This is part of The Pile, a partial archive of some open source mailing lists and newsgroups.
Date: Wed, 8 May 2002 01:42:42 -0700 From: Michael A Nachbaur <mike@nachbaur.com> To: modperl@apache.org Subject: [RFC] Dynamic image generator handler This is an request for comments. If you don't care about dynamic image generation with mod_perl, or don't care about offering or reading about suggestions, you can safely ignore this. Also, be forewarned, this was written in StarOffice, and then copied/pasted into my email program, and hand tweaked, so some things may not have made the transition properly. Dynamic Image Manipulator ------------------------- *) Overview This is a mod_perl handler, not directly tied in with my content management system, but is/will be used extensively by it. The premise is to dynamically generate images, cache them, and present them to browser clients. The URI, as well as Apache configuration directives, is used to determine what is to be generated. *) Basic Uses The most basic uses of this application will to dynamically generate TTF text for titles, buttons, sidebars, etc. The current version of this code does this, and quite well. Foreground and background colors, font name (with bold/italic support), font size, image size (or automatically detected based on the size of the text), and rotation. The basic text support could be extended to allow for images to be overlayed on the text (or placed under the text), or stretch images similarly to how Enlightenment displays window manager themes. Other uses planned would be to manipulate existing images. For instance, if an image on a website needs a thumbnail, medium size and full-size view, normally a person must make all versions by hand. If any formatting needs to be done, like borders or drop-shadows, this increases complexity. If a person could just drop an image in a directory, and link to that image, the image could automatically be resized, borders added, drop shadows put in place. The resulting image would then be cached, and outputted. *) URI Arguments Information about what is to be done is passed through the URI. This works for simple tasks like text display, but if anything more complicated is to be done, external configuration files must be used. We'll get to that in a bit. Essentially, arguments are passed using the PATH_INFO HTTP header. We want the browser to think this is an actual file, instead of a dynamically generated image, so that the browser is more inclined to cache the content. So, a typical query would be: http://localhost/genText/font=ArialBold;size=24;fgcolor=#ffffff; bgcolor=#000000;rotate=90;text=This+Is+The+Text Resizing an image could be accomplished by doing: http://localhost/genImage/source=/images/ducks.jpg;scale-ratio=1:1; width=120;height=80;border-size:1px;border-color:#000000; shadow-color:#000000;shadow-angle:270;shadow-distance:5px This would resize an image to the indicated width/height. The "scale-ratio" argument would limit the width/height ratio, so the maximum dimension would be used. The other attributes are obvious. *) Configuration Files Lets assume that we are going to scale an image, add borders to it which consist of other images, and add text captions over the image. This would result in such a long URI, that browsers would probably truncate it. In addition, providing direct access to the browser opens up possibilities for DoS attacks. Therefore, a configuration file should be used. The config file must be flexible enough to allow a web page to provide various input, but have certain defaults set, and restricted. The proposed solution would be to have a config file that has preset default templates that the input arguments augment. For instance: <genimage> <preset name="thumbnail-image"> <image> <style> border-style: solid; border-color: #000000; border-width: 1px; shadow-distance: 5px; shadow-angle: 270; <!-- or something like 1.2rad --> shadow-color: #000000; </style> <content name="src"/> </image> <image> <style href="/css/watermark.css"/> <!