Improve caching of special case paths in GrStencilAndCoverPathRenderer

src/gpu/GrPath.cpp

Index: src/gpu/GrPath.cpp
diff --git a/src/gpu/GrPath.cpp b/src/gpu/GrPath.cpp
index e76bdf2466208384ba453e0f21c4a827a4a6e3f1..5b75683628f427301b03103501a60ac0cf2bc32f 100644
--- a/src/gpu/GrPath.cpp
+++ b/src/gpu/GrPath.cpp
@@ -7,14 +7,168 @@
 
 #include "GrPath.h"
 
-void GrPath::ComputeKey(const SkPath& path, const GrStrokeInfo& stroke, GrUniqueKey* key) {
-    static const GrUniqueKey::Domain kPathDomain = GrUniqueKey::GenerateDomain();
+namespace {
+// Verb count limit for generating path key from content of a volatile path.
+// The value should accomodate at least simple rects and rrects.
+static const int kSimpleVolatilePathVerbLimit = 10;
+
+inline static bool compute_key_for_line_path(const SkPath& path, const GrStrokeInfo& stroke,
+                                             GrUniqueKey* key) {
+    SkPoint pts[2];
+    if (!path.isLine(pts)) {
+        return false;
+    }
+    SK_COMPILE_ASSERT((sizeof(pts) % sizeof(uint32_t)) == 0 && sizeof(pts) > sizeof(uint32_t),
+                      pts_needs_padding);
+
+    const int kBaseData32Cnt = 1 + sizeof(pts) / sizeof(uint32_t);
+    int strokeDataCnt = stroke.computeUniqueKeyFragmentData32Cnt();
+    static const GrUniqueKey::Domain kOvalPathDomain = GrUniqueKey::GenerateDomain();
+    GrUniqueKey::Builder builder(key, kOvalPathDomain, kBaseData32Cnt + strokeDataCnt);
+    builder[0] = path.getFillType();
+    memcpy(&builder[1], &pts, sizeof(pts));
+    if (strokeDataCnt > 0) {
+        stroke.asUniqueKeyFragment(&builder[kBaseData32Cnt]);
+    }
+    return true;
+}
+
+inline static bool compute_key_for_oval_path(const SkPath& path, const GrStrokeInfo& stroke,
+                                             GrUniqueKey* key) {
+    SkRect rect;
+    if (!path.isOval(&rect)) {
+        return false;
+    }
+    SK_COMPILE_ASSERT((sizeof(rect) % sizeof(uint32_t)) == 0 && sizeof(rect) > sizeof(uint32_t),
+                      rect_needs_padding);
+
+    const int kBaseData32Cnt = 1 + sizeof(rect) / sizeof(uint32_t);
     int strokeDataCnt = stroke.computeUniqueKeyFragmentData32Cnt();
-    GrUniqueKey::Builder builder(key, kPathDomain, 2 + strokeDataCnt);
+    static const GrUniqueKey::Domain kOvalPathDomain = GrUniqueKey::GenerateDomain();
+    GrUniqueKey::Builder builder(key, kOvalPathDomain, kBaseData32Cnt + strokeDataCnt);
+    builder[0] = path.getFillType();
+    memcpy(&builder[1], &rect, sizeof(rect));
+    if (strokeDataCnt > 0) {
+        stroke.asUniqueKeyFragment(&builder[kBaseData32Cnt]);
+    }
+    return true;
+}
+
+// Encodes the full path data to the unique key for very small, volatile paths. This is typically
+// hit when clipping stencils the clip stack. Intention is that this handles rects too, since
+// SkPath::isRect seems to do non-trivial amount of work.
+inline static bool compute_key_for_simple_path(const SkPath& path, const GrStrokeInfo& stroke,
+                                               GrUniqueKey* key) {
+    if (!path.isVolatile()) {
+        return false;
+    }
+
+    // The check below should take care of negative values casted positive.
+    const int verbCnt = path.countVerbs();
+    if (verbCnt > kSimpleVolatilePathVerbLimit) {
+        return false;
+    }
+
+    // If somebody goes wild with the constant, it might cause an overflow.
+    SK_COMPILE_ASSERT(kSimpleVolatilePathVerbLimit <= 100,
+                      big_simple_volatile_path_verb_limit_may_cause_overflow);
+
+    const int pointCnt = path.countPoints();
+    if (pointCnt < 0) {
+        SkASSERT(false);
+        return false;
+    }
+
+    // Construct counts that align as uint32_t counts.
+#define ARRAY_DATA32_COUNT(array_type, count) \
