feat: implement pixel-perfect custom rendering for block elements, powerline and box drawing

- Render block elements (U+2580-U+259F), box drawing lines, and powerline characters using precise GPUI vector paths instead of fonts.

- Snap logical coordinates to exact physical pixels using window.scale_factor() to perfectly eliminate SDF anti-aliasing gaps and bleeding.

- Fixes visual seams in terminal UI layouts.

src/terminal/custom_blocks.rs

@@ -0,0 +1,251 @@
+use gpui::{Bounds, Hsla, Path, Pixels, Window, fill, point, px, size};
+
+pub fn is_custom_block_supported(c: char) -> bool {
+    match c as u32 {
+        0x2580..=0x258F | 0x2590 | 0x2594..=0x259F => true, // Block Elements
+        0x2500 | 0x2502 | 0x250C | 0x2510 | 0x2514 | 0x2518 | 0x251C | 0x2524 | 0x252C | 0x2534 | 0x253C => true, // Light lines
+        0x2501 | 0x2503 | 0x250F | 0x2513 | 0x2517 | 0x251B | 0x2523 | 0x252B | 0x2533 | 0x253B | 0x254B => true, // Heavy lines
+        0xE0B0..=0xE0B6 => true, // Powerline
+        _ => false,
+    }
+}
+
+pub fn paint_custom_block(
+    window: &mut Window,
+    c: char,
+    raw_x: f32,
+    raw_y: f32,
+    raw_w: f32,
+    raw_h: f32,
+    color: Hsla,
+) -> bool {
+    let scale = window.scale_factor();
+
+    let x = px((raw_x * scale).round() / scale);
+    let y = px((raw_y * scale).round() / scale);
+    let w = px(((raw_x + raw_w) * scale).round() / scale) - x;
+    let h = px(((raw_y + raw_h) * scale).round() / scale) - y;
+
+    let mut painted = false;
+
+    // Helper to paint a quad snapping its true physical boundaries to integer physical pixels
+    let mut paint_quad = |qx: Pixels, qy: Pixels, qw: Pixels, qh: Pixels| {
+        let l = px((qx.as_f32() * scale).round() / scale);
+        let t = px((qy.as_f32() * scale).round() / scale);
+        let r = px(((qx + qw).as_f32() * scale).round() / scale);
+        let b = px(((qy + qh).as_f32() * scale).round() / scale);
+        window.paint_quad(fill(Bounds::new(point(l, t), size(r - l, b - t)), color));
+        painted = true;
+    };
+
+    let px_1 = px(1.0);
+    let px_2 = px(2.0);
+
+    // Box drawing thickness
+    let light = (w * 0.1).max(px_1);
+    let heavy = (w * 0.2).max(px_2);
+    let cx = x + w / 2.0;
+    let cy = y + h / 2.0;
+
+    match c as u32 {
+        // --- Block Elements (U+2580..=U+259F) ---
+        0x2580 => paint_quad(x, y, w, h / 2.0),
+        0x2581 => paint_quad(x, y + h * 7.0 / 8.0, w, h / 8.0),
+        0x2582 => paint_quad(x, y + h * 3.0 / 4.0, w, h / 4.0),
+        0x2583 => paint_quad(x, y + h * 5.0 / 8.0, w, h * 3.0 / 8.0),
+        0x2584 => paint_quad(x, y + h / 2.0, w, h / 2.0),
+        0x2585 => paint_quad(x, y + h * 3.0 / 8.0, w, h * 5.0 / 8.0),
+        0x2586 => paint_quad(x, y + h / 4.0, w, h * 3.0 / 4.0),
+        0x2587 => paint_quad(x, y + h / 8.0, w, h * 7.0 / 8.0),
+        0x2588 => paint_quad(x, y, w, h),
+        0x2589 => paint_quad(x, y, w * 7.0 / 8.0, h),
+        0x258A => paint_quad(x, y, w * 3.0 / 4.0, h),
+        0x258B => paint_quad(x, y, w * 5.0 / 8.0, h),
+        0x258C => paint_quad(x, y, w / 2.0, h),
+        0x258D => paint_quad(x, y, w * 3.0 / 8.0, h),
+        0x258E => paint_quad(x, y, w / 4.0, h),
+        0x258F => paint_quad(x, y, w / 8.0, h),
+        0x2590 => paint_quad(x + w / 2.0, y, w / 2.0, h),
+        0x2594 => paint_quad(x, y, w, h / 8.0),
+        0x2595 => paint_quad(x + w * 7.0 / 8.0, y, w / 8.0, h),
+        0x2596 => paint_quad(x, y + h / 2.0, w / 2.0, h / 2.0),
+        0x2597 => paint_quad(x + w / 2.0, y + h / 2.0, w / 2.0, h / 2.0),
+        0x2598 => paint_quad(x, y, w / 2.0, h / 2.0),
+        0x2599 => {
+            paint_quad(x, y, w / 2.0, h);
+            paint_quad(x + w / 2.0, y + h / 2.0, w / 2.0, h / 2.0);
+        }
+        0x259A => {
