Name MESA_screen_surface Name Strings EGL_MESA_screen_surface Contact Brian Paul To discuss, join the dri-egl@lists.freedesktop.org list. Status Preliminary - totally subject to change. Version 11 (27 January 2006) Number TBD Dependencies EGL 1.0 or later. Overview EGL 1.1 supports three types of drawing surfaces: * Window surfaces * Pixmap surfaces * Pbuffer surfaces This extension defines a fourth type of drawing surface: * Screen surface A screen surface is a surface for which the (front) color buffer can be directly displayed (i.e. scanned out) on a monitor (such as a flat panel or CRT). In particular the color buffer memory will be allocated at a location in VRAM (and in a suitable format) which can be displayed by the graphics hardware. Note that the width and height of the screen surface need not exactly match the monitor's current resolution. For example, while the monitor may be configured to to show 1024x768 pixels, the associated screen surface may be larger, such as 1200x1000. The "screen origin" attribute will specify which region of the screen surface which is visible on the monitor. The screen surface can be scrolled by changing this origin. This extension also defines functions for controlling the monitor's display mode (width, height, refresh rate, etc), and specifing which screen surface is to be displayed on a monitor. The new EGLModeMESA type and related functions are very similar to the EGLConfig type and related functions. The user may get a list of supported modes for a screen and specify the mode to be used when displaying a screen surface. Issues 1. Should EGL_INTERLACE be a supported mode attribute? Arguments against: No, this should be provided by another extension which would also provide the mechanisms needed to play back interlaced video material correctly on hardware that supports it. This extension should prefer non-interlaced modes. [M. Danzer] Arguments for: An interlaced display can be of use without considering video material. Being able to query whether a screen is operating in interlaced mode can be used by applications to control their drawing. For example: avoid drawing 1-pixel-wide horizontal lines if screen is interlaced. [B. Paul] Resolution: Defer for future extension? 2. Should EGL_REFRESH_RATE be a supported mode attribute? Arguments for: Yes, it's been shown that applications and/or users need to select modes by this. [M. Danzer] Many examples have been given in which it's desirable to let the user choose from a variety of refresh rates without having to restart/reconfigure. [B. Paul] Arguments against: TBD. Resolution: Yes. 3. Exactly how should the list of modes returned by eglChooseConfigMESA be sorted? Current method is described in the text below. Subject to change. Alternately, leave the sorting order undefined so that each implementation can return the modes in order of "most desirable" to "least desirable" which may depend on the display technology (CRT vs LCD, etc) or other factors. 4. How should screen blanking be supported? Note that a screen can be disabled or turned off by calling eglShowSurface(dpy, scrn, EGL_NO_SURFACE, EGL_NO_MODE_MESA). But what about power-save mode? I would defer this to other extensions that depend on this one. I can imagine people wanting different semantics not just in relation to the power management API being exposed (DPMS or whatever) but also relating to what events can trigger EGL_CONTEXT_LOST. Also I'm not sure whether power management commands are properly operations on the Display or on a screen surface. [A. Jackson] 5. Should the EGL_PHYSICAL_SIZE_EGL query be kept? The size information isn't always reliable (consider video projectors) but can still be used to determine the pixel aspect ratio. Resolution: Omit. The EGL 1.2 specification includes queries for the display resolution and pixel aspect ratio. 6. Should detailed mode timing information be exposed by this API? Probably not. Instead, offer that information in a layered extension. 7. How should the notion of a screen's "native" mode be expressed? For example, LCD panels have a native resolution and refresh rate that looks best but other sub-optimal resolutions may be supported. The mode attribute EGL_OPTIMAL_MESA will be set for modes which best match the screen. [M. Danzer] 8. Should eglQueryModeStringMESA() be included? This function returns a human-readable string which corresponds to an EGLMode. Arguments for: A mode name such as "HDTV-720P" might mean more to users than "1280x720@60Hz" if the later were generated via code. Arguments against: There's no standard syntax for the strings. May cause more trouble than it's worth. Postpone for future extension. [A. Jackson] Latest discussion leaning toward omitting this function. 9. Should we use "Get" or "Query" for functions which return state? The EGL 1.x specification doesn't seem to be totally consistent in this regard, but "Query" is used more often. Use "Get" for mode-related queries (as for EGLConfigs) but "Query" for everything else. 10. What should be the default size for screen surfaces? For Pbuffer surfaces the default width and height are zero. We'll do the same for screen surfaces. Since there's no function to resize surfaces it's useless to have a 0x0 screen, but this isn't a situation that'll normally be encountered. 