-- The above-referenced file has the following contents: opacity: 80%; position: top; --> <content>/images/watermark.gif</content> </image> <text> <style> font-face: Arial; font-size: 10px; color: #000000; border-style: solid; border-color: #ffffff; opacity: 80%; text-align: right; </style> <content>Copyright © 2002 Foo Bar Industries</content> </text> <text> <style> font-face: Arial; font-size: 14px; color: #ffffff; text-align: left; position: top; </style> <content name="date"/> </text> </preset> </genimage> As you can see, the above configuration file uses CSS. It makes sense to leverage that, although I'm not certain how difficult it would be to interface with CSS files. As far as I know, there are Perl CSS parsers, but I have yet to use them. The configuration for a preset config template would be layered, so the earlier the definition, the lower the layer is. The real important part here, is the "name" attribute of any element, as this identifies where input can be indicated. The above preset could be used by invoking the following URI. http://localhost/genImage/preset=thumbnail-image;src=/images/ducks.jpg As you can see, the preset is invoked by passing it's name as an attribute, and any element that has a name attribute, it's value can be provided on the URI. If an element has both a value and a name attribute, the value in the config file can be used as a default. *) Caching Schemes A caching scheme similar to AxKit could be used. The current module takes all the input arguments, sorts them (including all values that are not provided, for completeness), and takes it's MD5 checksum. That becomes the image's filename on the system. It is placed in a temporary directory, and any further requests to that same URI, the file is pulled from the filesystem without regenerating the image. Further, the code has been blatantly ripped off from AxKit, which separates the directory into two sub-levels, to prevent performance problems of having too many files in one directory. Note: To prevent the filesystem from filling up, due to DoS attacks, it may be prudent to have a cron job periodically cull files that have the oldest access time. *) Image Manipulation Modules My current code uses GD for text writing, and I'm quite happy with it. It is extremely fast, and creates nice text output when compiled with a TTF font engine. Looking forward however, it may not be as desirable if things like drop shadows is to be done. GD can work with multiple images, can resize them, etc, but the advanced features are still unknown. *) File Expiration Headers and Browser Caching With my current code, it seems that browsers are reluctant to cache these dynamically generated images. I have passed Expires: headers to tell the browser to cache file file for a long period of time (2+ weeks), but I have been unsuccessful. I know the caching headers are complex, and needs more than one simple header, but fixing this has moved to the back-burner of my project. However, if more complicated processing is to be done, and with more images, it will be crucial to make browsers cache these images. *) Current and Future Uses Currently, the few production sites I have running my TTF text image code, perform quite well, if a little slow on loading toolbar images and the like; this should be improved with proper HTTP caching headers. It has proven very convenient. I build sites for customers using XML and XSL, with an XML configuration file describing the "sitemap" layout. This way, a document can have a tag indicating which sitemap location it occupies, and breadcrumb trails, sidebar sitemap trees, title bar text and page titles all can be displayed without any per-page editing. The addition of the TTF image code is wonderful, because now I can even have section titles, often placed in toolbars or headers, generated dynamically. I have recently released version 1.0 of an all-XML content management system (although it is not yet available for public use...sorry), and this means people can edit their entire site, not just plain text. They can completely change their sitemap structure interactively, and all site images relating to the sitemap automagically change. Looking forward, I would like to be able to use this for more than just text. I'd like my customers to be able to select an image, set the maximum size, check a few boxes or radio buttons to say what formatting options they'd like, and the image is automagically resized without wasting disk space or taking a long time to download. It also saves me, as a web developer, from having to mess around with adding borders, drop shadows, and other menial changes to an image every time the customer gets it into their head to add a new picture. I'm sure there are plenty of other uses for this, but I'll leave it at this. I have another, similar image module, which generates web-based graphs using the same sort of URI structure, but it is severely limited. It is a component of my content management system used to show a user how much space of their quota is used (3D pie chart). *) Summary