Solaris X Window System Developer's Guide

Selecting a Visual for an Overlay/Underlay Window

Portable applications using overlays can search for an appropriate overlay visual to use for a given underlay visual, or vice versa. Each X screen supporting the overlay extension defines a set of overlay visuals whose windows are best for use as children of underlay windows. For each underlay visual, there is a set of optimal overlay visuals. Together, all combinations of underlay visuals and their optimal overlay visuals form the set of optimal overlay/underlay pairs for that screen. The overlay and underlay visuals of an optimal pair are partners of each other.

The routine XSolarisOvlSelectPartner allows the client to select, given an underlay visual, an optimal overlay that meets certain criteria. Inversely, it also allows the client to select an optimal underlay visual given an overlay visual. The client is assured that, short of X errors not related to overlays, it can successfully create a window with the returned visual.

This routine searches through the optimal partners of the given visual, applying the criteria specified. It returns a success or failure status depending on whether it finds a visual that meets the criteria. A criterion can be one of two types:

  1. Hard criterion – A criterion that must be satisfied. Only visuals that meet hard criteria are candidates for successful matches.

  2. Soft criterion – A desirable criterion, but one that is not required.

The visual that matches all hard criteria and the most soft criteria is chosen, and its attributes are returned. If two or more visuals are found that meet all of the hard criteria and the same number of soft criteria, one of them will be chosen and returned. It is implementation dependent which one is chosen.

The syntax and arguments for XSolarisOvlSelectPartner are shown below.


XSolarisOvlSelectPartner (Display *display, int screen,   VisualID vid,

XSolarisOvlSelectType seltype, int numCriteria,   XSolarisOvlVisualCriteria

*pCriteria,   XVisualInfo *visinfoReturn,   unsigned long



Specifies the connection to the X server. 


An integer specifying the screen for the visual vid.


The XID of the visual to find a partner for. 


The type of selection that is to be done.


The number of XSolarisOvlVisualCriteria structures in the pCriteria array.


An array of criteria structures in priority order from high to low specifying the criteria to be used in selecting the visual. 


A pointer to a caller provided XVisualInfo structure. On successful return, this structure contains a description of the chosen visual.


A pointer to a bitmask that describes the criteria that were not satisfied. This return argument is meaningful only when the routine returns a value of XSolarisOvlQualifiedSuccess, or XSolarisOvlCriteriaFailure.

Argument Types

XSolarisOvlSelectType is an enumeration defining two types of selections that can be done in XSolarisOvlSelectPartner. It is defined as:


enum {  XSolarisOvlSelectBestOverlay,  XSolarisOvlSelectBestUnderlay, }


XSolarisOvlVisualCriteria is a structure defining various criteria to be used during visual selection, along with indications of the stringency of the criteria. This structure is defined as:


struct {  unsigned long     hardCriteriaMask;

unsigned long     softCriteriaMask;

int     c_class;  unsigned int     depth;  unsigned

int     minColors;  unsigned int     minRed;  unsigned int     minGreen;

    unsigned int      minBlue;  unsigned int     minBitsPerRGB;

unsigned  int     minBuffers; }


hardCriteriaMask and softCriteriaMask are bitmasks whose values can be the logical OR of any of the following bitmasks:


XSolarisOvlVisualClass          (1L<<0) #define

XSolarisOvlDepth          (1L<<1) #define

XSolarisOvl			MinColors							(1L<<2) #define

XSolarisOvlMinRed										(1L<<3) #define

XSolarisOvl		MinGreen								(1L<<4) #define

XSolarisOvl			MinBlue							(1L<<5) #define

XSolarisOvlMinBitsPerRGB      (1L<<6) #define

XSolarisOvl			MinBuffers							(1L<<7) #define

XSolarisOvlUnsharedPixels          (1L<<8) #define

XSolarisOvlUnsharedColors          (1L<<9) #define

XSolarisOvlPreferredPartner										(1L<<10)

Return Types

XSolarisOvlSelectStatus is a value that indicates whether the routine succeeded in finding a visual and, if it failed, the reason for the failure. The return value can be one of:


enum { 	XSolarisOvlSuccess, 	XSolarisOvlQualifiedSuccess,

	XSolarisOvlCriteriaFailure, 	XSolarisOvlFailure, }


Multiple Criteria Sets

XSolarisOvlSelectPartner supports a degradation sequence of criteria sets. This means that multiple criteria sets can be specified in a single call. First, the routine attempts to find a visual matching the first criteria set. If a visual is found that meets all of the hard criteria of the first set, this visual is chosen. If no visual meets all hard criteria of the first set, the routine performs a search using the second criteria set. This process continues until either a visual is found that meets the hard criteria of some criteria set, or all sets have been used to search. This degradation sequence allows clients to specify the criteria for the most preferred visual as the first criteria set. Visuals that are acceptable but are less desirable can be specified in criteria sets following the first criteria set. This allows the search to proceed through a progressive relaxation in the client's requirements for the visual with a single subroutine call.

Any of the possible criteria can be specified either as a hard or soft criteria for a particular criteria set. For a given set, hardCriteriaMask is the logical OR of the criteria bitmasks that are to be applied as hard criteria during the search. Likewise, softCriteriaMask is the logical OR of the soft criteria bitmasks.

Some criteria have values associated with them. These values are provided by other data members in the XSolarisOvlVisualCriteria structure. In the criteria descriptions that follow, these data members are mentioned where applicable.

If either hardCriteriaMask of a criteria set is to 0, any visual will match that criteria set with a hard match. Likewise, setting the softCriteriaMask of a criteria set to 0, is sufficient to guarantee at least a soft match for that criteria set.