Android – drawing multiline text on bitmap

25. 09. 2018

ALERT: This article might be outdated and not fit for your needs. In order to enjoy its updated version, visit Android Guide To: Drawing Text Over Bitmap

This improves method from my previous blog post to work with multiline text. The StaticLayout class does the trick.

Measure height of multiline text

To center text vertically we need to know text height. Instantiate StaticLayout with text width according to your needs, for us it is simple the width of Bitmap/Canvas minus 16dp padding. The getHeight() then returns height of text.

Positioning text on Canvas

There are four simple steps to position text on Canvas:

  • Save the current matrix and clip with Canvas.save().
  • Apply translation to Canvas matrix with Canvas.translate(x,y).
  • Draw StaticLayout on Canvas with StaticLayout.draw(canvas).
  • Revert matrix translation with Canvas.restore() method.

Complete source code

public Bitmap drawMultilineTextToBitmap(Context gContext,
                                   int gResId,
                                   String gText) {

  // prepare canvas
  Resources resources = gContext.getResources();
  float scale = resources.getDisplayMetrics().density;
  Bitmap bitmap = BitmapFactory.decodeResource(resources, gResId);

  android.graphics.Bitmap.Config bitmapConfig = bitmap.getConfig();
  // set default bitmap config if none
  if(bitmapConfig == null) {
    bitmapConfig = android.graphics.Bitmap.Config.ARGB_8888;
  }
  // resource bitmaps are imutable,
  // so we need to convert it to mutable one
  bitmap = bitmap.copy(bitmapConfig, true);

  Canvas canvas = new Canvas(bitmap);

  // new antialiased Paint
  TextPaint paint=new TextPaint(Paint.ANTI_ALIAS_FLAG);
  // text color - #3D3D3D
  paint.setColor(Color.rgb(61, 61, 61));
  // text size in pixels
  paint.setTextSize((int) (14 * scale));
  // text shadow
  paint.setShadowLayer(1f, 0f, 1f, Color.WHITE);

  // set text width to canvas width minus 16dp padding
  int textWidth = canvas.getWidth() - (int) (16 * scale);

  // init StaticLayout for text
  StaticLayout textLayout = new StaticLayout(
    gText, paint, textWidth, Layout.Alignment.ALIGN_CENTER, 1.0f, 0.0f, false);

  // get height of multiline text
  int textHeight = textLayout.getHeight();

  // get position of text's top left corner
  float x = (bitmap.getWidth() - textWidth)/2;
  float y = (bitmap.getHeight() - textHeight)/2;

  // draw text to the Canvas center
  canvas.save();
  canvas.translate(x, y);
  textLayout.draw(canvas);
  canvas.restore();

  return bitmap;
}

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