Levels / Solid Material Mask
A level may contain sky, dirt, and grass, but it is the solid material mask that determines the physicality of the objects depicted in the level. A solid material mask is a huge grid of invisible blocks representing solid material and empty space throughout the level. Objects can move freely through areas marked as empty space, but they can not pass through areas of solid material. Each of the blocks in a solid material mask measures 8 by 8 pixels, so levels can have very detailed contours.

Besides solid material and empty space, the solid material mask allows for a third kind of material: ledge material. This type of material acts like solid material upon objects that are falling downward, but it acts like empty space upon objects that are moving in any other direction. This kind of material is used to construct ledges that characters can land on from above, or jump onto from below.

Information on designing solid material masks is available in the Solid Material Mask Editing section.