Family 1 — Text · rung 1.4 (move text)

The "make it move" rung of the Text ladder. It prints one line, then scrolls the whole text background horizontally every frame, so the message marches across the screen like a marquee and wraps around seamlessly — without ever rewriting the tilemap.

Screenshot

What you'll learn

Text lives on a background layer, so you move it exactly like any other BG — with bgSetScroll(0, x, 0) on BG1 (the text layer).
Scroll writes are buffered: bgSetScroll() stores a value and marks it dirty; the NMI handler pushes it to the PPU during VBlank, so the scroll never tears.
A 32×32 tilemap is exactly one screen wide (256 px), so incrementing the horizontal offset wraps the message around — a continuous marquee for free.

SNES concepts

The PPU has hardware scroll registers per background. You never redraw the tilemap to move text — you change where the PPU starts reading it. Increasing BG1's horizontal offset scrolls the view right, so the content appears to travel left. Because the tilemap width equals the screen width, the wrap is seamless and costs nothing per frame beyond a single register update.

How to build

make -C examples/text/scroll_message

Run scroll_message.sfc in luna. You should see OPENSNES – TEXT THAT MOVES! scrolling right-to-left forever.

Modules used

console, dma, text, background, sprite

Ladder

← 1.1 print_string · → 1.5 text effects (typewriter, wave, fade, colour-cycle)