gizmo-crt-shader

This libretro shader tries to mimic crt behaviour without extensive use of scanlines and replicating CRT pixel patterns.

Assumptions for shader development

• CRT output is much more vivid compared to a LCD. There a small deviations in color and position. A CRT always seems to restless.
• A CRT has no fixed resolution. Fractional scaling is no problem.
• If you take a look at CRT vs LCD comparisons it's obvious that phosphor not only changes color from black to red/green/blue. The spatial extent also changes. Scanlines are good visible in dark regions but they are almost invisible in bright regions.

Implementation

• A small portion of static noise was added to make the output a little bit restless
• To allow fractional scaling, horizontal subpixel scaling for LCDs with RGB patterns was implemented. To get smooth vertical scaling "improved bilinear interpolation" from Inigo Quilez was implemented.
• A scanline or "pixel separation" function was implemented which takes the brightness of the current pixel into account and produces a thicker or thinner "scanline".

Examples

Subpixel scaling

Scanlines

Horizontal Blur

Variants

gizmo-crt.glslp

Default v0.3 variant.

gizmo-crt-n64.glslp

Default v0.3 variant with vertical and horizontal blur for n64.

gizmo-crt-megadrive.glslp

Default v0.3 variant with horizontal blur and 4:3 aspect for megadrive.

gizmo-crt-snes.glslp

Default v0.3 variant with 4:3 aspect for snes.

Results

Comparison

gizmo-crt

CRT-Royal

CRT-PI

Nearest neighbor vs shader comparison

gizmo-crt-n64-curvator vs bilinear vs nearest neighbor