[BUG] `DrawShapedText` throws an exception

[Youssef1313]

Description

DrawShapedText

Code

public void Render(SKSurface surface)
{
    var paint = new SKPaint
    {
        TextEncoding = SKTextEncoding.Utf16,
        IsStroke = false,
        IsAntialias = true,
        LcdRenderText = true,
        SubpixelText = true
    };

    surface.Canvas.DrawShapedText(line, 0, 0, paint);
}

Expected Behavior

No crash

Actual Behavior

Exception due to paint.GetFont().Typeface being null in:

https://github.com/mono/SkiaSharp/blob/2ad29861d5a40d3bf78c28ab0a9cb02a8f0fe437/source/SkiaSharp.HarfBuzz/SkiaSharp.HarfBuzz.Shared/CanvasExtensions.cs#L10-L17

as the constructor doesn't accept null

https://github.com/mono/SkiaSharp/blob/2ad29861d5a40d3bf78c28ab0a9cb02a8f0fe437/source/SkiaSharp.HarfBuzz/SkiaSharp.HarfBuzz.Shared/SKShaper.cs#L15-L17

The code was working with DrawText, and I'm switching to DrawShapedText to fix the RTL languages.

Basic Information

• Version with issue: 2.80.0
• Last known good version: N/A
• IDE:
• Platform Target Frameworks:
  • Android:
  • iOS:
  • Linux:
  • macOS:
  • Tizen:
  • tvOS:
  • UWP:
  • watchOS:
  • Windows Classic:
• Target Devices:

Detailed IDE/OS information (click to expand)

``` PASTE ANY DETAILED VERSION INFO HERE ```

Screenshots

Reproduction Link

[taublast]

When drawing at 0,0 you are drawing outside the canvas bounds, which might result in a crash depending on the drawing context. For example, in case of a hardware-accelerated surface you'll crash 100%. When drawing text coordinates are the lower-left corner of the text, not top-left one.

[Gillibald]

Text is drawn at the baseline

[Youssef1313]

The outlined crash is probably less-relevant with the deprecation of SKPaint.Font. The overload I was using in this issue is now deprecated anyway.