fix tab rendering - waybe wreckless

1 files changed, 56 insertions, 13 deletions

diff --git a/src/file_pane.zig b/src/file_pane.zig
index c0a2350d..b0921bd0 100644
--- a/src/file_pane.zig
+++ b/src/file_pane.zig
@@ -17,6 +17,39 @@ const tracy = @import("tracy.zig");
 
 const SYNTAX_CONTEXT_AFTER_ROWS: usize = 2;
 
+pub fn byteDisplayWidth(byte: u8) usize {
+    return if (byte == '\t') config.tab_width else 1;
+}
+
+pub fn displayWidth(text: []const u8) usize {
+    var width: usize = 0;
+    for (text) |byte| width +|= byteDisplayWidth(byte);
+    return width;
+}
+
+/// Source byte at a zero-based display column. Every cell occupied by a tab
+/// maps back to that one tab byte.
+pub fn byteAtDisplay(text: []const u8, display_col: usize) usize {
+    var col: usize = 0;
+    for (text, 0..) |byte, i| {
+        const next = col +| byteDisplayWidth(byte);
+        if (display_col < next) return i;
+        col = next;
+    }
+    return text.len;
+}
+
+fn fitEnd(text: []const u8, start: usize, width: usize) usize {
+    var end = start;
+    var used: usize = 0;
+    while (end < text.len) : (end += 1) {
+        const next = used +| byteDisplayWidth(text[end]);
+        if (next > width) return if (end == start) start + 1 else end;
+        used = next;
+    }
+    return end;
+}
+
 pub fn lineCount(content: []const u8) usize {
     return std.mem.count(u8, content, "\n") + 1;
 }
@@ -258,16 +291,17 @@ fn fillBody(dst: ?[]u8, pane: *Pane, f: *File, width: usize, record_wrap: bool)
             // panicking — see test/snapshots/badutf.snap. It cannot overflow
             // the pane either: a UTF-8 sequence is never fewer bytes than the
             // cells it draws in.
-            const take = if (width == 0) text.len - at else @min(width, text.len - at);
+            const end = if (width == 0) text.len else fitEnd(text, at, width);
+            const take = end - at;
             const cut = if (pane.hscroll > 0 and width == 0)
                 @min(@as(usize, @intCast(pane.hscroll)), take)
             else
                 0;
-            const shown = text[at + cut .. at + take];
+            const shown = text[at + cut .. end];
             if (dst) |out| @memcpy(out[written..][0..shown.len], shown);
             written += shown.len;
-            if (width > 0 and at + take < text.len) {
-                at += take;
+            if (width > 0 and end < text.len) {
+                at = end;
             } else {
                 abs += 1;
                 at = 0;
@@ -364,16 +398,25 @@ pub fn recolorSyntax(p: *Pardes, pane: *Pane, f: *File, r: pardes.Rect, tx: u16,
                 line.len;
         }
         var c: usize = 0;
-        while (hs + c < limit and config.PREFIX_W + c < tw) : (c += 1) {
+        var screen_c: usize = 0;
+        while (hs + c < limit and config.PREFIX_W + screen_c < tw) : (c += 1) {
+            const cells = byteDisplayWidth(line[hs + c]);
             const idx = base + hs + c;
-            if (idx < f.highlight_start) continue;
-            const hidx = idx - f.highlight_start;
-            if (hidx >= f.highlights.len) continue;
-            const ss = synStyle(p, @enumFromInt(f.highlights[hidx])) orelse continue;
-            const cell = s.at(tx + @as(u16, @intCast(config.PREFIX_W + c)), body_y + vr);
-            if (cell.default) continue;
-            cell.style.fg = .{ .rgb = ss.fg };
-            cell.style.bold = ss.bold;
+            if (idx >= f.highlight_start) {
+                const hidx = idx - f.highlight_start;
+                if (hidx < f.highlights.len) {
+                    if (synStyle(p, @enumFromInt(f.highlights[hidx]))) |ss| {
+                        var fill: usize = 0;
+                        while (fill < cells and config.PREFIX_W + screen_c + fill < tw) : (fill += 1) {
+                            const cell = s.at(tx + @as(u16, @intCast(config.PREFIX_W + screen_c + fill)), body_y + vr);
+                            if (cell.default) continue;
+                            cell.style.fg = .{ .rgb = ss.fg };
+                            cell.style.bold = ss.bold;
+                        }
+                    }
+                }
+            }
+            screen_c += cells;
         }
     }
 }