scroll by full tab height when tabs are on the right

platform/platform-api/src/com/intellij/ui/tabs/impl/JBTabsImpl.java

@@ -235,7 +235,7 @@ public class JBTabsImpl extends JComponent
       @Override
       public void mouseWheelMoved(MouseWheelEvent e) {
         if (mySingleRowLayout.myLastSingRowLayout != null) {
-          mySingleRowLayout.scroll(e.getUnitsToScroll() * 10);
+          mySingleRowLayout.scroll(e.getUnitsToScroll() * mySingleRowLayout.getScrollUnitIncrement());
           revalidateAndRepaint(false);
         }
       }

platform/platform-api/src/com/intellij/ui/tabs/impl/singleRow/ScrollableSingleRowLayout.java

@@ -60,6 +60,17 @@ public class ScrollableSingleRowLayout extends SingleRowLayout {
     myScrollSelectionInViewPending = true;
   }
 
+  public int getScrollUnitIncrement() {
+    if (myLastSingRowLayout != null) {
+      final List<TabInfo> visibleInfos = myLastSingRowLayout.myVisibleInfos;
+      if (visibleInfos.size() > 0) {
+        final TabInfo info = visibleInfos.get(0);
+        return getStrategy().getScrollUnitIncrement(myTabs.myInfo2Label.get(info));
+      }
+    }
+    return 0;
+  }
+
   private void doScrollSelectionInView(SingleRowPassInfo passInfo) {
     int offset = -myScrollOffset;
     for (TabInfo info : passInfo.myVisibleInfos) {
@@ -68,8 +79,11 @@ public class ScrollableSingleRowLayout extends SingleRowLayout {
         if (offset < 0) {
           scroll(offset);
         }
-        else if (offset + length > passInfo.toFitLength - getStrategy().getMoreRectAxisSize()) {
-          scroll(offset + length - passInfo.toFitLength + getStrategy().getMoreRectAxisSize());
+        else {
+          final int maxLength = passInfo.toFitLength - getStrategy().getMoreRectAxisSize();
+          if (offset + length > maxLength) {
+            scroll(offset + length - maxLength);
+          }
         }
         break;
       }

platform/platform-api/src/com/intellij/ui/tabs/impl/singleRow/SingleRowLayout.java

@@ -132,6 +132,10 @@ public class SingleRowLayout extends TabLayout {
   public void scroll(int units) {
   }
 
+  public int getScrollUnitIncrement() {
+    return 0;
+  }
+
   public void scrollSelectionInView(List<TabInfo> visibleInfos) {
   }
 

platform/platform-api/src/com/intellij/ui/tabs/impl/singleRow/SingleRowLayoutStrategy.java

@@ -80,6 +80,14 @@ public abstract class SingleRowLayoutStrategy {
    */
   public abstract boolean drawPartialOverflowTabs();
 
+  /**
+   * Return the change of scroll offset for every unit of mouse wheel scrolling.
+   *
+   * @param label the first visible tab label
+   * @return the scroll amount
+   */
+  public abstract int getScrollUnitIncrement(TabLabel label);
+
   abstract static class Horizontal extends SingleRowLayoutStrategy {
     protected Horizontal(final SingleRowLayout layout) {
       super(layout);
@@ -140,6 +148,11 @@ public abstract class SingleRowLayoutStrategy {
     public boolean drawPartialOverflowTabs() {
       return true;
     }
+
+    @Override
+    public int getScrollUnitIncrement(TabLabel label) {
+      return 10;
+    }
   }
 
   static class Top extends Horizontal {
@@ -302,6 +315,11 @@ public abstract class SingleRowLayoutStrategy {
     public boolean drawPartialOverflowTabs() {
       return false;
     }
+
+    @Override
+    public int getScrollUnitIncrement(TabLabel label) {
+      return label.getPreferredSize().height;
+    }
   }
 
   static class Left extends Vertical {