Fix SVGPong slide crash in Viewer

SVGPong relies on onOnceBeforeDraw() to initialize, but when switching
slides via Viewer's UI, onAnimate() is fired before the first paint.

Change-Id: I7be133072ec635975f7463538cd42edb69696b3f
Reviewed-on: https://skia-review.googlesource.com/79424
Reviewed-by: Brian Osman <brianosman@google.com>
Commit-Queue: Florin Malita <fmalita@chromium.org>

1 files changed, 12 insertions, 10 deletions

diff --git a/samplecode/SampleSVGPong.cpp b/samplecode/SampleSVGPong.cpp
index 590ec1824b..9fc7953048 100644
--- a/samplecode/SampleSVGPong.cpp
+++ b/samplecode/SampleSVGPong.cpp
@@ -179,19 +179,21 @@ protected:
     }
 
     bool onAnimate(const SkAnimTimer& timer) override {
-        SkScalar dt = (timer.msec() - fLastTick) * fTimeScale;
-        fLastTick = timer.msec();
-
-        fPaddle0.posTick(dt);
-        fPaddle1.posTick(dt);
-        fBall.posTick(dt);
+        // onAnimate may fire before the first draw.
+        if (fDom) {
+            SkScalar dt = (timer.msec() - fLastTick) * fTimeScale;
+            fLastTick = timer.msec();
 
-        this->enforceConstraints();
+            fPaddle0.posTick(dt);
+            fPaddle1.posTick(dt);
+            fBall.posTick(dt);
 
-        fPaddle0.updateDom();
-        fPaddle1.updateDom();
-        fBall.updateDom();
+            this->enforceConstraints();
 
+            fPaddle0.updateDom();
+            fPaddle1.updateDom();
+            fBall.updateDom();
+        }
         return true;
     }