Please try using this CVS snapshot:

  http://snaps.php.net/php5.2-latest.tar.gz
 
For Windows:

  http://windows.php.net/snapshots/

And use the bundled GD library!

I tried php5.2-200810262330 (PHP 5.2.7RC3-dev), using bundled gd.
There is no difference. The problem is still there, and the image is
the same as in 5.2.6.

Assigned to the GD maintainer.

Lines *do* have the expected style, *EXCEPT* when they are at a 0 or 180 degree angle (e.g. x1==x2).  That is where the 'bug' is at.  This is probably because imageline tries to be more efficient than it should be, drawing a fast rectangle instead of a thick line.

In any case, the style pattern is applied towards the flow of the line instead of linear.  This is the correct approach imho and should not be changed.  To achieve the same style pattern with a line twice as thick you should double your imagesetstyle as well.  E.G. in your test case, 16+4+8+4 for thickness 1 would become 32+8+16+8 for thickness 2.

When you adjust your test case like this, you will see that all works as expected except for horizontal lines.  Thus, GD maintainer, please adjust the inner workings of imageline so it won't paint a rectangle instead of a thick line (at least not for thickness>1 or when using styled lines).

jacQues

OK, thanks, now I understand what it is doing.  It is applying the pixels from the style across the width of the line first, then along the length second. But I don't agree that it is working correctly. I think the width and style should be independent, and I think the current behavior may be unintentional.  Because gdImageSetPixel increments the style pointer for every pixel, then the order in which the higher-level drawing routines put down the pixels makes a difference in how the pattern is applied. Surely this cannot be useful.

As an example, the problem you found with horizontal and vertical lines. If the width is > 1, these are optimized as filled rectangles. But filled rectangles with IMG_COLOR_STYLED are unpredictable, because the result depends on the remainder when dividing the rectangle width by the style array size. (Try drawing 2 filled rectangles with an IMG_COLOR_STYLED pattern, where 1 rectangle is 1 pixel wider than the other. They will look very different.)

I would like to hear what the PHP GD maintainer thinks about this.

(FYI, now using PHP-5.3.3 with same results)

> Lines *do* have the expected style, *EXCEPT* when they are at a
> 0 or 180 degree angle (e.g. x1==x2).

This issue seems to have been fixed in the meantime, see
<http://imgur.com/AIn9RLh>.

> I think the width and style should be independent, and I think
> the current behavior may be unintentional.

Even if it had been unintentional, changing it now would be a
massive BC break. However, I believe the behavior is intentional,
because as it is you can apply 2D styles instead of 1D styles
only. If you have the need for linear styles, you can use a
function such as ImageStyleThicken() contributed by jacQues.

All in all, this issue seems to be a documentation problem. The
imagesetstyle man page should be improved to document how the
function works for thick lines, and probably a respective example
should be added.

I agree that changing the way it works would be bad, and the way it works should be better documented.

I do not agree that the issue raised by "jacQues" has been fixed. After replicating my pattern bits by the line thickness, as stated in that comment, I do see reasonable thick styled lines, except for horizontal lines.  Horizontal thick lines patterns look scrambled to me.  (jacQues said in 2010 that vertical lines were also bad. I don't see that now - my vertical lines seem OK.)

Now using php-5.6.8; same results with php-5.5.24.

Sorry for the late reply.

> Horizontal thick lines patterns look scrambled to me.

Indeed! I had a closer look at the issue, and found that
horizontal and vertical lines do call gdImageFilledRectangle when
the thickness is greater than 1 for performance reasons.

The relevant code of gdImageFilledRectangle[1] loops over the x
and y coordinates, and calls gdImageSetPixel which iterates over
the style pattern[2]. As is, this works fine for vertical lines,
but not for horizontal lines. Swapping the for loops in
gdImageFilledRectangle will make horizontal lines look fine, but
will break vertical lines.

I'm not sure (yet) how to solve this issue, but anyhow, this is an
issue that should preferably be fixed upstream in libgd. I'll file
a bug report there later, and switch this ticket to "suspended"
until a resolution is found.

[1] <https://github.com/php/php-src/blob/PHP-5.6.9/ext/gd/libgd/gd.c#L2145-L2149>
[2] <https://github.com/php/php-src/blob/PHP-5.6.9/ext/gd/libgd/gd.c#L724-L735>

I have filed a ticket against libgd now.

I've noticed a minor issue wrt. to jacQues' ImageStyleThicken()
function: it only works correctly for even thickness values,
because libgd rounds odd thickness values to the next smaller even
value.

The libgd ticket: <https://github.com/libgd/libgd/issues/167>.

The bug has been fixed in libgd, so I'm reopening.