XFree86-DGA is not intended as a direct rendering API, but rather, as a mechanism to "get the X Server out of the way" so that some other direct rendering API can have full access to the hardware. With this in mind, DGA does provide clients some direct access to the hardware without requiring a separate rendering API, but this access is limited to direct linear framebuffer access.
Most of the reasons for the XFree86-DGA extension's existence are now better served in other ways. Further development of this extension is not expected, and it may be deprecated in a future release. The features that continue to be useful will either be provided through other existing mechanisms, or through an extension that address those needs more specifically.
XFree86-DGA is initialized by passing a number corresponding to a valid XDGAMode to XDGASetMode(). Clients can get a list of valid modes from XDGAQueryModes(). Each XDGAMode corresponds to a different framebuffer layout.
XDGAQueryModes() returns a pointer to an array of XDGAModes which are valid for the given screen. num is the number of elements in the array. The returned array can be freed with XFree(3). The XDGAMode structure is as follows:
typedef struct {
int num;
char *name;
float verticalRefresh;
int flags;
int imageWidth;
int imageHeight;
int pixmapWidth;
int pixmapHeight;
int bytesPerScanline;
int byteOrder;
int depth;
int bitsPerPixel;
unsigned long redMask;
unsigned long greenMask;
unsigned long blueMask;
short visualClass;
int viewportWidth;
int viewportHeight;
int xViewportStep;
int yViewportStep;
int maxViewportX;
int maxViewportY;
int viewportFlags;
int reserved1;
int reserved2;
} XDGAMode;
XDGASetMode() initialises the XDGAMode corresponding to num. To exit DGA mode and return to normal server operation, call XDGASetMode() with num set to zero. XDGASetMode() returns a pointer to an XDGADevice if successful. The XDGADevice can be freed with XFree(3). The XDGADevice structure is as follows:
typedef struct {
XDGAMode mode;
unsigned char *data;
Pixmap pixmap;
} XDGADevice;
XDGAQueryExtension() checks for the presence of the extension and returns the event and error bases.
XDGAQueryVersion() returns the XFree86-DGA major and minor version numbers.
XDGAOpenFramebuffer() maps the framebuffer memory. The client needs sufficient privileges to be able to do this. XDGAOpenFramebuffer() should be called prior to initializing a DGA mode if direct framebuffer access is desired for that mode. XDGAOpenFramebuffer() does not need to be called if direct framebuffer access is not required. If the framebuffer is opened,
XDGACloseFramebuffer() should be called prior to client exit to unmap the memory.
XDGAChangePixmapMode() can be used to change between two pixmap sizes in cases where a Pixmap is available for Xlib rendering. The following values for the mode parameter are available:
XDGASetViewport() sets the upper left-hand corner of the rectangle of framebuffer that is to be displayed on the screen. Not all locations may be supported by the hardware and requested locations will be adjusted according to the xViewportStep and yViewportStep fields in the XDGAMode.
flags can be XDGAFlipRetrace or XDGAFlipImmediate to adjust the viewport location at the next vertical retrace or immediately. Values other than the supported values advertised in the mode's viewportFlags field will result in hardware-specific default behavior. XDGAFlipImmediate will block until the flip is completed. XDGAFlipRetrace will generally NOT block so it is necessary to monitor the viewport status with XDGAGetViewportStatus(). XDGAFlipImmediate requests during pending XDGAFlipRetrace requests will be ignored.
XDGAGetViewportStatus() keeps track of the XDGASetViewport() requests still pending. The return value of the function will have consecutive bits set (LSB justified), each bit representing a pending viewport change. For example:
while(XDGAGetViewportStatus(dpy, screen));
waits for all pending viewport changes to finish.
while(0x2 & XDGAGetViewportStatus(dpy, screen));
waits until all but the last viewport changes have completed.
XDGACreateColormap() is similar to the Xlib function XCreateColormap(3) except that it takes an XDGADevice as an argument instead of a Window and Visual. Though XCreateColormap(3) may create usable colormaps in some cases, XDGACreateColormap() is the preferred method for creating colormaps in DGA since there may not be an advertised visual compatible with the DGA device.
XDGAInstallColormap() must be used to install colormaps in DGA mode. XInstallColormap(3) will not work.
XDGASelectInput() enables DGA's own event mechanism. This function is similar to XSelectInput(3), and all Xlib Key, Button and Motion masks are supported. The following DGA events are defined:
typedef struct {
int type; /* ButtonPress or ButtonRelease + the DGA event base*/
unsigned long serial; /* # or last request processed by the server */
Display *display; /* Display the event was read from */
int screen; /* The screen number the event came from */
Time time; /* milliseconds */
unsigned int state; /* key or button mask */
unsigned int button; /* detail */
} XDGAButtonEvent;
typedef struct {
int type; /* KeyPress or KeyRelease + the DGA event base*/
unsigned long serial; /* # or last request processed by the server */
Display *display; /* Display the event was read from */
int screen; /* The screen number the event came from */
Time time; /* milliseconds */
unsigned int state; /* key or button mask */
unsigned int keycode; /* detail */
} XDGAKeyEvent;
typedef struct {
int type; /* MotionNotify + the DGA event base*/
unsigned long serial; /* # or last request processed by the server */
Display *display; /* Display the event was read from */
int screen; /* The screen number the event came from */
Time time; /* milliseconds */
unsigned int state; /* key or button mask */
int dx; /* relative pointer motion */
int dy; /* relative pointer motion */
} XDGAMotionEvent;
XDGAKeyEventToXKeyEvent() is a helper function to translate XDGAKeyEvents into XKeyEvents suitable for use with XLookupKeysym(3).
XDGAFillRectangle(), XDGACopyArea(), and XDGACopyTransparentArea() are included with some reservation since DGA is not intended as a rendering API. These are merely convenience routines and are optionally supported. The associated flags will be set in the XDGAMode's flags field if these functions are supported. These functions will be no-ops otherwise. they do not provide direct access to the hardware, but are simply context-less operations performed by the server.
XDGASync() blocks until all server rendering to the framebuffer completes. If Xlib or the 3 rendering functions above are used, XDGASync() must be called before the client directly accesses the framebuffer as the server rendering is asynchronous with the client and may have not completed. This is especially important if the XDGAConcurrentAccess flag is not set in the XDGAMode's flags field since concurrent access by the server and client may result in a system lockup.