Attempt to stabilize shadow_utils GM for replay configs

Change-Id: I0ed15ab102fa1e0a364d5f3a953bedd8afbda3c3
Reviewed-on: https://skia-review.googlesource.com/8853
Commit-Queue: Brian Salomon <bsalomon@google.com>
Reviewed-by: Mike Klein <mtklein@chromium.org>

3 files changed, 17 insertions, 1 deletions

diff --git a/gm/shadowutils.cpp b/gm/shadowutils.cpp
index 96554f10e7..fd02d92133 100644
--- a/gm/shadowutils.cpp
+++ b/gm/shadowutils.cpp
@@ -8,6 +8,7 @@
 #include "gm.h"
 #include "SkCanvas.h"
 #include "SkPath.h"
+#include "SkMutex.h"
 #include "SkShadowUtils.h"
 
 void draw_shadow(SkCanvas* canvas, const SkPath& path, int height, SkColor color, SkPoint3 lightPos,
@@ -22,6 +23,14 @@ static constexpr int kW = 700;
 static constexpr int kH = 800;
 
 DEF_SIMPLE_GM(shadow_utils, canvas, kW, kH) {
+    // SkShadowUtils uses a cache of SkVertices meshes. The vertices are created in a local
+    // coordinate system and then translated when reused. The coordinate system depends on
+    // parameters to the generating draw. To avoid slight rendering differences due to this property
+    // we only allow one thread into this GM at a time and we reset the cache before each run.
+    static SkMutex gMutex;
+    SkAutoMutexAcquire mutexLock(&gMutex);
+    SkShadowUtils::ClearCache();
+
     SkTArray<SkPath> paths;
     paths.push_back().addRoundRect(SkRect::MakeWH(50, 50), 10, 10);
     SkRRect oddRRect;
diff --git a/include/utils/SkShadowUtils.h b/include/utils/SkShadowUtils.h
index 795c2cf2ce..60ce6ffe30 100644
--- a/include/utils/SkShadowUtils.h
+++ b/include/utils/SkShadowUtils.h
@@ -22,6 +22,7 @@ public:
                            const SkPoint3& lightPos, SkScalar lightRadius,
                            SkScalar ambientAlpha, SkScalar spotAlpha, SkColor color,
                            uint32_t flags = SkShadowFlags::kNone_ShadowFlag);
+    static void ClearCache();
 };
 
 #endif
diff --git a/src/utils/SkShadowUtils.cpp b/src/utils/SkShadowUtils.cpp
index 8374aef68f..86aba797d6 100644
--- a/src/utils/SkShadowUtils.cpp
+++ b/src/utils/SkShadowUtils.cpp
@@ -83,6 +83,10 @@ sk_sp<GrFragmentProcessor> SkGaussianColorFilter::asFragmentProcessor(GrContext*
 
 namespace {
 
+uint64_t resource_cache_shared_id() {
+    return 0x2020776f64616873llu;  // 'shadow  '
+}
+
 /** Factory for an ambient shadow mesh with particular shadow properties. */
 struct AmbientVerticesFactory {
     SkScalar fRadius = SK_ScalarNaN;  // NaN so that isCompatible will always fail until init'ed.
@@ -381,7 +385,7 @@ void draw_shadow(const FACTORY& factory, SkCanvas* canvas, ShadowedPath& path, S
         keyStorage.reset(keyDataBytes + sizeof(SkResourceCache::Key));
         key = new (keyStorage.begin()) SkResourceCache::Key();
         path.writeKey((uint32_t*)(keyStorage.begin() + sizeof(*key)));
-        key->init(&kNamespace, 0, keyDataBytes);
+        key->init(&kNamespace, resource_cache_shared_id(), keyDataBytes);
         SkResourceCache::Find(*key, FindVisitor<FACTORY>, &context);
     }
 
@@ -522,3 +526,5 @@ void SkShadowUtils::DrawShadow(SkCanvas* canvas, const SkPath& path, SkScalar oc
         draw_shadow(factory, canvas, shadowedPath, color);
     }
 }
+
+void SkShadowUtils::ClearCache() { SkResourceCache::PostPurgeSharedID(resource_cache_shared_id()); }