Skia / SkiaSharp - Rotating shapes around their own vertical axis - animation

Question

I generate the scene above using the OnDraw method below:
protected override void OnDraw(SKCanvas canvas, int width, int height)
{
int i = 0;
int step = 0;
List<SKRect> rects = new List<SKRect>();
// get the 2D equivalent of the 3D matrix
var rotationMatrix = rotationView.Matrix;
// get the properties of the rectangle
var length = Math.Min(width / 6, height / 6);
canvas.Clear(EffectMedia.Colors.XamarinLightBlue);
foreach (var n in numbers)
{
var rect = new SKRect(0 + step, 0, 100 + step, 100);
rects.Add(rect);
step += 120;
}
//var sideHoriz = rotationMatrix.MapPoint(new SKPoint(0, 1)).Y > 0;
var sideVert = rotationMatrix.MapPoint(new SKPoint(1, 0)).X > 0;
var paint = new SKPaint
{
Color = sideVert ? EffectMedia.Colors.XamarinPurple : EffectMedia.Colors.XamarinGreen,
Style = SKPaintStyle.Fill,
IsAntialias = true
};
// first do 2D translation to the center of the screen
canvas.Translate((width - (120 * numbers.Count)) / 2, height / 2);
// The following line is disabled because it makes the whole canvas rotate!
// canvas.Concat(ref rotationMatrix);
foreach (var n in numbers)
{
canvas.RotateDegrees((float)-3);
canvas.DrawRoundRect(rects[i], 30, 30, paint);
var shadow = SKShader.CreateLinearGradient(
new SKPoint(0, 0), new SKPoint(0, length * 2),
new[] { paint.Color.WithAlpha(127), paint.Color.WithAlpha(0) },
null,
SKShaderTileMode.Clamp);
var paintShadow = new SKPaint
{
Shader = shadow,
Style = SKPaintStyle.Fill,
IsAntialias = true,
BlendMode = SKBlendMode.SoftLight
};
foreach (var r in rects)
{
r.Offset(0, 105);
canvas.DrawRoundRect(r, 30, 30, paintShadow);
}
i++;
}
}
The idea is to make all those rounded boxes rotate (vertically) around their own axis.
I tried using SKPath + Transform, saving&restoring the rotationMatrix and/or the canvas but I can't find a way to have 6 rotating boxes ( canvas.Concat(ref rotationMatrix); makes the whole canvas rotate [*]).
Do you have any hint on how that can be achieved?
Note [*]: there's a call to rotationView.RotateYDegrees(5) every X milliseconds to update the rotationMatrix used by OnDraw.

Answer 1

This is what I'd like to achieve, any hints / directions would be really appreciated... :-)
The following piece of code rotates those shapes around their Z-axis:
canvas.Save();
canvas.RotateDegrees(degrees, rects[i].MidX, rects[i].MidY);
canvas.DrawRoundRect(rects[i], 30, 30, paint);
canvas.Restore();
Thanks