I have to make some subtle feature additions to this code within the next few weeks (months?), and instead of just performing a knee-jerk reaction and hacking on some cruft to my existing module, I wanted to open this up to the mod_perl developer community as a whole, to see if this is something others can use. If you like the idea, good for you. If you have constructive suggestions, I'd like to hear them (no "Images suck, use Lynx" comments please). If you would like to help, have the time to help, and have the skills necessary, please let me know because many eyes make all bugs shallow. === Date: Fri, 10 May 2002 08:32:55 +0200 From: Robert <robert@robert.cz> To: Michael A Nachbaur <mike@nachbaur.com> Subject: Re: [RFC] Dynamic image generator handler Take a look at Apache::ImageMagick - Robert (I'm using it to generate truetype titles and thumbnails at http://www.jalta.cz/ and it works fine) === Date: Fri, 10 May 2002 10:52:31 +0100 (BST) From: Mark Fowler <mark@twoshortplanks.com> To: Michael A Nachbaur <mike@nachbaur.com> Subject: Re: [RFC] Dynamic image generator handler On Wed, 8 May 2002, Michael A Nachbaur wrote: With regard to dynamic image creation > The most basic uses of this application will to dynamically generate TTF > text for titles, buttons, sidebars, etc. The current version of this > code does this, and quite well. Foreground and background colors, font > name (with bold/italic support), font size, image size (or automatically > detected based on the size of the text), and rotation. I've been working on something like this using GD. Mainly I've been thinking about the interface which (as always) seems to the hardest thing to do properly. It's not an Apache module (though it is designed with mod_perl in mind.) Some form of wrapping module would have to go around it. Hmm. How about I upload the POD so you can see what I mean. htpp://2shortplanks.com/temp/gdti/ Note that this is a work in progress. This code doesn't work yet (though previous hacky versions did.) Yours sounds much more advanced. > The basic text support could be extended to allow for images to be > overlayed on the text (or placed under the text), or stretch images > similarly to how Enlightenment displays window manager themes. Hmm, yes. I have it so the image can be aligned in various ways. It's not quite up to stretching it yet, but we shall see. > Other uses planned would be to manipulate existing images. For instance, > if an image on a website needs a thumbnail, medium size and full-size > view, normally a person must make all versions by hand. If any > formatting needs to be done, like borders or drop-shadows, this > increases complexity. If a person could just drop an image in a > directory, and link to that image, the image could automatically be > resized, borders added, drop shadows put in place. The resulting image > would then be cached, and outputted. Hmm, getting a little complicated here. My program outputs a GD::Image object when done. The idea is that you can then use GD to implement any of the things you're missing. Also, the stages where it draws the background, the border, the text, and so on are all different methods. This allows you to override these methods with your own ones in subclasses, so you can intercept the image creation at various stages and step in to do things first (e.g. draw to the background before the bg image is drawn) > *) URI Arguments > > Information about what is to be done is passed through the URI. This > works for simple tasks like text display, but if anything more > complicated is to be done, external configuration files must be used. > We'll get to that in a bit. I was working on several different encoding schemes that you could use on the URL. Primarily these were: * Base64 alike encoding * A scheme where " " was replaced with "_" and entities could be used Primely I'm only concerned about the text that you want rendered. Everything else was going to be read from a config file/set in the httpd.conf. I was also planning to implement Template Toolkit plugins to allow you to easily create these images. > Essentially, arguments are passed using the PATH_INFO HTTP header. We > want the browser to think this is an actual file, instead of a > dynamically generated image, so that the browser is more inclined to > cache the content. So, a typical query would be: > > http://localhost/genText/font=ArialBold;size=24;fgcolor=#ffffff; > bgcolor=#000000;rotate=90;text=This+Is+The+Text This is indeed a key concept. More importantly I designed my schemes so