PolyLine problems
lazarus / 39-Graphics

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mtanner · 2017-01-07 18:08

I have a simple component, created in code, based on TGraphicControl,
also tried TPaintBox.  Just to start, I'm just trying to draw a line
around the canvas area, with thickness of the line set by a variable,
call it PenWidth. In the Paint routine I set up the Pen, and then
have:

var TestPoints:array[0..4] of TPoint;
var XL,XR,YT,TB:integer;

XL:=PenWidth;
XR:=Width-PenWidth;
YT:=PenWidth;
YB:=Height-PenWidth;

TestPoint[0]:=TPoint(XL,YT);
TestPoint[1]:=TPoint(XR,YT);
TestPoint[2]:=TPoint(XR,YB);
TestPoint[3]:=TPoint(XL,YB);
TestPoint[4]:=TPoint(XL,YT);

Canvas.PolyLine(TestPoints);

My problem is that I get a line across the top, and down the left side
of the canvas area. However much I try reducing the values of XR and
YB (so they are definitely within the canvas area) the lines do not
appear.

I think I must be doing something idiotic. This is such a simple
problem I just cannot see why it's not working.

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bytebites · 2017-01-07 19:10

You fill TestPoint-array and paint TestPoints-array.

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derek.john.evans · 2017-01-08 04:13

Try using moveto/lineto's and see if you get what you want.

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mtanner · 2017-01-08 08:38

Thanks for the comments. I discovered what the problem, or at least
the solution, is.

Height and Width of the control seem unreliable. If I use
ClientRect.Right and ClientRect.Bottom instead, then I get the results
I expect. Though I do not understand why the Height/Width of the
control shouldnot work ok.