EnvironmentHandler

Environment handlers render the backdrop, the points at infinity that aren't covered by anything in the scene. This is the natural place to draw the sky, the distant horizon, or a procedural nebula in space.

Handler Activation Function

   XCALL_( int ) MyEnvironment( long version, GlobalFunc *global,
      LWEnvironmentHandler *local, void *serverData );

The local argument to an environment handler's activation function is an LWEnvironmentHandler.

   typedef struct st_LWEnvironmentHandler {
      LWInstanceFuncs *inst;
      LWItemFuncs     *item;
      LWRenderFuncs   *rend;
      LWError         (*evaluate) (LWInstance, LWEnvironmentAccess *);
      unsigned int    (*flags) (LWInstance);
   } LWEnvironmentHandler;

The first three members of this structure point to the standard handler functions. In addition to these, an environment handler provides an evaluation function and a flags function.

evaluate( instance, access )

This is where the environment handler does its work. At each time step in the animation, the evaluation function is called for each affected pixel in the image. The access argument, described below, contains information about the environment to be colored.

flags( instance )

Returns an int. The flags are

LWENF_TRANSPARENT

Interface Activation Function

   XCALL_( int ) MyInterface( long version, GlobalFunc *global,
      ??? *???, void *serverData );

TBD

Environment Access

This is the structure passed to the handler's evaluation function.

   typedef struct st_LWEnvironmentAccess {
      LWEnvironmentMode mode;
      double            h[2], p[2];
      LWDVector         dir;
      double            colRect[4][3];
      double            color[3];
   } LWEnvironmentAccess;

mode

The context of the evaluation. Currently this distinguishes between rendering (EHMODE_REAL) and lower quality previewing (EHMODE_PREVIEW).

h, p

The extents, in polar coordinates, of a rectangular area of the backdrop. Heading h is the angle around the Y axis and pitch p is the angle around the X axis. They're expressed in radians. In preview mode, the area will be relatively large, while in real mode the area will generally be the size of a pixel.

colRect

In preview mode, this is where the evaluation function returns the color at the corners of the rectangular area defined by h and p. The preview display interpolates between these at points inside the rectangle.

colRect[0] gets the color of (h[0], p[0])
colRect[1] gets the color of (h[0], p[1])
colRect[2] gets the color of (h[1], p[0])
colRect[3] gets the color of (h[1], p[1])

color

In real mode, this is where the evaluation function returns the color of the rectangle defined by h and p.