rla20@duts.ccc.amdahl.com (Roger L Allen) (09/06/90)
Currently, I am working on my own Gif viewer. Mostly it is for my own
personal enjoyment (agony) but if I can get this @#$%&* thing to work
maybe I will make it a shareware product in an already packed market.
ANYWAY, I am having a frustrating time with the palette manager and
getting the correct colors on the screen. I've read the IM V PM Chapter,
I've read all the c.s.m.p items that seemed relevant and I'm still
confused. Does Apple have a document written so mere humans can
understand the Palette Manager?
So, here is what the program is doing:
1. Read in all the Gif header stuff and set up a Palette of all
the colors that the image needs. (pmTolerant, 0 tolerance--I
tried pmExplicit & pmAnimated to no avail)
2. Open up a window that the image will go into, attach the Palette
and activate it.
3. Now, here is the tricky part...
Read in the gif picture data and store it in an off-screen
bitmap. BUT, each gif data byte is really an index into
its own CLUT (the palette I spoke of), it is not a RGB value.
So, Parts 1 & 2 went pretty well and I learned alot of interesting info
along the way. But, Part 3 is causing me some grief.
What I have tried:
I tried just putting the raw data into the bitmap via the baseAddr ptr.
--no luck here, even when I did a Palette2CMap for the window. The
indexes seemed to change and the picture turned psychadelic(sp?)
I also tried using PmSetForeColor(gifIndex) and then plotting the points
as they are decoded--also no luck, I don't think the palette is loaded
to this bitmap.
So, as you can see I need help. Please email me and I will summarize
and re-post if the answers are helpful.
Thanks,
Roger Allen
rla20@DUTS.ccc.amdahl.comrussotto@eng.umd.edu (Matthew T. Russotto) (09/07/90)
In article <3cR602lw02Cj01@JUTS.ccc.amdahl.com> rla20@DUTS.ccc.amdahl.com (Roger Allen) writes: >Currently, I am working on my own Gif viewer. Mostly it is for my own >personal enjoyment (agony) but if I can get this @#$%&* thing to work >maybe I will make it a shareware product in an already packed market. > >ANYWAY, I am having a frustrating time with the palette manager and >getting the correct colors on the screen. I've read the IM V PM Chapter, >I've read all the c.s.m.p items that seemed relevant and I'm still >confused. Does Apple have a document written so mere humans can >understand the Palette Manager? No. You have to have an IQ of at least 300, like all Apple technicians :-) (the company average IQ is within reason thanks to management and marketing) >So, here is what the program is doing: > > 1. Read in all the Gif header stuff and set up a Palette of all > the colors that the image needs. (pmTolerant, 0 tolerance--I > tried pmExplicit & pmAnimated to no avail) pmExplicit is wrong, though pmExplicit+pmTolerant under 32-bit quickdraw would simplify things somewhat-- but don't do it, it is unfriendly to ask for specific entries. pmTolerant, 0 tolerance is correct. > 2. Open up a window that the image will go into, attach the Palette > and activate it. Right. > > 3. Now, here is the tricky part... > Read in the gif picture data and store it in an off-screen > bitmap. BUT, each gif data byte is really an index into > its own CLUT (the palette I spoke of), it is not a RGB value. No big deal. What you do is make a translation table between the gif values and the actual pixel values as assigned in the offscreen buffer. I.e. make your offscreen buffer with a copy of the device color table and do a for (i=0; i < numcolors; i++) trans[i] = Color2Index(&gifpal[i]); Where gifpal is an array of RGB colors derived from the GIF color tables. Then, before you stuff the data in, run it through trans, thus: *(baseaddr + x + y * rowbytes) = trans[gifdatabyte]; The other method, very easy if you use the new 32-bit quickdraw routines documented in d e v e l o p issue 1, is to set up a NewGWorld with a color table derived from the GIF palettes. Then just stuff the raw data to the buffer, SetGWorld appropriately, and, you have it. (screen updates are slower this way, but there are some other advantages). I refer you to that issue of develop for more info.