Avoid caching mImage on the main render loop and use clipping.

+ Added a session flag that avoids caching mImage. This is useful when
mImage is just a Graphics2D wrapper that might change at any time.
+ Make GcSnapshot aware of the clipping so it doesn't need to render the
whole area if not needed.

Change-Id: Ie0134c2bc2741b5fa6648313864c851bbac066cf
(cherry picked from commit 2c5e85b303)

tools/layoutlib/bridge/src/com/android/layoutlib/bridge/impl/GcSnapshot.java

@@ -35,6 +35,7 @@ import java.awt.AlphaComposite;
 import java.awt.Color;
 import java.awt.Composite;
 import java.awt.Graphics2D;
+import java.awt.Rectangle;
 import java.awt.RenderingHints;
 import java.awt.Shape;
 import java.awt.geom.AffineTransform;
@@ -615,8 +616,22 @@ public class GcSnapshot {
                 return;
             }
 
-            int width = layer.getImage().getWidth();
-            int height = layer.getImage().getHeight();
+            int width;
+            int height;
+            Rectangle clipBounds = originalGraphics.getClipBounds();
+            if (clipBounds != null) {
+                if (clipBounds.width == 0 || clipBounds.height == 0) {
+                    // Clip is 0 so no need to paint anything.
+                    return;
+                }
+                // If we have clipBounds available, use them as they will always be
+                // smaller than the full layer size.
+                width = clipBounds.width;
+                height = clipBounds.height;
+            } else {
+                width = layer.getImage().getWidth();
+                height = layer.getImage().getHeight();
+            }
 
             // Create a temporary image to which the color filter will be applied.
             BufferedImage image = new BufferedImage(width, height,

tools/layoutlib/bridge/src/com/android/layoutlib/bridge/impl/RenderSessionImpl.java

@@ -554,7 +554,14 @@ public class RenderSessionImpl extends RenderAction<SessionParams> {
                 // draw the views
                 // create the BufferedImage into which the layout will be rendered.
                 boolean newImage = false;
-                if (newRenderSize || mCanvas == null) {
+
+                // When disableBitmapCaching is true, we do not reuse mImage and
+                // we create a new one in every render.
+                // This is useful when mImage is just a wrapper of Graphics2D so
+                // it doesn't get cached.
+                boolean disableBitmapCaching = Boolean.TRUE.equals(params.getFlag(
+                    RenderParamsFlags.FLAG_KEY_DISABLE_BITMAP_CACHING));
+                if (newRenderSize || mCanvas == null || disableBitmapCaching) {
                     if (params.getImageFactory() != null) {
                         mImage = params.getImageFactory().getImage(
                                 mMeasuredScreenWidth,
@@ -581,8 +588,12 @@ public class RenderSessionImpl extends RenderAction<SessionParams> {
                     Bitmap bitmap = Bitmap_Delegate.createBitmap(mImage,
                             true /*isMutable*/, hardwareConfig.getDensity());
 
-                    // create a Canvas around the Android bitmap
-                    mCanvas = new Canvas(bitmap);
+                    if (mCanvas == null) {
+                        // create a Canvas around the Android bitmap
+                        mCanvas = new Canvas(bitmap);
+                    } else {
+                        mCanvas.setBitmap(bitmap);
+                    }
                     mCanvas.setDensity(hardwareConfig.getDensity().getDpiValue());
                 }