ggiCheckMode, ggiCheckTextMode, ggiCheckGraphMode, ggiCheckSimpleMode -
Check or negotiate a text/graphics mode on a visual
int ggiCheckMode(ggi_visual_t visual, ggi_mode *tm);
int ggiCheckTextMode(ggi_visual_t visual, int cols, int rows,
int vcols, int vrows, int fontx, int fonty,
ggi_graphtype type, ggi_mode *suggested_mode);
int ggiCheckGraphMode(ggi_visual_t visual, int x, int y,
int xv, int yv, ggi_graphtype type,
int ggiCheckSimpleMode(ggi_visual_t visual, int xsize, int ysize,
int frames, ggi_graphtype type, ggi_mode *md);
ggiCheckMode checks whether or not the given mode will work on the
visual. If it does not work, it will modify the values of passed
ggi_mode(3) structure so that the mode works. This mode negotiation
allows the application to discover modes that are both supported by the
visual and suitable to the application.
ggiCheckTextMode checks whether the text mode with the given visible
and virtual dimensions and the font size is supported.
ggiCheckGraphMode checks whether the graphics mode with the given
visible and virtual dimensions and type is supported.
ggiCheckSimpleMode checks whether the graphics mode with the given
visible dimensions, type, and number of buffers is supported. This is
used in lieu of ggiCheckGraphMode if multiple buffering is desired.
For ggiCheckTextMode, ggiCheckGraphMode and ggiCheckSimpleMode,
suggested_mode is either NULL or a pointer to a ggi_mode(3) which will
be filled in with the negotiated mode parameters.
For ggiCheckTextMode and ggiCheckGraphMode, a return of 0 means that
the corresponding set mode call for this mode would succeed. Otherwise,
the mode given cannot be set. In this case, suggested_mode is changed
to the suggested mode.
If the only modifications made to the structure is replacing GGI_AUTO
or GT_AUTO value, the functions return success.
RULES FOR MODE NEGOTIATION
First, if GGI_AUTO (or GT_AUTO for the graphtype) is specified for any
of the members of tm, these are filled in with the recommended values.
The values could be to a maximum, preferred, or GGI_DEFMODE resolution,
and will be compatible with any other constraints.
An application that does not care about a specific parameter should
always specify GGI_AUTO or GT_AUTO for it.
The resulting mode is guaranteed to be valid; if not, the application
can assume that it cannot set any mode on the given visual and give up.
The suggested mode is derived as follows:
1 Resolutions are always adjusted up. If you want the next lower,
start out at 1x1 (or somewhere else reasonable) and jump up the
Only if the maximum resolution would be exceeded, resolutions are
adjusted down to the maximum.
The above applies to visible and virtual size. If there is
interference between them, the visible size is satisfied first if
possible, then the virtual size.
The adjustment of one value do not normally affect other values.
For example, if (visible) 320x100 (virtual 320x200) is requested,
the visible size may be adjusted to 320x200, but virtual size will
be left alone. Of course, if the virtual size becomes less than
visible size, then it will be adjusted as well.
2 Font sizes are handled the other way round: they are adjusted down
except when there is nothing below.
3 A specific graphtype is changed only if the card does not support
it at all. If the maximum resolution is exceeded, then that is
adjusted down and not the graphtype. This assumes, that if you
request true-color, you really want that and not so badly the
resolution you requested. If this is not the case, you can still
retry with another graphtype or GT_AUTO.
If graphtype is changed, it is adjusted in ascending order if
possible: e.g. 1->4->8->15->16->24/32 bit. So you always get a mode
which can do more than you requested. Only when no better modes are
available, the type is adjusted down.
Try a 320x200x8 mode:
err = ggiCheckGraphMode(vis, 320, 200, GGI_AUTO, GGI_AUTO, GT_8BIT,
/* Check if returned mode is ok... */
ggiOpen(3), ggiSetMode(3), ggi_mode(3)