This introduces the fundamental knowledge about Skia which is open-source project used in Android. In this, it contains the history of skia, and the roll of skia in Android.

1. Skia
Date : 2014/10/8
Author : Ryan Chou
Copyright © 2014 Realtek Semiconductor Corp.

2. Outline
 What is Skia
 Skia in Android
 Reference
 Q & A

3. Outline
 What is Skia
 Skia in Android
 Reference
 Q & A

4. What is Skia
 A 2D graphic engine for drawing Text, Geometries, and Images
 A compact open source graphics library written in C++, and licensed
under New BSD free software license
 Developed by Skia Inc., which was acquired by Google in 2005
 Used in Chrome browser, Chrome OS, Firefox browser, Firefox OS,
and Android
 Back-ends
 CPU-based software rasterization, PDF output, GPU-accelerated
OpenGL
 Front-ends
 SVG, PostScript, PDF, SWF and Adobe illustrator files
 Its competitor is also well-known : Cairo
 Open source library under GNU Lesser General Public License (LGPL)
 Written in C
 Skia is more compatible in mobile device

5. Outline
 What is Skia
 Skia in Android
 Reference
 Q & A

6. Skia in Android
 The source is located in external/skia, which major serves as
 Image decoder and encoder
 2D graphic render

7. File system
 src/animator: implement animation effect
 src/core : implement core of Skia, which is graphic rendering
 src/gl : implement graphic library. The engine is OpenGL or OpenGL
ES.
 src/images : implement image related part and support decoding
and encoding of images of some common image format (bmp, gif,
png, jpg…)
 src/ports : defines the porting layer, including Font, Event, File,
Thread, Time, XMLParser
 src/svg : support of SVG
 src/utils : assistant tools
 src/views : UI (Not adopted in Android)
 src/xml : implement XML DOM and Parser

8. Architecture of Image Decoder
APP (MediaBrowser/RealtekGallery2)
Framework (BitmapFactory)
Skia
DecodReg
jpeg png gif webp bmp
libjpeg libpng libgif
JNI

9. Architecture of Image Encoder
JNI
APP
Framework (Bitmap::Compress)
Skia
EncodeReg
jpeg png gif webp bmp
libjpeg libpng libgif

10. Skia Drawing Primitive API
Overview
 Drawing basic primitives include rectangles, rounded rectangles, ovals,
circles, arcs, paths, lines, text, bitmaps, and sprites. Paths allow for the
creation of more advanced shapes. Each path can be made up for multiple
contours (or continuous sections), each consisting of linear, quadratic, and
cubic segments.
 A Canvas encapsulates all of the state about drawing into a device (bitmap).
 A reference to the device
 A stack of matrix/clip values
 While the Canvas holds the state of the drawing device, the state (style) of
the object being drawn is held by the Paint, which is provided as a
parameter to each of the draw() methods. The Paint holds attributes such as
color, typeface, textSize, strokeWidth, shader (e.g. gradients, patterns), etc

11. Example: Skia API

12. Skia Rendering Pipeline
Source:
http://www.xenomachina.com/2011/05/androids-2d-canvas-rendering-pipeline.html

13. Skia back-end
 Render in software
1) Create a native window and then
2) Wrap a pointer to its buffer as an SkBitmap
3) Initialize an SkCanvas with the bitmap
 Render in hardware acceleration
1) Create a GLES2 window or framebufffer
2) Create the appropriate GrContext, SkGpuDevice and SkGpuCanvas

14. How Views are Drawn in
Android pre 3.0
Source: http://developer.android.com/guide/topics/ui/how-android-draws.html

15. Why New Drawing Model in
Android post-3.0?

16. Hardware-accelerated 2D
Rendering
 Since Android 3.x, more complex than before
 Major idea : transform the implementation of 2D Graphics APIs into
OpenGL ES requests
 Textures, Shader, GLContext, pipeline, …
 Major parts for hardware-accelerated 2D Rendering
 Primitive Drawing: Shape, Text, Image
 Layer/Surface Compositing

17. Control hardware accelerations
 Application level
 <application android:hardwareAccelerated=“true”>
 Default value
 False in Android 3.x; True in Android 4.x
 Activity
 <activity android:hardwareAccelerated=“true”>
 Window
 getWindow().setFlags(WindowManager.LayoutParams.FLAG_HARDW
ARE_ACCELERATED,WindowManager.LayoutParams.FLAG_HARDW
ARE_ACCELERATED)
 CANNOT disable hardware acceleration at the window level
 View
 setLayerType(View.LAYER_TYPE_SOFTWARE, null)
 CANNOT disable hardware acceleration at the view level

18. How Views are Drawn (Since
3.0)

19. Display List
 A display list is a series of graphics commands that define an output
image. The image is created (rendered) by executing the command.
 A display list can represent both two-and three-dimensional scenes.
Systems that make use of a display list to store the scene are called
retained mode systems as opposed to immediate mode systems.
(From Wikipedia)
http://en.wikipedia.org/wiki/Display_list
http://developer.android.com/guide/topics/graphics/hardware-accel.html

20. Display List in Android (Since
3.0)
 A display list records a series of graphics related operation and can replay them later.
Display lists usually built by recording operations on a android.graphics.Canvas.
Replaying the operations from a display list avoids executing views drawing code on
every frame, and is thus much more efficient.

21. How Views are Drawn (Since
3.0)

22. Display List Properties (Since
4.1)

23. Android 2D Graphics
Architecture

24. Android 2D Graphics Libraries

25. Outline
 What is Skia
 Skia in Android
 Reference
 Q & A

26. Reference
 Bezier Curve, http://en.wikipedia.org/wiki/B%C3%A9zier_curve#Quadratic_B.C3.A9zier_curves
 Android Skia和2D圖形系統, ailyanlu, Mar. 16, 2012,
http://wenku.baidu.com/view/3a915fe94afe04a1b071dee6.html
 Android圖片編碼解碼實現方案(skia), Arrow, Jan 25, 2013,
http://blog.csdn.net/myarrow/article/details/8540990
 Android 3.0 Hardware Acceleration, Romain Guy, Mar. 2011,
http://android-developers.blogspot.kr/2011/03/android-30-hardware-acceleration.html
 Android 4.0 Graphics and Animations, Romain Guy, Nov. 2011,
http://android-developers.blogspot.kr/2011/11/android-40-graphics-and-animations.html
 iOS vs. Android ICS : Hardware Accelerated Graphics Pipelines, Nathan De Vries, Nov. 2011,
http://atnan.com/blog/2011/11/10/ios-vs-android-ics-hardware-accelerated-graphics-pipelines
 Learning about Android Graphics Subsystem, MIPS Developer Team, Apr. 2012,
http://blog.imgtec.com/news/learning-about-the-android-graphics-subsystem
 Hardware Accelerated 2D Rendering for Android, Jim Huang, Feb 19, 2013,
http://www.slideshare.net/jserv/accel2drendering?related=1
 Skia & FreeType Android 2D Graphics Essentials, Kyungmin Lee, 2012,
http://www.slideshare.net/snailee/skia-freetype-android-2d-graphics-essentials?related=2
 Hardware Acceleration, http://developer.android.com/guide/topics/graphics/hardware-accel.html
 Android Skia圖形渲染, http://www.3g-edu.org/news/art045.htm
 Android SKia 渲染概述, http://www.3g-edu.org/news/art044.htm

27. Q & A