The following are brief descriptions of the layers library functions and
related routines from the graphics library.  See the Amiga ROM Kernel
Reference Manual: Includes and Autodocs for details on each function call.


                  Table 30-5: Layers Library Functions
  ______________________________________________________________________
 |                                                                      |
 |              Function                   Description                  |
 |======================================================================|
 |              newlayerinfo()  allocating a layer_info structure.      |
 |          disposelayerinfo()  deallocating a layer_info structure.    |
 |----------------------------------------------------------------------|
 |        createupfrontlayer()  make a new layer in front of others.    |
 |         createbehindlayer()  make a new layer behind others.         |
 |               deletelayer()  remove and delete an existing layer.    |
 |----------------------------------------------------------------------|
 |                 movelayer()  change the position (not depth) of a    |
 |                              layer.                                  |
 |                 sizelayer()  change the size of a layer.             |
 |               scrolllayer()  change the internal coordinates of a    |
 |                              layer.                                  |
 |----------------------------------------------------------------------|
 |               behindlayer()  depth arrange a layer behind others.    |
 |              upfrontlayer()  depth arrange a layer in front of       |
 |                              others.                                 |
 |        movelayerinfrontof()  depth arrange a layer to a specific     |
 |                              position.                               |
 |----------------------------------------------------------------------|
 |                whichlayer()  find the frontmost layer at a position. |
 |----------------------------------------------------------------------|
 |  swapbitsrastportcliprect()  fast, non-layered and non-damaging      |
 |                              display operation.                      |
 |----------------------------------------------------------------------|
 |               beginupdate()  synchronize optimized refreshing for    |
 |                              layer.                                  |
 |                 endupdate()  end optimized layer refresh.            |
 |----------------------------------------------------------------------|
 |                 locklayer()  lock out rendering in a single layer.   |
 |               unlocklayer()  release locklayer() lock.               |
 |                locklayers()  lock out rendering in all layers of a   |
 |                              display.                                |
 |              unlocklayers()  release locklayers() lock.              |
 |             locklayerinfo()  gain exclusive access to the display's  |
 |                              layers.                                 |
 |           unlocklayerinfo()  release locklayerinfo() lock.           |
 |----------------------------------------------------------------------|
 |         installclipregion()  add a clipping region to a layer.       |
 |______________________________________________________________________|


The following routines from graphics library are also required for certain
layers library functions:

  ______________________________________________________________________
 |                                                                      |
 |            Routine                        Description                |
 |======================================================================|
 |         locklayerrom()  same as locklayer(), from layers library.    |
 |       unlocklayerrom()  release locklayerrom() lock.                 |
 |  attemptlocklayerrom()  lock layer only if it is immediately         |
 |                         available.                                   |
 |----------------------------------------------------------------------|
 |            newregion()  create a new, empty region.                  |
 |        disposeregion()  dispose of an existing region and its        |
 |                         rectangles.                                  |
 |----------------------------------------------------------------------|
 |        andrectregion()  and a rectangle into a region.               |
 |         orrectregion()  or a rectangle into a region.                |
 |        xorrectregion()  exclusive-or a rectangle into a region.      |
 |      clearrectregion()  clear a region.                              |
 |      andregionregion()  and two regions together.                    |
 |       orregionregion()  or two regions together.                     |
 |      xorregionregion()  exclusive-or two regions together.           |
 |          clearregion()  clear a region.                              |
 |______________________________________________________________________|