Change half-float conversion to use 1.0 multiplier

cc/resources/video_resource_updater.h

Index: cc/resources/video_resource_updater.h
diff --git a/cc/resources/video_resource_updater.h b/cc/resources/video_resource_updater.h
index a42784c9b999ca948b2ed1f4ee32fb8e09f10cf5..b9b5b95c02631e476cf1fbd76347af5052506b42 100644
--- a/cc/resources/video_resource_updater.h
+++ b/cc/resources/video_resource_updater.h
@@ -80,14 +80,28 @@ class CC_EXPORT VideoResourceUpdater
   VideoFrameExternalResources CreateExternalResourcesFromVideoFrame(
       scoped_refptr<media::VideoFrame> video_frame);
 
-  // Convert an array of short integers into an array of half-floats.
-  // |src| is an array of integers in range 0 .. 2^{bits_per_channel} - 1
-  // |num| is number of entries in input and output array.
-  // The numbers stored in |dst| will be half floats in range 0.0..1.0
-  static void MakeHalfFloats(const uint16_t* src,
-                             int bits_per_channel,
-                             size_t num,
-                             uint16_t* dst);
+  // Base class for converting short integers to half-floats.
+  // TODO(hubbe): Move this to media/.
+  class HalfFloatMaker {
+   public:
+    // Convert an array of short integers into an array of half-floats.
+    // |src| is an array of integers in range 0 .. 2^{bits_per_channel} - 1
+    // |num| is number of entries in input and output array.
+    // The numbers stored in |dst| will be half floats in range 0.0..1.0

[fbarchard1, 2016/10/21 22:46:06]

This comment needs update?

[hubbe, 2016/10/21 22:55:04]

Will fix in separate cl (Since this one is checked in now)

+    virtual void MakeHalfFloats(const uint16_t* src,
+                                size_t num,
+                                uint16_t* dst) = 0;
+    // The half-floats made needs by this class will be in the range
+    // [Offset() .. Offset() + 1.0/Multiplier]. So if you want results
+    // in the 0-1 range, you need to do:
+    //   (half_float - Offset()) * Multiplier()
+    // to each returned value.
+    virtual float Offset() const = 0;
+    virtual float Multiplier() const = 0;
+  };
+
+  static std::unique_ptr<HalfFloatMaker> NewHalfFloatMaker(
+      int bits_per_channel);
 
  private:
   class PlaneResource {