George Peter Staplin Oct 5, 2007 - Here is a simple tutorial for those of you using megaimage and related extensions from megapkg.
Common setup code
set dir [file dirname [info script]] set ext [info sharedlibextension] load [file join $dir megaimage$ext] load [file join $dir megaimagetk$ext] load [file join $dir jpegext2$ext] Jpegext2 ;#caveat load [file join $dir pngext2$ext] Pngext2
Decoding a JPEG, adding a blue rectangle, and then encoding a JPEG
set fd [open "some.jpg" r] fconfigure $fd -translation binary set buf [jpegext2:decode [read $fd]] close $fd set obj [megaimage $buf] set x 20 set y 30 set width 200 set height 200 set color [list 0 0 255 255] $obj rectangle $x $y $width $height $color set fd [open "output.jpg" w] fconfigure $fd -translation binary puts -nonewline $fd [jpegext2:encode [$obj getdata]] close $fd
jpegext2:encode takes an optional argument after the megaimage data for the quality. Quality should be an integer in the range of 1-100.
Blending Objects Over a Base
set obj [megaimage-blank 800 600] $obj setall [list 127 127 127 255] set overlay [megaimage-blank 200 200] $overlay setall [list 100 100 200 200]; #RGBA set x 0 set y 0 $obj blendobj $x $y $overlay set x 180 set y 180 $obj blendobj $x $y $overlay
pngext2:decode and pngext2:encode are similar to jpegext2, but have some important differences:
% pngext2:decode wrong # args: should be "pngext2:decode file|data filename|data"
% pngext2:encode wrong # args: should be "pngext2:encode data ?-alpha boolean?"
-alpha 1 is the default. -alpha is mostly of interest if you want to make the image a little smaller by eliminating the alpha channel.
Note: if pngext2:decode file $filename is causing segfaults it's probably due to a problem with Tcl_StatBuf size differing. In your build.conf you'll probably want to add the necessary -D to make tcl.h use the right struct stat when building pngext2. For example with unix-like systems: -D_LARGEFILE64_SOURCE=1 -DTCL_WIDE_INT_TYPE=long\\\ long
Using Megaimagetk
# Making a megaimage object from a photo image. set obj [megaimage [megaimage.from.photo $photo_handle]] # Make a photo instance have the same data as a megaimage object. set p [image create photo] megaimage.to.photo [$obj getdata] $p
megaimagetk has more features, but those can get you started.
Cleaning up Megaimage Objects
set obj [megaimage-blank 800 600]
rename $obj {}
set obj [megaimage $someBufferSource]
rename $obj {}Q. What is the data returned by jpegext2:decode?
A. It's a ByteArray result with a header at the start, followed by RGBA data.
Q. What is the data returned by jpegext2:encode?
A. It's a ByteArray result with the JPEG header and data, that can be written to the disk and opened in other programs that understand the JPEG format.