get introspection in lua

hello,

I was willing to write a lua script that changes some values (like exposure) in a bunch of pictures, I didn't found any.

I thougth to start writing a "tool" to do this, it is far from ready but i think it is a good starting point if someone would like to collaborate

I never used lua before so you may find some weird syntax, you can find the code here
https://repl.it/@VincenzoG/Darktable-xmp

example code:

require "tools/xmp_utility"

input = "0000000010c7babce0ce773e00004842000080c0"

exposure_params = {mode = 1, black = 2, exposure = 3, deflicker_percentile = 4, deflicker_target_level = 5}
exposure_table = dt_xmp_decode(input)

print(table.concat(exposure_table, " "))
print("Mode:", exposure_table[exposure_params.mode])
print("black:", exposure_table[exposure_params.black])
print("exposure:", exposure_table[exposure_params.exposure])
print("deflicker_percentile:", exposure_table[exposure_params.deflicker_percentile])
print("deflicker_target_level:", exposure_table[exposure_params.deflicker_target_level])

print(dt_xmp_encode(exposure_table))

exposure_table[exposure_params.exposure] = exposure_table[exposure_params.exposure] - 0.02
print("new exposure:", exposure_table[exposure_params.exposure])
print(dt_xmp_encode(exposure_table))

and it's output:

0 -0.022799998521805 0.24200010299683 50 -4
Mode:   0
black:  -0.022799998521805
exposure:   0.24200010299683
deflicker_percentile:   50
deflicker_target_level: -4
0000000010c7babce0ce773e00004842000080c0
new exposure:   0.22200010299683
0000000010c7babcfe53633e00004842000080c0

todo list:

• use compressed values: i found on google some part of code but i didn't integrated them, yet, you could find them in the base64.lua file
• automatically read/write the params: this can be done knowing the file path and using one of the already existing xml library for lua

If someone would like to collaborate tell me!

Start by reviewing the linked Darktable-xmp script and the base64.lua file mentioned in the TODO list. Clarify the intended introspection interface and how existing Lua XML libraries should read and write params. Done would require an agreed scope plus working compressed-value handling and automatic parameter read/write.