Re: [WWdevel] Re: [webwork-user] Re: pdf generation problem and image problem

[Arnold P. <ap...@ma...>]

At 11:18 PM 8/29/2005, Sam Hathaway wrote:

I just uploaded the following change to Constants.pm

################################################################################
# WeBWorK::PG::ImageGenerator
################################################################################

# Arguments to pass to dvipng. This is dependant on the version of dvipng.
#
# For dvipng versions 0.x
#     $WeBWorK::PG::ImageGenerator::DvipngArgs = "-x4000.5 -bgTransparent 
-Q6 -mode toshiba -D180";
# For dvipng versions 1.0 to 1.5
#     $WeBWorK::PG::ImageGenerator::DvipngArgs = "-bgTransparent -D120 -q 
-depth";
#
# For dvipng versions 1.6 (and probably above)
#     $WeBWorK::PG::ImageGenerator::DvipngArgs = "-bgtransparent -D120 -q 
-depth";
# Note: In 1.6 and later, bgTransparent gives alpha-channel transparency while
# bgtransparent gives single-bit transparency. If you use alpha-channel 
transparency,
# the images will not be viewable with MSIE.  bgtransparent works for 
versions lower
# than 1.6, but does not give transparent backgrounds.
#
$WeBWorK::PG::ImageGenerator::DvipngArgs = "-bgtransparent -D120 -q -depth";

I think this is a reasonable compromise. Note that at least for dvipng 1.5 
there is a difference between
-bgTransparent and -bgtransparent but at least both do work.  When I looked 
for documentation all I found
was "-bg s" where "s" is TeX-style colors but I never found a list of 
TeX-style colors.

Arnie

>On Aug 29, 2005, at 20:02, Davide P.Cervone wrote:
>
>>>>If you change -bgTransparent to -bgtransparent (i.e., remove the
>>>>capitalization)
>>>
>>>Is this a bug in Constants.pm?
>>
>>No, it's a bug in MSIE.  :-)
>>
>>In dvipng prior to version 1.6, both forms meant the same thing.
>>In 1.6 and later, the first gets you alpha-channel transparency
>>while the second gets your single-bit transparency.  While every
>>other modern browser handles alpha-channel transparency, MSIE only
>>does this if you include a horrible proprietary call to a special
>>image filter that references the alpha image and link the source
>>image to a blank image file (if I remember correctly).  I would
>>love to switch to alpha-channel transparency so that the background
>>colors work better, but as long as we are saddled with the
>>lumbering and decrepit beast known as MSIE, we have to dump down to
>>its (in-)capabilities.  Not that I'm upset by this.  >:-p
>>
>>The upshot is, though, that Constants.pm probably should have the
>>lower-case transparency to avoid the alpha-channel problem.
>
>Right, that's what I meant. -bgTransparent is not a valid switch to
>dvipng, so Constants.pm is wrong.
>  -sam
>
>
>

Prof. Arnold K. Pizer
Dept. of Mathematics
University of Rochester
Rochester, NY 14627
(585) 275-7767