+            paint_quad(x, y, w / 2.0, h / 2.0);
+            paint_quad(x + w / 2.0, y + h / 2.0, w / 2.0, h / 2.0);
+        }
+        0x259B => {
+            paint_quad(x, y, w, h / 2.0);
+            paint_quad(x, y + h / 2.0, w / 2.0, h / 2.0);
+        }
+        0x259C => {
+            paint_quad(x, y, w, h / 2.0);
+            paint_quad(x + w / 2.0, y + h / 2.0, w / 2.0, h / 2.0);
+        }
+        0x259D => paint_quad(x + w / 2.0, y, w / 2.0, h / 2.0),
+        0x259E => {
+            paint_quad(x + w / 2.0, y, w / 2.0, h / 2.0);
+            paint_quad(x, y + h / 2.0, w / 2.0, h / 2.0);
+        }
+        0x259F => {
+            paint_quad(x + w / 2.0, y, w / 2.0, h);
+            paint_quad(x, y + h / 2.0, w / 2.0, h / 2.0);
+        }
+
+        // --- Basic Box Drawing (U+2500..=U+257F) ---
+        // Light lines
+        0x2500 => paint_quad(x, cy - light / 2.0, w, light), // Horizontal
+        0x2502 => paint_quad(cx - light / 2.0, y, light, h), // Vertical
+        0x250C => { // Down + Right
+            paint_quad(cx - light / 2.0, cy - light / 2.0, light, h / 2.0 + light / 2.0);
+            paint_quad(cx - light / 2.0, cy - light / 2.0, w / 2.0 + light / 2.0, light);
+        }
+        0x2510 => { // Down + Left
+            paint_quad(cx - light / 2.0, cy - light / 2.0, light, h / 2.0 + light / 2.0);
+            paint_quad(x, cy - light / 2.0, w / 2.0 + light / 2.0, light);
+        }
+        0x2514 => { // Up + Right
+            paint_quad(cx - light / 2.0, y, light, h / 2.0 + light / 2.0);
+            paint_quad(cx - light / 2.0, cy - light / 2.0, w / 2.0 + light / 2.0, light);
+        }
+        0x2518 => { // Up + Left
+            paint_quad(cx - light / 2.0, y, light, h / 2.0 + light / 2.0);
+            paint_quad(x, cy - light / 2.0, w / 2.0 + light / 2.0, light);
+        }
+        0x251C => { // Vertical + Right
+            paint_quad(cx - light / 2.0, y, light, h);
+            paint_quad(cx - light / 2.0, cy - light / 2.0, w / 2.0 + light / 2.0, light);
+        }
+        0x2524 => { // Vertical + Left
+            paint_quad(cx - light / 2.0, y, light, h);
+            paint_quad(x, cy - light / 2.0, w / 2.0 + light / 2.0, light);
+        }
+        0x252C => { // Horizontal + Down
+            paint_quad(x, cy - light / 2.0, w, light);
+            paint_quad(cx - light / 2.0, cy - light / 2.0, light, h / 2.0 + light / 2.0);
+        }
+        0x2534 => { // Horizontal + Up
+            paint_quad(x, cy - light / 2.0, w, light);
+            paint_quad(cx - light / 2.0, y, light, h / 2.0 + light / 2.0);
+        }
+        0x253C => { // Vertical + Horizontal (Cross)
+            paint_quad(x, cy - light / 2.0, w, light);
+            paint_quad(cx - light / 2.0, y, light, h);
+        }
+        
+        // Heavy lines
+        0x2501 => paint_quad(x, cy - heavy / 2.0, w, heavy), // Heavy Horizontal
+        0x2503 => paint_quad(cx - heavy / 2.0, y, heavy, h), // Heavy Vertical
+        0x250F => { // Heavy Down + Right
+            paint_quad(cx - heavy / 2.0, cy - heavy / 2.0, heavy, h / 2.0 + heavy / 2.0);
+            paint_quad(cx - heavy / 2.0, cy - heavy / 2.0, w / 2.0 + heavy / 2.0, heavy);
+        }
+        0x2513 => { // Heavy Down + Left
+            paint_quad(cx - heavy / 2.0, cy - heavy / 2.0, heavy, h / 2.0 + heavy / 2.0);
+            paint_quad(x, cy - heavy / 2.0, w / 2.0 + heavy / 2.0, heavy);
+        }
+        0x2517 => { // Heavy Up + Right
+            paint_quad(cx - heavy / 2.0, y, heavy, h / 2.0 + heavy / 2.0);
+            paint_quad(cx - heavy / 2.0, cy - heavy / 2.0, w / 2.0 + heavy / 2.0, heavy);
+        }
+        0x251B => { // Heavy Up + Left
+            paint_quad(cx - heavy / 2.0, y, heavy, h / 2.0 + heavy / 2.0);
