Add option for vertical scrolling support in Android App.

A potential customer (currently a free user) contacted us asking
that MuPDF be extended to support vertical scrolling rather than
horizontal scrolling. He supplied a partially working patch.

We reviewed his patch, and found the bit he'd missed, which he added
and it now works for his purposes. We also spotted some places
where his patch is incorrect in general though (and will go wrong
for cases where PDF files have varying page sizes).

This is a commit of a correct version. ReaderView gains a
HORIZONTAL_SCROLLING boolean that is set to true currently to
maintain the normal behaviour. Change it to false and we will
scroll vertically instead.

Possibly we could add a button to allow this to be a runtime option,
but that's a future enhancement.

1 files changed, 72 insertions, 15 deletions

diff --git a/platform/android/src/com/artifex/mupdfdemo/ReaderView.java b/platform/android/src/com/artifex/mupdfdemo/ReaderView.java
index 7cfcf4d1..e27f0bbf 100644
--- a/platform/android/src/com/artifex/mupdfdemo/ReaderView.java
+++ b/platform/android/src/com/artifex/mupdfdemo/ReaderView.java
@@ -32,6 +32,8 @@ public class ReaderView
 	private static final float MAX_SCALE        = 5.0f;
 	private static final float REFLOW_SCALE_FACTOR = 0.5f;
 
+	private static final boolean HORIZONTAL_SCROLLING = true;
+
 	private Adapter           mAdapter;
 	private int               mCurrent;    // Adapter's index for the current view
 	private boolean           mResetLayout;
@@ -373,7 +375,7 @@ public class ReaderView
 			Rect bounds = getScrollBounds(v);
 			switch(directionOfTravel(velocityX, velocityY)) {
 			case MOVING_LEFT:
-				if (bounds.left >= 0) {
+				if (HORIZONTAL_SCROLLING && bounds.left >= 0) {
 					// Fling off to the left bring next view onto screen
 					View vl = mChildViews.get(mCurrent+1);
 
@@ -383,8 +385,19 @@ public class ReaderView
 					}
 				}
 				break;
+			case MOVING_UP:
+				if (!HORIZONTAL_SCROLLING && bounds.top >= 0) {
+					// Fling off to the top bring next view onto screen
+					View vl = mChildViews.get(mCurrent+1);
+
+					if (vl != null) {
+						slideViewOntoScreen(vl);
+						return true;
+					}
+				}
+				break;
 			case MOVING_RIGHT:
-				if (bounds.right <= 0) {
+				if (HORIZONTAL_SCROLLING && bounds.right <= 0) {
 					// Fling off to the right bring previous view onto screen
 					View vr = mChildViews.get(mCurrent-1);
 
@@ -394,6 +407,17 @@ public class ReaderView
 					}
 				}
 				break;
+			case MOVING_DOWN:
+				if (HORIZONTAL_SCROLLING && bounds.bottom <= 0) {
+					// Fling off to the bottom bring previous view onto screen
+					View vr = mChildViews.get(mCurrent-1);
+
+					if (vr != null) {
+						slideViewOntoScreen(vr);
+						return true;
+					}
+				}
+				break;
 			}
 			mScrollerLastX = mScrollerLastY = 0;
 			// If the page has been dragged out of bounds then we want to spring back
@@ -544,10 +568,15 @@ public class ReaderView
 		if (!mResetLayout) {
 			// Move to next or previous if current is sufficiently off center
 			if (cv != null) {
+				boolean move;
 				cvOffset = subScreenSizeOffset(cv);
 				// cv.getRight() may be out of date with the current scale
 				// so add left to the measured width for the correct position
-				if (cv.getLeft() + cv.getMeasuredWidth() + cvOffset.x + GAP/2 + mXScroll < getWidth()/2 && mCurrent + 1 < mAdapter.getCount()) {
+				if (HORIZONTAL_SCROLLING)
+					move = cv.getLeft() + cv.getMeasuredWidth() + cvOffset.x + GAP/2 + mXScroll < getWidth()/2;
+				else
+					move = cv.getTop() + cv.getMeasuredHeight() + cvOffset.y + GAP/2 + mYScroll < getHeight()/2;
+				if (move && mCurrent + 1 < mAdapter.getCount()) {
 					postUnsettle(cv);
 					// post to invoke test for end of animation
 					// where we must set hq area for the new current view
@@ -558,7 +587,11 @@ public class ReaderView
 					onMoveToChild(mCurrent);
 				}
 
