xterm audit: DECOM (origin mode)

src/terminal/Terminal.zig

@@ -2170,6 +2170,20 @@ test "Terminal: fullReset with a non-empty pen" {
     try testing.expect(cell.fg.eql(.{}));
 }
 
+test "Terminal: fullReset origin mode" {
+    var t = try init(testing.allocator, 10, 10);
+    defer t.deinit(testing.allocator);
+
+    t.setCursorPos(3, 5);
+    t.modes.set(.origin, true);
+    t.fullReset(testing.allocator);
+
+    // Origin mode should be reset and the cursor should be moved
+    try testing.expectEqual(@as(usize, 0), t.screen.cursor.y);
+    try testing.expectEqual(@as(usize, 0), t.screen.cursor.x);
+    try testing.expect(!t.modes.get(.origin));
+}
+
 test "Terminal: input with no control characters" {
     var t = try init(testing.allocator, 80, 80);
     defer t.deinit(testing.allocator);

src/termio/Exec.zig

@@ -1749,7 +1749,9 @@ const StreamHandler = struct {
             // Schedule a render since we changed colors
             .reverse_colors => try self.queueRender(),
 
-            // Origin resets cursor pos
+            // Origin resets cursor pos. This is called whether or not
+            // we're enabling or disabling origin mode and whether or
+            // not the value changed.
             .origin => self.terminal.setCursorPos(1, 1),
 
             .enable_left_and_right_margin => if (!enabled) {

website/app/vt/modes/decom/page.mdx

@@ -0,0 +1,64 @@
+import VTMode from "@/components/VTMode";
+
+# Origin (DECOM)
+
+<VTMode value={6} />
+
+Changes the origin of grid coordinates to be relative to the current scroll
+region.
+
+When set or unset, this invokes [Cursor Position (CUP)](/vt/cup) with row 1 and
+column 1. If origin mode is set, this will position the cursor to the
+top-left location of the current scroll region. If origin mode is not set,
+this will position the cursor to the top-left location of the screen. The
+cursor position will be set even if the origin mode is _unchanged_.
+
+The following commands are affected by origin mode. Please see their
+respective documentation for details on how origin mode impacts their
+behavior.
+
+- [Carriage Return (CR)](/vt/cr)
+- [Cursor Position Set (CUP)](/vt/cup)
+- [Cursor Position Report (CPR)](/vt/cpr)
+- [Save Cursor (DECSC)](/vt/decsc)
+- [Restore Cursor (DECRC)](/vt/decrc)
+- [Horizontal Position Absolute (HPA)](/vt/hpa)
+- [Vertical Position Absolute (VPA)](/vt/vpa)
+- [Horizontal Position Relative (HPR)](/vt/hpr)
+- [Vertical Position Relative (VPR)](/vt/vpr)
+- [Cursor Backward Tabulation (CBT)](/vt/cbt)
+- [Screen Alignment Test (DECALN)](/vt/decaln)
+- [Full Reset (RIS)](/vt/ris)
+- [Soft Reset (DECSTR)](/vt/decstr)
+
+## Validation
+
+### DECOM V-1: Unset No Margins
+
+```bash
+printf "\033[H"
+printf "\033[2J"
+printf "ABC\n"
+printf "\033[?6l"
+printf "X"
+```
+
+```
+|XBC_____|
+|________|
+```
+
+### DECOM V-1: Set No Margins
+
+```bash
+printf "\033[H"
+printf "\033[2J"
+printf "ABC\n"
+printf "\033[?6h"
+printf "X"
+```
+
+```
+|XBC_____|
+|________|
+```