logcat: Support auto scroll lock.

Another go at adding support for automatically enabling/disabling
scroll lock. Past attempts have been brittle because of differences
in how Windows, Linux and Mac handle the scrollbar.

The key to getting this work consistently across platforms seems
to be in explicitly setting the range of values for the scrollbar.
Setting the maximum to be a high enough value relative to the
thumb allows accurate detection of even minor movements away from
the bottom of the scrollbar.

Change-Id: Ic3259cc4e2e8a20f3a87ce4bf234217cea792f88

2 files changed, 46 insertions, 4 deletions

diff --git a/ddms/app/src/com/android/ddms/PrefsDialog.java b/ddms/app/src/com/android/ddms/PrefsDialog.java
index 84304df..acadeb8 100644
--- a/ddms/app/src/com/android/ddms/PrefsDialog.java
+++ b/ddms/app/src/com/android/ddms/PrefsDialog.java
@@ -461,6 +461,12 @@ public final class PrefsDialog {
                         "Maximum number of logcat messages to buffer",
                         getFieldEditorParent());
                 addField(maxMessages);
+
+                BooleanFieldEditor autoScrollLock = new BooleanFieldEditor(
+                        LogCatPanel.AUTO_SCROLL_LOCK_PREFKEY,
+                        "Automatically enable/disable scroll lock based on the scrollbar position",
+                        getFieldEditorParent());
+                addField(autoScrollLock);
             }
         }
     }
diff --git a/ddms/libs/ddmuilib/src/com/android/ddmuilib/logcat/LogCatPanel.java b/ddms/libs/ddmuilib/src/com/android/ddmuilib/logcat/LogCatPanel.java
index e7dcec9..9f38b29 100644
--- a/ddms/libs/ddmuilib/src/com/android/ddmuilib/logcat/LogCatPanel.java
+++ b/ddms/libs/ddmuilib/src/com/android/ddmuilib/logcat/LogCatPanel.java
@@ -19,13 +19,13 @@ package com.android.ddmuilib.logcat;
 import com.android.ddmlib.DdmConstants;
 import com.android.ddmlib.IDevice;
 import com.android.ddmlib.Log.LogLevel;
+import com.android.ddmuilib.AbstractBufferFindTarget;
+import com.android.ddmuilib.FindDialog;
 import com.android.ddmuilib.ITableFocusListener;
 import com.android.ddmuilib.ITableFocusListener.IFocusedTableActivator;
-import com.android.ddmuilib.FindDialog;
 import com.android.ddmuilib.ImageLoader;
 import com.android.ddmuilib.SelectionDependentPanel;
 import com.android.ddmuilib.TableHelper;
-import com.android.ddmuilib.AbstractBufferFindTarget;
 
 import org.eclipse.jface.action.Action;
 import org.eclipse.jface.action.MenuManager;
@@ -69,6 +69,7 @@ import org.eclipse.swt.widgets.FileDialog;
 import org.eclipse.swt.widgets.Label;
 import org.eclipse.swt.widgets.Listener;
 import org.eclipse.swt.widgets.Menu;
+import org.eclipse.swt.widgets.ScrollBar;
 import org.eclipse.swt.widgets.Table;
 import org.eclipse.swt.widgets.TableColumn;
 import org.eclipse.swt.widgets.TableItem;
@@ -97,6 +98,9 @@ public final class LogCatPanel extends SelectionDependentPanel
     /** Preference key to use for storing font settings. */
     public static final String LOGCAT_VIEW_FONT_PREFKEY = "logcat.view.font";
 
+    /** Preference key to use for deciding whether to automatically en/disable scroll lock. */
+    public static final String AUTO_SCROLL_LOCK_PREFKEY = "logcat.view.auto-scroll-lock";
+
     // Preference keys for message colors based on severity level
     private static final String MSG_COLOR_PREFKEY_PREFIX = "logcat.msg.color.";
     public static final String VERBOSE_COLOR_PREFKEY = MSG_COLOR_PREFKEY_PREFIX + "verbose"; //$NON-NLS-1$
@@ -171,6 +175,7 @@ public final class LogCatPanel extends SelectionDependentPanel
 
     private boolean mShouldScrollToLatestLog = true;
     private ToolItem mScrollLockCheckBox;
+    private boolean mAutoScrollLock;
 
     private String mLogFileExportFolder;
 
