Stroke has incorrect geometry when the thickness is very large

[alexeevilya]

Hi, guys! I've got a problem when trying to scale the stroke, keeping the thickness. When I change the stroke thickness to some large value, it draws incorrectly.

Please, look at the picture:

Here is project src:
https://www.dropbox.com/s/om7v84i2iibpp53/pathTest.zip?dl=0

Thanks!

[alexeevilya]

Another artifact:

I think it has the same cause.

[IonSwitz]

Yeah, setting the thickness to a large value ( you dont have to scale the stroke to make it appear) can make the joints degenerate. It is an unfortunate side effect of the math code. The rectangles that are created to draw the lines become overlapped and it looks very bad.

You can try to solve the same problem by drawing 2 quadrilaterals on a piece of paper to fit every type of joint in every angle. It rapidly becomes very hard to make the joint look good without overdraw or disfigured shapes as a result :)

[alexeevilya]

Ion, thanx, but are you sure that nothing can be done? (until a certain scale, everything looks great).
For my app it is a catastrophic problem (

[IonSwitz]

What is the actual problem you are trying to solve?

Is it the scaling? Or is it when you need to draw lines with many control points?

If it is the scaling, you can do the scaling math on the vertices of the Stroke yourself, before you add them as vertices to the Stroke, and keep the thickness constant (and small) so the artifacts aren't as visible.

In the second example, what is the goal there? If you wish to draw smooth curves, check out the ShapeEx.graphics.NaturalCubicSplineTo method

[IonSwitz]

Well, I have to agree that I do find something odd that goes beyond what should be expected when the line turns on itself with large thickness... There is definitely something wrong. I will try to look into it, even though I doubt I will find the bug tonight.

[IonSwitz]

Could you please test with the following additional code:

                if ( elbowThickness > d0 )
                    elbowThickness = d0;
                if ( elbowThickness > d1 )
                    elbowThickness = d1;

Add that to the Stroke class, around line 353, as the last four lines in the "if ( treatAsRegular )" statement.

I know this is probably cumbersome for you to test, but I would like to see the effect of this on the problems you are seeing. I don't want to submit it as a fix, but it seems to make some of my test cases look better (if not perfect)

Just let me know what happens, ok?

[alexeevilya]

Ion, Thank you very much for your care and help to solve this problem! Unfortunately, that kills one problem, but born another. There's a new artifact:

In the real application, it looks like this,
before:

after:

[IonSwitz]

Ah, ok. Can I ask you how many points you have per stroke in your "real" application? It looks like a program to map sailing boats, perhaps?

The original problem occurs when the thickness of a joint gets thicker than the distance of the line segments, and the fix tried to correct that. It seems to me that you have a very large amount of data points in your "real" application, making each line segment between two vertices pretty small compared to the thickness?

IF that is the case, the thickness will rapidly get thicker than each line segment, and what I would do in that case would be to "clean" the input data, removing points that are (more or less) on the same line, or points that create "dents" in the line.

[IonSwitz]

If you try this instead:
if ( elbowThickness > d0 )
elbowThickness = vThickness;
if ( elbowThickness > d1 )
elbowThickness = vThickness;

could you let me know the difference?

[alexeevilya]

Ion, yes, it is a sailing boats map application. As for the number of vertices, then I use simplify algorithm, and there is a one vertex for the one really map point after simplifying.
Sorry for my English, one moment ... ;)

[IonSwitz]

Don't worry about your English, I understand you fine. I am sorry I can't help you very well.

[alexeevilya]

Thank you, now I'm testing the new changes by you.

[alexeevilya]

Oh my God! ;)

[alexeevilya]

By the way, my other sandbox to test an application is project, that reference is attached above.
https://www.dropbox.com/s/om7v84i2iibpp53/pathTest.zip?dl=0

[IonSwitz]

The lines get very thin in some places, but the bad joints look better.. Hmmm..