ui/console-vc: implement DCH (delete) and ICH (insert) commands

This patch implements DCH (delete character) and ICH (insert
character) commands.

DCH - Delete Character:
   "As characters are deleted, the remaining characters between the
    cursor and right margin move to the left. Character attributes move
    with the characters. The terminal adds blank spaces with no visual
    character attributes at the right margin. DCH has no effect outside
    the scrolling margins" [1].

ICH - Insert Character:
   "The ICH sequence inserts Pn blank characters with the normal
    character attribute. The cursor remains at the beginning of the
    blank characters. Text between the cursor and right margin moves to
    the right. Characters scrolled past the right margin are lost. ICH
    has no effect outside the scrolling margins" [2].

Without these commands console is barely usable.

[1] https://vt100.net/docs/vt510-rm/DCH.html
[1] https://vt100.net/docs/vt510-rm/ICH.html

Signed-off-by: Roman Penyaev <r.peniaev@gmail.com>
Cc: "Marc-André Lureau" <marcandre.lureau@redhat.com>
Cc: qemu-devel@nongnu.org
Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Message-ID: <20250226075913.353676-6-r.peniaev@gmail.com>

ui/console-vc.c

@@ -645,6 +645,88 @@ static void vc_set_cursor(VCChardev *vc, int x, int y)
     s->y = y;
 }
 
+/**
+ * vc_csi_P() - (DCH) deletes one or more characters from the cursor
+ * position to the right. As characters are deleted, the remaining
+ * characters between the cursor and right margin move to the
+ * left. Character attributes move with the characters.
+ */
+static void vc_csi_P(struct VCChardev *vc, unsigned int nr)
+{
+    QemuTextConsole *s = vc->console;
+    TextCell *c1, *c2;
+    unsigned int x1, x2, y;
+    unsigned int end, len;
+
+    if (!nr) {
+        nr = 1;
+    }
+    if (nr > s->width - s->x) {
+        nr = s->width - s->x;
+        if (!nr) {
+            return;
+        }
+    }
+
+    x1 = s->x;
+    x2 = s->x + nr;
+    len = s->width - x2;
+    if (len) {
+        y = (s->y_base + s->y) % s->total_height;
+        c1 = &s->cells[y * s->width + x1];
+        c2 = &s->cells[y * s->width + x2];
+        memmove(c1, c2, len * sizeof(*c1));
+        for (end = x1 + len; x1 < end; x1++) {
+            vc_update_xy(vc, x1, s->y);
+        }
+    }
+    /* Clear the rest */
+    for (; x1 < s->width; x1++) {
+        vc_clear_xy(vc, x1, s->y);
+    }
+}
+
+/**
+ * vc_csi_at() - (ICH) inserts `nr` blank characters with the default
+ * character attribute. The cursor remains at the beginning of the
+ * blank characters. Text between the cursor and right margin moves to
+ * the right. Characters scrolled past the right margin are lost.
+ */
+static void vc_csi_at(struct VCChardev *vc, unsigned int nr)
+{
+    QemuTextConsole *s = vc->console;
+    TextCell *c1, *c2;
+    unsigned int x1, x2, y;
+    unsigned int end, len;
+
+    if (!nr) {
+        nr = 1;
+    }
+    if (nr > s->width - s->x) {
+        nr = s->width - s->x;
+        if (!nr) {
+            return;
+        }
+    }
+
+    x1 = s->x + nr;
+    x2 = s->x;
+    len = s->width - x1;
+    if (len) {
+        y = (s->y_base + s->y) % s->total_height;
+        c1 = &s->cells[y * s->width + x1];
+        c2 = &s->cells[y * s->width + x2];
+        memmove(c1, c2, len * sizeof(*c1));
+        for (end = x1 + len; x1 < end; x1++) {
+            vc_update_xy(vc, x1, s->y);
+        }
+    }
+    /* Insert blanks */
+    for (x1 = s->x; x1 < s->x + nr; x1++) {
+        vc_clear_xy(vc, x1, s->y);
+    }
+}
+
 /**
  * vc_save_cursor() - saves cursor position and character attributes.
  */
@@ -847,6 +929,9 @@ static void vc_putchar(VCChardev *vc, int ch)
                     break;
                 }
                 break;
+            case 'P':
+                vc_csi_P(vc, vc->esc_params[0]);
+                break;
             case 'm':
                 vc_handle_escape(vc);
                 break;
@@ -870,6 +955,9 @@ static void vc_putchar(VCChardev *vc, int ch)
             case 'u':
                 vc_restore_cursor(vc);
                 break;
+            case '@':
+                vc_csi_at(vc, vc->esc_params[0]);
+                break;
             default:
                 trace_console_putchar_unhandled(ch);
                 break;