ShrlAlgoToolkit/NeuWPF/NeoUI/Controls/SplashWindow/Border.cs

namespace NeoUI.Controls;

public class Border : System.Windows.Controls.Border
{
    protected override Geometry? GetLayoutClip(Size layoutSlotSize)
    {
        if (!ClipToBounds)
        {
            return base.GetLayoutClip(layoutSlotSize);
        }

        var borderThickness = BorderThickness;
        var cornerRadius = CornerRadius;
        var renderSize = RenderSize;

        if (renderSize.Width <= 0 || renderSize.Height <= 0)
        {
            return null;
        }

        var rect = new Rect(0, 0, renderSize.Width, renderSize.Height);
        var radii = new Radii(cornerRadius, borderThickness, true);

        var layoutGeometry = new StreamGeometry();
        using var ctx = layoutGeometry.Open();
        GenerateGeometry(ctx, rect, radii);

        layoutGeometry.Freeze();
        return layoutGeometry;
    }

    internal static void GenerateGeometry(StreamGeometryContext ctx, Rect rect, Radii radii)
    {
        //
        //  compute the coordinates of the key points
        //

        Point topLeft = new(radii.LeftTop, 0);
        Point topRight = new(rect.Width - radii.RightTop, 0);
        Point rightTop = new(rect.Width, radii.TopRight);
        Point rightBottom = new(rect.Width, rect.Height - radii.BottomRight);
        Point bottomRight = new(rect.Width - radii.RightBottom, rect.Height);
        Point bottomLeft = new(radii.LeftBottom, rect.Height);
        Point leftBottom = new(0, rect.Height - radii.BottomLeft);
        Point leftTop = new(0, radii.TopLeft);

        //
        //  check key points for overlap and resolve by partitioning radii according to
        //  the percentage of each one.
        //

        //  top edge is handled here
        if (topLeft.X > topRight.X)
        {
            var v = radii.LeftTop / (radii.LeftTop + radii.RightTop) * rect.Width;
            topLeft.X = v;
            topRight.X = v;
        }

        //  right edge
        if (rightTop.Y > rightBottom.Y)
        {
            var v = radii.TopRight / (radii.TopRight + radii.BottomRight) * rect.Height;
            rightTop.Y = v;
            rightBottom.Y = v;
        }

        //  bottom edge
        if (bottomRight.X < bottomLeft.X)
        {
            var v = radii.LeftBottom / (radii.LeftBottom + radii.RightBottom) * rect.Width;
            bottomRight.X = v;
            bottomLeft.X = v;
        }

        // left edge
        if (leftBottom.Y < leftTop.Y)
        {
            var v = radii.TopLeft / (radii.TopLeft + radii.BottomLeft) * rect.Height;
            leftBottom.Y = v;
            leftTop.Y = v;
        }

        //
        //  add on offsets
        //

        Vector offset = new(rect.TopLeft.X, rect.TopLeft.Y);
        topLeft += offset;
        topRight += offset;
        rightTop += offset;
        rightBottom += offset;
        bottomRight += offset;
        bottomLeft += offset;
        leftBottom += offset;
        leftTop += offset;

        //
        //  create the border geometry
        //
        ctx.BeginFigure(topLeft, true /* is filled */, true /* is closed */);

        // Top line
        ctx.LineTo(topRight, true /* is stroked */, false /* is smooth join */);

        // Upper-right corner
        var radiusX = rect.TopRight.X - topRight.X;
        var radiusY = rightTop.Y - rect.TopRight.Y;
        if (!MathHelper.IsZero(radiusX) || !MathHelper.IsZero(radiusY))
        {
            ctx.ArcTo(rightTop, new Size(radiusX, radiusY), 0, false, SweepDirection.Clockwise, true, false);
        }

        // Right line
        ctx.LineTo(rightBottom, true /* is stroked */, false /* is smooth join */);

        // Lower-right corner
        radiusX = rect.BottomRight.X - bottomRight.X;
        radiusY = rect.BottomRight.Y - rightBottom.Y;
        if (!MathHelper.IsZero(radiusX) || !MathHelper.IsZero(radiusY))
        {
            ctx.ArcTo(bottomRight, new Size(radiusX, radiusY), 0, false, SweepDirection.Clockwise, true, false);
        }

        // Bottom line
        ctx.LineTo(bottomLeft, true /* is stroked */, false /* is smooth join */);

        // Lower-left corner
        radiusX = bottomLeft.X - rect.BottomLeft.X;
        radiusY = rect.BottomLeft.Y - leftBottom.Y;
        if (!MathHelper.IsZero(radiusX) || !MathHelper.IsZero(radiusY))
        {
            ctx.ArcTo(leftBottom, new Size(radiusX, radiusY), 0, false, SweepDirection.Clockwise, true, false);
        }

        // Left line
        ctx.LineTo(leftTop, true /* is stroked */, false /* is smooth join */);

        // Upper-left corner
        radiusX = topLeft.X - rect.TopLeft.X;
        radiusY = leftTop.Y - rect.TopLeft.Y;
        if (!MathHelper.IsZero(radiusX) || !MathHelper.IsZero(radiusY))
        {
            ctx.ArcTo(topLeft, new Size(radiusX, radiusY), 0, false, SweepDirection.Clockwise, true, false);
        }
    }

    internal struct Radii
    {
        internal Radii(CornerRadius radii, Thickness borders, bool outer)
        {
            var left = 0.5 * borders.Left;
            var top = 0.5 * borders.Top;
            var right = 0.5 * borders.Right;
            var bottom = 0.5 * borders.Bottom;

            if (outer)
            {
                if (MathHelper.IsZero(radii.TopLeft))
                {
                    LeftTop = TopLeft = 0.0;
                }
                else
                {
                    LeftTop = radii.TopLeft + left;
                    TopLeft = radii.TopLeft + top;
                }
                if (MathHelper.IsZero(radii.TopRight))
                {
                    TopRight = RightTop = 0.0;
                }
                else
                {
                    TopRight = radii.TopRight + top;
                    RightTop = radii.TopRight + right;
                }
                if (MathHelper.IsZero(radii.BottomRight))
                {
                    RightBottom = BottomRight = 0.0;
                }
                else
                {
                    RightBottom = radii.BottomRight + right;
                    BottomRight = radii.BottomRight + bottom;
                }
                if (MathHelper.IsZero(radii.BottomLeft))
                {
                    BottomLeft = LeftBottom = 0.0;
                }
                else
                {
                    BottomLeft = radii.BottomLeft + bottom;
                    LeftBottom = radii.BottomLeft + left;
                }
            }
            else
            {
                LeftTop = Math.Max(0.0, radii.TopLeft - left);
                TopLeft = Math.Max(0.0, radii.TopLeft - top);
                TopRight = Math.Max(0.0, radii.TopRight - top);
                RightTop = Math.Max(0.0, radii.TopRight - right);
                RightBottom = Math.Max(0.0, radii.BottomRight - right);
                BottomRight = Math.Max(0.0, radii.BottomRight - bottom);
                BottomLeft = Math.Max(0.0, radii.BottomLeft - bottom);
                LeftBottom = Math.Max(0.0, radii.BottomLeft - left);
            }
        }

        internal double LeftTop;
        internal double TopLeft;
        internal double TopRight;
        internal double RightTop;
        internal double RightBottom;
        internal double BottomRight;
        internal double BottomLeft;
        internal double LeftBottom;
    }
}

file static class MathHelper
{
    internal const double DBL_EPSILON = 2.2204460492503131e-016;

    public static bool IsZero(double value) => Math.Abs(value) < 10.0 * DBL_EPSILON;
}