A Guide to the Graphics of the Sega Mega Drive / Genesis

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Full-Screen Scrolling

The Mega Drive has two background planes that can be scrolled independently of each other either horizontally, vertically, or on both axes.

The first stage from Revenge of Shinobi, showing two scrolling background planes.

A parallax effect can be created by scrolling the planes at different rates relative to each other. This effect adds a sense of depth by having the more distant background scroll at a slower rate than the foreground.

Here are the two planes from the Revenge of Shinobi example:

Plane A from the Revenge of Shinobi example.
Plane B from the Revenge of Shinobi example.

The foreground, Plane A, scrolls at a rate of two pixels per frame, while the background, Plane B, scrolls at a rate of one pixel per frame.

The VDP also supports a window plane, which is actually rendered as a portion of Plane A. The window plane never scrolls and is typically used to display player information. The above Revenge of Shinobi example shows the window plane on Plane A.

Here is an example from Twinkle Tale of vertical full-screen scrolling:

A scene from Twinkle Tale showing vertical scrolling on both background planes.

Horizontal and vertical scrolling are achieved in the same way, although the horizontal scroll offsets are stored in VRAM while the vertical scroll offsets have their own area of memory called VSRAM (Vertical Scroll RAM). Horizontal and vertical scrolling can be combined to scroll diagonally, as well.

Next: Row / Column Scrolling

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List of Effects:
  1. Introduction
  2. Full-Screen Scrolling
  3. Row / Column Scrolling
  4. Line Scrolling
  5. Animation
  6. Multi-Jointed Characters
  7. Tilting / Rotation
  8. Scaling
  9. Shadow and Highlight
  10. Transparency
  11. Silhouette
  12. Palette Swapping
  13. Vertical Scaling
  14. Sprite Raster Effects

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