Android Canvas和Bitmap結合繪圖詳解流程

Posted on 2021-11-02 by WalkonNet

Rect/RectF

存儲四個值的矩形類：左側、頂部、右側和底部。可用於直接在畫佈上繪制或僅用於存儲要繪制的對象的大小。Rect和RectF類之間的區別在於 RectF 存儲浮點值，而Rect類存儲整數。

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

一個3 x 3的矩陣，用於存儲可用於轉換畫佈的信息。矩陣可以存儲以下類型的變換信息：縮放、傾斜、旋轉、平移。而每種變換方式都對應著三種方法：set方法將用新值替換當前的Matrix，不管之前Matrix的值是什麼。pre和post 方法將在當前Matrix包含的任何內容之前或之後應用新的轉換。

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

隻有平移，旋轉值和縮放值被重置

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

先進行平移(200f, 100f)，然後進行縮放(3f, 1f)，然後進行縮放(0.5f, 1f)，最後進行平移(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);

先進行平移(200f, 100f)，然後進行縮放(1f, 1f)，最後進行縮放(5f, 1f)。因為用瞭set方法所以平移(200f, 0f)和縮放(0.5f, 1f)被覆蓋，不起作用

假如先進行平移(x, y)，再進行縮放(sx, sy)，那麼看到的平移效果等同於(x*sx, y*sy)，因為縮放是將整個畫佈或者坐標系進行縮放的

Canvas

Canvas相當於Android的畫佈，可以把畫佈想象成一塊內存空間，也就是一個Bitmap。Canvas的API提供一整套在這個Bitmap上進行繪圖的操作方法。

drawBitmap(Bitmap bitmap, Matrix matrix, Paint paint)

使用指定的矩陣繪制位圖，繪制的時候會使用矩陣進行變換，矩陣和畫筆可以傳入空值

drawBitmap (Bitmap bitmap, Rect src, Rect dst, Paint paint)

將傳入的源圖bitmap指定的矩形區域src繪制到目標矩形區域dst中，如果矩形區域src傳入空值，則表示繪制整個源圖到目標矩形區域dst中，繪制的時候源圖或子集自動縮放/平移以填充目標矩形。如果繪制對應的畫筆通過方法setMaskFilter指定瞭超出原始位圖寬/高的掩碼過濾器（如BlurMaskFilter），則會位圖將繼續被繪制，就像在具有CLAMP模式的著色器中一樣。因此，原始寬/高之外的顏色將是復制的邊緣顏色。因為源矩形區域src對應的坐標空間是相對於源圖的，而目標矩形區域dst對應的坐標空間是繪制視圖對應的坐標空間，因此要控制好對應的縮放因子。

drawBitmap (Bitmap bitmap, Rect src, RectF dst, Paint paint)

矩陣示例：

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);

矩形區域示例：

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;
}

Bitmap

位圖，點陣圖，可以理解為int[] buffer，用來存儲每個像素點的容器。

Bitmap.createBitmap(int width, int height, Bitmap.Config config)
Bitmap.createBitmap(Bitmap src)
Bitmap.createBitmap(Bitmap source, int x, int y, int width, int height)
Bitmap.createBitmap(Bitmap source, int x, int y, int width, int height,Matrix m, boolean filter)
BitmapFactory.decodeByteArray(byte[] data, int offset, int length, BitmapFactory.Options opts)
BitmapFactory.decodeFile(String pathName, Options opts)
BitmapFactory.decodeStream(InputStream is, Rect outPadding,Options opts)

createBitmap生成示例：

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;
}

BitmapFactory生成示例：

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;
	}

註意：通過Bitmap.createBitmap生成的Bitmap對象是可變對象，可以向Bitmap上繪制內容，而通過BitmapFactory生成的Bitmap對象必須指定BitmapFactory.Options.inMutable = true，否則就是不可變對象，不能向上面繪制內容。

感謝大傢的支持，如有錯誤請指正，如需轉載請標明原文出處！

到此這篇關於Android Canvas和Bitmap結合繪圖詳解流程的文章就介紹到這瞭,更多相關Android 繪圖內容請搜索WalkonNet以前的文章或繼續瀏覽下面的相關文章希望大傢以後多多支持WalkonNet！

Android Canvas和Bitmap結合繪圖詳解流程

目錄

Rect/RectF

Matrix

Canvas

Bitmap

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目錄

Rect/RectF

Matrix

Canvas

Bitmap

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