+            paint_quad(x, cy - heavy / 2.0, w / 2.0 + heavy / 2.0, heavy);
+        }
+        0x2523 => { // Heavy Vertical + Right
+            paint_quad(cx - heavy / 2.0, y, heavy, h);
+            paint_quad(cx - heavy / 2.0, cy - heavy / 2.0, w / 2.0 + heavy / 2.0, heavy);
+        }
+        0x252B => { // Heavy Vertical + Left
+            paint_quad(cx - heavy / 2.0, y, heavy, h);
+            paint_quad(x, cy - heavy / 2.0, w / 2.0 + heavy / 2.0, heavy);
+        }
+        0x2533 => { // Heavy Horizontal + Down
+            paint_quad(x, cy - heavy / 2.0, w, heavy);
+            paint_quad(cx - heavy / 2.0, cy - heavy / 2.0, heavy, h / 2.0 + heavy / 2.0);
+        }
+        0x253B => { // Heavy Horizontal + Up
+            paint_quad(x, cy - heavy / 2.0, w, heavy);
+            paint_quad(cx - heavy / 2.0, y, heavy, h / 2.0 + heavy / 2.0);
+        }
+        0x254B => { // Heavy Vertical + Horizontal (Cross)
+            paint_quad(x, cy - heavy / 2.0, w, heavy);
+            paint_quad(cx - heavy / 2.0, y, heavy, h);
+        }
+
+        // --- Powerline ---
+        0xE0B0 => { // Rightward Solid Arrow
+            let mut path = Path::new(point(x, y));
+            path.line_to(point(x + w, y + h / 2.0));
+            path.line_to(point(x, y + h));
+            path.line_to(point(x, y));
+            window.paint_path(path, color);
+            painted = true;
+        }
+        0xE0B2 => { // Leftward Solid Arrow
+            let mut path = Path::new(point(x + w, y));
+            path.line_to(point(x, y + h / 2.0));
+            path.line_to(point(x + w, y + h));
+            path.line_to(point(x + w, y));
+            window.paint_path(path, color);
+            painted = true;
+        }
+        0xE0B1 => { // Rightward Line Arrow
+            let t = px(1.0);
+            let mut p = Path::new(point(x, y));
+            p.line_to(point(x + w, y + h / 2.0));
+            p.line_to(point(x + w - t, y + h / 2.0));
+            p.line_to(point(x, y + t));
+            p.line_to(point(x, y));
+            window.paint_path(p, color);
+            let mut p2 = Path::new(point(x, y + h));
+            p2.line_to(point(x + w, y + h / 2.0));
+            p2.line_to(point(x + w - t, y + h / 2.0));
+            p2.line_to(point(x, y + h - t));
+            p2.line_to(point(x, y + h));
+            window.paint_path(p2, color);
+            painted = true;
+        }
+        0xE0B3 => { // Leftward Line Arrow
+            let t = px(1.0);
+            let mut p = Path::new(point(x + w, y));
+            p.line_to(point(x, y + h / 2.0));
+            p.line_to(point(x + t, y + h / 2.0));
+            p.line_to(point(x + w, y + t));
+            p.line_to(point(x + w, y));
+            window.paint_path(p, color);
+            let mut p2 = Path::new(point(x + w, y + h));
+            p2.line_to(point(x, y + h / 2.0));
+            p2.line_to(point(x + t, y + h / 2.0));
+            p2.line_to(point(x + w, y + h - t));
+            p2.line_to(point(x + w, y + h));
+            window.paint_path(p2, color);
+            painted = true;
+        }
+
+        // Half arches (Powerline rounded)
+        0xE0B4 => { // Rightward Solid Semicircle
+            let mut path = Path::new(point(x, y));
+            path.curve_to(point(x, y + h), point(x + w * 2.0, y + h / 2.0));
+            path.line_to(point(x, y));
+            window.paint_path(path, color);
+            painted = true;
+        }
+        0xE0B6 => { // Leftward Solid Semicircle
+            let mut path = Path::new(point(x + w, y));
+            path.curve_to(point(x + w, y + h), point(x - w, y + h / 2.0));
+            path.line_to(point(x + w, y));
+            window.paint_path(path, color);
+            painted = true;
+        }
+
+        _ => {}
+    }
+
+    painted
+}

