[GTK] Momentum scrolling stops abruptly before websites end

https://bugs.webkit.org/show_bug.cgi?id=193350

Patch by Alexander Mikhaylenko <exalm7659@gmail.com> on 2019-01-31
Reviewed by Carlos Garcia Campos.

Don't immediately set velocity to 0 when position reaches upper or bottom limit.
Instead, set it to the overshot distance, so that position exactly matches upper
or lower limit on the next frame, and then clamp velocity to 0 using the existing
mechanism.

* platform/ScrollAnimationKinetic.cpp:
(WebCore::ScrollAnimationKinetic::PerAxisData::animateScroll):

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@240789 268f45cc-cd09-0410-ab3c-d52691b4dbfc

diff --git a/Source/WebCore/ChangeLog b/Source/WebCore/ChangeLog
index 11b5c56..1308d80 100644 (file)
--- a/Source/WebCore/ChangeLog
+++ b/Source/WebCore/ChangeLog
@@ -1,3 +1,18 @@
+2019-01-31  Alexander Mikhaylenko  <exalm7659@gmail.com>
+
+        [GTK] Momentum scrolling stops abruptly before websites end
+        https://bugs.webkit.org/show_bug.cgi?id=193350
+
+        Reviewed by Carlos Garcia Campos.
+
+        Don't immediately set velocity to 0 when position reaches upper or bottom limit.
+        Instead, set it to the overshot distance, so that position exactly matches upper
+        or lower limit on the next frame, and then clamp velocity to 0 using the existing
+        mechanism.
+
+        * platform/ScrollAnimationKinetic.cpp:
+        (WebCore::ScrollAnimationKinetic::PerAxisData::animateScroll):
+
 2019-01-31  Michael Catanzaro  <mcatanzaro@igalia.com>
 
         Unreviewed, fix incorrect string format

diff --git a/Source/WebCore/platform/ScrollAnimationKinetic.cpp b/Source/WebCore/platform/ScrollAnimationKinetic.cpp
index 7466ee9..ac9f2f0 100644 (file)
--- a/Source/WebCore/platform/ScrollAnimationKinetic.cpp
+++ b/Source/WebCore/platform/ScrollAnimationKinetic.cpp
@@ -89,12 +89,14 @@ bool ScrollAnimationKinetic::PerAxisData::animateScroll(Seconds timeDelta)
     m_velocity = -decelFriction * m_coef2 * exponentialPart;
 
     if (m_position < m_lower) {
+        m_velocity = m_lower - m_position;
         m_position = m_lower;
-        m_velocity = 0;
     } else if (m_position > m_upper) {
+        m_velocity = m_upper - m_position;
         m_position = m_upper;
-        m_velocity = 0;
-    } else if (fabs(m_velocity) < 1 || (lastTime && fabs(m_position - lastPosition) < 1)) {
+    }
+
+    if (fabs(m_velocity) < 1 || (lastTime && fabs(m_position - lastPosition) < 1)) {
         m_position = round(m_position);
         m_velocity = 0;
     }