-				if (cv.getLeft() - cvOffset.x - GAP/2 + mXScroll >= getWidth()/2 && mCurrent > 0) {
+				if (HORIZONTAL_SCROLLING)
+					move = cv.getLeft() - cvOffset.x - GAP/2 + mXScroll >= getWidth()/2;
+				else
+					move = cv.getTop() - cvOffset.y - GAP/2 + mYScroll >= getHeight()/2;
+				if (move && mCurrent > 0) {
 					postUnsettle(cv);
 					// post to invoke test for end of animation
 					// where we must set hq area for the new current view
@@ -638,12 +671,18 @@ public class ReaderView
 			cvLeft   += corr.x;
 			cvTop    += corr.y;
 			cvBottom += corr.y;
-		} else if (cv.getMeasuredHeight() <= getHeight()) {
+		} else if (HORIZONTAL_SCROLLING && cv.getMeasuredHeight() <= getHeight()) {
 			// When the current view is as small as the screen in height, clamp
 			// it vertically
 			Point corr = getCorrection(getScrollBounds(cvLeft, cvTop, cvRight, cvBottom));
 			cvTop    += corr.y;
 			cvBottom += corr.y;
+		} else if (!HORIZONTAL_SCROLLING && cv.getMeasuredWidth() <= getWidth()) {
+			// When the current view is as small as the screen in width, clamp
+			// it horizontally
+			Point corr = getCorrection(getScrollBounds(cvLeft, cvTop, cvRight, cvBottom));
+			cvRight  += corr.x;
+			cvLeft   += corr.x;
 		}
 
 		cv.layout(cvLeft, cvTop, cvRight, cvBottom);
@@ -651,21 +690,39 @@ public class ReaderView
 		if (mCurrent > 0) {
 			View lv = getOrCreateChild(mCurrent - 1);
 			Point leftOffset = subScreenSizeOffset(lv);
-			int gap = leftOffset.x + GAP + cvOffset.x;
-			lv.layout(cvLeft - lv.getMeasuredWidth() - gap,
-					(cvBottom + cvTop - lv.getMeasuredHeight())/2,
-					cvLeft - gap,
-					(cvBottom + cvTop + lv.getMeasuredHeight())/2);
+			if (HORIZONTAL_SCROLLING)
+			{
+				int gap = leftOffset.x + GAP + cvOffset.x;
+				lv.layout(cvLeft - lv.getMeasuredWidth() - gap,
+						(cvBottom + cvTop - lv.getMeasuredHeight())/2,
+						cvLeft - gap,
+						(cvBottom + cvTop + lv.getMeasuredHeight())/2);
+			} else {
+				int gap = leftOffset.y + GAP + cvOffset.y;
+				lv.layout((cvLeft + cvRight - lv.getMeasuredWidth())/2,
+						cvTop - lv.getMeasuredHeight() - gap,
+						(cvLeft + cvRight + lv.getMeasuredWidth())/2,
+						cvTop - gap);
+			}
 		}
 
 		if (mCurrent + 1 < mAdapter.getCount()) {
 			View rv = getOrCreateChild(mCurrent + 1);
 			Point rightOffset = subScreenSizeOffset(rv);
-			int gap = cvOffset.x + GAP + rightOffset.x;
-			rv.layout(cvRight + gap,
-					(cvBottom + cvTop - rv.getMeasuredHeight())/2,
-					cvRight + rv.getMeasuredWidth() + gap,
-					(cvBottom + cvTop + rv.getMeasuredHeight())/2);
+			if (HORIZONTAL_SCROLLING)
+			{
+				int gap = cvOffset.x + GAP + rightOffset.x;
+				rv.layout(cvRight + gap,
+						(cvBottom + cvTop - rv.getMeasuredHeight())/2,
+						cvRight + rv.getMeasuredWidth() + gap,
+						(cvBottom + cvTop + rv.getMeasuredHeight())/2);
+			} else {
+				int gap = cvOffset.y + GAP + rightOffset.y;
+				rv.layout((cvLeft + cvRight - rv.getMeasuredWidth())/2,
+						cvBottom + gap,
+						(cvLeft + cvRight + rv.getMeasuredWidth())/2,
+						cvBottom + gap + rv.getMeasuredHeight());
+			}
 		}
 
 		invalidate();