[gimp] app: Smoother zooming while dragging with the mouse

[Jehan <jehanp src gnome org>]

commit 8b1025919f374e4885c575b264fcf76916193767
Author: woob <thetoastcaper gmail com>
Date:   Mon Feb 7 20:06:01 2022 -0500

    app: Smoother zooming while dragging with the mouse
    
    Changes the behavior of gimp_display_shell_scale_drag() to factor in
    the distance dragged, rather than just scaling a flat +/- 10% for each
    detected movement event. The factor by which to change the scaling is
    also altered from 10% at each movement event, to 1% compounded for
    each pixel of distance dragged.
    This makes zooming via Ctrl + Middle Click or Ctrl + Spacebar behave
    more consistently and less jittery versus the previous method, while
    offering more fine grained control.

 app/display/gimpdisplayshell-scale.c | 18 ++++--------------
 1 file changed, 4 insertions(+), 14 deletions(-)
---
diff --git a/app/display/gimpdisplayshell-scale.c b/app/display/gimpdisplayshell-scale.c
index 24c7d234f9..4c2450fcbf 100644
--- a/app/display/gimpdisplayshell-scale.c
+++ b/app/display/gimpdisplayshell-scale.c
@@ -813,20 +813,10 @@ gimp_display_shell_scale_drag (GimpDisplayShell *shell,
     {
       gimp_display_shell_push_zoom_focus_pointer_pos (shell, start_x, start_y);
 
-      if (delta_y > 0.0)
-        {
-          gimp_display_shell_scale (shell,
-                                    GIMP_ZOOM_TO,
-                                    scale * 1.1,
-                                    GIMP_ZOOM_FOCUS_POINTER);
-        }
-      else /* delta_y < 0.0 */
-        {
-          gimp_display_shell_scale (shell,
-                                    GIMP_ZOOM_TO,
-                                    scale * 0.9,
-                                    GIMP_ZOOM_FOCUS_POINTER);
-        }
+      gimp_display_shell_scale (shell,
+                                GIMP_ZOOM_TO,
+                                scale * exp (0.01 * delta_y),
+                                GIMP_ZOOM_FOCUS_POINTER);
 
       if (shell->zoom_focus_point)
         {