[gimp] app: improve GimpToolLine slider motion clamping/constraint

[N/A <ell src gnome org>]

commit 2d11d29157086417c0106175c73eb0045b73f1c8
Author: Ell <ell_se yahoo com>
Date:   Sun Jul 30 13:49:21 2017 -0400

    app: improve GimpToolLine slider motion clamping/constraint
    
    During constrained motion, round the slider value before clamping
    it, so that the slider limits are always enforced.  Additionally,
    snap the slider to 1/12-ths of the line length, rather than
    1/24-ths.
    
    Make sure that sliders can never have negative-zero values, which
    can result in a -inf base for spiral.

 app/display/gimptoolline.c |    6 ++++--
 1 files changed, 4 insertions(+), 2 deletions(-)
---
diff --git a/app/display/gimptoolline.c b/app/display/gimptoolline.c
index 36596b2..a957646 100644
--- a/app/display/gimptoolline.c
+++ b/app/display/gimptoolline.c
@@ -733,11 +733,13 @@ gimp_tool_line_point_motion (GimpToolLine *line,
                  (private->y2 - private->y1) * (y - private->y1);
             t /= length_sqr;
 
+            if (constrain)
+              t = RINT (12.0 * t) / 12.0;
+
             t = CLAMP (t, slider->min, slider->max);
             t = CLAMP (t, 0.0, 1.0);
 
-            if (constrain)
-              t = RINT (24.0 * t) / 24.0;
+            t = fabs (t); /* avoid negative zero */
 
             slider->value = t;