[Android]在圖上畫圖與dp<=>px轉換

有兩種做法:
1.以Canvas畫在指定位址與縮放，再將Canvas所畫的Bitmap拿來用
2.以Layout檔Inflate，再將View轉為Bitmap拿來用
結論:
第二種方法較快且容易擴充與調整

方法一:
Bitmap org = BitmapFactory.decodeResource(getResources(), R.drawable.empty_pinpoint);
Bitmap pinPoint = Bitmap.createScaledBitmap(org, dp2px(52), dp2px(68), true);
Canvas pinPointCanvas = new Canvas(pinPoint);

Bitmap head = BitmapFactory.decodeResource(getResources(), R.drawable.test_head);
pinPointCanvas.drawBitmap(head, null, new Rect(dp2px(6), dp2px(3), dp2px(46), dp2px(43)), null);

ImageView view = (ImageView) findViewById(R.id.imgResult);
view.setImageBitmap(pinPoint);


方法二:

        //1. Make a bitmap to draw to.
        Bitmap bmp = Bitmap.createBitmap(480, 800, Bitmap.Config.ARGB_8888);

        //2. We need a Canvas to handle drawing to the bitmap. Bitmap has no draw methods of its own.
        Canvas canvas = new Canvas(bmp);

        //3. Get a reference to the LayoutInflater.
        LayoutInflater inflater = (LayoutInflater) getSystemService(Context.LAYOUT_INFLATER_SERVICE);

        //4. Inflate the layout we want to draw.
        View layout = inflater.inflate(R.layout.layout_to_draw, null);

        //5. Call setDrawingCacheEnabled to true, since the default is false. 
        layout.setDrawingCacheEnabled(true);

        //6. Tell the layout how big it should be. In this case we are using the full size of the canvas.
        layout.measure(MeasureSpec.makeMeasureSpec(canvas.getWidth(), MeasureSpec.EXACTLY), MeasureSpec.makeMeasureSpec(canvas.getHeight(), MeasureSpec.EXACTLY));

        //7. Now we apply the measures so that it embiggens to the correct size before drawing.
        layout.layout(0, 0, layout.getMeasuredWidth(), layout.getMeasuredHeight());

        //8. Finally, we draw the bitmap. Mission accomplished. But of course we still can't see the bitmap. So...
        canvas.drawBitmap(layout.getDrawingCache(), 0, 0, null);

        //9. Get reference to an ImageView that you want to hold your bitmap. 
        ImageView view = (ImageView) findViewById(R.id.image_to_show);

        //10. Set the bitmap as the ImageView's Image Bitmap.
        view.setImageBitmap(bmp);



dp<=>px轉換

    private int dp2px(int dp) {
        DisplayMetrics displayMetrics = getResources().getDisplayMetrics();
        return (int)((dp * displayMetrics.density) + 0.5);
    }