Introduction

As you know Android doesn’t support SVG format. But benefits of SVG are obvious. First, it’s scalable. You don’t need to have pictures in different resolutions, no need to scale, for example, bitmap image with a quality loss. SVG image can be scaled to any resolution and the quality will be the same. Second, SVG is an ordinary XML file, so it’s size can be much lesser than the raster format file of the same picture. Moreover, you can change a picture on the fly due to this feature.You can open SVG file in an ordinary text editor and look how it’s composed. And so on… But as Android doesn’t deal with SVG it will imply some native coding. The good news are there won’t be a lot of native coding. There are some open source libraries for parsing and rasterizing SVG format.

Prerequisites  

There are a lot of tutorials how to begin the native development for the Android platform, so I won’t repeat all of them here, just will give some useful tips.
  • First, you need the Eclipse IDE. You can download it at [1].  
  • Or as an alternative you can use Motodev Studio [2]. I prefer the second one as it has some delicious features. BTW you can install Motodev Studio as a plugin for the Eclipse IDE. I couldn’t setup it on OpenSUSE, but as the plugin it works fine.
  • Once Eclipse is installed add CDT plugin to it.
  • Add Android plugin [3].
  • After that add Eclipse Sequoyah[4] plugin needed for the native debugging. But make sure you installed CDT before Sequoyah. As the Sequoyah project claims it installs all dependencies it didn’t really installed CDT in my case. Wile installing Sequoyah make sure you unchecked “Group Items by Category” and checked “Sequoyah Android Native Support”.
  • Also Windows users will need cygwin[5] (Add the Cygwin/bin path to your system.). While installing it, setup development tools.
  • Download Android SDK [6].
  • And at last you will need Android NDK. Download CrystaX NDK[7]. It has support for C++ exceptions, RTTI and Standard C++ Library.
  • In Eclipse preferences set Android SDK & NDK locations. That’s all for now.

First Approach.  

For the first approach I will use android-libsvg [8] library. Really it depends on libsvg, libpng, libjpeg, libexpat and zlib. But at this moment it has support for almost all features of SVG format. To get it sources create android-libsvg folder somewhere in a file system and go to this folder in console (in cygwin for windows users) and run “bzr branch lp:libsvg-android” command. Bazaar will download sources to this folder.

The Beginning.  

Ok. Create a new Android project “ImageViewSvg”. Now right click on the project and go to AndroidTools/Add Native support. It will create “jni” folder in the project. Delete all stuff from it and copy contents of “jni” folder of android-libsvg project. Refresh jni folder in the project. Let’s look at Android.mk file in “jni” folder. I'll explain some variables:

LOCAL_PATH := $(call my-dir) – my-dyr macro sets LOCAL_PATH variable used to locate source files into current directory.

include $(CLEAR_VARS) – clears all local variables.

LOCAL_MODULE – the name of the library

LOCAL_CFLAGS – sets compiler flags and some include directories.

LIBJPEG_SOURCES, … - the list of sources files for each library that will be used

LOCAL_LDLIBS – links to additional libraries

LOCAL_SRC_FILES – the list of all source files to be compiled, here it contains all sources for all libraries.

BUILD_SHARED_LIBRARY – link to mk file to build shared library

For more information please see ANDROID-MK.TXT in NDK.

Sometimes on Windows, after restarting IDE, it can’t run ndk-build. Then right click the project and go to “Build Path/Configure Build Path” and change “Build command” to something like “bash /cygdrive/c/ndk/ndk-build”.

Next create com.toolkits.libsvgandroid package and copy there SvgRaster.java from the libsvg-android project. Preparations are over.

The ImageViewSvg Class.  

To make ImageView class to support SVG format it’s enough to inherit from it and override some methods. But I want it to set standard android:src attribute as SVG file and to be able to pick the file from standard “drawable” folder vs. “raw” folder. At the beginning let’s make all logic to be done in the constructor. To get access to the android:src attribute add attrs.xml file to the res/values folder:
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<?xml version="1.0" encoding="utf-8"?>
<resources>
 <declare-styleable name="ImageViewSvg">
  <attr name="android:src"/>
 </declare-styleable>
</resources>
Let’s look at ImageView class constructor sources. It contains following code:
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Drawable d = a.getDrawable(com.android.internal.R.styleable.ImageView_src);
        if (d != null) {
            setImageDrawable(d);
        }
And look at setImageBitmap method. It just calls setImageDrawable. So we can use it in our constructor if we have corresponding bitmap. But what about getting file from “drawable” folder. Nothing supernatural – get resource ID from the android:src attribute and read raw file into an input stream. Next, libandroidsvg gives us a way to parse SVG file:

So, the constructor will look like this:
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public ImageViewSvg(Context context, AttributeSet attrs, int defStyle) {

