Drawing a Symbol at different locations

[whugemann]

I would like to draw arrows with varying orientation and location onto an image. My basic code is

double oX = 100;
double oY = 100;
using var image = new MagickImage(MagickColors.White, 200, 200);
PointD[] points = new PointD[7] {
new PointD( oX-40, oY+10 ), new PointD( oX+0, oY+10 ), new PointD( oX+0, oY+30 ),
new PointD( oX+40, oY+0 ),
new PointD( oX+0, oY-30 ),new PointD( oX+0, oY-10 ), new PointD( oX-40, oY-10 ) };

DrawablePolyline pl = new DrawablePolyline(points);
image.Draw(pl);
image.Write(@"C:\tmp\__Gutachten\wmpr2\arrow.png"); 

and it's functioning. Of course it would be more straightforward if I would define the 'pure' arrow and assign the offset (an possibly orientation) later, preferably in a function with the object and the desired location and orientation as parameters.

The PointD list is however write protected; this is why I directly calculated the absolute coordinates when creating the list.

Using the SVG version of IM's drawing strategies, which directly uses relative coordinates, moving the arrow symbol becomes easier, the essential part of the code now being:

PointD[] points = new PointD[7] {
new PointD( 0, -10 ), new PointD( 40,   0 ), new PointD( 0, -20 ),
new PointD( 20, 25 ),
new PointD( -20, 25 ),new PointD( 0, -20 ), new PointD( -40, 0 ) };

var paths = new List<IPath>
{
   new PathMoveToAbs(new PointD(50, 50)),
   new PathLineToRel(points.ToList()),
   new PathMoveToAbs(new PointD(100, 100)),
   new PathLineToRel(points.ToList())
};

using var image = new MagickImage(MagickColors.White, 200, 200);
DrawablePath pt = new DrawablePath(paths);
image.Draw(pt);

AFAIK, SVG doesn't offer a mechanism to rotate the coordinate system (?). Again, the PointD list is write protected.
So, what's the strategy for rotating the arrow symbol?

[dlemstra]

How would you do this on the command line?

[whugemann]

I don't think that there is a way to do that directly on the command line.

In my original solution in VB Script, which I now try to transfer to C#/Magick.NET, I had a two-dimensional field Point(7,5) for the vertex coordinates and transformed / scaled these as needed, writing them into another field, which I then used to construct the command line.
What seems to hinder me in C# is the fact that PoinD.X and .Y are only readable once you have created a new instance.

Maybe the solution in C# is obvious and I just don't see it.

[dlemstra]

Aah okay just wanted to make sure you didn't have an issue translating something from the command line to C# code. I made classes immutable where that made sense. But now I am wondering if I should not allow you to change the values of a PointD element. Looking at the code I don't see a good reason why you are not allowed to do this.

[whugemann]

I really wondered why you made PointD immutable, but I attributed this to my lack of understanding of the details ...

[dlemstra]

I pushed a patch to make it mutable and that will come available in the next release.