Work in progress & posted for your suggestions. This is a good PNG reader (includes progressive display/interlacing--rare indeed) & the writer is in progress & will be posted next month, hopefully. In order to use this, you'll need ZLIB.DLL and a link for a VB-friendly version of that free DLL is near the top of the main class. Currently not Win95/NT4 capable, but working on that too. Again, this is a work in progress. The PNG format contains many color-related "chunks" that I don't currently have the knowledge to implement. If you know how to handle any chunks that are unhandled in the project, please email me. In IDE, this thing crawls, but compiled it is up to 10x faster & can display full screen PNGs very quickly. Hoping to hear from you all. When the PNG Writer is ready, will repost with the changes--expected to be massive. Added step-by-step instructions at top of stdPNG class for using the zlib DLL. Tweaked to fix minor errors I mentioned in remarks below. Added a readme file, more properties/options (like global AlphaBlend), and more comments. I think the reader is now good to go pending any bug reports & my TODO list I added at top of the main class. The writer is next.
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please take a look at : http://www.planet-source-code.com/vb/scripts/ShowCode.asp?txtCodeId=56537&lngWId=1 (If this comment was disrespectful, please report it.)
It is really nice to see that somebody from VB World has taken PNG seriously. Please look for MNG as well. The structure of MNG is quite similar as GIF (I mean the way it packs image frames and stores frame-delay information in it).
There is a DLL called "FreeImage.dll" (developed in C). Few months ago a wrapper module for this DLL was available on TheVBZone.com website (now he has decided it to sell it for a few $$ !). This is really a nice DLL and I think its licensing issue is just like ZLib DLL. Not sure. Please checkout this FreeImage.dll; it really has some potential. By the way, really eager to see your PNG Maker. When it was required in one of my projcts, I used PajantImage Shareware OCX to create PNG/MNG images; just for your information.
Good start ... please continue ...
-- Ruturaj (If this comment was disrespectful, please report it.)
Enmity; that post is what insprired this one. Ruturaj; I am familiar with FreeImage & wanted to try & do this w/o using that huge DLL. GDI+ can do PNGs also but has O/S rqmts & doesn't seem to handle all transparencies correctly--or I might just be using it wrong :) I'd imagine MNG would be very similar; want to finish understanding PNG first. (If this comment was disrespectful, please report it.)
Now this is fantastic :) The speed, options etc. I love it...and can't wait to see it grow :)
I hope the save part will be as good as well...
Another thing would be nice (if it could be done): How about aplying an over all alpha (to blend the png with the background - with a specified alpha - and offcourse combined with the png's alpha)...
Also, how about some color settings? - the ability to apply a custom palette - like Winamp does with color schemes?
Othervise, it is fantastic.... (If this comment was disrespectful, please report it.)
LiTe-Thanx. Oricron; good ideas: 1) Overall alpha? Easy. 2) Palette swapping? For 256color & below only? If so, easy & will be available via a property that can be called during the ProgressiveDisplay event; just before PNG is converted to BMP. If for 24+bpp, then have no clue--suggestions? As for the Save part? That is going to be a 1st cut & others will have to provide feedback for optimizations. Filtering the PNG is what will be time consuming as their are 5 filter types. How to determine best/fastest method? PNG specs have hints, but not very informative. This will be trial & error I'm afraid. (If this comment was disrespectful, please report it.)
Why not just use gdiplus.dll and have the best of all worlds? gif, png, jpg, bmp, etc. I've been able to do more with it than with anything else. :) (If this comment was disrespectful, please report it.)
Even unfinished, another phenomenal effort from you Keith. Maybe if I study hard I'll be able to understand some of it! (If this comment was disrespectful, please report it.)
Just a piece of general feedback (1) This code has failed to open any of my PNG files (whereas the code posted by Alred Koppold has no such problem). (2) One does not need to use zLib to load PNG file - if use it in vb, have to use the earlier version. (3) "tRNS" is prohibited for color types 4 and 6, since a full alpha channel is already present in those cases. (4) Compared with MNG, animated GIF is like a kid. There is no comparison at all in terms of difficulties (e.g. all browsers can only handle a very limited no. of types of MNG, Paintshop Pro also). (5) Compareing to brossers, FreeImage.dll handles PNG differently (browsers invariably use white background) and FreeImage.dll cannot cope with many types of MNG).
