().map(|p| {
-                let p = Point::from(p);
-                let scale = scale_factor.max(0.01);
-                Point::new(p.x / scale, p.y / scale)
-            })
+        None => None,
+    }
+}
+
+pub(crate) fn cursor_position_with_trailing_space_fallback(
+    buffer: &mut Buffer,
+    current_char_byte_cursor: ByteCursor,
+) -> Option<Point> {
+    let cursor = current_char_byte_cursor.cursor;
+    let mut caret_position = {
+        let mut editor = Editor::new(&mut *buffer);
+        editor.set_cursor(cursor);
+        editor.cursor_position().map(Point::from)?
+    };
+
+    if let Some(run_line_width) = run_line_width_for_cursor_with_matching_vertical_position(
+        &*buffer,
+        cursor,
+        caret_position.y,
+    ) {
+        if run_line_width > caret_position.x {
+            caret_position.x = run_line_width;
+        }
+    }
+
+    Some(caret_position)
+}
+
+fn run_line_width_for_cursor_with_matching_vertical_position(
+    buffer: &Buffer,
+    cursor: Cursor,
+    cursor_y_position: f32,
+) -> Option<f32> {
+    for run in buffer.layout_runs() {
+        if run.line_i != cursor.line {
+            continue;
+        }
+
+        let cursor_is_at_line_end = cursor.index == run.text.len();
+        let line_has_trailing_whitespace = run
+            .text
+            .chars()
+            .last()
+            .map(|character| character.is_whitespace())
+            .unwrap_or(false);
+
+        if !cursor_is_at_line_end || !line_has_trailing_whitespace {
+            continue;
+        }
+
+        let same_visual_line = (run.line_top - cursor_y_position).abs() <= 1.0;
+        if same_visual_line {
+            return Some(run.line_w);
         }
     }
+
+    None
 }
 
 /// Hit-test a character under a LOGICAL pixel coordinate, accounting for scroll and scale.

src/buffer_utils.rs

@@ -5,8 +5,8 @@
 
 use crate::action::{Action, ActionResult};
 use crate::buffer_utils::{
-    adjust_vertical_scroll_to_make_caret_visible, char_under_position, update_buffer,
-    vertical_offset,
+    adjust_vertical_scroll_to_make_caret_visible, char_under_position,
+    cursor_position_with_trailing_space_fallback, update_buffer, vertical_offset,
 };
 use crate::byte_cursor::ByteCursor;
 use crate::math::Size;
@@ -958,17 +958,15 @@ impl<T> TextState<T> {
         // Return caret position in LOGICAL pixels relative to viewport
         let horizontal_scroll_device = self.buffer.scroll().horizontal;
         let scale = self.params.scale_factor().max(0.01);
-        let mut editor = Editor::new(&mut self.buffer);
-        editor.set_cursor(self.cursor.cursor);
-
-        editor.cursor_position().map(|pos| {
-            // pos from cosmic_text is in DEVICE pixels
-            let mut point_device = Point::from(pos);
-            // Adjust by horizontal scroll (device px)
-            point_device.x -= horizontal_scroll_device;
-            // Convert to logical
-            Point::new(point_device.x / scale, point_device.y / scale)
-        })
+        cursor_position_with_trailing_space_fallback(&mut self.buffer, self.cursor).map(
+            |mut point_device| {
+                // pos from cosmic_text is in DEVICE pixels
+                // Adjust by horizontal scroll (device px)
+                point_device.x -= horizontal_scroll_device;
+                // Convert to logical
+                Point::new(point_device.x / scale, point_device.y / scale)
+            },
+        )
     }
 
