I made a quick port of the 'zfast_lcd' shader from RetroArch, and thought I'd share...
The attached zip file contains two variants:
- zfast_lcd: This is a very simple shader (minimal performance impact) that creates an LCD effect by adding a subtle grid lattice to the screen
- zfast_lcd+nds_color: This is the same as 'zfast_lcd', but also incorporates the 'nds-color' shader from RetroArch, which applies colour correction to simulate the display characteristics of a DS Phat. It has slightly higher system requirements, but it's still quite 'light' and is the one I would recommend.
Both shaders work correctly with 'High-Resolution 3D Rendering' turned ON or OFF.
NB: These shaders are intended for use with a high resolution display (at least 1080p). If you try to run them at a lower resolution, you'll probably need to play around with integer screen scaling to avoid ugly aliasing effects.
EDIT1: Oh snap - I can't seem to do anything right this week... I just realised that the zfast_lcd+nds_color shader I posted was tweaked for a particular device of mine with a non-standard gamma level. For most LCD panels, 'display_gamma' should be 2.2, not 2.4. I have updated the attached zip file with the corrected shader - please re-download if you have the old one!
EDIT2: I noticed that the default 'nds-color' shader from RetroArch has been updated with tweaked colour correction values (it's a tiny difference, but I guess it's more accurate). I've updated the 'zfast_lcd+nds_color' shader accordingly - please re-download the attached zip file!