strokewidth

[rmabry]

Here's a nit-picky little thing (I'm using 6.3.1). If you don't specify -stroke on the command line, then setting -strokewidth has no effect and a strokewidth of 1 is produced (in the default stroke color black). So the following produces a black line of strokewidth 1.

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convert logo: -strokewidth 10 -draw "line 30,30 60,30" ...

This seems wrong. Of course, adding -stroke black gives the expected result.

On the other hand, in PerlMagick one can omit the stroke color and get the correct stroke width:

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$image->Draw(strokewidth =>10, primitive => 'line', points => '30,30 60,30')

Rick

[rmabry]

Here's a nit-picky little thing (I'm using 6.3.1).

Here's something less picky, more complicated.

There seems to be an inconsistency in the type of lines produced with various strokewidths. In the following image, the numbers correspond to the strokewidths set for various Draw/line/strokewidth commands for vertical line segments starting at integer coordinates. The top set of line segments is produced by setting strokewidth, the bottom set are segments whose width matches the number, for comparison. All lines start



(A magnified version is here.)

The results:

• 0: A strokewidth set to 0 gives a drawn stroke of width 1, so it is as if the strokewidth were set to 1. In my view, a strokewidth explicitly set to zero should give no drawing.
  
  1, 3, 5, etc: Odd strokewidths are fine.
  
  2: Anomolously, this produces an antialiased line centered at y+0.5, not a bad result, splitting the difference in this way. But ...
  
  4, 6, 8, etc: All of these produce segments of widths one greater than the strokewidth (i.e., widths 5, 7, 9, etc.), which seems just plain wrong.

Moreover, the strokewidth of 2 seems to give a rounded cap at the endpoints, while none of the higher widths do this.

I'm stroking out here.

Rick

[magick]

It always a question of default values. By default fill is set to opaque black and stroke is transparent. This was reversed in PerlMagick but for sake of consistency between the command line and PerlMagick was patched recently so both produce the same result. The secret to success is to specify precisely what you want such as -fill none -stroke red -strokewidth 10.

[magick]

We're aware of problems with strokewidth. We have not come up with a solution just yet. You are welcome of course to take a look at magick/drawing.c and fix the problem. Its perplexed us for a number of years now and we wrote the code!

[rmabry]

You are welcome of course to take a look at magick/drawing.c and fix the problem.

I looked. I shrank back in horror! Actually, I remember looking at this a long time ago and feeling more brave. It is a heroic undertaking to attempt this. I am no hero.

Its perplexed us for a number of years now and we wrote the code!

I have years of back-perplexedness in other areas I must look to first, but thanks for the kind offer! I wish I did have time for it because I now need an accurate version of the stroke. I'll ponder other solutions meanwhile.

Rick

[anthony]

You can also read all about this in the IM Examples....
Drawing Lines, Line Width and Stroke
http://www.cit.gu.edu.au/~anthony/graph ... trokewidth

The example set above this on some of the weirder stroke effects (at '-strokewidth 0' is also a good read.

what actually happend for lines is they are drawn twice, once with fill and once with stroke.
The fill produces thin lines. the stroke produces a controled thick line, weird but it is versitle and it works.