Create GrDraw and start fast pathing src over rects

src/gpu/draws/GrDraw.h

+/*
+ * Copyright 2015 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#ifndef GrDraw_DEFINED
+#define GrDraw_DEFINED
+
+#include "GrNonAtomicRef.h"
+
+#include "GrRenderTarget.h"
+
+class GrDrawTarget;
+
+#define GRDRAW_ASSERT_OWNED_RESOURCE(R) SkASSERT(!(R) || (R)->getContext() == fContext)
+
+/*
+ * GrDraw is a virtual class which captures the scope of the entry point on SkGpuDevice where it
+ * originates.  After creation, it lives on the GrPipeline where it used as a potential fast path
+ * for batching.

[bsalomon, 2015/09/23 13:49:38]

"fast path" needs some explanation. something about skipping intermediate
transformations and pushing a new bit of geometry directly into an existing
batch.

[joshualitt, 2015/09/25 18:17:12]

Acknowledged.

+ *
+ * A GrDraw must be able to fully draw itself if fastpath batching is not possible
+ */
+
+class GrDraw {
+public:
+    GrDraw() : fClassID(kIllegalDrawClassID) {}
+    virtual ~GrDraw() {}
+
+    virtual void execute(GrDrawTarget*) const=0;

[robertphillips, 2015/09/25 12:48:49]

Some comments about how these class IDs work and what is expected of derived
classes ?

// Each derived class must have a unique class id. This is achieved by providing
each
// derived class with a templatized version of ClassID() which uses the
GrDraw-global
// gCurrDrawClassID counter.

[joshualitt, 2015/09/25 18:17:12]

Acknowledged.

+    uint32_t classID() const { SkASSERT(!fClassID == kIllegalDrawClassID); return fClassID; }
+    template <typename PROC_SUBCLASS> static uint32_t ClassID() {
+         static uint32_t kClassID = GenID(&gCurrDrawClassID);
+         return kClassID;
+    }
+
+protected:
+    static uint32_t GenID(int32_t* idCounter) {
+        // The atomic inc returns the old value not the incremented value. So we add
+        // 1 to the returned value.
+        uint32_t id = static_cast<uint32_t>(sk_atomic_inc(idCounter)) + 1;
+        if (!id) {
+            SkFAIL("This should never wrap as it should only be called once for each GrDraw "
+                   "subclass.");
+        }
+        return id;
+    }
+
+    enum {
+        kIllegalDrawClassID = 0
+    };
+
+    static int32_t gCurrDrawClassID;

[robertphillips, 2015/09/25 12:48:49]

Do we need/even use 'fClassID'. Don't we just call <derived-class>::ClassID() ?

[joshualitt, 2015/09/25 18:17:12]

Acknowledged.

+    uint32_t fClassID;
+
+    friend class GrDrawSnap; // for class ID stuff
+};
+

[robertphillips, 2015/09/25 12:48:48]

I second the motion for a comment

[joshualitt, 2015/09/25 18:17:12]

Acknowledged.

+class GrDrawSnap : public GrNonAtomicRef {

[bsalomon, 2015/09/23 13:49:38]

/** ... */

[joshualitt, 2015/09/25 18:17:12]

Acknowledged.

+public:
+    GrDrawSnap() : fClassID(GrDraw::kIllegalDrawClassID) {}
+    uint32_t classID() const {

[robertphillips, 2015/09/25 12:48:49]

use != ?

+        SkASSERT(!fClassID == GrDraw::kIllegalDrawClassID);
+        return fClassID;
+    }
+
+protected:
+    uint32_t fClassID;
+    typedef GrNonAtomicRef INHERITED;
+};
+
+#endif