[Feature Request] Add option for bilinear downscaling

[EPeanutG]

Would it be possible to implement a downscaling algorithm that can actually downsample? (ex: bilinear downsampling) The default downscaling in ShaderGlass right now (with the "Pixel Size" option) looks pretty jagged, without much anti-aliasing.

Comparison:

• Original image
  
• Downscaled with ShaderGlass
  
• Downscaled with Photoshop (bilinear resampling option)
  

With crt-royale applied:

• ShaderGlass downscaling
  
• Photoshop bilinear downscaling
  

The difference is particularly noticeable on Bowser's spikes, which are much more smooth with bilinear downsampling.

[mausimus]

I see, it's a pretty unique use case where you have hi-res & low-res output from the emulator at the same time. Pixel Size option in SG is there to match pre-scaling of the input so shaders can correctly calculate scanlines. But I should be able to add linear filter option, it's pretty straightforward.