Android Canvas和Bitmap结合绘图详解流程

private static Bitmap createDrawableBitmap(Drawable drawable) {
    int width = drawable.getIntrinsicWidth();
    int height = drawable.getIntrinsicHeight();
    if (width <= 0 || height <= 0) {
        return null;
    }
    float scale = Math.min(1.0f, ((float) MAX_IMAGE_SIZE) / ((float) (width * height)));
    if ((drawable instanceof BitmapDrawable) && scale == 1.0f) {
        return ((BitmapDrawable) drawable).getBitmap();
    }
    int bitmapWidth = (int) (((float) width) * scale);
    int bitmapHeight = (int) (((float) height) * scale);
    Bitmap bitmap = Bitmap.createBitmap(bitmapWidth, bitmapHeight, Config.ARGB_8888);
    Canvas canvas = new Canvas(bitmap);
    Rect existingBounds = drawable.getBounds();
    int left = existingBounds.left;
    int top = existingBounds.top;
    int right = existingBounds.right;
    int bottom = existingBounds.bottom;
    drawable.setBounds(0, 0, bitmapWidth, bitmapHeight);
    drawable.draw(canvas);
    drawable.setBounds(left, top, right, bottom);
    return bitmap;
}

Matrix m = new Matrix();
m.setRotate(90);
m.setScale(3f,1f);
m.setTranslate(200, 200);

Matrix m = new Matrix();
m.preScale(3f,1f);
m.preTranslate(200f, 100f);
m.postScale(0.5f, 1f);
m.postTranslate(100f, 0f);

Matrix m = new Matrix();
m.postTranslate(200f, 0f);
m.preScale(0.5f, 1f);
m.setScale(1f, 1f);
m.postScale(5f, 1f);
m.preTranslate(200f, 100f);

Bitmap background = Bitmap.createBitmap((int)width, (int)height, Config.ARGB_8888);
float originalWidth = originalImage.getWidth(); 
float originalHeight = originalImage.getHeight();

Canvas canvas = new Canvas(background);

float scale = width / originalWidth;

float xTranslation = 0.0f;
float yTranslation = (height - originalHeight * scale) / 2.0f;

Matrix transformation = new Matrix();
transformation.postTranslate(xTranslation, yTranslation);
transformation.preScale(scale, scale);

Paint paint = new Paint();
paint.setFilterBitmap(true);

canvas.drawBitmap(originalImage, transformation, paint);

public Bitmap cropCircle(Bitmap bitmap) {
  Bitmap output = Bitmap.createBitmap(bitmap.getWidth(),
      bitmap.getHeight(), Config.ARGB_8888);
  Canvas canvas = new Canvas(output);
  final int color = 0xff424242;
  final Paint paint = new Paint();
  final Rect rect = new Rect(0, 0, bitmap.getWidth(), bitmap.getHeight());
  paint.setAntiAlias(true);
  canvas.drawARGB(0, 0, 0, 0);
  paint.setColor(color);
  canvas.drawCircle(bitmap.getWidth() / 2, bitmap.getHeight() / 2,
      bitmap.getWidth()/2, paint);
  paint.setXfermode(new PorterDuffXfermode(Mode.SRC_IN));
  canvas.drawBitmap(bitmap, rect, rect, paint);
  return output;
}

public Bitmap transform(Bitmap source) {
  int size = Math.min(source.getWidth(), source.getHeight());
  int x = (source.getWidth() - size) / 2;
  int y = (source.getHeight() - size) / 2;
  Bitmap squaredBitmap = Bitmap.createBitmap(source, x, y, size, size);
  if (squaredBitmap != source) {
    source.recycle();
  }
  Bitmap bitmap = Bitmap.createBitmap(size, size, source.getConfig());
  Canvas canvas = new Canvas(bitmap);
  Paint avatarPaint = new Paint();
  BitmapShader shader = new BitmapShader(squaredBitmap, BitmapShader.TileMode.CLAMP, BitmapShader.TileMode.CLAMP);
  avatarPaint.setShader(shader);
  Paint outlinePaint = new Paint();
  outlinePaint.setColor(Color.WHITE);
  outlinePaint.setStyle(Paint.Style.STROKE);
  outlinePaint.setStrokeWidth(STROKE_WIDTH);
  outlinePaint.setAntiAlias(true);
  float r = size / 2f;
  canvas.drawCircle(r, r, r, avatarPaint);
  canvas.drawCircle(r, r, r - STROKE_WIDTH / 2, outlinePaint);
  squaredBitmap.recycle();
  return bitmap;
}

private static Bitmap decodeSampledBitmapFromUrl(String url, int reqWidth, int reqHeight) throws IOException {

	    // First decode with inJustDecodeBounds=true to check dimensions
	    final Options options = new Options();
	    options.inJustDecodeBounds = true;
	    
	    InputStream stream = fetchStream(url);
	    BitmapFactory.decodeStream(stream, null, options);
	    stream.close();

	    // Calculate inSampleSize
	    options.inSampleSize = calculateInSampleSize(options, reqWidth, reqHeight);
	    // Decode bitmap with inSampleSize set
	    options.inJustDecodeBounds = false;
	    
	    stream = fetchStream(url);
	    Bitmap bitmap = BitmapFactory.decodeStream(stream, null, options);
	    stream.close();
	    
	    return bitmap;
	}
	
	private static InputStream fetchStream(String urlString) throws IllegalStateException, IOException {
		
		DefaultHttpClient httpClient = new DefaultHttpClient();
		HttpGet request = new HttpGet(urlString);
		HttpResponse response = httpClient.execute(request);
		return response.getEntity().getContent();
	}
	
	private static int calculateInSampleSize(Options options, int reqWidth, int reqHeight) {
		// Raw height and width of image
		final int height = options.outHeight;
		final int width = options.outWidth;
		int inSampleSize = 1;

		if (height > reqHeight || width > reqWidth) {

			// Calculate ratios of height and width to requested height and width
			final int heightRatio = Math.round((float) height / (float) reqHeight);
			final int widthRatio = Math.round((float) width / (float) reqWidth);

			// Choose the smallest ratio as inSampleSize value, this will guarantee
			// a final image with both dimensions larger than or equal to the
			// requested height and width.
			inSampleSize = heightRatio < widthRatio ? heightRatio : widthRatio;
		}

		return inSampleSize;
	}