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Skia & Freetype - Android 2D Graphics Essentials

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Material presented at the 10th Korea Android Conference, Oct. 2012.

Skia & Freetype - Android 2D Graphics Essentials

  1. 1. Skia & FreeType Android 2D Graphics Essentials Kyungmin Lee Software Platform Lab., LG Electronics The 10th Kandroid Conference
  2. 2. Goal S/W 플랫폼에 있어 GUI(Graphical User Interface) 시스템은 해당 플랫폼의 성능을 결정짓는 매우 중요한 요소이다. Android 역시 새로운 버전을 발표할 때마다 GUI 시스템의 성능을 꾸준히 개선하여 최근에 릴리즈된 Jelly Bean에 와서는 iOS에 필적할만한 성능을 보여주고 있다. 이번 세션에서는 이벤트 처리 기술과 더불어 GUI 시스템의 한 축을 이루고 있는 2D Graphics 기술을 Android에서 어떻게 활용하고 발전시켜 왔는지에 대해 살펴본다. 1. Skia: 2D Graphics Library  Skia in Android  Skia API Overview  Skia Rendering Pipeline  Skia Backends: Raster, OpenGL, PDF, ... 2. FreeType: Font Engine  FreeType in Android  FreeType API Overview  Font Rasterization: Scan-conversion, Hinting, … 3. Android 2D Graphics Essentials  Evolution of Drawing Models: GPUI (UI on the GPU), Display List, Display List Properties, View Layers, …  Android 2D Graphics Architecture (From Conference Program Overview) The 9th Kandroid Conference
  3. 3. Skia is Greek for “shadow” Skia is a complete 2D graphic library for drawing Text, Geometries, and Images. • 3x3 matrices w/ perspective • antialiasing, transparency, filters • shaders, xfermodes, maskfilters, patheffects Mike Reed • subpixel text Device backends for Skia currently include: • Raster • OpenGL • PDF • XPS • Picture (for recording and then playing back into another Canvas) (From Project’s Home) The Skia Graphics Engine is a compact open source graphics library written in C++. It was originally developed by Skia Inc., which was subsequently acquired by Google in 2005, who then released the software as open source licensed under the New BSD License free software license. Now known as skia, it is currently used in Mozilla Firefox, Google Chrome, Chrome OS, Chromium OS, and Android; and the Skia library is present on the BlackBerry PlayBook though the extent of its usage is unclear. Skia's drawing has back-ends for a standard CPU-based software rasterizer, PDF, and OpenGL The 10th Kandroid Conference (From Wikipedia)
  4. 4. Skia in Android Skia (svn) 2006-09 2006-09 r1 r2 2006-11 r3 2008-11 r4 2009-03 r100 2011-03 r1000 2011-07 r2000 2012-01 r3000 2012-05 r4000 2012-08 r5000 2012-10 r6022 Skia in Android … 2008-10 … ??? ~700 total commit # Added Removed The 10th Kandroid Conference
  5. 5. Skia API Overview A Canvas encapsulates all of the state about drawing into a device (bitmap). This includes a reference to the device itself, and a stack of matrix/clip values. For any given draw call (e.g. drawRect), the geometry of the object being drawn is transformed by the concatenation of all the matrices in the stack. The transformed geometry is clipped by the intersection of all of the clips in the stack. 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. 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 of multiple contours (or continuous sections), each consisting of linear, quadratic, and cubic segments Drawing Primitives Canvas Paint The 10th Kandroid Conference Bitmap