     fn align_vertically(&mut self) {
@@ -1159,23 +1157,61 @@ impl<T> TextState<T> {
         let base_color = cosmic_text::Color::rgba(0, 0, 0, 0);
         let text_width = width;
         let text_height = height;
+        let horizontal_scroll_device = self.buffer.scroll().horizontal.round() as i64;
         // TODO: make an atlas via an adapter trait or something that can be passed to here from the renderer
         self.buffer.draw(
             &mut ctx.font_system,
             &mut ctx.swash_cache,
             base_color,
             |x, y, mut w, mut h, color| {
-                // Clip to buffer bounds
-                let (x0, y0) = ((x as u32).min(text_width), (y as u32).min(text_height));
-                if x0 >= text_width || y0 >= text_height || w == 0 || h == 0 {
+                if w == 0 || h == 0 {
                     return;
                 }
-                if x0 + w > text_width {
-                    w = text_width - x0;
+
+                // Use signed clipping first because scrolled glyphs can produce negative device
+                // coordinates. Casting negatives to unsigned would incorrectly wrap and skip
+                // visible glyph portions near the viewport edge.
+                // Cosmic-text horizontal scroll is not reflected in draw callback coordinates,
+                // so apply it explicitly here to keep rasterized output in sync with the buffer.
+                let mut x_device = x as i64 - horizontal_scroll_device;
+                let mut y_device = y as i64;
+                let mut width_device = w as i64;
+                let mut height_device = h as i64;
+
+                if x_device < 0 {
+                    let cut = -x_device;
+                    if cut >= width_device {
+                        return;
+                    }
+                    x_device = 0;
+                    width_device -= cut;
+                }
+                if y_device < 0 {
+                    let cut = -y_device;
+                    if cut >= height_device {
+                        return;
+                    }
+                    y_device = 0;
+                    height_device -= cut;
+                }
+
+                if x_device >= text_width as i64 || y_device >= text_height as i64 {
+                    return;
                 }
-                if y0 + h > text_height {
-                    h = text_height - y0;
+                let max_width = text_width as i64 - x_device;
+                let max_height = text_height as i64 - y_device;
+                width_device = width_device.min(max_width);
+                height_device = height_device.min(max_height);
+
+                if width_device <= 0 || height_device <= 0 {
+                    return;
                 }
+
+                let x0 = x_device as u32;
+                let y0 = y_device as u32;
+                w = width_device as u32;
+                h = height_device as u32;
+
                 // Precompute the 4-byte pixel once per rectangle and use row-wise fills
                 let mut packed_px = [0u8; 4];
                 match alpha_mode {

src/state.rs

@@ -233,3 +233,39 @@ pub fn test_insert_newline_at_end_of_text() {
     assert_eq!(text_state.text(), "Hello\n\n");
     assert_eq!(text_state.cursor_char_index(), Some(6));
 }
+
+#[test]
+pub fn test_click_after_text_then_insert_keeps_caret_moving_forward() {
+    let mut ctx = TextContext::default();
+    let initial_text = "Hehe".to_string();
+
+    let mut text_state = TextState::new_with_text(initial_text, &mut ctx.font_system, ());
+    text_state.set_outer_size(&Point::from((200.0, 25.0)));
+    text_state.is_editable = true;
+    text_state.is_editing = true;
+    text_state.is_selectable = true;
+    text_state.are_actions_enabled = true;
+    text_state.recalculate(&mut ctx);
+
+    // Click in trailing empty space to place caret at the end.
+    text_state.handle_press(&mut ctx, Point::new(198.0, 10.0));
+    assert_eq!(text_state.cursor_char_index(), Some(4));
+    let caret_x_before_insert = text_state
+        .caret_position_relative()
+        .expect("Caret should be visible")
+        .x;
+
+    let result = text_state.apply_action(&mut ctx, &Action::InsertChar("x".into()));
+    assert!(matches!(result, ActionResult::TextChanged));
+    assert_eq!(text_state.text(), "Hehex");
+    assert_eq!(text_state.cursor_char_index(), Some(5));
+
+    let caret_x_after_insert = text_state
+        .caret_position_relative()
+        .expect("Caret should be visible")
+        .x;
+    assert!(
+        caret_x_after_insert > caret_x_before_insert,
+        "Caret should move to the right after inserting at end. before={caret_x_before_insert}, after={caret_x_after_insert}"
+    );
+}