Change half-float conversion to use 1.0 multiplier

cc/resources/video_resource_updater.h

 // Copyright 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef CC_RESOURCES_VIDEO_RESOURCE_UPDATER_H_
 #define CC_RESOURCES_VIDEO_RESOURCE_UPDATER_H_
 
 #include <stddef.h>
 #include <stdint.h>
 
@@ skipping 62 matching lines @@
 class CC_EXPORT VideoResourceUpdater
     : public base::SupportsWeakPtr<VideoResourceUpdater> {
  public:
   VideoResourceUpdater(ContextProvider* context_provider,
                        ResourceProvider* resource_provider);
   ~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 {
    public:
     PlaneResource(unsigned resource_id,
                   const gfx::Size& resource_size,
                   ResourceFormat resource_format,
                   gpu::Mailbox mailbox);
     PlaneResource(const PlaneResource& other);
 
@@ skipping 88 matching lines @@
   // Recycle resources so that we can reduce the number of allocations and
   // data transfers.
   ResourceList all_resources_;
 
   DISALLOW_COPY_AND_ASSIGN(VideoResourceUpdater);
 };
 
 }  // namespace cc
 
 #endif  // CC_RESOURCES_VIDEO_RESOURCE_UPDATER_H_