that they could actually be saved to disk with that filename. One possible idea would be to place the image creation in an ErrorHandler which returns the image and writes it to the correct location on disk. Thus the next time the image is called the perl code is skipped all together and the image is simply sucked off of the disk. I think Randal did a column on something like this a while back. > *) Configuration Files I was thinking of using a system accessible in the httpd.conf for the apache module. > The real important part here, is the "name" attribute of any > element, as this identifies where input can be indicated. In my scheme each location was a different font. So: http://twoshortplanks.com/f/xmason/1st.jpg Is the image "1st" in the "xmason" style. (yes, that link works) An important aspect is that styles in my system can be created from other styles using the ->clone() method. So for example, to create heading2 you could use: my $heading2 = $heading1->clone(text_size => ($heading1->text_size() * 0.8)); All the other attributes would stay the same (colour, background image etc, etc.) The configuration file should reflect that. > *) Caching Schemes I hadn't really considered caching systems. Sounds good. > Note: To prevent the filesystem from filling up, due to DoS attacks, it > may be prudent to have a cron job periodically cull files that have the > oldest access time. Or have the handler do it itself after it's returned an image. You'd also want the handler to keep a scoreboard of how many images have been generated in the last x minutes to stop generating for things like runaway spiders (though OTOH, this could probably be better handled by another module somewhere else in the chain) > My current code uses GD for text writing As does mine. TBH, the hardest thing I had was designing the interface and doing the maths to work out where everything goes when you've got several competing criteria manipulating the image. The underlying image system wasn't that important. I'd considered renaming GD::TextImage to TextImage::GD should TextImage::ImageMagick etc should happen. > *) File Expiration Headers and Browser Caching Not even considered. > *) Current and Future Uses > I have recently released version 1.0 of an all-XML content management > system (although it is not yet available for public use...sorry), and > this means people can edit their entire site, not just plain text. They > can completely change their sitemap structure interactively, and all > site images relating to the sitemap automagically change. I was planning to do something similar with Template Toolkit and the XML::XPath plugin. > Looking forward, I would like to be able to use this for more than just > text. I'd like my customers to be able to select an image, set the > maximum size, check a few boxes or radio buttons to say what formatting > options they'd like, and the image is automagically resized without > wasting disk space or taking a long time to download. Disk space cheap, CPU cycles expensive. > I'm sure there are plenty of other uses for this, but I'll leave it at > this. I'm warey of creating a all too powerful module. It's taken me an age to come up with an interface that I think (IMHO) that has a sensible user interface. I wouldn't want to create something too powerful. I've left hooks in my code. That's all I can do. > I have to make some subtle feature additions to this code within the > next few weeks (months?), and instead of just performing a knee-jerk > reaction and hacking on some cruft to my existing module, I wanted to > open this up to the mod_perl developer community as a whole, to see if > this is something others can use. It sounds good to me. Later. Mark. -- s'' Mark Fowler London.pm Bath.pm http://www.twoshortplanks.com/ mark@twoshortplanks.com ';use Term'Cap;$t=Tgetent Term'Cap{};print$t->Tputs(cl);for$w(split/ +/ ){for(0..30){$|=print$t->Tgoto(cm,$_,$y)." $w";select$k,$k,$k,.03}$y+=2} === To: Michael A Nachbaur <mike@nachbaur.com> Cc: modperl@apache.org Subject: Re: [RFC] Dynamic image generator handler From: merlyn@stonehenge.com (Randal L. Schwartz) Date: 10 May 2002 06:39:47 -0700 >>>>> "Michael" == Michael A Nachbaur <mike@nachbaur.com> writes: Michael> This is a mod_perl handler, not directly tied in with my Michael> content management system, but is/will be used extensively by Michael> it. The premise is to dynamically generate images, cache Michael> them, and present them to browser clients. The URI, as well Michael> as Apache configuration directives, is used to