diff --git a/tools/viewer/SkottieSlide.cpp b/tools/viewer/SkottieSlide.cpp
index 063330e925..a364bb1099 100644
--- a/tools/viewer/SkottieSlide.cpp
+++ b/tools/viewer/SkottieSlide.cpp
@@ -77,3 +77,16 @@ bool SkottieSlide::onChar(SkUnichar c) {
 
     return INHERITED::onChar(c);
 }
+
+bool SkottieSlide::onMouse(SkScalar x, SkScalar y, sk_app::Window::InputState state, uint32_t) {
+    switch (state) {
+    case sk_app::Window::kUp_InputState:
+        fShowAnimationInval = !fShowAnimationInval;
+        fAnimation->setShowInval(fShowAnimationInval);
+        break;
+    default:
+        break;
+    }
+
+    return true;
+}
diff --git a/tools/viewer/SkottieSlide.h b/tools/viewer/SkottieSlide.h
index a287a6855c..ac26d2f3c1 100644
--- a/tools/viewer/SkottieSlide.h
+++ b/tools/viewer/SkottieSlide.h
@@ -27,6 +27,7 @@ public:
     bool animate(const SkAnimTimer&) override;
 
     bool onChar(SkUnichar) override;
+    bool onMouse(SkScalar x, SkScalar y, sk_app::Window::InputState, uint32_t modifiers) override;
 
 private:
     SkString                            fPath;
diff --git a/tools/viewer/SlideDir.cpp b/tools/viewer/SlideDir.cpp
index da8685ddf7..ba3bbbae12 100644
--- a/tools/viewer/SlideDir.cpp
+++ b/tools/viewer/SlideDir.cpp
@@ -337,8 +337,8 @@ void SlideDir::unload() {
 }
 
 SkISize SlideDir::getDimensions() const {
-    return  SkSize::Make(fWinSize.width(),
-                         fCellSize.height() * (fSlides.count() / fColumns)).toCeil();
+    return SkSize::Make(fWinSize.width(),
+                        fCellSize.height() * (1 + (fSlides.count() - 1) / fColumns)).toCeil();
 }
 
 void SlideDir::draw(SkCanvas* canvas) {
@@ -414,5 +414,5 @@ const SlideDir::Rec* SlideDir::findCell(float x, float y) const {
               row = static_cast<int>(y / fCellSize.height()),
               idx = row * fColumns + col;
 
-    return idx <= fRecs.count() ? &fRecs[idx] : nullptr;
+    return idx < fRecs.count() ? &fRecs[idx] : nullptr;
 }