Mode 7 perspective with HDMA split-screen (F-Zero style). More...

#include <snes.h>
#include "res/ground.inc"
#include "res/sky.inc"

Functions
void	asm_setupHdmaPerspective (u16 sx, u16 sy)
	Sky (Mode 3, BG2) tiles and 64x32 tilemap, from data.asm. Loaded with dmaCopyVram() to VRAM $5000 (tiles) and $4000 (map).
int	main (void)
	Entry point – F-Zero-style Mode 7 perspective with HDMA split-screen.

Variables
u16	pad0
	Mode 7 ground tilemap (128x128 entries, one byte per tile index).
u16	sx
u16	sy

Detailed Description

Mode 7 perspective with HDMA split-screen (F-Zero style).

Creates an F-Zero-style pseudo-3D ground plane by combining two BG modes on a single screen using HDMA mid-frame register switching. The top portion (96 scanlines) displays a Mode 3 sky background, while the bottom portion (128 scanlines) renders a Mode 7 ground plane with per-scanline perspective scaling. Four HDMA channels cooperate each frame: one switches BGMODE from Mode 3 to Mode 7 at the split line, another toggles the main screen layer enable (BG2 for sky, BG1 for ground), and two more write per-scanline M7A and M7D values to create the perspective foreshortening effect where distant rows appear more compressed.

SNES Concepts

Mid-frame BG mode switching via HDMA (Mode 3 sky + Mode 7 ground)
Per-scanline M7A/M7D writes for perspective projection
HDMA-driven main screen layer enable toggling
Mode 7 ground plane scrolling with D-pad input
Multi-channel HDMA coordination (4 channels synchronized)

What to Observe

The screen is split: a flat sky image on top and a perspective ground below
Press D-pad to scroll the ground plane in any direction
Distant ground rows appear more compressed (perspective foreshortening)

Modules Used: console, dma, background, sprite, input, mode7

See also: mode7.h, hdma.h, background.h, input.h

Function Documentation

◆ asm_setupHdmaPerspective()

void asm_setupHdmaPerspective	(	u16	sx,
		u16	sy )

extern

Sky (Mode 3, BG2) tiles and 64x32 tilemap, from data.asm. Loaded with dmaCopyVram() to VRAM $5000 (tiles) and $4000 (map).

Build and activate the 4-channel HDMA perspective split.

Configures four HDMA channels that cooperate each frame:

Channel A: Switches BGMODE register from Mode 3 (sky) to Mode 7 (ground) at the split scanline (scanline 96).
Channel B: Toggles TM (main screen enable) from BG2 (sky) to BG1 (ground).
Channel C: Writes per-scanline M7A values for horizontal perspective scaling.
Channel D: Writes per-scanline M7D values for vertical perspective scaling.

The perspective tables compress distant rows and expand near rows, creating the illusion of a 3D ground plane receding into the horizon. The scroll offsets (sx, sy) control the camera position on the Mode 7 ground.

Parameters

sx	Horizontal scroll offset for the Mode 7 ground plane.
sy	Vertical scroll offset for the Mode 7 ground plane.

◆ main()

int main ( void )

Entry point – F-Zero-style Mode 7 perspective with HDMA split-screen.

Sets up a dual-mode display: the top 96 scanlines render a Mode 3 sky background (BG2), while the bottom 128 scanlines render a Mode 7 ground plane (BG1) with per-scanline perspective scaling via HDMA. The D-pad scrolls the ground plane. HDMA tables are rebuilt every frame by the assembly helper to reflect the current scroll position.

Returns: Does not return (infinite loop).

Variable Documentation

◆ pad0

u16 pad0

Mode 7 ground tilemap (128x128 entries, one byte per tile index).

Mode 7 tilemaps are 128x128 bytes. Each byte is a tile index (0-255) referencing the 8bpp tile set. Loaded to VRAM via dmaCopyVramMode7() which handles the interleaved format (map in low bytes, tiles in high bytes).

Mode 7 ground tile pixel data (256 tiles, 64 bytes each = 16KB).

Each tile is 8x8 pixels at 8bpp (one byte per pixel, 64 bytes/tile). Written to the high bytes of VRAM words by dmaCopyVramMode7().

256-color palette for the ground plane (512 bytes). Current joypad button state