Fix for Issue "Ugly rendering during scale DImuthuUpe#156"

- add option renderDuringScale to PdfView
- conditionally call loadPageByOffset from DragPinchManager.onScroll

Author: hansinator85

android-pdf-viewer/src/main/java/com/github/barteksc/pdfviewer/DragPinchManager.java

@@ -43,6 +43,7 @@ class DragPinchManager implements GestureDetector.OnGestureListener, GestureDete
     private boolean swipeVertical;
 
     private boolean scrolling = false;
+    private boolean scaling = false;
 
     public DragPinchManager(PDFView pdfView, AnimationManager animationManager) {
         this.pdfView = pdfView;
@@ -131,8 +132,9 @@ public boolean onScroll(MotionEvent e1, MotionEvent e2, float distanceX, float d
         if (isZooming() || isSwipeEnabled) {
             pdfView.moveRelativeTo(-distanceX, -distanceY);
         }
-        pdfView.loadPageByOffset();
-
+        if (!scaling || pdfView.doRenderDuringScale()) {
+          pdfView.loadPageByOffset();
+        }
         return true;
     }
 
@@ -174,13 +176,15 @@ public boolean onScale(ScaleGestureDetector detector) {
 
     @Override
     public boolean onScaleBegin(ScaleGestureDetector detector) {
+        scaling = true;
         return true;
     }
 
     @Override
     public void onScaleEnd(ScaleGestureDetector detector) {
         pdfView.loadPages();
         hideHandle();
+        scaling = false;
     }
 
     @Override

android-pdf-viewer/src/main/java/com/github/barteksc/pdfviewer/PDFView.java

@@ -51,7 +51,6 @@
 import com.shockwave.pdfium.PdfiumCore;
 
 import java.io.File;
-import java.io.IOException;
 import java.io.InputStream;
 import java.util.ArrayList;
 import java.util.List;
@@ -262,6 +261,14 @@ ScrollHandle getScrollHandle() {
      */
     private boolean annotationRendering = false;
 
+    /**
+     * True if the view should render during scaling - default<br/>
+     * Can not be forced on older API versions (< Build.VERSION_CODES.KITKAT) as the GestureDetector does
+     * not detect scrolling while scaling.<br/>
+     * False otherwise
+     */
+    private boolean renderDuringScale = true;
+
     /**
      * Construct the initial view
      */
@@ -1095,6 +1102,14 @@ public boolean isAnnotationRendering() {
         return annotationRendering;
     }
 
+    public void enableRenderDuringScale(boolean renderDuringScale) {
+        this.renderDuringScale = renderDuringScale;
+    }
+
+    public boolean doRenderDuringScale() {
+        return renderDuringScale;
+    }
+
     public PdfDocument.Meta getDocumentMeta() {
         if (pdfDocument == null) {
             return null;