ccpr: Abstract the draws list in a separate class

Bug: skia:
Change-Id: I583c1bdc470e5830d041955d14b164fc00d5d014
Reviewed-on: https://skia-review.googlesource.com/129227
Reviewed-by: Brian Salomon <bsalomon@google.com>
Commit-Queue: Chris Dalton <csmartdalton@google.com>

1 files changed, 61 insertions, 0 deletions

diff --git a/src/gpu/ccpr/GrCCSTLList.h b/src/gpu/ccpr/GrCCSTLList.h
new file mode 100644
index 0000000000..3b478e9842
--- /dev/null
+++ b/src/gpu/ccpr/GrCCSTLList.h
@@ -0,0 +1,61 @@
+/*
+ * Copyright 2018 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#ifndef GrCCSTLList_DEFINED
+#define GrCCSTLList_DEFINED
+
+#include "SkArenaAlloc.h"
+
+/**
+ * A singly-linked list whose head element is a local class member. This is required by
+ * GrCCDrawPathsOp because the owning opList is unknown at the time of creation, so we can't use its
+ * associated allocator to create the first element.
+ */
+template<typename T> class GrCCSTLList {
+public:
+    GrCCSTLList(T&& head) : fHead(std::move(head)) {}
+
+    ~GrCCSTLList() {
+        T* draw = fHead.fNext; // fHead will be destructed automatically.
+        while (draw) {
+            T* next = draw->fNext;
+            draw->~T();
+            draw = next;
+        }
+    }
+
+    const T& head() const { return fHead; }
+    T& head() { return fHead; }
+
+    void append(GrCCSTLList&& right, SkArenaAlloc* alloc) {
+        T* nextTail = (&right.fHead == right.fTail) ? nullptr : right.fTail;
+        T* newRightHead =
+                new (alloc->makeBytesAlignedTo(sizeof(T), alignof(T))) T(std::move(right.fHead));
+
+        // Finish the move of right.fHead.
+        right.fHead.fNext = nullptr;
+        right.fTail = &right.fHead;
+
+        fTail->fNext = newRightHead;
+        fTail = !nextTail ? newRightHead : nextTail;
+    }
+
+    struct Iter {
+        bool operator!=(const Iter& that) { return fCurr != that.fCurr; }
+        const T& operator*() { return *fCurr; }
+        void operator++() { fCurr = fCurr->fNext; }
+        const T* fCurr;
+    };
+    Iter begin() const { return Iter{&fHead}; }
+    Iter end() const { return Iter{nullptr}; }
+
+private:
+    T fHead;
+    T* fTail = &fHead;
+};
+
+#endif