+    static_cast<int>((((count) * sizeof(array_type) + sizeof(uint32_t) - 1) / sizeof(uint32_t)))
+
+    const int verbData32Cnt = ARRAY_DATA32_COUNT(uint8_t, verbCnt);
+    const int pointData32Cnt = ARRAY_DATA32_COUNT(SkPoint, pointCnt);
+
+#undef ARRAY_DATA32_COUNT
+
+    // The unique key data is a "message" with following fragments:
+    // 0) domain, key length, uint32_t for fill type and uint32_t for verbCnt
+    //   (fragment 0, fixed size)
+    // 1) verb and point data (varying size)
+    // 2) stroke data (varying size)
+
+    const int baseData32Cnt = 2 + verbData32Cnt + pointData32Cnt;
+    const int strokeDataCnt = stroke.computeUniqueKeyFragmentData32Cnt();
+    static const GrUniqueKey::Domain kSimpleVolatilePathDomain = GrUniqueKey::GenerateDomain();
+    GrUniqueKey::Builder builder(key, kSimpleVolatilePathDomain, baseData32Cnt + strokeDataCnt);
+    int i = 0;
+    builder[i++] = path.getFillType();
+
+    // Serialize the verbCnt to make the whole message unambiguous.
+    // We serialize two variable length fragments to the message:
+    // * verb and point data (fragment 1)
+    // * stroke data (fragment 2)
+    // "Proof:"
+    // Verb count establishes unambiguous verb data.
+    // Unambiguous verb data establishes unambiguous point data, making fragment 1 unambiguous.
+    // Unambiguous fragment 1 establishes unambiguous fragment 2, since the length of the message
+    // has been established.
+
+    builder[i++] = SkToU32(verbCnt); // The path limit is compile-asserted above, so the cast is ok.
+
+    // Fill the last uint32_t with 0 first, since the last uint8_ts of the uint32_t may be
+    // uninitialized. This does not produce ambiguous verb data, since we have serialized the exact
+    // verb count.
+    if (verbData32Cnt != static_cast<int>((verbCnt * sizeof(uint8_t) / sizeof(uint32_t)))) {
+        builder[i + verbData32Cnt - 1] = 0;
+    }
+    path.getVerbs(reinterpret_cast<uint8_t*>(&builder[i]), verbCnt);
+    i += verbData32Cnt;
+
+    SK_COMPILE_ASSERT(((sizeof(SkPoint) % sizeof(uint32_t)) == 0) &&
+                      sizeof(SkPoint) > sizeof(uint32_t), skpoint_array_needs_padding);
+
+    // Here we assume getPoints does a memcpy, so that we do not need to worry about the alignment.
+    path.getPoints(reinterpret_cast<SkPoint*>(&builder[i]), pointCnt);
+    SkDEBUGCODE(i += pointData32Cnt);
+
+    SkASSERT(i == baseData32Cnt);
+    if (strokeDataCnt > 0) {
+        stroke.asUniqueKeyFragment(&builder[baseData32Cnt]);
+    }
+    return true;
+}
+
+inline static void compute_key_for_general_path(const SkPath& path, const GrStrokeInfo& stroke,
+                                                GrUniqueKey* key) {
+    const int kBaseData32Cnt = 2;
+    int strokeDataCnt = stroke.computeUniqueKeyFragmentData32Cnt();
+    static const GrUniqueKey::Domain kGeneralPathDomain = GrUniqueKey::GenerateDomain();
+    GrUniqueKey::Builder builder(key, kGeneralPathDomain, kBaseData32Cnt + strokeDataCnt);
     builder[0] = path.getGenerationID();
     builder[1] = path.getFillType();
     if (strokeDataCnt > 0) {
-        stroke.asUniqueKeyFragment(&builder[2]);
+        stroke.asUniqueKeyFragment(&builder[kBaseData32Cnt]);
+    }
+}
+
+}
+
+void GrPath::ComputeKey(const SkPath& path, const GrStrokeInfo& stroke, GrUniqueKey* key,
+                        bool* outIsVolatile) {
+    if (compute_key_for_line_path(path, stroke, key)) {
+        *outIsVolatile = false;
+        return;
     }
+
+    if (compute_key_for_oval_path(path, stroke, key)) {
+        *outIsVolatile = false;
+        return;
+    }
+
+    if (compute_key_for_simple_path(path, stroke, key)) {
+        *outIsVolatile = false;
+        return;
+    }
+
+    compute_key_for_general_path(path, stroke, key);
+    *outIsVolatile = path.isVolatile();
 }