A 50 % blend of two layers without colour math: SETINI bit 3 interleaves the sub screen and the main screen column by column.

BG1 (red horizontal bars) is on the main screen, BG2 (blue vertical bars, scrolling) on the sub screen, and colour math is off: without pseudo-hires the sub screen never reaches the output. With it, the PPU outputs 512 pixels per line, the sub screen on the even columns and the main screen on the odd ones; a CRT on composite blends each pair, and so does an emulator's 256-pixel view — purple where the bars cross. Press A to toggle it.

Build & Run

cd $OPENSNES_HOME

make -C examples/color/pseudo_hires

Open pseudo_hires.sfc in luna (or any SNES emulator) and press A.

SNES Concepts

SETINI ($2133) bit 3, pseudo-hires, through videoSetPseudoHires(): the lib keeps a shadow of the write-only register
Main and sub screen designation (setMainScreen, setSubScreen) without colour math: the sub screen is seen only through pseudo-hires
The interleave: sub screen on the even columns, main screen on the odd ones (snesdev-wiki, PPU registers and Uncommon graphics mode games; anomie's register doc; the wiki's Backgrounds page has the inverse, a known error)
Why use it: a transparency effect that leaves colour math free for something else; the price is horizontal detail, and on a sharp RGB display the columns show as stripes rather than a blend
Tiles built at run time with tileEncode4bpp() — no asset file

What You'll See

Purple squares where red and blue cross, half-bright red and blue elsewhere, black in between.
A: pseudo-hires off — only the red bars remain. A again: back on.
In luna's native 512-pixel output (--native-res), the even columns carry BG2's blue and the odd ones BG1's red, one by one.

Testing

testing/manifests/color_pseudo_hires.toml presses A twice and checks SETINI ($08, $00, $08), the screen designations and that BG2 keeps scrolling.

Modules Used

Module	Purpose
console	System initialization, videoSetPseudoHires()
dma	Palettes, tiles and maps to CGRAM / VRAM
background	BG1 / BG2 char and map bases, BG2 scroll
input	The A button
tile	The two tiles, built from pixels