A Viewport Overlay Capability

Using DSAs you can add graphic overlays to your dungeon.  The overlay graphics are stored in file CSBGraphics.dat and each has a number.  Th &OVERLAY word in your DSA code selects an overlay and provides information as to what percentage of the original viewport is to be displayed and what percentage of the Overlay.  For example, you might select 90% viewport and 10% Overlay to give a slightly hazy effect of fog.  If you were to select 100% overlay then you would not be able to see anything in the original viewport graphic.  There is a demonstration of using Overlays to create the appearance of being under water.

The &OVERLAY word requires 5 parameters, like this:

0 50 0 0 12 &OVERLAY
p1 = flags

p2 = 50 = transparency

p3 = 0 = timeout (if non-zero - Number of ticks of clock before overlay is automatically removed)

p4 = various uses

p5 = 12 = overlay number

The overlays themselves are stored in CSBGraphics.dat as type 'Viewport Overlay'.  Each must be a 256-color bitmap (.bmp) format and be exactly 224 pixels wide by 136 pixels high.

There is also a capability of changing the Viewport Palette.