  // Let's try load supported by ImageView formats
  super(context, attrs, defStyle);
        
        if(this.getDrawable() == null)
        {
         //  Get defined attributes
            TypedArray a = context.obtainStyledAttributes(attrs,
                    R.styleable.ImageViewSvg, defStyle, 0);
                        
            // Getting a file name
            CharSequence cs = a.getText(R.styleable.ImageViewSvg_android_src);
            String file = cs.toString();
            
            // Is it SVG file?
            if (file.endsWith(".svg")) {
             
             // Retrieve ID of the resource
                int id = a.getResourceId(R.styleable.ImageViewSvg_android_src, -1);
                if(id != -1){
                try {
                  // Get the input stream for the raw resource
                  InputStream inStream = getResources().openRawResource(id);
                  int size = inStream.available();
                  
                  // Read into the buffer
                  byte[] buffer = new byte[size];
                  inStream.read(buffer);
      inStream.close();
      
      // And make a string
      mSvgContent = EncodingUtils.getString(buffer, "UTF-8");
      
      // Parse it
               mSvgId = SvgRaster.svgAndroidCreate();
               SvgRaster.svgAndroidParseBuffer(mSvgId, mSvgContent.toString());
               SvgRaster.svgAndroidSetAntialiasing(mSvgId, true);
                                                   
               mIsSvg = true; 

      
     } catch (IOException e) {
      mIsSvg = false;
      e.printStackTrace();
     }                 
                }
            }
        }
 }
Another problem is that SVG doesn’t have a size. It’s scalable and it’s all. Moreover ImageView layout parameters can be set to wrap_content, fill_parent or we can set predefined size of the image. But when a layout is required Android set’s the size and we can override onSizeChanged method. The only problem is wrap_content attribute. In this case the size will be 0. The idea is to replace wrap_content with fill_parent on the fly. But doing it in the constructor will give nothing. If you debug through source codes you will see that parent layout drags layout parameters from attributes directly and calls setLayoutParams method. Let’s override it:
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@Override 
 public void setLayoutParams(ViewGroup.LayoutParams params){
  if(mIsSvg)
  {
   // replace WRAP_CONTENT if needed
   if(params.width == ViewGroup.LayoutParams.WRAP_CONTENT
     && getSuggestedMinimumWidth() == 0)
    params.width = ViewGroup.LayoutParams.FILL_PARENT;
   if(params.height == ViewGroup.LayoutParams.WRAP_CONTENT
     && getSuggestedMinimumHeight() == 0)
    params.height = ViewGroup.LayoutParams.FILL_PARENT;
  }
  super.setLayoutParams(params);
 }
And onSizeChanged:
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@Override 
 public void onSizeChanged(int w, int h, int ow, int oh){
  if(mIsSvg){   
   //Create the bitmap to raster svg to
    Canvas canvas = new Canvas();      
   mBitmap = Bitmap.createBitmap(w, h, Bitmap.Config.ARGB_8888);
   canvas.setBitmap(mBitmap);
   // Render SVG with use of libandroidsvg
   SvgRaster.svgAndroidRenderToArea(
     mSvgId, canvas,
     0, 0, canvas.getWidth(), canvas.getHeight());     
   this.setImageBitmap(mBitmap);    
  }
  else
   super.onSizeChanged(w, h, ow, oh);
 }
And at last it’s the time to try it. Create following layout:
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<?xml version="1.0" encoding="utf-8"?>
  <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
   android:background="#AA0000"
   android:layout_height="fill_parent" 
   android:layout_width="fill_parent"
   android:layout_weight="1.0" 
   android:gravity="center"
   >
   <com.imageviewsvg.controls.ImageViewSvg
    android:src="@drawable/lion" 
    android:layout_width="100dip"
    android:layout_height="100dip" 
    android:id="@+id/svgview"
    android:layout_gravity="center" 
    />
  </LinearLayout>
And run: pic1.JPG

Debugging Native Code. 

To debug native code you can follow instructions given by Carlos Souto at Sequoyah Project [9]. But at first time some things are unclear. So there are several tips:

- while configuring c++ debug configuration the application really must be app_process, don’t care Eclipse says the program doesn’t exist it will be created later.
- you should run ndk-gdb each time you run debugging. Sometimes the command should be ndk-gdb –adb=/tools/adb –force
- Don’t forget to set "debuggable" in the manifest.

Second Approach. Anti Grain Geometry. 

There is another library you can use to rasterize SVG files. It’s Anti Grain Geometry[10]. The only extra library will be needed is libexpat. We already have it in our project. In the jni folder create folders like this:
pic2.JPG Copy corresponding files from agg sources folder into gpc/include/src folders. There in examples folder you can find svg_viewer folder. Copy all files except svg_test into aggsvg jni folder. It will parse and rasterize SVG with use of AGG. But it has only basic support for SVG and can’t parse complicated stuff. You should extend the parser by yourself. In aggsvg-android folder create aggsvgandroid.cpp file. The example parses SVG from a file system. To parse a string add the following method to a parser class:
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void parser::parse(const char *chars, int length){

     char msg[1024];

     XML_Parser p = XML_ParserCreate(NULL);
     if(p == 0)
     {
      throw exception("Couldn't allocate memory for parser");
     }

     XML_SetParamEntityParsing(p, XML_PARAM_ENTITY_PARSING_ALWAYS);
     XML_UseForeignDTD(p, true);

     XML_SetUserData(p, this);
     XML_SetElementHandler(p, start_element, end_element);
     XML_SetCharacterDataHandler(p, content);

     int done = 0;
     std::string str = std::string(chars);
     std::istringstream inputString(str);

     while(true){
      if(done)
       break;
            size_t len = inputString.readsome(m_buf, buf_size);
            done = len < buf_size;
            if(!XML_Parse(p, m_buf, len, done))
            {
                sprintf(msg,
                    "%s at line %d\n",
                    XML_ErrorString(XML_GetErrorCode(p)),
                    (int)XML_GetCurrentLineNumber(p));
                throw exception(msg);
            }
     }
        XML_ParserFree(p);

        char* ts = m_title;
        while(*ts)
        {
            if(*ts < ' ') *ts = ' ';
            ++ts;
        }

    }
At the end of Android.mk file add section to build another library. It’s pretty simple. Just clear variables after first library build and set them to build another library. And here is the class to rasterize with use of AGG:
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class SvgRasterizer{
 agg::svg::path_renderer m_path;
    double m_min_x;
    double m_min_y;
    double m_max_x;
    double m_max_y;
    double m_x;
    double m_y;
    pix_format_e pixformat;
 agg::rendering_buffer m_rbuf_window;

public:
 SvgRasterizer(pix_format_e format, uint32_t width, uint32_t height, void *pixels) : \
  m_path(), \
  m_min_x(0.0), \
  m_min_y(0.0), \
  m_max_x(0.0), \
  m_max_y(0.0), \
  pixformat(format)
 {
  m_rbuf_window.attach((unsigned char*)pixels, width, height, 4*width);
 }

 void parse_svg(const char* svg, int length){
  // Create parser
  agg::svg::parser p(m_path);
  // Parse SVG
  p.parse(svg, length);
  // Make all polygons CCW-oriented
  m_path.arrange_orientations();
  // Get bounds of the image defined in SVG
        m_path.bounding_rect(&m_min_x, &m_min_y, &m_max_x, &m_max_y);
 }


 void rasterize_svg()
 {
  typedef agg::pixfmt_rgba32 pixfmt;
  typedef agg::renderer_base renderer_base;
  typedef agg::renderer_scanline_aa_solid renderer_solid;

        pixfmt pixf(m_rbuf_window);
        renderer_base rb(pixf);
        renderer_solid ren(rb);

        agg::rasterizer_scanline_aa<> ras;
        agg::scanline_p8 sl;
        agg::trans_affine mtx;

        double scl;
        // Calculate the scale the image to fit given bitmap
        if(m_max_y > m_max_x)
         scl = pixf.height()/m_max_y;
        else
         scl = pixf.width()/m_max_x;

        // Default gamma as is
        ras.gamma(agg::gamma_power(1.0));
        mtx *= agg::trans_affine_scaling(scl);

        m_path.expand(0.0);

        // Render image
        m_path.render(ras, sl, ren, mtx, rb.clip_box(), 1.0);

        ras.gamma(agg::gamma_none());
 }
};
And in sources I’ve added an ability to test both approaches:
pic3.JPG

Conclusion 

So, there is at last two ways to show SVG file in Android. The main benefit of libsvg-android is that it is ready to use, but it more than three times slower than AGG, with which you should extend SVG parser by your own. Also with AGG you get extra features for the image processing. I’ve just used ImageView in the layout, but to use it programmatically you, of cause, should override more methods, such as setImageResource for example.
That’s all. Thanks!

Resources 

  1. http://www.eclipse.org
  2. http://developer.motorola.com/docstools/motodevstudio 
  3. http://developer.android.com/guide/developing/tools/adt.html
  4. http://www.eclipse.org/sequoyah/
  5. http://www.cygwin.com/
  6. http://developer.android.com/sdk/index.html
  7. http://www.crystax.net/android/ndk-r4.php?lang=en
  8. https://launchpad.net/libsvg-android
  9. http://www.eclipse.org/sequoyah/documentation/native_debug.php
  10. http://www.antigrain.com/