src/terminal/element.rs

@@ -12,6 +12,7 @@ use gpui_component::ActiveTheme as _;
 
 use crate::Ashell;
 use crate::terminal::{RenderSnapshot, ViewportSelection};
+use crate::terminal::custom_blocks::{paint_custom_block, is_custom_block_supported};
 
 #[derive(Clone, Copy)]
 struct TerminalMetrics {
@@ -138,9 +139,19 @@ pub struct PrepaintState {
     metrics: TerminalMetrics,
     rects: Vec<LayoutRect>,
     runs: Vec<BatchedTextRun>,
+    custom_blocks: Vec<LayoutCustomBlock>,
     cursor: Option<CursorLayout>,
 }
 
+#[derive(Clone)]
+struct LayoutCustomBlock {
+    c: char,
+    row: i32,
+    col: i32,
+    cells: usize,
+    color: Hsla,
+}
+
 struct TerminalInputHandler {
     view: Entity<Ashell>,
     element_bounds: Bounds<Pixels>,
@@ -331,9 +342,10 @@ impl TerminalElement {
         }
     }
 
-    fn layout_grid(&self, cx: &App) -> (Vec<LayoutRect>, Vec<BatchedTextRun>) {
+    fn layout_grid(&self, cx: &App) -> (Vec<LayoutRect>, Vec<BatchedTextRun>, Vec<LayoutCustomBlock>) {
         let mut rects = Vec::new();
         let mut runs = Vec::new();
+        let mut custom_blocks = Vec::new();
         let mut current_run: Option<BatchedTextRun> = None;
 
         for render_cell in &self.snapshot.cells {
@@ -371,6 +383,24 @@ impl TerminalElement {
             }
 
             let style = self.cell_run_style(cell, cx);
+
+            // Box Drawing & Block Elements interception
+            let is_custom_block = is_custom_block_supported(cell.c);
+
+            if is_custom_block {
+                if let Some(run) = current_run.take() {
+                    runs.push(run);
+                }
+                custom_blocks.push(LayoutCustomBlock {
+                    c: cell.c,
+                    row: render_cell.row,
+                    col: render_cell.col,
+                    cells: if cell.flags.contains(Flags::WIDE_CHAR) { 2 } else { 1 },
+                    color: style.color,
+                });
+                continue;
+            }
+
             if let Some(run) = current_run.as_mut() {
                 if run.can_append(&style, render_cell.row, render_cell.col) {
                     run.append(cell.c, cell.zerowidth());
@@ -402,7 +432,7 @@ impl TerminalElement {
             runs.push(run);
         }
 
-        (merge_rects(rects), runs)
+        (merge_rects(rects), runs, custom_blocks)
     }
 
     fn cursor_layout(&self, cx: &App) -> Option<CursorLayout> {
@@ -458,7 +488,7 @@ impl Element for TerminalElement {
         cx: &mut App,
     ) -> Self::PrepaintState {
         let _ = self.base_text_style(cx);
-        let (rects, runs) = self.layout_grid(cx);
+        let (rects, runs, custom_blocks) = self.layout_grid(cx);
         PrepaintState {
             bounds,
             metrics: TerminalMetrics {
@@ -467,6 +497,7 @@ impl Element for TerminalElement {
             },
             rects,
             runs,
+            custom_blocks,
             cursor: self.cursor_layout(cx),
         }
     }
@@ -489,6 +520,20 @@ impl Element for TerminalElement {
             run.paint(prepaint.bounds.origin, prepaint.metrics, window, cx);
         }
 
+        for block in &prepaint.custom_blocks {
+            let x = prepaint.bounds.origin.x.as_f32() + block.col as f32 * prepaint.metrics.cell_width.as_f32();
+            let y = prepaint.bounds.origin.y.as_f32() + block.row as f32 * prepaint.metrics.line_height.as_f32();
+            paint_custom_block(
+                window,
+                block.c,
+                x,
+                y,
+                prepaint.metrics.cell_width.as_f32() * block.cells as f32,
+                prepaint.metrics.line_height.as_f32(),
+                block.color,
+            );
+        }
+
         window.handle_input(
             &self.focus_handle,
             TerminalInputHandler {

src/terminal/mod.rs

@@ -1,5 +1,6 @@
 pub mod element;
 pub mod input;
+pub mod custom_blocks;
 
 use std::sync::mpsc::Sender;