Android Question DrawPath() problem with Clipping? [SOLVED]

W. Graf

Licensed User
Longtime User

I'm having a question about ImageView, Canvas and DrawPath().

I want to draw multiple lines with DrawPath with this Code (see also attachment for a demo):

Dim canvas1 As Canvas

Dim PolygonPath As Path
PolygonPath.Initialize (64,154)
PolygonPath.LineTo (113,234)
PolygonPath.LineTo (193,114)
PolygonPath.LineTo (203,80)
PolygonPath.LineTo (293,54)
PolygonPath.LineTo (423,24)

canvas1.DrawPath(PolygonPath,Colors.Cyan, False, 12dip)

Problem 1: there is often something like a "gap" in the line. If I remove a few points in the middle, then the gap sometimes disappears ... but this is no solution, because I need the points ;-)
Problem 2: the line on the end (on the right) is conical? Why is it not "normal" (angular)?

After many hours of investigation, I found the reason for it: ClipPath() and RemoveClip().
My first I thought: "Ok, I remove the lines and everything is working fine". And it really worked fine!

Do you know some reason, why I should use these lines?
I found the code above many months ago. Somebody posted it in a thread in this forum for a demo. Since I found this thread, I used it as template. But I never knew, why I have to use the clipper?

Do you think, it is bad, not to use the clipping-functions?

Thank you!!
BR Wolfgang


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Licensed User
Longtime User
What exactly do you want to achieve?
Clipping is used if you want to limit the surface of the drawing.

Your PolygonPath is not a polygon, its a polyline, its not closed.
To get a polygon you need to add at the and a LineTo to the first point!

In your case, if you want to draw the polyline you must not use ClipPath and RemovePath!

Attached your modified project showing the differences.


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W. Graf

Licensed User
Longtime User
Hi Klaus,

thanks a lot. Great demo!!!

Polygon: you are right, it is a polyline (-> copy&paste-error).

Ok, it's good to know about the B4A-canvas-limitation. I have no problem about this - I only want to know it ;-)

Up to now, I totally misunderstood the Clipping-functions. But because of your demo, I understand what it is now.
Many many thanks for your time and work!!

Have a great weekend!
BR Wolfgang
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