SKCanvas rendering rotated image very slow compared to System.Drawing (4x slower)

[MathieuJack]

Rendering a rotated bitmap with SKCanvas is slow, compared with System.Drawing (4x slower)
See below code, it produces following output:
rotation: 20°
Skia: 6860ms
System.Drawing: 1643ms

       float rotation = 20;
        Console.WriteLine("rotation: "+rotation+"°");

        // Skia part...
        MemoryStream imageStream = new MemoryStream(new WebClient().DownloadData(@"https://via.placeholder.com/450"));
        SKBitmap skBitmapToBlit = SKBitmap.Decode(imageStream);
        SKBitmap renderSkBitmap = new SKBitmap(512, 512, isOpaque: false);
        SKCanvas canvas = new SKCanvas(renderSkBitmap);
        SKPaint paint = new SKPaint()
        {
            FilterQuality = SKFilterQuality.High
        };
        canvas.RotateDegrees(rotation);
        var sw = Stopwatch.StartNew();
        for (int i=0; i<100; i++)
        {             
            canvas.DrawBitmap(skBitmapToBlit, new SKPoint(10, 10), paint);
        };
        Console.WriteLine("Skia: "+sw.ElapsedMilliseconds + "ms");

        // System.Drawing part...
        imageStream = new MemoryStream(new WebClient().DownloadData(@"https://via.placeholder.com/450"));
        Bitmap gdiBitmapToBlit = new Bitmap(imageStream);
        Bitmap renderGdiBitmap = new Bitmap(512, 512, System.Drawing.Imaging.PixelFormat.Format32bppArgb);
        Graphics graphics = Graphics.FromImage(renderGdiBitmap);
        graphics.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.Bicubic;
        graphics.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.HighSpeed;
        var matrix = new Matrix();
        matrix.Rotate(rotation);
        graphics.Transform=matrix;
        sw = Stopwatch.StartNew();
        for (int i = 0; i < 100; i++)
        {
            graphics.DrawImage(gdiBitmapToBlit, new PointF(10, 10));
        };
        Console.WriteLine("System.Drawing: " + sw.ElapsedMilliseconds + "ms");

Note that, without rotating, Skia is much faster than System.Drawing (36x faster).

Symptom : Skia 4x slower than System.Drawing, with provided code.
Expected : Skia faster than System.Drawing, with provided code.

• Version with issue: 1.68.0
• Last known good version: N/A
• IDE: Visual Studio
• Platform Target Frameworks: .net framework 4.7

VS bug #776803

[TabishRafiq]

Having the same issue. did u find any solution?

[mattleibow]

Interesting. How does the draw speed compare when the rotation is 0, and when at 90? Also, What happens if you drop the filter quality?

I'll have to setup some benchmarks - but it may be related to #686. In the skia forums, there are orders of magnitude improvements for clang. I am busy having a look at clang for Linux #767 and going to do some tests.

[MathieuJack]

@mattleibow If I drop filter quality, then performances get "normal" again (about as fast as System.Drawing with same quality)
But quality is then too low to be used when working with images, so this solution should not be considered as a workaround.

I don't understand the #686 Clang compiler discussion, since I thought Skia was HW accelerated. Talking about a compiler optimisation let us think that image rotation is done by SW. Is it the case?

[pauldendulk]

@mattleibow For Mapsui this is a blocking issue. Moving the map around is very choppy even with a single image. Our next release will be with 1.60.3.