flutter::ImageGenerator Class Reference

The minimal interface necessary for defining a decoder that can be used for both single and multi-frame image decoding. Image generators can also optionally support decoding into a subscaled buffer. Implementers of ImageGenerator regularly keep internal state which is not thread safe, and so aliasing and parallel access should never be done with ImageGenerators. More...

#include <image_generator.h>

Inheritance diagram for flutter::ImageGenerator:

Classes
struct	FrameInfo
	Info about a single frame in the context of a multi-frame image, useful for animation and blending. More...

Public Member Functions
virtual	~ImageGenerator ()
virtual const SkImageInfo &	GetInfo ()=0
	Returns basic information about the contents of the encoded image. This information can almost always be collected by just interpreting the header of a decoded image.
virtual unsigned int	GetFrameCount () const =0
	Get the number of frames that the encoded image stores. This method is always expected to be called before GetFrameInfo, as the underlying image decoder may interpret frame information that is then used when calling GetFrameInfo.
virtual unsigned int	GetPlayCount () const =0
	The number of times an animated image should play through before playback stops.
virtual const FrameInfo	GetFrameInfo (unsigned int frame_index)=0
	Get information about a single frame in the context of a multi-frame image, useful for animation and frame blending. This method should only ever be called after GetFrameCount has been called. This information is nonsensical for single-frame images.
virtual SkISize	GetScaledDimensions (float scale)=0
	Given a scale value, find the closest image size that can be used for efficiently decoding the image. If subpixel image decoding is not supported by the decoder, this method should just return the original image size.
virtual bool	GetPixels (const SkImageInfo &info, void *pixels, size_t row_bytes, unsigned int frame_index=0, std::optional< unsigned int > prior_frame=std::nullopt)=0
	Decode the image into a given buffer. This method is currently always used for sub-pixel image decoding. For full-sized still images, GetImage is always attempted first.
sk_sp< SkImage >	GetImage ()
	Creates an SkImage based on the current ImageInfo of this ImageGenerator.

Static Public Attributes
static const unsigned int	kInfinitePlayCount
	Frame count value to denote infinite looping.

Detailed Description

The minimal interface necessary for defining a decoder that can be used for both single and multi-frame image decoding. Image generators can also optionally support decoding into a subscaled buffer. Implementers of ImageGenerator regularly keep internal state which is not thread safe, and so aliasing and parallel access should never be done with ImageGenerators.

See also

ImageGenerator::GetScaledDimensions

Definition at line 27 of file image_generator.h.

Constructor & Destructor Documentation

~ImageGenerator()

flutter::ImageGenerator::~ImageGenerator ( )

virtualdefault

Member Function Documentation

GetFrameCount()

virtual unsigned int flutter::ImageGenerator::GetFrameCount ( ) const

pure virtual

Get the number of frames that the encoded image stores. This method is always expected to be called before GetFrameInfo, as the underlying image decoder may interpret frame information that is then used when calling GetFrameInfo.

Returns

The number of frames that the encoded image stores. This will always be 1 for single-frame images.

Implemented in flutter::testing::FakeImageGenerator, flutter::testing::SinglePixelImageGenerator, flutter::BuiltinSkiaImageGenerator, flutter::BuiltinSkiaCodecImageGenerator, flutter::APNGImageGenerator, and flutter::AndroidImageGenerator.

GetFrameInfo()

virtual const FrameInfo flutter::ImageGenerator::GetFrameInfo ( unsigned int  frame_index )

pure virtual

Get information about a single frame in the context of a multi-frame image, useful for animation and frame blending. This method should only ever be called after GetFrameCount has been called. This information is nonsensical for single-frame images.

Parameters

[in]

frame_index

The index of the frame to get information about.

Returns

Information about the given frame. If the image is single-frame, a default result is returned.

See also

GetFrameCount

Implemented in flutter::testing::FakeImageGenerator, flutter::testing::SinglePixelImageGenerator, flutter::BuiltinSkiaImageGenerator, flutter::BuiltinSkiaCodecImageGenerator, flutter::APNGImageGenerator, and flutter::AndroidImageGenerator.

GetImage()

sk_sp< SkImage > flutter::ImageGenerator::GetImage

(

)

Creates an SkImage based on the current ImageInfo of this ImageGenerator.

Returns

A new SkImage containing the decoded image data.

Definition at line 19 of file image_generator.cc.

