Fix interaction of insch() with selection highlights.

Previously I had unthinkingly called the general-purpose
check_selection() routine to indicate that I was going to mess with n
character cells right of the cursor position, causing the selection
highlight to be removed if it intersected that region. This is all
wrong, since actually the whole region from cursor to EOL is modified
by any character insertion or deletion, so if we were going to call
check_selection it should be on that whole region. (Quick demo: select
part of the line to the right of the cursor, then emit ESC[P or ESC[@
and see the text move left or right while the highlight stays put.)

So we could just call check_selection() on that larger affected
region, and that would be correct. However, we can do something
slightly more elegant in the case where the selection is contained
entirely within the subregion that moves to one side (as opposed to
the characters that actually vanish at one or other end): we can move
the selection highlight with the text under it, to preserve the visual
reminder of which text was selected for as long as possible.

[originally from svn r10097]

diff --git a/terminal.c b/terminal.c
index d6a754c916faace187bb6347933006b6cb521498..bd77f2397878d085a6646ca508a80acb1405c448 100644 (file)
--- a/terminal.c
+++ b/terminal.c
@@ -2380,16 +2380,51 @@ static void insch(Terminal *term, int n)
 {
     int dir = (n < 0 ? -1 : +1);
     int m, j;
-    pos cursplus;
+    pos eol;
     termline *ldata;
 
     n = (n < 0 ? -n : n);
     if (n > term->cols - term->curs.x)
        n = term->cols - term->curs.x;
     m = term->cols - term->curs.x - n;
-    cursplus.y = term->curs.y;
-    cursplus.x = term->curs.x + n;
-    check_selection(term, term->curs, cursplus);
+
+    /*
+     * We must de-highlight the selection if it overlaps any part of
+     * the region affected by this operation, i.e. the region from the
+     * current cursor position to end-of-line, _unless_ the entirety
+     * of the selection is going to be moved to the left or right by
+     * this operation but otherwise unchanged, in which case we can
+     * simply move the highlight with the text.
+     */
+    eol.y = term->curs.y;
+    eol.x = term->cols;
+    if (poslt(term->curs, term->selend) && poslt(term->selstart, eol)) {
+        pos okstart = term->curs;
+        pos okend = eol;
+        if (dir > 0) {
+            /* Insertion: n characters at EOL will be splatted. */
+            okend.x -= n;
+        } else {
+            /* Deletion: n characters at cursor position will be splatted. */
+            okstart.x += n;
+        }
+        if (posle(okstart, term->selstart) && posle(term->selend, okend)) {
+            /* Selection is contained entirely in the interval
+             * [okstart,okend), so we need only adjust the selection
+             * bounds. */
+            term->selstart.x += dir * n;
+            term->selend.x += dir * n;
+            assert(term->selstart.x >= term->curs.x);
+            assert(term->selstart.x < term->cols);
+            assert(term->selend.x > term->curs.x);
+            assert(term->selend.x <= term->cols);
+        } else {
+            /* Selection is not wholly contained in that interval, so
+             * we must unhighlight it. */
+            deselect(term);
+        }
+    }
+
     check_boundary(term, term->curs.x, term->curs.y);
     if (dir < 0)
        check_boundary(term, term->curs.x + n, term->curs.y);