From 77f144de6798b3c0caadece63ae6fa68e3ed434f Mon Sep 17 00:00:00 2001
From: Pavel Fatin <pavel.fatin@jetbrains.com>
Date: Mon, 30 Jan 2017 22:32:39 +0100
Subject: [PATCH] true smooth scrolling: compatibility with a different
 encoding of absolute scrolling deltas in JetBrains Runtime

---
 .../ui/components/MouseWheelEventEx.java      | 36 +++++++++----------
 1 file changed, 17 insertions(+), 19 deletions(-)

diff --git a/platform/platform-api/src/com/intellij/ui/components/MouseWheelEventEx.java b/platform/platform-api/src/com/intellij/ui/components/MouseWheelEventEx.java
index 21d1fc26d9cd..bb4ca4dffd49 100644
--- a/platform/platform-api/src/com/intellij/ui/components/MouseWheelEventEx.java
+++ b/platform/platform-api/src/com/intellij/ui/components/MouseWheelEventEx.java
@@ -15,39 +15,37 @@
  */
 package com.intellij.ui.components;
 
-import com.intellij.util.MethodInvocator;
+import com.intellij.openapi.util.SystemInfo;
 
 import java.awt.event.MouseWheelEvent;
 
 /**
- * Accessor for absolute scrolling delta in the
- * <a href="https://github.com/JetBrains/jdk8u_jdk/commit/568f2dae82b0fe27b79ce6943071d89463758610">enhanced MouseWheelEvent</a>.
- * <p>
- * Should be paired up with our custom JRE (currently has has
- * an <a href="https://github.com/JetBrains/jdk8u_jdk/commit/a3cb8807b148879e9c70a74a8a16c30a28991581">implementation</a> for Mac OS X).
+ * Accessor for absolute scrolling delta in enhanced MouseWheelEvent.
  */
 class MouseWheelEventEx {
-  private static final MethodInvocator ourGetScrollingDeltaMethod = new MethodInvocator(false, MouseWheelEvent.class, "getScrollingDelta");
-
   /**
-   * Returns scrolling delta as an absolute value (if available).
-   * <p>
-   * Returns 0.0 when scrolling delta is available only as a number of "clicks" or
-   * as a fraction of a "click".
-   * <p>
-   * The method returns natural numbers, however, for future extensibility,
-   * the return type is declared as {@code double}.
+   * Returns scrolling delta as an absolute value (if available). Requires JetBrains Runtime.
    * <p>
    * Some devices (e.g. high-precision touchpads) may report scrolling deltas
    * in absolute values rather than in fractions of a "click". This data can be used,
    * for example, to implement pixel-perfect scrolling (which cannot be
    * implemented via the {@link MouseWheelEvent#getPreciseWheelRotation} method, as fractions
    * of scrolling "units" cannot be reliably translated to pixel-precise deltas).
+   * <p>
+   * JetBrains Runtime currently uses <code>preciseWheelRotation = 0.1 * scrollingDelta</code>
+   * mapping in Mac OS to encode absolute scrolling deltas as relative ones.
+   * <p>
+   * That approach is suboptimal, because it:
+   * 1) produces different dynamics of relative deltas (in Mac OS there's no reliable linear mapping between those values),
+   * 2) makes handling of true relative deltas impossible (as there's no way to distinguish them from the encoded absolute ones).
+   * <p>
+   * Ideally, we need to implement a method of distinguishing between the two kinds of scrolling deltas.
    *
-   * @param event the event
-   * @return negative values for scrolling up, positive values for scrolling down (natural numbers)
+   * @param e the event
+   * @return negative values for scrolling up, positive values for scrolling down
+   * 0.0 when absolute deltas are not supported or not available
    */
-  static double getScrollingDelta(MouseWheelEvent event) {
-    return ourGetScrollingDeltaMethod.isAvailable() ? (double)ourGetScrollingDeltaMethod.invoke(event) : 0.0D;
+  static double getScrollingDelta(MouseWheelEvent e) {
+    return SystemInfo.isJetbrainsJvm && SystemInfo.isMac ? 10.0D * e.getPreciseWheelRotation() : 0.0D;
   }
 }