From e4b844dea61d96ee863b0646b9fbe6dfc2783911 Mon Sep 17 00:00:00 2001
From: Mitchell Hashimoto <mitchell.hashimoto@gmail.com>
Date: Fri, 6 Oct 2023 16:58:48 -0700
Subject: [PATCH] terminal: CHT

---
 src/terminal/Terminal.zig         | 39 ++++++++++++++++-
 website/app/vt/cbt/page.mdx       |  4 +-
 website/app/vt/cht/page.mdx       | 70 +++++++++++++++++++++++++++++++
 website/app/vt/tab/page.mdx       |  8 ++++
 website/components/VTSequence.tsx |  1 +
 5 files changed, 119 insertions(+), 3 deletions(-)
 create mode 100644 website/app/vt/cht/page.mdx
 create mode 100644 website/app/vt/tab/page.mdx

diff --git a/src/terminal/Terminal.zig b/src/terminal/Terminal.zig
index b80556e07f..35e724abaa 100644
--- a/src/terminal/Terminal.zig
+++ b/src/terminal/Terminal.zig
@@ -1497,7 +1497,7 @@ pub fn horizontalTab(self: *Terminal) !void {
     const tracy = trace(@src());
     defer tracy.end();
 
-    while (self.screen.cursor.x < self.cols - 1) {
+    while (self.screen.cursor.x < self.scrolling_region.right) {
         // Move the cursor right
         self.screen.cursor.x += 1;
 
@@ -2294,6 +2294,43 @@ test "Terminal: horizontal tabs" {
     try testing.expectEqual(@as(usize, 19), t.screen.cursor.x);
 }
 
+test "Terminal: horizontal tabs starting on tabstop" {
+    const alloc = testing.allocator;
+    var t = try init(alloc, 20, 5);
+    defer t.deinit(alloc);
+
+    t.screen.cursor.x = 8;
+    try t.print('X');
+    t.screen.cursor.x = 8;
+    try t.horizontalTab();
+    try t.print('A');
+
+    {
+        var str = try t.plainString(testing.allocator);
+        defer testing.allocator.free(str);
+        try testing.expectEqualStrings("        X       A", str);
+    }
+}
+
+test "Terminal: horizontal tabs with right margin" {
+    const alloc = testing.allocator;
+    var t = try init(alloc, 20, 5);
+    defer t.deinit(alloc);
+
+    t.scrolling_region.left = 2;
+    t.scrolling_region.right = 5;
+    t.screen.cursor.x = 0;
+    try t.print('X');
+    try t.horizontalTab();
+    try t.print('A');
+
+    {
+        var str = try t.plainString(testing.allocator);
+        defer testing.allocator.free(str);
+        try testing.expectEqualStrings("X    A", str);
+    }
+}
+
 test "Terminal: horizontal tabs back" {
     const alloc = testing.allocator;
     var t = try init(alloc, 20, 5);
diff --git a/website/app/vt/cbt/page.mdx b/website/app/vt/cbt/page.mdx
index 9c17e3736d..11ed989396 100644
--- a/website/app/vt/cbt/page.mdx
+++ b/website/app/vt/cbt/page.mdx
@@ -34,11 +34,11 @@ printf "A"
 |Ac________|
 ```
 
-### CBT V-2: Left Beyond First Column
+### CBT V-2: Left Starting After Tab Stop
 
 ```bash
 printf "\033[?W" # reset tab stops
-printf "\033[1;10"
+printf "\033[1;10H"
 printf "X"
 printf "\033[Z"
 printf "A"
diff --git a/website/app/vt/cht/page.mdx b/website/app/vt/cht/page.mdx
new file mode 100644
index 0000000000..61ca2743f4
--- /dev/null
+++ b/website/app/vt/cht/page.mdx
@@ -0,0 +1,70 @@
+import VTSequence from "@/components/VTSequence";
+
+# Cursor Horizontal Tabulation (CHT)
+
+<VTSequence sequence={["CSI", "Pn", "I"]} />
+
+Move the cursor `n` tabs right.
+
+The parameter `n` must be an integer greater than or equal to 1. If `n` is less than
+or equal to 0, adjust `n` to be 1. If `n` is omitted, `n` defaults to 1.
+
+The rightmost valid column for this operation is the rightmost column in
+the terminal screen or the [right margin](#TODO), whichever is smaller.
+This sequence does not change behavior with [origin mode](#TODO) set.
+
+Move the cursor right until the cursor position is on a tabstop. If the
+cursor would move past the rightmost valid column, the cursor remains at
+the rightmost valid column and the operation completes. Repeat this process
+`n` times.
+
+Tabstops are dynamic and can be set with escape sequences such as
+[horizontal tab set (HTS)](/vt/hts), [tab clear (TBC)](/vt/tbc), etc.
+A terminal emulator may default tabstops at any interval, though an interval
+of 8 spaces is most common.
+
+## Validation
+
+### CHT V-1: Right Beyond Last Column
+
+```bash
+printf "\033[?W" # reset tab stops
+printf "\033[100I" # assuming the test terminal has less than 800 columns
+printf "A"
+```
+
+```
+|_________A|
+```
+
+### CHT V-2: Right From Before a Tabstop
+
+```bash
+printf "\033[?W" # reset tab stops
+printf "\033[1;2H"
+printf "A"
+printf "\033[I"
+printf "X"
+```
+
+```
+|_A_____X__|
+```
+
+### CHT V-3: Right Margin
+
+```bash
+printf "\033[1;1H" # move to top-left
+printf "\033[0J" # clear screen
+printf "\033[?W" # reset tab stops
+printf "\033[?69h" # enable left/right margins
+printf "\033[3;6s" # scroll region left/right
+printf "\033[1;1H" # move cursor in region
+printf "X"
+printf "\033[I"
+printf "A"
+```
+
+```
+|__AX______|
+```
diff --git a/website/app/vt/tab/page.mdx b/website/app/vt/tab/page.mdx
new file mode 100644
index 0000000000..95b1b3b41c
--- /dev/null
+++ b/website/app/vt/tab/page.mdx
@@ -0,0 +1,8 @@
+import VTSequence from "@/components/VTSequence";
+
+# Tab (TAB)
+
+<VTSequence sequence="TAB" />
+
+This is an alias for [cursor horizontal tabulation (CHT)](/vt/cht) with
+`n = 1`.
diff --git a/website/components/VTSequence.tsx b/website/components/VTSequence.tsx
index 4717195629..23a69a77aa 100644
--- a/website/components/VTSequence.tsx
+++ b/website/components/VTSequence.tsx
@@ -45,6 +45,7 @@ function VTElem({ elem }: { elem: string }) {
 const special: { [key: string]: number } = {
   BEL: 0x07,
   BS: 0x08,
+  TAB: 0x09,
   LF: 0x0a,
   CR: 0x0d,
   ESC: 0x1b,