PNG cursor and x,y hotspot
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PNG cursor and x,y hotspot
by Eljay Love-Jensen
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Hi everyone,
I am using PNG to hold images to be used as cursors. Is there an appropriate public chunk or extension chunk wherein the x,y hotspot of the cursor is specified? It appears that 'oFFs' could be used/misused/abused that way -- but the semantics of 'oFFs' isn't quite right (hence the misused/abused). In the interim, I'm storing the x,y hotspot information in a sidecar XML file. The interim solution is acceptable to me as the production solution. Thanks, --Eljay ------------------------------------------------------------------------- This SF.Net email is sponsored by the Moblin Your Move Developer's challenge Build the coolest Linux based applications with Moblin SDK & win great prizes Grand prize is a trip for two to an Open Source event anywhere in the world http://moblin-contest.org/redirect.php?banner_id=100&url=/ _______________________________________________ png-mng-misc mailing list png-mng-misc@... https://lists.sourceforge.net/lists/listinfo/png-mng-misc |
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Re: PNG cursor and x,y hotspot
by Glenn Randers-Pehrson
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On Tue, Dec 2, 2008 at 12:49 PM, Eljay Love-Jensen <eljay451@...> wrote:
> Hi everyone, > > I am using PNG to hold images to be used as cursors. > > Is there an appropriate public chunk or extension chunk wherein the > x,y hotspot of the cursor is specified? > > It appears that 'oFFs' could be used/misused/abused that way -- but > the semantics of 'oFFs' isn't quite right (hence the misused/abused). > > In the interim, I'm storing the x,y hotspot information in a sidecar > XML file. The interim solution is acceptable to me as the production > solution. I would not recommend using oFFs for this purpose. We proposed a chunk, maybe 10 or 11 years ago, in which a baseline could be defined. Either that or some revision of it could be used. What is the nature of "hotspot information"? I'm guessing number of hotspots unit x[0] y[0] radius[0] action number[0] x[1] etc Glenn ------------------------------------------------------------------------- This SF.Net email is sponsored by the Moblin Your Move Developer's challenge Build the coolest Linux based applications with Moblin SDK & win great prizes Grand prize is a trip for two to an Open Source event anywhere in the world http://moblin-contest.org/redirect.php?banner_id=100&url=/ _______________________________________________ png-mng-misc mailing list png-mng-misc@... https://lists.sourceforge.net/lists/listinfo/png-mng-misc |
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Re: PNG cursor and x,y hotspot
by John Bowler
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From: Eljay Love-Jensen [mailto:eljay451@...]
>Is there an appropriate public chunk or extension chunk wherein the >x,y hotspot of the cursor is specified? > >It appears that 'oFFs' could be used/misused/abused that way -- but >the semantics of 'oFFs' isn't quite right (hence the misused/abused). IMO the definition of oFFs is weird - back to front (it's a coordinate within an underspecified container, not a coordinate within the image) and ill defined (the definition of the coordinate space is basically absent as a result of ambiguity.) Still, you could use a negative x and y to indicate the anchor point of the cursor offset from the image top left... >In the interim, I'm storing the x,y hotspot information in a sidecar >XML file. The interim solution is acceptable to me as the production >solution. Much better IMO is to invent your own private chunk or (second best) use tEXt keywords. You can do either of these in whatever way you like, just so long as you obey the chunk naming conventions by making the second letter of your 4 character chunk name lower case or obey the keyword naming conventions by not reusing an existing registered keyword (unlikely.) Indeed, you could put the whole XML sidecar in a keyword - perhaps not the best solution, but certainly permitted. To use a private chunk (e.g. cuRS) it is safest, though not an absolute requirement, to include some identifiable signature at the start of the chunk. After that simply define the values you require in some appropriate way - e.g: 4 bytes: 16 Length 4 bytes: cuRS Chunk type (name) 8 bytes: cursor00 signature 4 bytes: [x] 32 bit integer x hotspot within image Offset from left column 4 bytes: [y] 32 bit integer y hotspot within image Offset from top row 4 bytes: [CRC] 32 bit CRC Then write code for a private chunk handler that can be used from libpng. This is an entirely appropriate use for a private chunk - it's probably a rare thing to need in a PNG image and it's obviously very application specific (i.e. even if an image contains a cuRS chunk very few apps will need to read it.) If you publish the spec and the chunk handler code then it may well gain wide spread use among those applications that need it. John Bowler <jbowler@...> ------------------------------------------------------------------------- This SF.Net email is sponsored by the Moblin Your Move Developer's challenge Build the coolest Linux based applications with Moblin SDK & win great prizes Grand prize is a trip for two to an Open Source event anywhere in the world http://moblin-contest.org/redirect.php?banner_id=100&url=/ _______________________________________________ png-mng-misc mailing list png-mng-misc@... https://lists.sourceforge.net/lists/listinfo/png-mng-misc |
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Re: PNG cursor and x,y hotspot
by John Bowler
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From: glennrp@... [mailto:glennrp@...]
>oFFs works fine for us in ImageMagick. We use it exactly the same as >the offsets in a GIF multi-image file, as offsets from the "main" window. It works for a cursor too - the only sensible interpretation is that it is the displacement of the PNG image to align the hot spot of the cursor. The problem is that the interpretation is context sensitive and it only works in precisely those cases enumerated in the spec. For example, how should it be interpreted when a PNG image containing oFFs is embedded in an HTML/CSS page? John Bowler <jbowler@...> ------------------------------------------------------------------------- This SF.Net email is sponsored by the Moblin Your Move Developer's challenge Build the coolest Linux based applications with Moblin SDK & win great prizes Grand prize is a trip for two to an Open Source event anywhere in the world http://moblin-contest.org/redirect.php?banner_id=100&url=/ _______________________________________________ png-mng-misc mailing list png-mng-misc@... https://lists.sourceforge.net/lists/listinfo/png-mng-misc |
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