private GradientLine GetGradientLine(SKRectI boxBounds, double angleDegrees)
{
// Calculation
// https://medium.com/@patrickbrosset/do-you-really-understand-css-linear-gradients-631d9a895caf
var angleRadians = GradientMath.ToRadians(GradientMath.FromDegrees(angleDegrees));
var lineLength =
Math.Abs(boxBounds.Width * Math.Sin(angleRadians)) +
Math.Abs(boxBounds.Height * Math.Cos(angleRadians));
var center = new SKPoint(boxBounds.MidX, boxBounds.MidY);
var yDiff = (float)(Math.Sin(angleRadians - Math.PI / 2) * lineLength / 2);
var xDiff = (float)(Math.Cos(angleRadians - Math.PI / 2) * lineLength / 2);
return(new GradientLine
{
Start = new SKPoint(
center.X - xDiff,
center.Y - yDiff),
End = new SKPoint(
center.X + xDiff,
center.Y + yDiff),
Length = lineLength,
Angle = angleRadians
});
}
public double CalculateRenderOffset(double offset, int width, int height)
{
// Here the Pythagorean Theorem + Trigonometry is applied
// to figure out the length of the gradient, which is needed to accurately calculate offset.
// https://en.wikibooks.org/wiki/Trigonometry/The_Pythagorean_Theorem
var angleRad = GradientMath.ToRadians(_gradient.Angle);
var computedLength = Math.Sqrt(Math.Pow(width * Math.Cos(angleRad), 2) + Math.Pow(height * Math.Sin(angleRad), 2));
return(computedLength != 0 ? offset / computedLength : 1);
}
internal bool TryConvertTurnToAngle(string token, out double angle)
{
if (token.TryExtractNumber("turn", out var turn))
{
angle = GradientMath.FromDegrees(360 * turn);
return(true);
}
angle = 0;
return(false);
}
internal bool TryConvertTurnToAngle(string token, out double angle)
{
if (Offset.TryExtractNumber(token, "turn", out var turn))
{
angle = GradientMath.RotateBy180(360 * turn);
return(true);
}
angle = 0;
return(false);
}
internal bool TryConvertDegreeToAngle(string token, out double angle)
{
if (token.TryExtractNumber("deg", out var degrees))
{
angle = GradientMath.FromDegrees(degrees);
return(true);
}
// For "0" deg is optional
if (token.Equals("0", StringComparison.OrdinalIgnoreCase))
{
angle = GradientMath.FromDegrees(0);
return(true);
}
angle = 0;
return(false);
}
private string GetGradient(Gradient gradient)
{
if (gradient is LinearGradient linear)
{
var type = linear.IsRepeating ? "repeating-linear-gradient" : "linear-gradient";
var angle = $"{GradientMath.FromDegrees(linear.Angle)}deg";
return($"{type}({angle}, {GetColors(linear)})");
}
if (gradient is RadialGradient radial)
{
var type = radial.IsRepeating ? "repeating-radial-gradient" : "radial-gradient";
return($"{type}({GetShapeAndSize(radial)} {GetPosition(radial)}, {GetColors(radial)})");
}
return(string.Empty);
}
public void CalculateGeometry(ILinearGradient gradient, RectangleF boxBounds)
{
// Calculation
// https://medium.com/@patrickbrosset/do-you-really-understand-css-linear-gradients-631d9a895caf
var angleDegrees = gradient.Angle;
var angleRadians = GradientMath.ToRadians(GradientMath.RotateBy180(angleDegrees));
var lineLength =
Math.Abs(boxBounds.Width * Math.Sin(angleRadians)) +
Math.Abs(boxBounds.Height * Math.Cos(angleRadians));
var center = boxBounds.Center;
var yDiff = (float)(Math.Sin(angleRadians - Math.PI / 2) * lineLength / 2);
var xDiff = (float)(Math.Cos(angleRadians - Math.PI / 2) * lineLength / 2);
Start = new PointF(center.X - xDiff, center.Y - yDiff);
End = new PointF(center.X + xDiff, center.Y + yDiff);
Length = lineLength;
Angle = angleRadians;
}