determine what Michael> is to be generated. Like <http://www.stonehenge.com/merlyn/LinuxMag/col33.html> perhaps? Been there, Done that. Feel free to steal the code. === Date: Fri, 10 May 2002 10:46:11 -0700 From: Michael A Nachbaur <mike@nachbaur.com> To: Robert <robert@robert.cz> Cc: modperl@apache.org Subject: Re: [RFC] Dynamic image generator handler On Fri, 10 May 2002 08:32:55 +0200 Robert <robert@robert.cz> wrote: > Take a look at Apache::ImageMagick In my benchmarks I ran, ImageMagick was way slower than GD. I wrote a little test, rendering a little text image of 120x30. With ImageMagick, I was getting 0.3 rps, and under GD with similar circumstances I was getting 1.5rps. I'm sure I could've optimized the ImageMagick one a bit further, but that quick test settled it for me. I looked at Apache::ImageMagick last night however, and although it seems pretty usefull, it doesn't really address what I want to do with my module. === Date: Fri, 10 May 2002 11:07:31 -0700 From: Michael A Nachbaur <mike@nachbaur.com> To: Mark Fowler <mark@twoshortplanks.com> Cc: modperl@apache.org Subject: Re: [RFC] Dynamic image generator handler On Fri, 10 May 2002 10:52:31 +0100 (BST) Mark Fowler <mark@twoshortplanks.com> wrote: > > The basic text support could be extended to allow for images to be > > overlayed on the text (or placed under the text), or stretch images > > similarly to how Enlightenment displays window manager themes. > > Hmm, yes. I have it so the image can be aligned in various ways. > It's not quite up to stretching it yet, but we shall see. I'm not either, all my module supports currently is text. > > Essentially, arguments are passed using the PATH_INFO HTTP header. > > We want the browser to think this is an actual file, instead of a > > dynamically generated image, so that the browser is more inclined to > > cache the content. So, a typical query would be: > > > > http://localhost/genText/font=ArialBold;size=24;fgcolor=#ffffff; > > bgcolor=#000000;rotate=90;text=This+Is+The+Text > > This is indeed a key concept. More importantly I designed my schemes > so that they could actually be saved to disk with that filename. One > possible idea would be to place the image creation in an ErrorHandler > which returns the image and writes it to the correct location on disk. > Thus the next time the image is called the perl code is skipped all > together and the image is simply sucked off of the disk. I think > Randal did a column on something like this a while back. Yes, like I say in my caching section, I sort the arguments and then MD5 them, and thats the name of the file on disk. So /tmp/Imagecache/0/1/A/098FAD9 etc. I actually do this process in the URI Transformation phase. I intercept a request, check to see if the given arguments already has a cache entry on disk, and if so, I change $r->filename() to that location on disk. Otherwise, I generate it, and again point to that filename...I then let Apache serve the file. > > *) Configuration Files > > I was thinking of using a system accessible in the httpd.conf for the > apache module. I want to stay away from httpd.conf-based config files. Although great for most things, the configuration of different image styles can be very site-specific, so I wouldn't want to have to reboot every time someone makes a change. In addition to this, I would like image styles to be editable through my Content Management System; if it's based in the httpd.conf (or even an .htaccess file), that means I'm giving a customer access to the control of the webserver, and that makes the hair stand up on the back of my neck. Rather, I could define an XML configuration file, and use a directive in the httpd.conf (or .htaccess) to point to the relevant configuration file for that site/location. > > *) Caching Schemes > > I hadn't really considered caching systems. Sounds good. > > > Note: To prevent the filesystem from filling up, due to DoS attacks, > > it may be prudent to have a cron job periodically cull files that > > have the oldest access time. > > Or have the handler do it itself after it's returned an image. You'd > also want the handler to keep a scoreboard of how many images have > been generated in the last x minutes to stop generating for things > like runaway spiders (though OTOH, this could probably be better > handled by another module somewhere else in the chain) I'm trying to keep from tying up the httpd processes unnecessarily. I just want to generate an image, and then pass it off to apache as fast as possible. If I have to disk scan (or even