The attribute Function

 

int attribute (int mode, int type, void *data)
The mode-parameter may have the following values, but not every mode and type will work together. For the correct specification see the appropriate table. The modes PRE and POST are used in the transformation function and only mentioned here for completeness.

   /* modes */
   G_MODE_QUERY
   G_MODE_GET
   G_MODE_SET
   G_MODE_PRE
   G_MODE_POST
   G_MODE_SWAP

This paragraph describes the possible modes and their functionality:

• G_MODE_QUERY This mode will return exactly one integer value, whereas zero equals 'no' or 'off', one equals 'yes' or 'on' and minus one represents an error condition. The third item data is ignored at all.
• G_MODE_GET In this mode the demanded data will be given back by the third item, which is casted to the correct data type. On successful completion the return value is zero, otherwise minus one.
• G_MODE_SET In this mode the attribute will be set to the given data. Same error handling as in G_MODE_GET.
• G_MODE_SWAP A special mode, which is only used for the attribute "double-buffer" and described there.

Now the list of attributes, which can be demanded or set by the attribute() function. The attributes are not only depending upon the graphic-hardware, but mostly on the device-driver.

  G_RASTER_ABILITY
  G_COLOR_ABILITY
  G_ZBUFF_ABILITY
  G_RESOLUTION
  G_ASPECTRATIO
  G_BACKGROUND_COLOR
  G_LINE_COLOR
  G_LINE_TYPE
  G_ANTIALIAS
  G_DEPTHCUE
  G_PATCH_SUPROP
  G_TEXT_COLOR
  G_TEXT_TYPE
  G_DOUBLEBUFFER
  G_LIGHT_MODEL
  G_LIGHT_NUMBER
  G_HAS_DOUBLEBUFFER
  G_ORIGIN
  G_TEXTURE

The following table shows the possible combinations of modes, types and the appropriate data-type needed. (-- means data ignored, return value of one means yes)

 attribute          modes        *data                comment
 ---------          -----        -----                -------
 G_RASTER_ABILITY   QUERY          -                  hardw. for raster graphic
 G_COLOR_ABILITY    QUERY          -                  hardware for colors
 G_ZBUFF_ABILITY    QUERY          -                  hardware z-buffering
 G_RESOLUTION       GET | SET    RESOLUTION_TYPE xy   size of window in pixel
 G_ASPECTRATIO      GET          double aspect        win_size_x / win_size_y
                                                      (only 1.0 for now)
 G_BACKGROUND_COLOR GET | SET    VEC3 rgb
 G_LINE_COLOR       GET | SET    VEC3 rgb
 G_LINE_TYPE        GET | SET    int itype            (only X11: default = 0, 
                                                       dashed < 0 < thickness)
 G_ANTIALIAS        GET | SET    int yes_no
 G_DEPTHCUE         GET | SET    DEPTHCUE_TYPE depthcue
 G_PATCH_SUPROP     GET | SET    SUPROP_DEV suprop
 G_TEXT_COLOR       GET | SET    VEC3 rgb
 G_TEXT_TYPE         -             -                  (not implemented)
 G_DOUBLEBUFFER     GET|SET|SWAP int yes_no
 G_LIGHT_MODEL      SET          int on_off           inhibit light calculation
 G_LIGHT_NUMBER     QUERY          -                  number of light sources 
 G_HAS_DOUBLEBUFFER  -             -                  (not implemented)
 G_ORIGIN           GET | SET    RESOLUTION_TYPE xy   position of window

In the table above the following typedefs are used:

 int on_off, yes_no;          /*  NO, OFF or YES, ON */

 typedef struct suprop_dev {
  double emission[3];  /* rgb color emission (incl. intensity) */
  double ambient[3];   /* ambient rgb reflectance              */
  double diffuse[3];   /* diffuse rgb reflectance              */
  double specular[3];  /* specular rgb reflectance             */
  double specular_exp; /* specular reflectance exponent        */
  double transparency; /* transparency factor (0..1)           */
 } SUPROP_DEV;

 typedef struct depthcue_type {
  int on_off; /* OFF, ON */
  double zmin; /* dist. where depth cueing begins (full intensity) */
  double zmax; /* dist. where depth cueing ends (reduced intensity)*/
  double dark; /* max. reduction of intensity (0.0 <= dark <= 1.0) */
 } DEPTHCUE_TYPE;