@@ -207,6 +212,7 @@ public final class LogCatPanel extends SelectionDependentPanel
 
         mFont = getFontFromPrefStore();
         loadMessageColorPreferences();
+        mAutoScrollLock = mPrefStore.getBoolean(AUTO_SCROLL_LOCK_PREFKEY);
     }
 
     private void loadMessageColorPreferences() {
@@ -244,6 +250,7 @@ public final class LogCatPanel extends SelectionDependentPanel
         mPrefStore.setDefault(LogCatMessageList.MAX_MESSAGES_PREFKEY,
                 LogCatMessageList.MAX_MESSAGES_DEFAULT);
         mPrefStore.setDefault(DISPLAY_FILTERS_COLUMN_PREFKEY, true);
+        mPrefStore.setDefault(AUTO_SCROLL_LOCK_PREFKEY, true);
 
         /* Default Colors for different log levels. */
         PreferenceConverter.setDefault(mPrefStore, LogCatPanel.VERBOSE_COLOR_PREFKEY,
@@ -298,6 +305,8 @@ public final class LogCatPanel extends SelectionDependentPanel
                     mReceiver.resizeFifo(mPrefStore.getInt(
                             LogCatMessageList.MAX_MESSAGES_PREFKEY));
                     reloadLogBuffer();
+                } else if (changedProperty.equals(AUTO_SCROLL_LOCK_PREFKEY)) {
+                    mAutoScrollLock = mPrefStore.getBoolean(AUTO_SCROLL_LOCK_PREFKEY);
                 }
             }
         });
@@ -682,13 +691,13 @@ public final class LogCatPanel extends SelectionDependentPanel
         mScrollLockCheckBox.setImage(
                 ImageLoader.getDdmUiLibLoader().loadImage(IMAGE_SCROLL_LOCK,
                         toolBar.getDisplay()));
-        mScrollLockCheckBox.setSelection(false);
+        mScrollLockCheckBox.setSelection(true);
         mScrollLockCheckBox.setToolTipText("Scroll Lock");
         mScrollLockCheckBox.addSelectionListener(new SelectionAdapter() {
             @Override
             public void widgetSelected(SelectionEvent event) {
                 boolean scrollLock = mScrollLockCheckBox.getSelection();
-                setScrollToLatestLog(!scrollLock);
+                setScrollToLatestLog(scrollLock);
             }
         });
     }
@@ -905,6 +914,33 @@ public final class LogCatPanel extends SelectionDependentPanel
                 dispose();
             }
         });
+
+        final ScrollBar vbar = mTable.getVerticalBar();
+        vbar.addSelectionListener(new SelectionAdapter() {
+            @Override
+            public void widgetSelected(SelectionEvent e) {
+                if (!mAutoScrollLock) {
+                    return;
+                }
+
+                boolean isAtBottom = (vbar.getThumb() + vbar.getSelection()) == vbar.getMaximum();
+                setScrollToLatestLog(isAtBottom);
+                mScrollLockCheckBox.setSelection(isAtBottom);
+            }
+        });
+
+        // Explicitly set the values to use for the scroll bar. In particular, we want these values
+        // to have a high enough accuracy that even small movements of the scroll bar have an
+        // effect on the selection. The auto scroll lock detection assumes that the scroll bar is
+        // at the bottom iff selection + thumb == max.
+        final int MAX = 10000;
+        final int THUMB = 10;
+        vbar.setValues(MAX - THUMB, // selection
+                0,                  // min
+                MAX,                // max
+                THUMB,              // thumb
+                1,                  // increment
+                THUMB);             // page increment
     }
 
     /** Setup menu to be displayed when right clicking a log message. */