Add whitelist parameter to refEncodedData

include/core/SkImageGenerator.h

Index: include/core/SkImageGenerator.h
diff --git a/include/core/SkImageGenerator.h b/include/core/SkImageGenerator.h
index 1a46f6b9cd7dfc39c753170b7da6046ed0877bb2..032be1b90746e7ea1cb0464e0ccfaf204d0dafaf 100644
--- a/include/core/SkImageGenerator.h
+++ b/include/core/SkImageGenerator.h
@@ -10,6 +10,7 @@
 
 #include "SkBitmap.h"
 #include "SkColor.h"
+#include "SkEncodedFormat.h"
 #include "SkImageInfo.h"
 #include "SkYUVSizeInfo.h"
 
@@ -26,7 +27,7 @@ class SkPicture;
 #ifdef SK_SUPPORT_LEGACY_REFENCODEDDATA_NOCTX
     #define SK_REFENCODEDDATA_CTXPARAM
 #else
-    #define SK_REFENCODEDDATA_CTXPARAM  GrContext* ctx
+    #define SK_REFENCODEDDATA_CTXPARAM  RefEncodedWhitelist* whitelist
 #endif
 
 /**
@@ -70,19 +71,37 @@ public:
     uint32_t uniqueID() const { return fUniqueID; }
 
     /**
-     *  Return a ref to the encoded (i.e. compressed) representation,
-     *  of this data. If the GrContext is non-null, then the caller is only interested in
-     *  gpu-specific formats, so the impl may return null even if they have encoded data,
-     *  assuming they know it is not suitable for the gpu.
+     *  A callback object passed to refEncodedData to determine whether the caller wants its format.
+     */
+    class RefEncodedWhitelist {
+    public:
+        virtual ~RefEncodedWhitelist() {}
+
+        /**
+         *  An implementation of onRefEncodedData may call this with the SkEncodedFormat representing
+         *  its encoded data. If the method returns false, the implementation need not return its data.
+         */
+        virtual bool includes(SkEncodedFormat) = 0;
+    };
+
+    /**
+     *  Return a ref to the encoded (i.e. compressed) representation of the image, or null if
+     *  no such encoded form is readily available. This is not meant to trigger a full-blown
+     *  encoding step, as the caller can always perform that itself. This is meant to give the
+     *  caller quick access to the encoded version iff it is already available.
      *
-     *  If non-NULL is returned, the caller is responsible for calling
-     *  unref() on the data when it is finished.
+     *  If whitelist is non-null, then the implementation may call it to preflight if the client
+     *  wants its format. If the generator readily has the encoded data available, it may ignore
+     *  the whitelist and just return its data. However, if there is a performance or other
+     *  constraint on returning the encoded data (e.g. the encoded data already exists, but is
+     *  not contiguous), calling the whitelist allows the generator to discover if its format is
+     *  not whitelisted, in which case the generator should just return null.
      */
-    SkData* refEncodedData(GrContext* ctx = nullptr) {
+    SkData* refEncodedData(RefEncodedWhitelist* whitelist = nullptr) {
 #ifdef SK_SUPPORT_LEGACY_REFENCODEDDATA_NOCTX
         return this->onRefEncodedData();
 #else
-        return this->onRefEncodedData(ctx);
+        return this->onRefEncodedData(whitelist);
 #endif
     }