(If this comment was disrespectful, please report it.)
For those of you that say it doesn't work or is missing the DLL, you didn't do as I asked and read the comments at the to of the class. It works on all PNGs I have tested: 100's. You didn't download the vb-friendly DLL from the site provided & didn't reanme it to zlibVB.dll and didn't place it in your systeem folder. Although Alfred's code can display PNGs w/o zlib, it cannot write PNGs. (If this comment was disrespectful, please report it.)
ZLIB FYI: Why did I rename the dll to zlibVB.dll vs leaving it as zlib.dll? If you already had ZLIB on your system, I didn't want you overwriting it with the VB-friendly version unknowingly. Placing the extracted/renamed dll in you project folder will not work -- put it in the systtem folder. The version I gave links to in my project is the most current version of zlib as of 5 Dec 05. (If this comment was disrespectful, please report it.)
I admire a lot their work and I aren't criticizing it, I clarify him that, I only want to inform you, so that you tell me that it can be happening and where I can discharge the zlibVB.dll.
Thanks for your help, I send you one of my PNG images. (If this comment was disrespectful, please report it.)
Excelent! But if you realy want to make this dll free, check out Marco v/d Berg's Deflate64/Inflate64 classes at: http://www.planetsourcecode.com/vb/scripts/ShowCode.asp?txtCodeId=58473&lngWId=1 . You might want to do some testing, but in my experiance they work great with PNG compression. (If this comment was disrespectful, please report it.)
Note: 2 minor typos & can affect image: 1) InitializeMatrix: Replace only 256 with 256& << must be Long vs Integer. 2) ConvertPNGtoBMP. Find tColor = ((pIndex+2) & replace with tColor = (m_Palette(pIndex + 2). (If this comment was disrespectful, please report it.)
After Looking through your code a little deaper; you might also want to check out Marco v/d Berg's other compression projects, especialy http://www.planetsourcecode.com/vb/scripts/ShowCode.asp?txtCodeId=53174&lngWId=1, which has a class to handle CRC32. (If this comment was disrespectful, please report it.)
Note: Another oops. ExtractText routine. Not concatenating. Change sText=sKeyWord to sText=sText & sKeyWord in the chnk_zTXt section. Will probably post one more update here when I am satisfied with the options to remove/replace transparent bkg colors. (If this comment was disrespectful, please report it.)
Shkyrockett, when I get the reader the way I want, I will do some speed comparisons with suggested links. If I find the VB-only code is significantly slower than using ZLib, I will keep ZLib & leave it to others to modify if desired. BTW, another coder mentioned that the CRC routine has a 64k limit before erroring out. Don't know for sure. (If this comment was disrespectful, please report it.)
Goldmine of information (as your submissions always are) on PNG processing and highly readable code. 5* (If this comment was disrespectful, please report it.)
NHGames, who are you to say something like that? Much less rate a one globe? You can't even code the simplest projects. Everyone search "NHGames" and see what garbage pops up... People like you are what make this site a joke. (If this comment was disrespectful, please report it.)
NHGames this ain't a useless project. Perhaps you just dont understand its concept, implementation, significance and overall code. LaVolpe's contributions have been the inspiration of a lot of programmers and commenting rudely is hardly acceptable for a person of his character.
BTW, nice work and please do continue, I've been learning a lot from you LaVolpe. (If this comment was disrespectful, please report it.)
Keith: Late comment - I found that to get the zlibvb.dll to be picked in the IDE when it is in the app folder only, just add App.Path (modified for backslash when in root) before "zlibvb.dll" in your ValidateDLLexists. (If this comment was disrespectful, please report it.)
Amazing! Works very nicely! (If this comment was disrespectful, please report it.)
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12/17/2005 5:36:08 AM: 