maintain a scoreboard in memory), I'm not sure how that would affect performance. It might not be a bad idea to add a scoreboard, but I don't want it to have to do too much. > > Looking forward, I would like to be able to use this for more than > > just text. I'd like my customers to be able to select an image, set > > the maximum size, check a few boxes or radio buttons to say what > > formatting options they'd like, and the image is automagically > > resized without wasting disk space or taking a long time to > > download. > > Disk space cheap, CPU cycles expensive. Disk space cheap, CPU cycles expensive, web developer time *really* expensive. So, auto-generate, and load from disk cache. > > I'm sure there are plenty of other uses for this, but I'll leave it > > at this. > > I'm warey of creating a all too powerful module. It's taken me an age > to come up with an interface that I think (IMHO) that has a sensible > user interface. I wouldn't want to create something too powerful. Unfortunately for me, I need to add these fancy-dancy features. The reason I'm coming back to this module of mine is because I need to have background images behind text, semi-transparency of multi-layered images, and resizing/scaling of images with borders and shadows, etc. === Date: Fri, 10 May 2002 11:11:53 -0700 From: Michael A Nachbaur <mike@nachbaur.com> To: merlyn@stonehenge.com (Randal L. Schwartz) Cc: modperl@apache.org Subject: Re: [RFC] Dynamic image generator handler On 10 May 2002 06:39:47 -0700 merlyn@stonehenge.com (Randal L. Schwartz) wrote: > Like <http://www.stonehenge.com/merlyn/LinuxMag/col33.html> > perhaps? Been there, Done that. Feel free to steal the code. Like that, but a bit more so. And I'd like to avoid ImageMagick like the plague. === Date: Fri, 10 May 2002 14:45:19 -0500 From: Ed <entropic@fldna.net> To: Michael A Nachbaur <mike@nachbaur.com> Cc: modperl@perl.apache.org Subject: Re: [RFC] Dynamic image generator handler On Fri, May 10, 2002 at 10:46:11AM -0700, Michael A Nachbaur wrote: > On Fri, 10 May 2002 08:32:55 +0200 > Robert <robert@robert.cz> wrote: > > > Take a look at Apache::ImageMagick > > In my benchmarks I ran, ImageMagick was way slower than GD. I wrote a > little test, rendering a little text image of 120x30. With ImageMagick, > I was getting 0.3 rps, and under GD with similar circumstances I was > getting 1.5rps. I'm sure I could've optimized the ImageMagick one a bit > further, but that quick test settled it for me. > > I looked at Apache::ImageMagick last night however, and although it > seems pretty usefull, it doesn't really address what I want to do with > my module. I'm using Imlib2 w/ the c interface (http://freshmeat.net/projects/imlib2perl/) I needed antialias lines, alpha's etc. I modified my app to use a 'dbi' like interface for potentially any media driver. The diferent 'media drivers', gd, imlib2, *pdf/*tex etc all have different ideas how to draw a line, circle, polygon, text, add colors etc. Now all I have to do to use diffent libraries such as Media->new(Driver => 'imlib2'), or Media->new(Driver => 'gd'), Media->new(Driver => 'svg'), Media->new(Driver => 'pdflib') etc. There are may libraries out there, gd, imlib, imlib2, libart, povray, gdk, flash, pdfAPI2, pdflib, tex, latex, svg, imager, imagemagic, ... There are may good reasons to be able to 'just drop in' a driver ... just look at why the unified interface 'DBI' was developed for RDBM's . Ed === Date: Fri, 10 May 2002 15:50:08 -0500 From: Ed <entropic@fldna.net> To: Michael A Nachbaur <mike@nachbaur.com> Cc: modperl@perl.apache.org Subject: Re: [RFC] Dynamic image generator handler On Wed, May 08, 2002 at 01:42:42AM -0700, Michael A Nachbaur wrote: > This is an request for comments. If you don't care about dynamic image > generation with mod_perl, or don't care about offering or reading about > suggestions, you can safely ignore this. Also, be forewarned, this was > written in StarOffice, and then copied/pasted into my email program, and > hand tweaked, so some things may not have made the transition properly. > > Dynamic Image Manipulator > ------------------------- > > *) Overview > > This is a mod_perl handler, not directly tied in with my content > management system, but is/will be used extensively by it. The premise is > to dynamically generate images, cache them, and present them to browser > clients. The URI, as well as Apache configuration directives, is used to > determine what is to be generated. > > *) Basic Uses > > The most basic uses of this application will to dynamically