Mode 7
SNES rotation and scaling
Mode 7 was the SNES's signature graphical feature, enabling real-time rotation and scaling of background layers to create pseudo-3D effects in racing games and RPG world maps.
Overview
The floor rushes toward you. Mode 7 was the Super Nintendo's showcase feature — hardware-accelerated rotation, scaling, and shearing of a single background layer via a 2D affine transformation matrix. Racing games created the illusion of 3D tracks. RPGs displayed rotating world maps. F-Zero and Super Mario Kart defined the SNES era.
Mode 7 is a screen mode, not a generic SNES feature — it occupies a specific graphics-mode slot ("mode 7" out of modes 0-7) and replaces the normal multi-BG layer model with a single transformable layer.
Fast facts
- Platform: Super Nintendo (exclusive at hardware level).
- Function: Affine transformation (rotation, scaling, shearing) of one background layer.
- Effect: Pseudo-3D ground planes, rotating maps.
- Limitation: Only one BG layer (BG1); no other layer can be on screen except sprites.
- Sprites: Not transformed by Mode 7 — they overlay the transformed BG normally.
How Mode 7 works
The PPU computes each output pixel via a 2×2 affine matrix transformation of the source background:
[ x' ] [ A B ] [ x − Cx ] [ Cx ]
[ ] = [ ] [ ] + [ ]
[ y' ] [ C D ] [ y − Cy ] [ Cy ]
where:
(x, y) = output screen coordinate
(x', y') = source texture coordinate
A, B, C, D = matrix elements (16-bit signed fixed-point at $211B-$2120)
(Cx, Cy) = rotation centre ($211F-$2120)The matrix elements A, B, C, D set rotation + scaling + shearing. Combined with HDMA (Horizontal DMA — see below), the matrix can be rewritten every scanline, producing perspective-projected ground planes.
| Step | Process |
|---|---|
| 1 | Source texture stored in VRAM as one large bitmap (typically 1024×1024 px) |
| 2 | CPU writes the 2×2 affine matrix to $211B-$2120 |
| 3 | Per scanline, hardware applies matrix to compute source coordinates |
| 4 | HDMA can change matrix elements per scanline → perspective-warp |
| 5 | Output pixel sampled from the source bitmap at (x', y') |
Technical capabilities
| Feature | Hardware support |
|---|---|
| Rotation | Any angle (matrix elements via 16-bit fixed-point) |
| Scaling | Zoom in/out, independent X/Y |
| Shearing | Skew transforms |
| Perspective | Simulated by varying matrix per scanline (HDMA) |
| Per-scanline change | HDMA writes new matrix at each line |
| Mirroring | Wrap modes for the source texture |
HDMA: the perspective trick
Mode 7 itself is just one matrix — same transform for every output pixel. To get perspective (the floor that converges to a horizon), the matrix must be different per scanline: closer to the horizon, the X/Y scale is large; near the bottom of the screen, scale is small. Each scanline has its own affine matrix.
HDMA ($420C / $4300-$437F) lets the CPU set up an HDMA transfer that automatically writes new matrix values to $211B-$2120 at each scanline transition. The CPU sets up the table once per frame; the PPU does the per-line writes for free.
Without HDMA, Mode 7 only produces "rotated/scaled images". With HDMA, it produces F-Zero's rushing road.
Famous Mode 7 games
| Title | Year | Use |
|---|---|---|
| F-Zero (Nintendo, 1990 launch title) | 1990 | Racing track with rushing horizon |
| Pilotwings (Nintendo) | 1990 | Flight perspective + DSP-1 enhancement chip |
| Super Mario Kart (Nintendo) | 1992 | Track surface |
| Final Fantasy IV / V / VI (Square) | 1991-94 | World map, airship, dragon flight |
| Contra III: The Alien Wars | 1992 | Rotating boss stages |
| Yoshi's Safari | 1993 | First-person rail-shooter via Super Scope |
| Star Fox (with Super FX) | 1993 | Mode 7 used for distant terrain alongside Super FX polygons |
F-Zero showcase
| Effect | Implementation |
|---|---|
| Track rushing | HDMA matrix scaling up per scanline as Y approaches bottom |
| Turns | Rotation matrix (cos/sin) updated each frame from steering input |
| Speed sense | Rapid HDMA matrix change rate at high speed |
| Horizon | Background layer (BG2 in extended Mode 7 if available, or simply scrolled BG1 above the transformed area) |
Limitations
| Constraint | Effect |
|---|---|
| Single layer | Mode 7 replaces the multi-BG layer model — only BG1 exists |
| No sprite scaling | Sprites overlay normally; "scaled sprites against Mode 7 floor" requires pre-scaled sprite art |
| Texture size | One source bitmap, typically 128×128 tiles = 1024×1024 px |
| Memory bandwidth | HDMA per-scanline matrix updates consume DMA cycles |
| CPU cost | Per-frame matrix calculation (cos/sin) is non-trivial without DSP chip |
Workarounds
| Technique | Purpose |
|---|---|
| DSP-1 enhancement chip | Offloads matrix maths (used in Pilotwings, Super Mario Kart) |
| Pre-scaled sprites | Fake sprite scaling against Mode 7 backgrounds |
| HDMA scripting | Pre-computed matrix tables for fixed effects |
| Combine with HDMA palette change | Add gradient sky + floor effect |
Competition comparison
| System | Mode 7 equivalent? |
|---|---|
| Mega Drive | No hardware affine; software rotation/scale via DMA tricks (Toy Story, Sonic 3D Blast) — slower, lower quality |
| PC Engine | No |
| Neo Geo | Hardware sprite scaling (no BG affine) — different feature, different aesthetic |
| SNES | Yes — hardware Mode 7 |
Mode 7 was a real SNES advantage. The Mega Drive could fake rotated backgrounds via expensive software, but at lower quality and with frame-rate cost. Sega's response was Sega Virtua Processor (SVP) chip in Virtua Racing (1994) — polygon rendering, a different solution to the same "we need 3D" problem.
DSP enhancement chips
Mode 7 alone is impressive; combined with the SNES's DSP-1 (or DSP-2/3/4, Cx4, etc.) it becomes much more flexible:
| Chip | Use |
|---|---|
| DSP-1 | Matrix multiplication; Pilotwings, Super Mario Kart, Top Gear 3000 |
| DSP-2 | Different firmware; Dungeon Master |
| DSP-3 / DSP-4 | Variants for specific games |
| Cx4 | Capcom's matrix coprocessor; Mega Man X2, X3 |
These chips are functionally programmable matrix-maths coprocessors that the SNES CPU offloads to. Without them, Mode 7 racing-game maths consume 30%+ of frame budget.
Legacy
| Impact | Significance |
|---|---|
| SNES identity | Mode 7 was Nintendo's marketing differentiator vs the Mega Drive |
| Racing genre | F-Zero / Super Mario Kart defined kart-racing; influenced Mario Kart on every subsequent platform |
| Technical benchmark | "Mode 7 effect" became shorthand for any hardware-accelerated affine transformation |
| Modern recreations | Game Boy Advance had similar affine modes; modern indie games emulate the Mode 7 look as a stylistic choice |
The Game Boy Advance (2001) shipped with Modes 1-2 supporting affine background transformation — essentially Mode 7 generalised. Mario Kart: Super Circuit and many GBA games inherit the SNES Mode 7 aesthetic directly.