Mouse rectangular region selection (bug#38013)

Make it possible to select a rectangular region using the mouse.
The standard binding is C-M-mouse-1.

* lisp/mouse.el (mouse-scroll-subr): Add ADJUST argument.
(mouse-drag-region-rectangle): New.
* lisp/rect.el (rectangle--reset-point-crutches): New.
(rectangle--reset-crutches): Use 'rectangle--reset-point-crutches'.
* src/xdisp.c (remember_mouse_glyph, syms_of_xdisp):
Add 'mouse-fine-grained-tracking'.
* doc/lispref/commands.texi (Motion Events):
Document 'mouse-fine-grained-tracking'.
* doc/emacs/frames.texi (Mouse Commands):
* doc/emacs/killing.texi (Rectangles):
* etc/NEWS: Document rectangular selection with the mouse.

1 files changed, 12 insertions, 0 deletions

diff --git a/src/xdisp.c b/src/xdisp.c
index 2b4dda27157..c4d23be4cde 100644
--- a/src/xdisp.c
+++ b/src/xdisp.c
@@ -2491,6 +2491,12 @@ remember_mouse_glyph (struct frame *f, int gx, int gy, NativeRectangle *rect)
   enum glyph_row_area area;
   int x, y, width, height;
 
+  if (mouse_fine_grained_tracking)
+    {
+      STORE_NATIVE_RECT (*rect, gx, gy, 1, 1);
+      return;
+    }
+
   /* Try to determine frame pixel position and size of the glyph under
      frame pixel coordinates X/Y on frame F.  */
 
@@ -34946,6 +34952,12 @@ The default is to use octal format (\200) whereas hexadecimal (\x80)
 may be more familiar to users.  */);
   display_raw_bytes_as_hex = false;
 
+  DEFVAR_BOOL ("mouse-fine-grained-tracking", mouse_fine_grained_tracking,
+    doc: /* Non-nil for pixel-wise mouse-movement.
+When nil, mouse-movement events will not be generated as long as the
+mouse stays within the extent of a single glyph (except for images).  */);
+  mouse_fine_grained_tracking = false;
+
 }