  6. 6. Skia API Overview SkRect rect; rect.set(0, 0, 150, 120); canvas->drawRect(rect, shapePaint); canvas->drawRoundRect(rect, 15, 15, shapePaint); canvas->drawOval(rect, shapePaint); canvas->drawCircle(60, 60, 60, shapePaint); // Arc without a wedge canvas->drawArc(rect, 0, 255, false, shapePaint); // Arc with a wedge from the center canvas->drawArc(rect, 0, 255, true, shapePaint); canvas->drawLine(0, 0, 150, 120, shapePaint); const char str[] = "Hello World!"; canvas->drawText(str, strlen(str), 75, 145, textPaint); // Load a bitmap from an image and draw it only if the load succeeds SkBitmap bitmap; if (SkImageDecoder::DecodeFile("app/native/icon.png", bitmap)) { canvas->drawBitmap(*bitmap, 0, 0, NULL); } SkPath path; path.moveTo(50, 50); // Specify endpoint using absolute coordinates path.lineTo(100, 100); // Specify endpoint using a relative offset from the last point path.rLineTo(50, 50); // Specify endpoint using absolute coordinates path.quadTo(120, 125, 150, 150); // Specify endpoint using a relative offset from the last point path.rQuadTo(20, 25, 50, 50); // Specify endpoint using absolute coordinates path.cubicTo(175, 175, 140, 120, 200, 200); // Specify endpoint using a relative offset from the last point path.rQuadTo(25, 25, -10, -30, 50, 50); The 10th Kandroid Conference canvas->drawPath(path, shapePaint);
  7. 7. Skia Rendering Pipeline SkCanvas draw*(…, SkPaint) Shading Rasterization Apply Shaders Scan Conversion Initial Path Initial Mask Apply Path Effects Rasterizer Apply Color Filters Apply Mask Filters Apply Stroke Styles SRC Image Mask Path Generation Initial SRC Image Transfer Path Blending Intermediate Image Modified DST Image Apply XferMode DST Image The 10th Kandroid Conference
  8. 8. Skia Backends To render with software Skia 1) Create a native window and then 2) Wrap a pointer to its buffer as an SkBitmap 3) Initialize an SkCanvas with the bitmap SkCanvas SkDevice SkBitmap To render with hardware-accelerated Skia 1) Create a GLES2 window or framebuffer and 2) Create the appropriate GrContext, SkGpuDevice, and SkGpuCanvas SkGpuCanvas SkGpuDevice GrContext The 10th Kandroid Conference
  9. 9. A Free, High-Quality, FreeType? and Portable Font Engine FreeType is a software library written in C that implements a font rasterization engine. It is used to render text on to bitmaps and provides support for other fontrelated operations. (From Wikipedia) FreeType 2 is a software font engine that is designed to be small, efficient, highly customizable, and portable while capable of producing high-quality output (glyph images). It can be used in graphics libraries, display servers, font conversion tools, text image generation tools, and many other products as well. Note that FreeType 2 is a font service and doesn't provide APIs to perform higherlevel features like text layout or graphics processing (e.g., colored text rendering, ‘hollowing’, etc.). However, it greatly simplifies these tasks by providing a simple, easy to use, and uniform interface to access the content of font files. By default, FreeType 2 supports the following font formats: TrueType (and collections), Type 1, CID-keyed Type 1, CFF, OpenType (both , TrueType and CFF variants), SFNT-based bitmap, X11 PCF, Windows FNT, BDF (including anti-aliased ones), PFR, Type 42 (limited support) David Turner Robert Wilhelm Werner Lemberg (From Project’s Home) The 10th Kandroid Conference
  10. 10. FreeType in Android FreeType2 2000-11 … 2.0.0 … 2007-07 2.3.5 2008-06 2.3.6 2009-03 FreeType2 in Android 2.3.9 ??? 2008-10 2009-06 2010-02 2.3.12 2010-03 2010-08 2.4.2 2010-11 2.4.4 2010-07 2.4.6 2010-10 2.4.7 2010-11 2.4.8 2012-03 2010-09 2.4.9 2011-01 2011-08 2011-11 2011-12 2012-03 2012-06 2.4.10 commit # ~1100 since 2007-07 ~50 The 10th Kandroid Conference Added Removed
  11. 11. FreeType API Glyph Outline (Lines + Curves) Quadratic Bé zier Curve Cubic Bé zier Curve The 10th Kandroid Conference
