Draw rotated text in SkiaSharp

Question

How to draw rotated text in SkiaSharp.

Currently I'm rotating the SKCanvas, drawing the text and then rotating it back. But I thought may be there is a more efficient way to do this.

canvas.RotateDegrees(45, 20, 20);
canvas.DrawText("Text", 20, 20, paint);
canvas.RotateDegrees(-45, 20, 20);

Answer 1

That is the correct way (the only way, I think).

It is not that inefficient as you are not really rotating the canvas, but rather adjusting the drawing matrix (an int[9] array). Under the hood it is doing something like this:

var m = SKMatrix.CreateRotation(45); // simple struct over int[9]
canvas.CurrentMatrix.Concat(m)       // simple multiplication

and then when you draw, it it just uses the matrix:

canvas.DrawText(text, matrix);

and when you rotate back, it just does the math again.

Another way is to save the canvas and then restore:

canvas.Save();
canvas.Rotate(45);
canvas.DrawText(text);
canvas.Restore();

This just makes a copy of the current matrix during the save. And when you restore, it just reverts it. This is a "better" way in that you can possible do a series of transformations, without having to reverse.

Or, you can make use of a convenience type:

// auto save
using (new SKAutoCanvasRestore(canvas)) {
    // do any transformations
    canvas.Rotate(45);
    // do serious work
    canvas.DrawText(text);
    // auto restore, even on exceptions or errors
}

Another, totally different way to draw text, is to draw along a path:

var path = new SKPath();
// create path ...

// draw using path
canvas.DrawText("text", path, hOffset: 0, vOffset: 0, paint);