                                        {
  SkImageInfo info = GetInfo();
 
  SkBitmap bitmap;
  if (!bitmap.tryAllocPixels(info)) {
    FML_DLOG(ERROR) << "Failed to allocate memory for bitmap of size "
                    << info.computeMinByteSize() << "B";
    return nullptr;
  }
 
  const auto& pixmap = bitmap.pixmap();
  if (!GetPixels(pixmap.info(), pixmap.writable_addr(), pixmap.rowBytes())) {
    FML_DLOG(ERROR) << "Failed to get pixels for image.";
    return nullptr;
  }
  bitmap.setImmutable();
  return SkImages::RasterFromBitmap(bitmap);
}

GetInfo()

virtual const SkImageInfo & flutter::ImageGenerator::GetInfo ( )

pure virtual

Returns basic information about the contents of the encoded image. This information can almost always be collected by just interpreting the header of a decoded image.

Returns

Size and color information describing the image.

Note

This method is executed on the UI thread and used for layout purposes by the framework, and so this method should not perform long synchronous tasks.

Implemented in flutter::testing::FakeImageGenerator, flutter::testing::SinglePixelImageGenerator, flutter::BuiltinSkiaImageGenerator, flutter::BuiltinSkiaCodecImageGenerator, flutter::APNGImageGenerator, and flutter::AndroidImageGenerator.

GetPixels()

virtual bool flutter::ImageGenerator::GetPixels ( const SkImageInfo &  info, void *  pixels, size_t  row_bytes, unsigned int  frame_index = 0, std::optional< unsigned int >  prior_frame = std::nullopt  )

pure virtual

Decode the image into a given buffer. This method is currently always used for sub-pixel image decoding. For full-sized still images, GetImage is always attempted first.

Parameters

[in]	info	The desired size and color info of the decoded image to be returned. The implementation of GetScaledDimensions determines which sizes are supported by the image decoder.
[in]	pixels	The location where the raw decoded image data should be written.
[in]	row_bytes	The total number of bytes that should make up a single row of decoded image data (i.e. width * bytes_per_pixel).
[in]	frame_index	Which frame to decode. This is only useful for multi-frame images.
[in]	prior_frame	Optional frame index parameter for multi-frame images which specifies the previous frame that should be use for blending. This hints to the decoder that it should use a previously cached frame instead of decoding dependency frame(s). If an empty value is supplied, the decoder should decode any necessary frames first.

Returns

True if the image was successfully decoded.

Note

This method performs potentially long synchronous work, and so it should never be executed on the UI thread. Image decoders do not require GPU acceleration, and so threads without a GPU context may also be used.

See also

GetScaledDimensions

Implemented in flutter::testing::FakeImageGenerator, flutter::testing::SinglePixelImageGenerator, flutter::APNGImageGenerator, flutter::AndroidImageGenerator, flutter::BuiltinSkiaImageGenerator, and flutter::BuiltinSkiaCodecImageGenerator.

GetPlayCount()

virtual unsigned int flutter::ImageGenerator::GetPlayCount ( ) const

pure virtual

The number of times an animated image should play through before playback stops.

Returns

If this image is animated, the number of times the animation should play through is returned, otherwise it'll just return 1. If the animation should loop forever, kInfinitePlayCount is returned.

Implemented in flutter::testing::FakeImageGenerator, flutter::testing::SinglePixelImageGenerator, flutter::BuiltinSkiaImageGenerator, flutter::BuiltinSkiaCodecImageGenerator, flutter::APNGImageGenerator, and flutter::AndroidImageGenerator.

GetScaledDimensions()

virtual SkISize flutter::ImageGenerator::GetScaledDimensions ( float  scale )

pure virtual

Given a scale value, find the closest image size that can be used for efficiently decoding the image. If subpixel image decoding is not supported by the decoder, this method should just return the original image size.

Parameters

[in]

scale

The desired scale factor of the image for decoding.

Returns

The closest image size that can be used for efficiently decoding the image.

Note

This method is called prior to GetPixels in order to query for supported sizes.

See also

GetPixels

Implemented in flutter::BuiltinSkiaImageGenerator, flutter::BuiltinSkiaCodecImageGenerator, flutter::APNGImageGenerator, flutter::AndroidImageGenerator, flutter::testing::FakeImageGenerator, and flutter::testing::SinglePixelImageGenerator.

Member Data Documentation

kInfinitePlayCount

const unsigned int flutter::ImageGenerator::kInfinitePlayCount

static

Initial value:

=
      std::numeric_limits<unsigned int>::max()

Frame count value to denote infinite looping.

Definition at line 30 of file image_generator.h.

---

The documentation for this class was generated from the following files:

• lib/ui/painting/image_generator.h
• lib/ui/painting/image_generator.cc