  12. 12. FreeType API FT_Library FT_Face FT_GlyphSlot FT_Error char* int library; face; slot; error; filename, text; pen_x, pen_y, n, num_chars; 1 Initialize the library 2 Load a font face ... /* initilization code */ error = FT_Init_FreeType( &library ); if ( error ) ... /* error handling code */ error = FT_New_Face( library, filename, 0, &face ); 3 if ( error ) ... /* error handling code */ error = FT_Set_Char_Size( face, 50 * 64, 0, 100, 0 ); if ( error ) ... /* error handling code */ slot = face->glyph; 4 for ( n = 0; n < num_chars; n++ ) { error = FT_Load_Char( face, text[n], FT_LOAD_DEFAULT ); if ( error ) continue; /* ignore errors */ error = FT_Render_Glyph( face, text[n], FT_RENDER_MODE_NORMAL ); if ( error ) continue; /* ignore errors */ 5 draw_bitmap( &slot->bitmap, pen_x + slot->bitmap_left, pen_y - slot->bitmap_top ); pen.x += slot->advance.x >> 6; } Set the character size (e.g., 50pt at 100dpi) Load a glyph image into the slot Convert the glyph’s outline to a bitmap 6 Draw the bitmap to a target surface 7 Release resources show_image(); FT_Done_Face ( face ); FT_Done_FreeType( library ); The 10th Kandroid Conference
  13. 13. Font Rasterization: Hinting Font hinting (also known as instructing) is the use of mathematical instructions to adjust the display of an outline font so that it lines up with a rasterized grid. At low screen resolutions, hinting is critical for producing a clear, legible text. It can be accompanied by antialiasing and (on liquid crystal displays) subpixel rendering for further clarity. Hints are usually created in a font editor during the typeface design process and embedded in the font. A font can be hinted either automatically (through processed algorithms based on the character outlines) or set manually. Most font editors are able to do automatic hinting, and this approach is suitable for many fonts. However, commercial fonts of the highest quality are often manually hinted to provide the sharpest appearance on computer displays. Verdana is one example of a font that contains a large amount of hinting data, much of which was accomplished manually by type engineer Tom Rickner. (From Wikipedia) The 10th Kandroid Conference
  14. 14. How Views are Drawn in Android pre-3.0? CPU Rasterization + GPU Composition ViewRootImpl performDraw() View draw(Canvas) View onDraw(Canvas) Canvas draw*(…, Paint) Android Framework (android.jar) SkCanvasGlue draw*(…, SkPaint) SkRasterizer rasterize(…) SkDraw draw*(..., SkPaint, ...) SkDevice draw*(..., SkPaint, ...) SkCanvas draw*(…, SkPaint) SkBlitter blit*(…) The 10th Kandroid Conference
  15. 15. Why New Drawing Models in Android post-3.0? CPU Rasterization + GPU Composition GPU Rasterization + GPU Composition GPUI Increased Number of Pixels Display List Display List Properties View Layers … Source: Accelerated Android Rendering, Google I/O 2011 The 10th Kandroid Conference
  16. 16. GPUI – UI on the GPU (since 3.0) android:handwareAccelerated="true" *GPUI GPU Rasterization + GPU Composition turned on by default from Android 4.0 ViewRootImpl performDraw() View draw(Canvas) View onDraw(Canvas) HardwareCanvas draw*(…, Paint) Android Framework (android.jar) android_view_GLES20Canvas _draw*(…, SkPaint) OpenGLRenderer draw*(…, SkPaint) GLES2/gl2.h glXXX(…) The 10th Kandroid Conference
  17. 17. Display List in General A display list (or display file) is a series of graphics commands that define an output image. The image is created (rendered) by executing the commands. … 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) Source: MSDN, The 10th Kandroid Conference
