Android Canvas和Bitmap結(jié)合繪圖詳解流程
Rect/RectF
存儲(chǔ)四個(gè)值的矩形類:左側(cè)、頂部、右側(cè)和底部??捎糜谥苯釉诋嫴忌侠L制或僅用于存儲(chǔ)要繪制的對象的大小。Rect和RectF類之間的區(qū)別在于 RectF 存儲(chǔ)浮點(diǎn)值,而Rect類存儲(chǔ)整數(shù)。
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(gè)3 x 3的矩陣,用于存儲(chǔ)可用于轉(zhuǎn)換畫布的信息。矩陣可以存儲(chǔ)以下類型的變換信息:縮放、傾斜、旋轉(zhuǎn)、平移。而每種變換方式都對應(yīng)著三種方法:set方法將用新值替換當(dāng)前的Matrix,不管之前Matrix的值是什么。pre和post 方法將在當(dāng)前Matrix包含的任何內(nèi)容之前或之后應(yīng)用新的轉(zhuǎn)換。
Matrix m = new Matrix(); m.setRotate(90); m.setScale(3f,1f); m.setTranslate(200, 200);
只有平移,旋轉(zhuǎn)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(jìn)行平移(200f, 100f),然后進(jìn)行縮放(3f, 1f),然后進(jìn)行縮放(0.5f, 1f),最后進(jìn)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(jìn)行平移(200f, 100f),然后進(jìn)行縮放(1f, 1f),最后進(jìn)行縮放(5f, 1f)。因?yàn)橛昧藄et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(jìn)行平移(x, y),再進(jìn)行縮放(sx, sy),那么看到的平移效果等同于(x*sx, y*sy),因?yàn)榭s放是將整個(gè)畫布或者坐標(biāo)系進(jìn)行縮放的
Canvas
Canvas相當(dāng)于Android的畫布,可以把畫布想象成一塊內(nèi)存空間,也就是一個(gè)Bitmap。Canvas的API提供一整套在這個(gè)Bitmap上進(jìn)行繪圖的操作方法。
- drawBitmap(Bitmap bitmap, Matrix matrix, Paint paint)
使用指定的矩陣?yán)L制位圖,繪制的時(shí)候會(huì)使用矩陣進(jìn)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(qū)域src繪制到目標(biāo)矩形區(qū)域dst中,如果矩形區(qū)域src傳入空值,則表示繪制整個(gè)源圖到目標(biāo)矩形區(qū)域dst中,繪制的時(shí)候源圖或子集自動(dòng)縮放/平移以填充目標(biāo)矩形。如果繪制對應(yīng)的畫筆通過方法setMaskFilter指定了超出原始位圖寬/高的掩碼過濾器(如BlurMaskFilter),則會(huì)位圖將繼續(xù)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(fù)制的邊緣顏色。因?yàn)樵淳匦螀^(qū)域src對應(yīng)的坐標(biāo)空間是相對于源圖的,而目標(biāo)矩形區(qū)域dst對應(yīng)的坐標(biāo)空間是繪制視圖對應(yīng)的坐標(biāo)空間,因此要控制好對應(yīng)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(qū)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(diǎn)陣圖,可以理解為int[] buffer,用來存儲(chǔ)每個(gè)像素點(diǎn)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; }
注意:通過Bitmap.createBitmap生成的Bitmap對象是可變對象,可以向Bitmap上繪制內(nèi)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(nèi)容。
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