unbuntu下编译skia

一、简介

      skia是谷歌的开源矢量图形引擎。早先由Skia公司开发，被谷歌收购以后，skia应用于chrome、chromium操作系统、chrome浏览器，以及Android操作系统。要研究它首要工作还是编译，以及运行测试代码。为了能尽快的编译skia，我选择了在vmware的ubuntu 10.4虚拟机上编译。

二、编译过程及测试代码

      1. 首先要安装skia源代码依赖的库，libfreetype和libpng。可以使用如下命令安装：

sudo apt-get install libfreetype6-dev

sudo apt-get -f install libpng12-dev

      2. 在～/下创建skia目录，进入～/skia目录，并使用如下命令下载skia源代码（当然，事先要安装svn工具），我checkout出来的版本号为624：

svn checkout http://skia.googlecode.com/svn/trunk/ skia-read-only/

      3. 进入～/skia/skia-read-only目录，使用如下命令编译skia源代码。编译完成后会在～/skia/skia-read-only/out目录下生成文件libskia.so。

make SKIA_BUILD_FOR=linux

      4. ～/skia/skia-read-only下，创建文件夹mytest，在其中添加文件test-skia.c，内容如下。具体使用的函数可参考其注释及skia文档。

   1: /* Simple vector graphics demo utilizing Skia toolkit.

   2:  * Authored by Jim Huang 

   3:  */

   4:  

   5: #include "SkBitmap.h"

   6: #include "SkDevice.h"

   7: #include "SkPaint.h"

   8: #include "SkRect.h"

   9: #include "SkImageEncoder.h"

  10:  

  11: int main()

  12: {

  13:     // Declare a raster bitmap, which has an integer width and height,

  14:     // and a format (config), and a pointer to the actual pixels.

  15:     // Bitmaps can be drawn into a SkCanvas, but they are also used to

  16:     // specify the target of a SkCanvas' drawing operations.

  17:     SkBitmap bitmap;

  18:     bitmap.setConfig(SkBitmap::kARGB_8888_Config, 200, 200);

  19:     bitmap.allocPixels();

  20:  

  21:     // A Canvas encapsulates all of the state about drawing into a

  22:     // device (bitmap).  This includes a reference to the device itself,

  23:     // and a stack of matrix/clip values. For any given draw call (e.g.

  24:     // drawRect), the geometry of the object being drawn is transformed

  25:     // by the concatenation of all the matrices in the stack. The

  26:     // transformed geometry is clipped by the intersection of all of the

  27:     // clips in the stack.

  28:     SkCanvas canvas(new SkDevice(bitmap));

  29:  

  30:     // SkPaint class holds the style and color information about how to

  31:     // draw geometries, text and bitmaps.

  32:     SkPaint paint;

  33:  

  34:     // SkIRect holds four 32 bit integer coordinates for a rectangle.

  35:     SkRect r;

  36:  

  37:     paint.setARGB(255, 255, 0, 0);

  38:     r.set(25, 25, 145, 145);

  39:     canvas.drawRect(r, paint); /** Draw the specified rectangle using

  40:                        the specified paint. The rectangle

  41:                        will be filled or stroked based on

  42:                        the Style in the paint. */

  43:  

  44:     paint.setARGB(255, 0, 255, 0);

  45:     r.offset(20, 20);

  46:     canvas.drawRect(r, paint);

  47:  

  48:     paint.setARGB(255, 0, 0, 255);

  49:     r.offset(20, 20);

  50:     canvas.drawRect(r, paint);

  51:  

  52:     // SkImageEncoder is the base class for encoding compressed images

  53:     // from a specific SkBitmap.

  54:     SkImageEncoder::EncodeFile("snapshot.png", bitmap,

  55:         SkImageEncoder::kPNG_Type,

  56:         /* Quality ranges from 0..100 */ 100);

  57:     return 0;

  58: }

在～/skia/skia-read-only/mytest目录下，使用如下命令编译test-skia.c文件：

g++ -I../include -I../include/core -I../include/images -I../include/config 

-Wall -o test-skia test-skia.c ../out/src/images/SkImageDecoder_libpng.o 

../out/libskia.a -lpng -lfreetype -lpthread -g

执行test-skia后，会在mytest目录下生成文件snapshot.png。

三、总结

      原先在编译Cairo库的时候，总是希望能将其运行在windows平台下。但实际情况是，那个平台编译方便就在那个平台，因为我们的目的不是为了编译而编译，我们需要的是了解要编译的库本身。关于skia功能的简单介绍，可以参见这里。

四、参考资料

      1. 在linux上编译skia