tmxrasterizer as a git diff tool: override search path, and allow explicitly writing to stdout

[eevee]

Two little features would make it much easier to plug tmxrasterizer into git as a map differ:

1. An argument for overriding the initial search path. The problem is, when git diffs two versions of the same file, it has to put at least one of them in a temporary file, and now it doesn't know where to find any of its tilesets. I know the original full path, but I have no way to provide it.

2. Writing the image to stdout. This isn't strictly necessary since tempfiles are always an option, but it did surprise me a little that giving - as the outfile path literally created a file named - :)

With both, I believe you could diff a map against its committed version with a oneliner (in zsh, anyway):

compare -metric PHASH =(tmxrasterizer -s 0.25 -p $(dirname $1) $2 -) =(tmxrasterizer -s 0.25 -p $(dirname $1) $5 -) png:- | display -title "$1" -

[eevee]

i fudged something similar by dumping the original file to a tempfile in the source directory (highly dubious), and i think this is a cool start:

[bjorn]

I quite like this idea! To implement this, the MapFormat interface would need to be extended with an option to read a map while using a custom search path:

tiled/src/libtiled/mapformat.h

Line 73 in 130b4f8

virtual std::unique_ptr<Map> read(const QString &fileName) = 0;

The TMX format already has a function that can be used to implement such an interface:

tiled/src/libtiled/mapreader.h

Line 68 in 130b4f8

std::unique_ptr<Map> readMap(QIODevice *device, const QString &path = QString());

The JsonMapFormat can also be quite trivially extended with such an overload. For other formats, I guess providing a default implementation that ignores the custom search path would be fine for now, so we don't need to change all the implementations.

Finally, we would add a Tiled::readMap overload that takes this search path, and we can use it in TmxRasterizer.

And I don't think it'll be an issue to get - to output a PNG to standard out, either. :-)