BDCFF Object 0002: Magic wall

Object number: $0002
Game class: Boulder Dash (by Peter Liepa)
Object name: Magic wall (or Enchanted wall?)

In this document:


Properties

Animate: no
Impact explosive: no
Chain explosion action: consumed
Explosion type: n/a
Rounded: no


Attributes

Attribute format: %00000000 00000000

There are no attributes for this object type. (There is a global attribute, being the state of the wall: dormant, on or expired, but that doesn't apply to individual pieces of magic wall.)


Graphics

When dormant or expired, the magic wall looks like ordinary brick wall: Brick wall graphic

When on, the magic wall animates in a 4-stage animation sequence: Magic wall animation sequence

This GIFs show the graphics from the C64 implementation of Boulder Dash (hence the graphics are 8 double-width pixels wide and 16 pixels high).


Interactions with other objects

Magic wall is inanimate. It doesn't actually do anything by itself, and therefore doesn't interact with any other objects.

Instead, other objects (boulder, diamond) interact with magic wall.


Specification

Magic wall starts life dormant, and visually looks just like ordinary brick wall, until a boulder or diamond falls on it. Then all magic wall in the cave gets turned on for a time: it sparkles in a distinctive way, it makes a continous tinkling sound, and in this time any boulder or diamond that hits the wall gets changed into a diamond or boulder respectively, and falls through, making an appropriate diamond sound or boulder sound respectively. After a certain time has elapsed (the magic wall milling time), the magic wall expires; it goes back to looking like ordinary brick wall, no longer makes any sound, and any boulder or diamond that fall on the wall just disappear (but still make the same sound as appropriate).

States of magic wall

  1. Dormant: Looks just like ordinary brick wall, until a boulder or diamond activates it.
  2. On: Sparkles, makes sound, and changes boulders and diamonds into diamonds and boulders, until the Magic Wall Milling Time runs out.
  3. Expired: Looks just like ordinary brick wall; any boulders and diamonds hitting it just disappear but still with a sound.

Objects move two squares in one frame

Note that when a boulder or diamond hits a magic wall (whether on or not), the object effectively moves two squares in one frame: one moment it's above the wall, the next moment it's two squares down, below the wall; it's never "inside" the wall. Note also that if there is any object underneath the wall at the point where the boulder or diamond falls through, the boulder or diamond is lost (which is sometimes a helpful way of getting rid of excess boulders).

Stationary objects don't fall through

Note that a stationary boulder or diamond sits on a magic wall without falling through or turning it on. Note also that magic wall isn't "rounded"; boulders and diamonds do not roll off magic wall like they do brick wall.

General Algorithm

See the boulder specification for how boulders (and diamonds) interact with magic wall.
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