From e54df488cd82761bfb0e9372aeae2acc5a1324d7 Mon Sep 17 00:00:00 2001
From: gmungoc <g.m.carstairs@dundee.ac.uk>
Date: Tue, 18 Jul 2017 13:02:15 +0100
Subject: [PATCH] JAL-147 corrected calculation of vertical scroll position
 and max

---
 src/jalview/appletgui/AlignmentPanel.java      |    9 ++++---
 src/jalview/gui/AlignmentPanel.java            |    9 ++++---
 src/jalview/viewmodel/ViewportRanges.java      |   32 +++++++++++++++++++++---
 test/jalview/viewmodel/ViewportRangesTest.java |   31 +++++++++++++++++++++++
 4 files changed, 72 insertions(+), 9 deletions(-)

diff --git a/src/jalview/appletgui/AlignmentPanel.java b/src/jalview/appletgui/AlignmentPanel.java
index edf6ad4..f8f31b2 100644
--- a/src/jalview/appletgui/AlignmentPanel.java
+++ b/src/jalview/appletgui/AlignmentPanel.java
@@ -994,11 +994,14 @@ public class AlignmentPanel extends Panel implements AdjustmentListener,
   private void setScrollingForWrappedPanel(int topLeftColumn)
   {
     int scrollPosition = vpRanges.getWrappedScrollPosition(topLeftColumn);
-    int maxScroll = vpRanges.getWrappedScrollPosition(vpRanges
-            .getVisibleAlignmentWidth() - 1);
+    int maxScroll = vpRanges.getWrappedMaxScroll(topLeftColumn);
 
+    /*
+     * a scrollbar's value can be set to at most (maximum-extent)
+     * so we add extent (1) to the maxScroll value
+     */
     vscroll.setUnitIncrement(1);
-    vscroll.setValues(scrollPosition, 1, 0, maxScroll);
+    vscroll.setValues(scrollPosition, 1, 0, maxScroll + 1);
   }
 
   protected Panel sequenceHolderPanel = new Panel();
diff --git a/src/jalview/gui/AlignmentPanel.java b/src/jalview/gui/AlignmentPanel.java
index 9d21a6c..a732527 100644
--- a/src/jalview/gui/AlignmentPanel.java
+++ b/src/jalview/gui/AlignmentPanel.java
@@ -902,11 +902,14 @@ public class AlignmentPanel extends GAlignmentPanel implements
   private void setScrollingForWrappedPanel(int topLeftColumn)
   {
     int scrollPosition = vpRanges.getWrappedScrollPosition(topLeftColumn);
-    int maxScroll = vpRanges.getWrappedScrollPosition(vpRanges
-            .getVisibleAlignmentWidth() - 1);
+    int maxScroll = vpRanges.getWrappedMaxScroll(topLeftColumn);
 
+    /*
+     * a scrollbar's value can be set to at most (maximum-extent)
+     * so we add extent (1) to the maxScroll value
+     */
     vscroll.setUnitIncrement(1);
-    vscroll.setValues(scrollPosition, 1, 0, maxScroll);
+    vscroll.setValues(scrollPosition, 1, 0, maxScroll + 1);
   }
 
   /**
diff --git a/src/jalview/viewmodel/ViewportRanges.java b/src/jalview/viewmodel/ViewportRanges.java
index 7c6b7ab..10cf583 100644
--- a/src/jalview/viewmodel/ViewportRanges.java
+++ b/src/jalview/viewmodel/ViewportRanges.java
@@ -563,14 +563,13 @@ public class ViewportRanges extends ViewportProperties
 
   /**
    * Answers the vertical scroll position (0..) to set, given the visible column
-   * that is at top left. Note that if called with the total visible width of
-   * the alignment, this gives the maximum cursor scroll value.
+   * that is at top left.
    * 
    * <pre>
    * Example:
    *    viewport width 40 columns (0-39, 40-79, 80-119...)
    *    column 0 returns scroll position 0
-   *    columns 0-40 return scroll position 1
+   *    columns 1-40 return scroll position 1
    *    columns 41-80 return scroll position 2
    *    etc
    * </pre>
@@ -587,8 +586,35 @@ public class ViewportRanges extends ViewportProperties
      * visible whole widths
      */
     int scroll = topLeftColumn / w;
+
+    /*
+     * add 1 for a part width if there is one
+     */
     scroll += topLeftColumn % w > 0 ? 1 : 0;
 
     return scroll;
   }
+
+  /**
+   * Answers the maximum wrapped vertical scroll value, given the column
+   * position (0..) to show at top left of the visible region.
+   * 
+   * @param topLeftColumn
+   * @return
+   */
+  public int getWrappedMaxScroll(int topLeftColumn)
+  {
+    int scrollPosition = getWrappedScrollPosition(topLeftColumn);
+
+    /*
+     * how many more widths could be drawn after this one?
+     */
+    int columnsRemaining = getVisibleAlignmentWidth() - topLeftColumn;
+    int width = getViewportWidth();
+    int widthsRemaining = columnsRemaining / width
+            + (columnsRemaining % width > 0 ? 1 : 0) - 1;
+    int maxScroll = scrollPosition + widthsRemaining;
+
+    return maxScroll;
+  }
 }
diff --git a/test/jalview/viewmodel/ViewportRangesTest.java b/test/jalview/viewmodel/ViewportRangesTest.java
index 86f0d62..70a3687 100644
--- a/test/jalview/viewmodel/ViewportRangesTest.java
+++ b/test/jalview/viewmodel/ViewportRangesTest.java
@@ -699,6 +699,37 @@ public class ViewportRangesTest {
     assertEquals(vrsmall.getViewportWidth(), 7);
     assertEquals(vrsmall.getStartRes(), 0);
   }
+
+  @Test(groups = { "Functional" })
+  public void testGetWrappedMaxScroll()
+  {
+    // generate an ungapped alignment of width 140
+    int alignmentWidth = 140;
+    AlignmentI al2 = gen.generate(alignmentWidth, 15, 1, 0, 5);
+    ViewportRanges vr = new ViewportRanges(al2);
+    vr.setStartEndRes(0, 39);
+    int width = vr.getViewportWidth(); // 40
+    int partWidth = alignmentWidth % width; // 20
+  
+    /*
+     * there are 3 * 40 remainder 20 residues
+     * number of widths depends on offset (scroll right)
+     * 4 widths (maxScroll = 3) if offset by 0 or more than 19 columns
+     * 5 widths (maxScroll = 4) if 1 <= offset <= 19
+     */
+    for (int col = 0; col < alignmentWidth; col++)
+    {
+      int offset = col % width;
+      if (offset > 0 && offset < partWidth)
+      {
+        assertEquals(vr.getWrappedMaxScroll(col), 4, "col " + col);
+      }
+      else
+      {
+        assertEquals(vr.getWrappedMaxScroll(col), 3, "col " + col);
+      }
+    }
+  }
 }
 
 // mock listener for property change events
-- 
1.7.10.2