**LAYER DIM** *x1*,*y1*,*x2*,*y2* sets the clip window for the current layer from (*x1*,*y1*) to (*x2*,*y2*). Areas of the layer outside this window are not visible. Note that all *Layer 1* modes and *Layer 0* share the same clip window; *Layer 2*, *Layer 3* and the *Sprite System* have their own separate clip windows. Refer to *Chapter 22* for more information on how clipping windows are defined using the *Next Registers*. The compound command: **LAYER CLEAR** will reset all layer information to defaults. This is also done by **NEW**. It resets banks, mode, *Layer 2* enable status, layer offsets / clipping windows and layer ordering. ### Tiling Since straight graphics commands can be slow, *NextBASIC* provides a set of commands that can help recreate parts of, or entire *Layer 2* and *LoRes* screens, very quickly; something that can be very useful especially when a lot of screen elements are being repeated. These screen elements are called *tiles* and much like their real-word counterparts, they are a self-contained graphical rectangular pattern. *Tiles* can be repeated as many times as we need them to, or be completely independent. Each *tile* can be *8x8 pixels* or *16x16* pixels in size. This allows a 16K *bank* to hold *256* 8x8 tiles or *64* 16x16 tiles. *Tiles* are numbered *0...255*. Therefore, a complete set of 8x8 *tiles* occupies a *single* 16K bank, and a complete set of 16x16 *tiles* occupies *four* 16K banks. If you use 16x16 *tiles*, you can restrict the *tile* number used and therefore reduce the memory requirements (e.g. if you need *64 or fewer* different *tiles*, only *1* 16K bank is required). Additionally for *tiles* to be recalled, a special linear map, called a *tilemap*[^p119-2], of 8-bit *tile* numbers is needed. The user can specify any width up to *2048 tiles*; each row of *tiles* follows directly after the previous one. The *tilemap* must be fully contained inside a single 16K bank. This gives a maximum *tilemap* size of *256x64*, *128x128*, *2048x8* etc. Any pixels in a *tile* which are the same colour as the current *global transparency colour* will not be written to the screen. If you want to draw pixels containing the *global transparency colour* you can temporarily change it to another colour (not used in your tiles) using the **PALETTE OVER** command before using **TILE**. Alternatively, you can use the **LAYER ERASE** command (see the *Quick erase and fill section* above) to clear regions of the screen to the *global transparency colour* before drawing tiles on top. *Layer 2* and *LoRes tilemaps* are stored separately, so you can use both simultaneously. The **TILE** commands affect the currently selected layer/mode. These are: **TILE BANK** *n* which defines bank *n* as containing the *tiles* (up to 4 banks n...n+3 if 16x16 tiles). **TILE DIM** *n*,*offset*,*w*,*tilesize* defines bank *n* as containing the *tilemap*, starting at offset *offset* in the bank. The *tilemap* is width *w* (1–2048) and uses *8x8* (tilesize=8) or *16x16* (tilesize=16) *tiles*. **TILE**\ **TILE AT** *x*,*y* Draws an entire screen from *tilemap*, from *tile offset x,y* in the *tilemap* (0,0 if not specified). **TILE** w,h\ **TILE** w,h **AT** x,y [^p119-2]: You may remember that we spoke of tiles before, when initially discussing Layer 3 in Chapter 14. The principle is the same (a repeated rectangular pattern) but the specifics change (9-bit colour vs. 4-bit or 1-bit colour and 16x16 -or- 8x8 pixel tiles vs. ONLY 8x8 pixel tiles).