[Tuxpaint-devel] Options for scaling starters & templates

[Bill K. <nb...@so...>]

When a starter image or template is not the exact same size
as the canvas, it will of course be scaled up or down.
We do not change the aspect ratio (change the shape, aka
squash or stretch) of the picture, though.

If the aspect ratio is not the same as the canvas (which it
frequently is note), it will scale up as large as it can
and then "smear" the edges that did not fill the canvas.
This can look really weird & ugly, especially with the
photographic ones (e.g., the rocky beach template).

I just started work to allow option files (plaintext config
files with the same name as the image file, but with ".dat"
extension; same as we do with stamps and brushes) to allow
this to be overridden for some starters & templates.

I have done so already with the wool mill machinery, the
rocky beach, and the reef (2-layer starter).  They've all
been set to use the same option, "autoscale=both".

The "autoscale" option allows you to tell Tux Paint whether it's okay
to scale the image up so much that the edges will be cropped away.
For example, a wide starter on a narrow canvas can be scaled up so
that it fits vertically, with the left/right sides getting discarded.

And conversely, a narrow starter on a wide canvas can be scaled up
so that it fits horizontally, with the top/bottom discarded.

If it only makes sense to allow one dimension to be discarded
(i.e., right & left is okay, but cutting off the top & bottom
would be bad), you can specify either "autoscale=horizontal"
or "autoscale=vertical".

If no scaling is specified, it will scale up as much as it
can without cropping anything, like it has been doing already.

Now, though, you can also specify whether or not to "smear"
(which will be the default), or to simply use a solid background color
(which you specify with "background=..." in the file; it supports
6- and 3-digit hex (e.g., #FFFFFF & #000) and decimal, just like the
color palette file does.  This would be good for B&W coloring-book
style starters (e.g., the skull SVG) which can sometimes end up
with a very faint edge getting smeared all the way down the canvas.

Note: If the "autoscale=both" option is set, the image will NEVER have
any bare edges, no matter the shape of the canvas.  So the background
setting (smear, or use a background color) is moot.

I posted a tweet on Twitter showing the rocky beach template,
with before & after in both portrait & landscape canvases of
rather extreme sizes (Tux Paint running at 1280x640 and 640x960).

https://twitter.com/billkendrick/status/1623989004436901890

For the rocky beach template, for example, I don't think what's
at the extreme edges "matters".  And I'd prefer to have a drawing
that looks like some nice rocks, regardless of my canvas'
aspect ratio, rather than weird smeary edges. :)

I need to test this a bunch more, document it (EXTENDING), and
add sensible defaults for any starters & templates that would
benefit from the different settings.

I cannot guarantee that Tux Paint will behave very well with starters
& templates [*] if you save a drawing, quit, change the canvas size
(via setting a different window size), launch Tux Paint again, and
open the image up again.  However, I don't think it's done a great
job with this _already_, so I'm not super concerned.

What you'll see is that I only apply this "scale & crop?" and
"background color or smear?" decision when loading the actual
starter/template images, and don't do it to the saved drawing.

It also gets a little tricky because as of late, we jam some
of the starter & template stuff (including the entire background
and foregrounds?!) into the PNG files, if I recall correctly.

Basically, woe is me, I don't think I can make this "perfect"...
but I think this improvement is probably beneficial.

Holler if you have other ideas or concerns!

-bill!

[*] Starters would be more adversely affected since there is a top
layer that applies itself to the image after every modification
(paint, stamp, etc.)  Warped & zoom-in/out effects could be seen.
Templates are less of a concern, as they only come into play -- the
same way as the starters' background layers -- when you use the
Eraser tool.

PS - This is https://sourceforge.net/p/tuxpaint/feature-requests/190/