CustomObjHandler
CustomObjInterface

Availability LightWave 6.0 | Component Layout | Header lwcustobj.h

Layout uses null objects as placeholders for animation data. Nulls can be used as parents to add degrees of freedom to the motion of other objects, or as references for texturing, or as camera targets. Plug-ins can also rely on nulls as a way for users to interactively set parameters.

A custom object handler can be associated with a null to customize its appearance in Layout's interface. This is useful for providing visual feedback about, for example, the range or magnitude of an effect controlled by the null. Custom nulls will often be an adjunct to a plug-in of another class that uses nulls for data entry, but they can also be used by themselves for things like guides and rulers.

When applied to non-null objects, a custom object plug-in supplements LightWave's drawing of the object in the interface. Hypervoxels, for example, uses a custom object handler to draw wireframe bounding spheres around the particles associated with an object.

Handler Activation Function

   XCALL_( int ) MyCustomObj( long version, GlobalFunc *global,
      LWCustomObjHandler *local, void *serverData );

The local argument to a custom object's activation function is an LWCustomObjHandler.

   typedef struct st_LWCustomObjHandler {
      LWInstanceFuncs *inst;
      LWItemFuncs     *item;
      LWRenderFuncs   *rend;
      void            (*evaluate)(LWInstance, const LWCustomObjAccess *);
      unsigned int    (*flags)   (LWInstance);
   } LWCustomObjHandler;

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

The context argument to the inst->create function is the LWItemID of the associated object.

evaluate( instance, access )
Draw the object on the interface using the information in the access structure, described below.
f = flags( instance )
Returns bit flags combined using bitwise-or. LWCOF_SCHEMA_OK, currently the only flag, tells Layout that you support drawing in schematic viewports.

Interface Activation Function

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

This is the standard interface activation for handlers. Users open a custom object's interface by pressing an Options button on the Geometry tab of the Object Properties panel.

Custom Object Access

The access structure contains drawing functions and fields indicating which of the interface views the object will be drawn in and whether the object is currently selected.

Within the limitations of the drawing functions, there aren't any restrictions on what your custom object may look like. But in most cases it will be helpful to users if your object's appearance is consistent in color and style with the rest of Layout's interface.

   typedef struct st_LWCustomObjAccess {
      int   view;
      int   flags;
      void *dispData;
      void (*setColor)   (void *, float rgba[4]);
      void (*setPattern) (void *, int lpat);
      void (*setTexture) (void *, int, unsigned char *);
      void (*setUVs)     (void *, double[2], double[2], double[2],
                            double[2]);
      void (*point)      (void *, double[3], int csys);
      void (*line)       (void *, double[3], double[3], int csys);
      void (*triangle)   (void *, double[3], double[3], double[3],
                            int csys);
      void (*quad)       (void *, double[3], double[3], double[3],
                            double[3], int csys);
      void (*circle)     (void *, double[3], double, int csys);
      void (*text)       (void *, double[3], const char *, int just,
                            int csys);
      LWDVector viewPos, viewDir;
   } LWCustomObjAccess;
view
The view the object will be drawn in. Possible values are

LWVIEW_ZY
LWVIEW_XZ
LWVIEW_XY
LWVIEW_PERSP
LWVIEW_LIGHT
LWVIEW_CAMERA
LWVIEW_SCHEMA

These refer to the orthographic, perspective, light, camera and schematic views available to the user in the Layout interface.

flags
Contains bitfields with information about the context of the render request. Currently the only flag defined is LWCOFL_SELECTED, which tells you whether the object should be rendered in its selected state.
dispData
An opaque pointer to private data used by Layout. Pass this as the first argument to the drawing functions.
setColor( dispData, rgba )
Set the current drawing color, including the alpha level. Calling this is optional. By default, all drawing is done in the color set by the user in the Scene panel when the custom object isn't selected, and in yellow when the object is selected. Color settings don't persist between calls to the evaluation function, nor do they change the settings in the Scene panel.
setPattern( dispData, linepat )
Set the current line pattern. The pattern codes are

LWLPAT_SOLID
LWLPAT_DOT
LWLPAT_DASH
LWLPAT_LONGDOT

As with setColor, calling setPattern is optional. By default, all drawing is done with solid lines. Line pattern settings don't persist between evaluations.

setTexture( dispData, size, imagebytes )
Set the current image for texture mapping. This image is mapped onto quads drawn by the quad function. The size is the width (and height) of the image in pixels and must be a power of 2. The pixel data is an OpenGL image in GL_RGBA format and GL_UNSIGNED_BYTE data type. Each pixel is represented by a set of four contiguous bytes containing red, green, blue and alpha values ranging from 0 to 255.
setUVs( dispData, uv0, uv1, uv2, uv3 )
Set the UVs for texture mapping. This sets the position of the texture image on each polygon drawn by the quad function until the next call to setUVs.
point( dispData, xyz, coord_sys )
Draw a point at the specified position. The point will be drawn in the color set by the most recent setColor call, or in the default color if no color was set. The coordinate system argument identifies the coordinates in which the position is expressed and may be one of the following.
LWCSYS_WORLD
"Absolute" coordinates, unaffected by the position, rotation and scale of the underlying null object.
LWCSYS_OBJECT
"Relative" coordinates. Layout will transform the point.
LWCSYS_ICON
A special coordinate system that works like LWCSYS_OBJECT but scales with the grid size. Layout's camera and light images are examples of the use of this mode.
line( dispData, end1, end2, coord_sys )
Draw a line between the specified endpoints using the current color and line pattern.
triangle( dispData, v1, v2, v3, coord_sys )
Draw a solid triangle with the specified vertices using the current color.
quad( dispData, v1, v2, v3, v4, coord_sys )
Draw a solid quadrangle with the specified vertices using the current color or texture.
circle( dispData, center, radius, coord_sys )
Draw a circle of the given radius around the specified center point using the current color and line pattern. Circles can only be drawn in the orthographic views, not in the light, camera or perspective views.
text( dispData, pos, textline, justify, coord_sys )
Draw a single line of text using the current color and line pattern. The justify argument determines whether the text will be drawn to the left (0) or right (2) of the position, or centered (1) on it.

History

In LightWave 7.0, LWCUSTOMOBJ_VERSION was incremented to 5 because of significant changes to the LWCustomObjAccess structure. The previous version of the structure looked like this. 

  typedef struct st_LWCustomObjAccess_V4 {
      int   view;
      int   flags;
      void *dispData;
      void (*setColor)   (void *, float rgb[3]);
      void (*setPattern) (void *, int lpat);
      void (*point)      (void *, double[3], int csys);
      void (*line)       (void *, double[3], double[3], int csys);
      void (*triangle)   (void *, double[3], double[3], double[3],
                            int csys);
      void (*circle)     (void *, double[3], double, int csys);
      void (*text)       (void *, double[3], const char *, int csys);
   } LWCustomObjAccess_V4;

The setTexture, setUVs and quad functions are missing, and the text function lacks the justification argument.

Example

The barn sample draws a simple barn or house shape. It's easy to tell which way this shape is pointing, which makes it useful for quickly testing programming assumptions about the effects of animation parameters on the orientation of objects.