Pixel scaling filter (hq2x, hq4x, scale2x...)

[Zegeri]

At least one of these algorithms should be implemented as an optional post-processing filter.

[carstene1ns]

👍
For reference: http://en.wikipedia.org/wiki/Image_scaling#Pixel_art_scaling_algorithms

Using most of them in a non-gpl project would mean have to reimplement them.
At least for scale2x this can be done easily and scale4x is just applied the same effect twice.
For hq2x there is a public domain implementation by byuu that can be abused (http://pastebin.com/YXpmqvW5)

The general problem is, that Player is using a feature of SDL2 that just scales the tiny image to display resolution. Scaling 320x240 to 640x480 by scale2x and then scaling to 1080px height by SDL2 will likely look bad. So this would mean to implement something in the middle.

[Ghabry]

hq4x is LGPL

[Ghabry]

scale2x is GPL

[vinipsmaker]

Another interesting filter is xBR: http://filthypants.blogspot.com.br/2012/03/xbr-vs-hqx-interpolation-filter.html

[carstene1ns]

Some comparison: