/// <summary>
/// Converts a LineString in world coordinates to a Skia path
/// </summary>
/// <param name="coordinates">List of points in Mapsui world coordinates</param>
/// <param name="viewport">Viewport implementation</param>
/// <param name="clipRect">Rectangle to clip to. All lines outside aren't drawn.</param>
/// <returns></returns>
public static SKPath ToSkiaPath(this LineString lineString, IReadOnlyViewport viewport, SKRect clipRect)
{
var coordinates = lineString.Coordinates;
// First convert List<Points> to screen coordinates
var vertices = ClippingFunctions.WorldToScreen(viewport, coordinates);
var path = new SKPath();
var lastPoint = SKPoint.Empty;
for (var i = 1; i < vertices.Count; i++)
{
// Check each part of LineString, if it is inside or intersects the clipping rectangle
var intersect = ClippingFunctions.LiangBarskyClip(vertices[i - 1], vertices[i], clipRect, out var intersectionPoint1, out var intersectionPoint2);
if (intersect != ClippingFunctions.Intersection.CompleteOutside)
{
// If the last point isn't the same as actual starting point ...
if (lastPoint.IsEmpty || !lastPoint.Equals(intersectionPoint1))
{
// ... than move to this point
path.MoveTo(intersectionPoint1);
}
// Draw line
path.LineTo(intersectionPoint2);
// Save last end point for later use
lastPoint = intersectionPoint2;
}
}
return(path);
}
/// <summary>
/// Converts a Polygon into a SKPath, that is clipped to clipRect, where exterior is bigger than interior
/// </summary>
/// <param name="polygon">Polygon to convert</param>
/// <param name="viewport">Viewport implementation</param>
/// <param name="clipRect">Rectangle to clip to. All lines outside aren't drawn.</param>
/// <param name="strokeWidth">StrokeWidth for inflating clipRect</param>
/// <returns></returns>
public static SKPath ToSkiaPath(this Polygon polygon, IReadOnlyViewport viewport, SKRect clipRect, float strokeWidth)
{
// Reduce exterior ring to parts, that are visible in clipping rectangle
// Inflate clipRect, so that we could be sure, nothing of stroke is visible on screen
var exterior = ClippingFunctions.ReducePointsToClipRect(polygon.ExteriorRing?.Coordinates, viewport, SKRect.Inflate(clipRect, strokeWidth * 2, strokeWidth * 2));
// Create path for exterior and interior parts
var path = new SKPath();
if (exterior.Count == 0)
{
return(path);
}
// Draw exterior path
path.MoveTo(exterior[0]);
for (var i = 1; i < exterior.Count; i++)
{
path.LineTo(exterior[i]);
}
// Close exterior path
path.Close();
foreach (var interiorRing in polygon.InteriorRings)
{
// note: For Skia inner rings need to be clockwise and outer rings
// need to be counter clockwise (if this is the other way around it also
// seems to work)
// this is not a requirement of the OGC polygon.
// Reduce interior ring to parts, that are visible in clipping rectangle
var interior = ClippingFunctions.ReducePointsToClipRect(interiorRing.Coordinates, viewport, SKRect.Inflate(clipRect, strokeWidth, strokeWidth));
if (interior.Count == 0)
{
continue;
}
// Draw interior paths
path.MoveTo(interior[0]);
for (var i = 1; i < interior.Count; i++)
{
path.LineTo(interior[i]);
}
}
// Close interior paths
path.Close();
return(path);
}
