Gettextbounds in android

Question

We used to find the rectangle which fits the given text, for example if give \"TESTING\" in gettextbounds api it will give a rectangle that fits the given string \"TESTING\"

Answer 1

I find this part of the API quite confusing, however I think I almost understood how it works. A call to getTextBounds() returns the smallest rectangle that would enclose all the characters drawn by a subsequent call to drawText() with x=0 and y=0. This is stated in slightly different words on the API reference. Everything that is in Paint and could affect the appearance of the text is taken into account. Here's an example:

Rect bounds = new Rect();

Paint paint = new Paint();
paint.setTextAlign(Align.LEFT);
paint.setTypeface(typeface);
paint.setTextSize(textSize);
paint.getTextBounds(text, 0, text.length(), bounds);

The reason why the rectangle has such exotic coordinates is because when you draw text with drawText(), the origin to which x and y are relative depends on the typographical properties of the Paint that you selected. For instance y is relative to the baseline, which is neither above nor below the font, but usually strikes it somewhere across the middle. For this reason the bounds rectangle will have (usually) a negative top and a positive bottom. The negative top means that the top of the text is above the baseline (y decreases going up), while the positive bottom means that the bottom of the text is below the baseline (y increases going down). It is interesting to note that when you measure a string such as "Hi" the bottom is likely to be 0, because those characters do not have a below the baseline part. On the contrary, when you measure a string like "Hg" you are likely to get a positive bottom, because the story of the g is below the baseline. I'm not sure how the horizontal position is estimated, though.

With this said, to draw the text of which you have computed the bounds you can do:

canvas.drawText(text, -bounds.left, -bounds.top, paint);

This will draw the text near to the upper left corner of the canvas. The coordinates of the upper left corner are (0, 0) so to move the text around you only have to add your desired amount of displacement:

canvas.drawText(text, -bounds.left + yourX, -bounds.top + yourY, paint);

Another example: if you want to create a bitmap that contains text, and you want to fit exactly the available space, you can do:

Bitmap bitmap = Bitmap.createBitmap(bounds.width(), bounds.height(), Bitmap.Config.ARGB_8888);
Canvas canvas = new Canvas(bitmap);
canvas.drawText(text, -bounds.left, -bounds.top, paint);

If you want to leave a few pixels to the left, right, top and bottom, let's say 2, you can do:

Bitmap bitmap = Bitmap.createBitmap(bounds.width() + 4, bounds.height() + 4, Bitmap.Config.ARGB_8888);
Canvas canvas = new Canvas(bitmap);
canvas.drawText(text, -bounds.left + 2, -bounds.top + 2, paint);