generate TTF > text for titles, buttons, sidebars, etc. The current version of this > code does this, and quite well. Foreground and background colors, font > name (with bold/italic support), font size, image size (or automatically > detected based on the size of the text), and rotation. > > The basic text support could be extended to allow for images to be > overlayed on the text (or placed under the text), or stretch images > similarly to how Enlightenment displays window manager themes. > > Other uses planned would be to manipulate existing images. For instance, > if an image on a website needs a thumbnail, medium size and full-size > view, normally a person must make all versions by hand. If any > formatting needs to be done, like borders or drop-shadows, this > increases complexity. If a person could just drop an image in a > directory, and link to that image, the image could automatically be > resized, borders added, drop shadows put in place. The resulting image > would then be cached, and outputted. > > *) URI Arguments > > Information about what is to be done is passed through the URI. This > works for simple tasks like text display, but if anything more > complicated is to be done, external configuration files must be used. > We'll get to that in a bit. > > Essentially, arguments are passed using the PATH_INFO HTTP header. We > want the browser to think this is an actual file, instead of a > dynamically generated image, so that the browser is more inclined to > cache the content. So, a typical query would be: > > http://localhost/genText/font=ArialBold;size=24;fgcolor=#ffffff; > bgcolor=#000000;rotate=90;text=This+Is+The+Text > > Resizing an image could be accomplished by doing: > > http://localhost/genImage/source=/images/ducks.jpg;scale-ratio=1:1; > width=120;height=80;border-size:1px;border-color:#000000; > shadow-color:#000000;shadow-angle:270;shadow-distance:5px > > This would resize an image to the indicated width/height. The > "scale-ratio" argument would limit the width/height ratio, so the > maximum dimension would be used. The other attributes are obvious. > > *) Configuration Files > Lets assume that we are going to scale an image, add borders to it which > consist of other images, and add text captions over the image. This > would result in such a long URI, that browsers would probably truncate > it. In addition, providing direct access to the browser opens up > possibilities for DoS attacks. Therefore, a configuration file should be > used. The config file must be flexible enough to allow a web page to > provide various input, but have certain defaults set, and restricted. > > The proposed solution would be to have a config file that has preset > default templates that the input arguments augment. For instance: > > <genimage> > <preset name="thumbnail-image"> > <image> > <style> > border-style: solid; > border-color: #000000; > border-width: 1px; > shadow-distance: 5px; > shadow-angle: 270; <!-- or something like 1.2rad --> > shadow-color: #000000; > </style> > <content name="src"/> > </image> > <image> > <style href="/css/watermark.css"/> > <!-- The above-referenced file has the following contents: > opacity: 80%; > position: top; > --> > <content>/images/watermark.gif</content> > </image> > <text> > <style> > font-face: Arial; > font-size: 10px; > color: #000000; > border-style: solid; > border-color: #ffffff; > opacity: 80%; > text-align: right; > </style> > <content>Copyright © 2002 Foo Bar Industries</content> > </text> > <text> > <style> > font-face: Arial; > font-size: 14px; > color: #ffffff; > text-align: left; > position: top; > </style> > <content name="date"/> > </text> > </preset> > </genimage> > > As you can see, the above configuration file uses CSS. It makes sense to > leverage that, although I'm not certain how difficult it would be to > interface with CSS files. As far as I know, there are Perl CSS parsers, > but I have yet to use them. The configuration for a preset config > template would be layered, so the earlier the definition, the lower the > layer is. The real important part here, is the "name" attribute of any > element, as this identifies where input can be indicated. The above > preset could be used by invoking the following URI. I used CSS.pm for a bit but it was too fat w/ Parse::RecDecent. To unify my app and the browser I use axkit to 'generate' the css from an xml file. <css> <selector name="back"> <color>black</color> <font-family>geneva</font-family> <font-family>arial</font-family> <font-size>7px</font-size> <background-color>white</background-color> </selector> </css> .back { color: black; font-family: geneva, arial; font-size: 7px; background-color: white; } Creating complicated css files are difficult but my drawing app can load its info from the uri, an xml file, a rdbm , Config::General, inifiles or whatever and use different output methods such as axkit's providers to parse the 'color config' to render the *.css file to the browser. This way the document, style, skin and images are all unified. Graphics::ColorNames works wonderfully to help handle all the different color needs. > > http://localhost/genImage/preset=thumbnail-image;src=/images/ducks.jpg > > As you can see, the preset is invoked by passing it's name as an > attribute, and any element that has a name attribute, it's value can be > provided on the URI. If an element has both a value and a name > attribute, the value in the config file can be used as a default. > > *) Caching Schemes > > A caching scheme similar to AxKit could be used. The current module > takes all the input arguments, sorts them (including all values that are > not provided, for completeness), and takes it's MD5 checksum. That > becomes the image's filename on the system. It is placed in a temporary > directory, and any further requests to that same URI, the file is pulled > from the filesystem without regenerating the image. Further, the code > has been blatantly ripped off from AxKit, which separates the directory > into two sub-levels, to prevent performance problems of having too many > files in one directory. > > Note: To prevent the filesystem from filling up, due to DoS attacks, it > may be prudent to have a cron job periodically cull files that have the > oldest access time. Cache::Cache is appropriate here ... > > *) Image Manipulation Modules > > My current code uses GD for text writing, and I'm quite happy with it. > It is extremely fast, and creates nice text output when compiled with a > TTF font engine. Looking forward however, it may not be as desirable if > things like drop shadows is to be done. GD can work with multiple > images, can resize them, etc, but the advanced features are still > unknown. > > *) File Expiration Headers and Browser Caching > > With my current code, it seems that browsers are reluctant to cache > these dynamically generated images. I have passed Expires: headers to > tell the browser to cache file file for a long period of time (2+ > weeks), but I have been unsuccessful. I know the caching headers are > complex, and needs more than one simple header, but fixing this has > moved to the back-burner of my project. However, if more complicated > processing is to be done, and with more images, it will be crucial to > make browsers cache these images. I create a digest w/ MD5 or SHA1 for the image/pdf and use it as the filename and the Cache::Cache key. The cache is easily invalidated if the source image file failes a -e test. I also use cron to delete stale image files. The generated now static image is redirected-to or referenced in the html. I found that it is important to complete the processing of the images before the referencing html document gets served, ... rather than having the html document initiate dynamic imbeded links to create the image. Letting apache serve images as static image-files has proved rock solid for me ... (note keep-alives). There is nothing worse than to pull a page and have to wait for each of the images to show up. Browsers, proxies and users are all real pains to deal w/ when the uri has a query string. Digest's are ugly but they play much better w/ everybody. 014d1c89fc3da6e15e0069000dfa381e44239af71021057594.png Ed === Date: Thu, 9 May 2002 12:39:38 -0700 From: Michael A Nachbaur <mike@nachbaur.com> To: modperl@apache.org Subject: [RFC] Dynamic image generator handler This is an request for comments. If you don't care about dynamic image generation with mod_perl, or don't care about offering or reading about suggestions, you can safely ignore this. Also, be forewarned, this was written in StarOffice, and then copied/pasted into my email program, and hand tweaked, so some things may not have made the transition properly. http://nachbaur.com/software/writing/rfc-imagegen.xhtml Just a note, I originally posted a text-version of this RFC to the mailing list (tried twice) but it never got through apparently. I'm guessing the mailing list blocked it since it was too big. Anyway, if anyone would prefer the text version, and you know why I wasn't able to post, let me know and I'll repost it. ===