Flip an SKPath using SkiaSharp - image

Question

I'm using slightly modified resize code based on example I found. However, on resize the everything is flipped. I would like to either flip it back or prevent it from flipping in the first place.
Here is my resize code:
private static void ResizePath(SKPath buildingPath, IEnumerable<Room> rooms)
{
var info = new SKImageInfo(512, 600, SKImageInfo.PlatformColorType, SKAlphaType.Premul);
var drawSpaceRect = SKRect.Create(info.Size);
//I need to find the size of the path
var buildingPathRect = buildingPath.TightBounds;
//I want to find the largest rectangle that can fit on my canvas maintaining the path's aspect ratio
var sketchRect = drawSpaceRect.AspectFit(buildingPathRect.Size);
//Now I need to transform the path to draw within the sketchRect
//First translate original path to its own origin
var firstTranslateM = SKMatrix.MakeTranslation(-buildingPathRect.Left, -buildingPathRect.Top);
//Next handle scaling. Since I maintained aspect ratio, I should be able to use either
//width or height to figure out scaling factor
var scalingFactor = sketchRect.Width/buildingPathRect.Width;
var scaleM = SKMatrix.MakeScale(scalingFactor, scalingFactor);
//Next I need to handle translation so path is centered on canvas
var secondTranslateM = SKMatrix.MakeTranslation(sketchRect.Left, sketchRect.Top);
//Finally I need to handle transforming the path to rotate 180 degrees
var rotationMatrix = SKMatrix.MakeRotationDegrees(180, sketchRect.MidX, sketchRect.MidY);
//Now combine the translation, scaling, and rotation into a single matrix by matrix multiplication/concatentation
var transformM = SKMatrix.MakeIdentity();
SKMatrix.PostConcat(ref transformM, firstTranslateM);
SKMatrix.PostConcat(ref transformM, scaleM);
SKMatrix.PostConcat(ref transformM, secondTranslateM);
SKMatrix.PostConcat(ref transformM, rotationMatrix);
//Now apply the transform to the path
foreach (var r in rooms)
{
r.Path.Transform(transformM);
}
}
Here is an example of what I want (ignore the line numbers):
Flipped to:
Any help would be appreciated.

Answer 1

This transformation should do what you are looking for. The terminology would be flip horizontal or reflect horizontal.
var Ma = new SKMatrix {Values = new float[] {-1, 0, 0, 1, 0, 0, 0, 0, 0}};
pathToFlip.Transform(Ma);