Add a synced interface to read images

[sprunk]

User story

Reading an image has many use cases that would be useful in synced.

• define a complex curve by drawing a 1xN gradient, for example for custom weapon damage fall-off.

• define metadata for map terrain simply by drawing over it.

• encoding spatial patterns in an image can generally result in both more readability and less verbosity compared to a bunch of numbers in a lua file.

In particular, the engine currently implements game design via the metalmap being part of the map format. Making it possible to read resource distribution from a raw image would let us decouple it. Mappers would probably be happy as well.

Request & implementation remarks

Add a synced interface to read a pixel from an image file, i.e.

local r, g, b, a = Spring.ReadPixel(img, x, y)

I am not specifying what the img param should be because there are caveats:

• if it is a filename then there are performance concerns.
• if it is a userdata handle (with corresponding Open/Close inteface) then there may some issues with sync-safety. I believe that synced states are 100% userdata-proof at the moment and that this is done for good reason. Maybe it's still fine but it seems scary.
• if it is a numerical handle then there's the issue of type safety and leaks. This is probably also fine.

[12345swordy]

Wouldn't be better to load all images from the map or the game and put it into a lua table for easy access?

[sprunk]

Access how? You could convert it into a 2d lua table so it's image[x][z] = {r, g, b, a} but that sounds like it would have pretty terrible perf and memory overhead. But sure, maybe there could be a Spring.ReadImageAsLuaTable("path") -> table.

[12345swordy]

Access it by having it load up when the game starts and close it when the game close.

[sprunk]

That would be bad, you'd load up a ton of garbage that you might use once and not need anymore afterwards.