Batch tool to list grAb values to console output

[MartinHowe]

I need to edit several dozen images that will not change their dimensions or the internal alignment. However, most image editing tools discard PNG chunks they don't know about, so the grAb values will need to be reimposed.

It's tedious and time consuming to do this in GUI tools, but while grabpng can be used to set the chunk, it can't output then to a terminal or textfile.

Does anyone know of a command line tool to do this? E.g., pnginfo bossa2a8.png >> sprites.grAb.txt ? DeuTex is supposedly able to do this, but it's not in the -help report

[Caligari87]

ImageMagick tools (convert, mogrify, identify, etc) will probably do what you want. Documentation seems a bit sparse on this point but it seems clearly able to read and write PNG chunks.

https://stackoverflow.com/questions/903 ... -png-image

I've also seen some mention of a tool called pngcheck.

https://unix.stackexchange.com/question ... s-metadata

[NeuralStunner]

ImageMagick is what Slade uses, so that should more or less work fine.

One thing to keep in mind: If you modify 256-color PNGs with transparency, it might resave them with the transparent index changed. This is what usually happens to me in Slade, at least.

[MartinHowe]

Thanks; I did look at some of these, but for setting, I can use GrabPNG in console mode, it works fine in WINE; however, reading the offsets and outputting them as text in batch mode is what's needed here.

These tools don't report on grAb; I've looked at many tools, including those above, but hardly anyone mentions the grAb chunk in their command line software. Is this a chunk special to ZDoom or is it part of an official definition somewhere?

[Caligari87]

So far as I'm aware, PNG can have arbitrary chunks of data attached to it, so grAB may not be in an official spec or directly recognized. It seems many tools may ignore or strip chunks they don't recognize, so look for an option to override that behavior.

If you are on Linux or can run Linux software (such as via WSL) it looks like there's also a utility called pngchunks which may be able to help. Seems there may be a Windows-compat version as well in PngUtils.

[phantombeta]

grAb is indeed special to ZDoom, so you won't find it outside of tools made for ZDoom modding. Unfortunately, a lot of programs always discard unknown chunks, even if it's stated to be safe to copy regardless. (which grAb is, since the 4th letter of the name is lowercase)
I do believe more programmer/scripter oriented tools tend to not do that, or at least let you request it to keep specific chunks. I'd imagine PNG-specific tools also do things properly here.

[MartinHowe]

Thanks @Caligari87; pngchunks was what I needed. I built it from source and stripped out everything except grAb recognition, to output like this:

wine ~/Desktop/GrAbPNG.exe -console -grab 64 32 meow.png

I can append every such line to a script then source it.

Yes this is a gross hack, but it will do for now

[MartinHowe]

While on the subject, I noticed that the default vertical offset for most monster sprites is their baseline is at -5; however, if you shoot a Zombieman then when his corpse is on the floor, you can't see the bottom of his body; this seems to be ZDoom's FLOORCLIP flag in action.

But I thought it was only supposed to do that on liquid textures? If I kill a Zombieman on E1M1 on the blue carpet area, it still happens

Can anyone tell me what is the reason for this?

[NeuralStunner]

In OpenGL, sprites are just flat planes and will clip into the floor. GZDoom adjusts the Y offset to avoid this, but by default if a certain percentage of the sprite is below the floor it won't adjust it.