master 12f666c1d5: Improve overscrolling support on Haiku

[Po Lu]

branch: master
commit 12f666c1d521668911b3e0143fafb8cf8bd7952b
Author: Po Lu <luangruo@yahoo.com>
Commit: Po Lu <luangruo@yahoo.com>

    Improve overscrolling support on Haiku
    
    * src/haiku_support.cc (class EmacsScrollBar): New field
    `real_max_value'.
    (MessageReceived): Set real max value.
    (MouseMoved): Get rid of magic numbers by using real max value
    instead.
---
 src/haiku_support.cc | 16 ++++++++++------
 1 file changed, 10 insertions(+), 6 deletions(-)

diff --git a/src/haiku_support.cc b/src/haiku_support.cc
index 98cc8e9314..5fc8d2675e 100644
--- a/src/haiku_support.cc
+++ b/src/haiku_support.cc
@@ -1569,7 +1569,8 @@ public:
   bool can_overscroll = false;
   BPoint last_overscroll;
   int last_reported_overscroll_value;
-  int max_value;
+  int max_value, real_max_value;
+  int overscroll_start_value;
 
   EmacsScrollBar (int x, int y, int x1, int y1, bool horizontal_p) :
     BScrollBar (BRect (x, y, x1, y1), NULL, NULL, 0, 0, horizontal_p ?
@@ -1593,7 +1594,8 @@ public:
        portion = msg->GetInt32 ("emacs:portion", 0);
        range = msg->GetInt32 ("emacs:range", 0);
        dragging = msg->GetInt32 ("emacs:dragging", 0);
-       proportion = (float) portion / range;
+       proportion = ((range <= 0 || portion <= 0)
+                     ? 1.0f : (float) portion / range);
        value = msg->GetInt32 ("emacs:units", 0);
        can_overscroll = msg->GetBool ("emacs:overscroll", false);
 
@@ -1616,6 +1618,7 @@ public:
                SetRange (0, range - portion);
                SetProportion (proportion);
                max_value = range - portion;
+               real_max_value = range;
 
                if (in_overscroll || value > max_value)
                  value = max_value;
@@ -1634,6 +1637,7 @@ public:
                old_value = value;
                SetValue (value);
                max_value = range - portion;
+               real_max_value = range;
              }
          }
       }
@@ -1879,21 +1883,20 @@ public:
            goto allow;
          }
 
-       range = max_value;
+       range = real_max_value;
        bounds = Bounds ();
        bounds.InsetBy (1.0, 1.0);
-       value = Value ();
+       value = overscroll_start_value;
        trough_size = BE_RECT_HEIGHT (bounds);
        trough_size -= BE_RECT_WIDTH (bounds) / 2;
        if (info.double_arrows)
          trough_size -= BE_RECT_WIDTH (bounds) / 2;
 
-       value += ((double) range / trough_size) * diff * 2;
+       value += ((double) range / trough_size) * diff;
 
        if (value != last_reported_overscroll_value)
          {
            last_reported_overscroll_value = value;
-           last_overscroll = point;
 
            value_event.scroll_bar = this;
            value_event.window = Window ();
@@ -1913,6 +1916,7 @@ public:
 
            if (value == Value () && Proportion () < 1.0f)
              {
+               overscroll_start_value = value;
                in_overscroll = true;
                last_overscroll = point;
                last_reported_overscroll_value = value;