  18. 18. Display List in Android (since 3.0) A display list records a series of graphics related operation and can replay them later. Display lists are usually built by recording operations on a Replaying the operations from a display list avoids executing views drawing code on every frame, and is thus much more efficient. <<enumeration>> DisplayList::Op[Non-Drawing] GLES20RecordingCanvas draw*(…, Paint) +Sav e +Restore +RestoreToCount +Sav eLayer +Sav eLayerAlpha +Translate +Rotate +Scale +Skew +SetMatrix +ConcatMatrix +ClipRect android_view_ GLES20Canvas_draw*(…) SkWriter32 write*(…) DisplayListRenderer draw*(…, SkPaint) SkReader32 read*() DisplayList replay(…) void* buffer GLES20Canvas drawDisplayList(…) draw*(…, SkPaint) OpenGLRenderer drawDisplayList(…) The 10th Kandroid Conference GLES2/gl2.h glXXX(…) <<enumeration>> DisplayList::Op[Drawing] +DrawDisplayList +DrawLayer +DrawBitmap +DrawBitmapMatrix +DrawBitmapRect +DrawBitmapData +DrawBitmapMesh +DrawPatch +DrawColor +DrawRect +DrawRoundRect +DrawCircle +DrawOv al +DrawArc +DrawPath +DrawLines +DrawPoints +DrawText +DrawTextOnPath +DrawPosText +ResetShader +SetupShader +ResetColorFilter +SetupColorFilter +ResetShadow +SetupShadow +ResetPaintFilter +SetupPaintFilter +DrawGLFunction
  19. 19. Display List Properties (since 4.1) + + + + + + + + + + + + + + + + + + + + + + bool mClipChildren; float mAlpha; int mMultipliedAlpha; bool mHasOverlappingRendering; float mTranslationX, mTranslationY; float mRotation, mRotationX, mRotationY; float mScaleX, mScaleY; float mPivotX, mPivotY; float mCameraDistance; int mLeft, mTop, mRight, mBottom; int mWidth, mHeight; int mPrevWidth, mPrevHeight; bool mPivotExplicitlySet; bool mMatrixDirty; bool mMatrixIsIdentity; uint32_t mMatrixFlags; SkMatrix* mTransformMatrix; Sk3DView* mTransformCamera; SkMatrix* mTransformMatrix3D; SkMatrix* mStaticMatrix; SkMatrix* mAnimationMatrix; bool mCaching; Without DisplayList Properties With DisplayList Properties Source: For Butter or Worse, Google I/O 2012 The 10th Kandroid Conference
  20. 20. View Layers (since 3.0) Layers = Off-screen Buffers or Caches View.setLayerType(int type, Paint p) [API Level 11] type View is H/W-Accelerated View is NOT H/W Accelerated LAYER_TYPE_NONE • • Rendered in H/W Directly into surface • • Rendered in S/W Directly into surface LAYER_TYPE_HARDWARE • • Rendered in H/W Into hardware texture • • Rendered in S/W Into bitmap LAYER_TYPE_SOFTWARE • • Rendered in S/W Into bitmap • • Rendered in S/W Into bitmap *Measured DisplayList::Op + DrawLayer + DrawBitmap when drawing a ListView with Android 3.0 on a Motorola XOOM Source: Accelerated Android Rendering, Google I/O 2011 The 10th Kandroid Conference
  21. 21. Android 2D Graphics Architecture Application (View) Render Script Canvas OpenGL ES HWUI EGL Skia AGL HGL Pixel Flinger GPU Surface SurfaceFlinger OpenGL ES HW Composer • • HGL = Hardware OpenGL ES AGL = Android’s Software OpenGL ES EGL AGL GPU Overlay HGL Pixel Flinger Frame Buffer The 10th Kandroid Conference
  22. 22. Android 2D Graphics Libraries
  23. 23. What-How-Why-Why not? What? Why? Why not? When? Who? How? Past Present The 10th Kandroid Conference Future
  24. 24. References • • • • • • • • • How about some Android graphics true facts?, Dianne Hackborn, Nov. 2011, Android 3.0 Hardware Acceleration, Romain Guy, Mar. 2011, Android 4.0 Graphics and Animations, Romain Guy and Chet Haase, Nov. 2011, Android Graphics, Animations and Tips & Tricks, Romain Guy and Chet Haase, Dec. 2010, Learning about Android Graphics Subsystem, Bhanu Chetlapalli, Apr. 2012, iOS vs. Android ICS: Hardware Accelerated Graphics Pipelines, Nathan de Vries, Nov. 2011, Android's 2D Canvas Rendering Pipeline, Laurence Gonsalves, May 2011, How FreeType's rasterizer work, David Turner, Feb. 2007, FreeType2 source/docs Android Graphics, Jim Huang, Sep. 2011, The 10th Kandroid Conference
  25. 25. The 10th Kandroid Conference