11. Should there be a function for resizing a screen surface? Suppose one wants to change the screen's size in the EGL application. Also suppose there's a hardware restriction such that only one screen surface can exist at a time (either for lack of memory or because of memory layout restrictions). The basic idea is that the currently displayed screen surface must be deallocated before a new one can be created. Perhaps a resize function would work better? 12. How should sub-pixel LCD color information be made available? What about the display's gamma value? Perhaps expose as additional read-only mode attributes. Perhaps postpone for a layered extension. 13. What happens if the user attempts to delete a screen surface that is currently being shown? Spec currently says that's illegal and that an error (TBD) will be generated. 14. What if the physical screen size can't be determined? Should a query of EGL_PHYSICAL_SIZE_MESA return [0,0]? Obsolete: EGL_PHYSICAL_SIZE_MESA not used. 15. Suppose the device's number of RAMDACs is different from the number of output ports. For example, a graphics card with two RAMDACs but three ports (VGA, DVI, TV). Address this in a follow-on extension. [Matthias Hopf] 16. How should we deal with on-the-fly device changes? For example, the monitor being unplugged and replaced by another with different characteristics? A HAL event could be received via DBUS in the application [J. Smirl, A. Jackson]. Should there be an EGL mechanism for detecting this? Maybe an EGL_SCREEN_LOST error (similar to EGL_CONTEXT_LOST) can be recorded when there's a screen change. At least then the application can poll to detect this situation. Maybe leave that to a future extension. See also the EGL_SCREEN_COUNT_MESA query. 17. What if pixel-accurate panning is not supported (see eglScreenPositionMESA)? [M. Danzer] Is this a common problem? Can we ignore it for now? 18. Should eglShowSurfaceMESA be renamed to eglShowScreenSurfaceMESA? Probably. New Procedures and Functions EGLBoolean eglChooseModeMESA(EGLDisplay dpy, EGLScreenMESA screen, const EGLint *attrib_list, EGLModeMESA *modes, EGLint modes_size, EGLint *num_modes) EGLBoolean eglGetModesMESA(EGLDisplay dpy, EGLScreenMESA screen, EGLModeMESA *modes, EGLint modes_size, EGLint *num_modes) EGLBoolean eglGetModeAttribMESA(EGLDisplay dpy, EGLModeMESA mode, EGLint attrib, EGLint *value) EGLBoolean eglGetScreensMESA(EGLDisplay dpy, EGLScreenMESA *screens, EGLint screens_size, EGLint *num_screens) EGLSurface eglCreateScreenSurfaceMESA(EGLDisplay dpy, EGLConfig config, const EGLint *attrib_list) EGLBoolean eglShowSurfaceMESA(EGLDisplay dpy, EGLScreenMESA screen, EGLSurface surface, EGLModeMESA mode) EGLBoolean eglScreenPositionMESA(EGLDisplay dpy, EGLScreenMESA screen, EGLint x, EGLint y) EGLBoolean eglQueryScreenMESA(EGLDisplay dpy, EGLScreenMESA screen, EGLint attrib, EGLint *value); EGLBoolean eglQueryScreenSurfaceMESA(EGLDisplay dpy, EGLScreenMESA screen, EGLSurface *surface) EGLBoolean eglQueryScreenModeMESA(EGLDisplay dpy, EGLScreenMESA screen, EGLModeMESA *mode) const char *eglQueryModeStringMESA(EGLDisplay dpy, EGLMode mode); New Types EGLModeMESA EGLScreenMESA New Tokens New error codes: EGL_BAD_SCREEN_MESA EGL_BAD_MODE_MESA Screen-related tokens: EGL_SCREEN_COUNT_MESA EGL_SCREEN_POSITION_MESA EGL_SCREEN_BIT_MESA EGL_SCREEN_POSITION_GRANULARITY_MESA Mode-related tokens: EGL_MODE_ID_MESA EGL_REFRESH_RATE_MESA EGL_INTERLACED_MESA EGL_OPTIMAL_MESA EGL_NO_MODE_MESA Additions to Chapter X of the EGL 1.1 Specification [XXX this all has to be rewritten to fit into the EGL specification and match the conventions of an EGL extension. For now, just list all the functions with brief descriptions.] EGLBoolean eglChooseModeMESA(EGLDisplay dpy, const EGLScreenMESA screen, EGLint *attrib_list, EGLModeMESA *modes, EGLint modes_size, EGLint *num_modes) Like eglChooseConfig, returns a list of EGLModes which match the given attribute list. This does not set the screen's current display mode. The attribute list is a list of token/value pairs terminated with EGL_NONE. Supported attributes include: Name Description --------------------- --------------------------------------------- EGL_WIDTH Mode width (resolution) EGL_HEIGHT Mode height (resolution) EGL_REFRESH_RATE_MESA The mode's refresh rate, multiplied by 1000 EGL_INTERLACED_MESA 1 indicates an interlaced mode, 0 otherwise EGL_OPTIMAL_MESA Set if the most is especially optimal for the screen (ex. for particular LCD resolutions) Any other token will generate the error EGL_BAD_ATTRIBUTE. The list of modes returned by eglChooseModeMESA will be sorted according to the following criteria. See the discussion of table 3.3 in the EGL specification for more information. Selection Sort Sort Attribute Default Criteria Order Priority -------------------- -------------- ----------- ------ -------- EGL_OPTIMAL_MESA EGL_DONT_CARE Exact 1,0 1 EGL_INTERLACED_MESA EGL_DONT_CARE Exact 0,1 2 EGL_REFRESH_RATE EGL_DONT_CARE AtLeast Larger 3 EGL_WIDTH EGL_DONT_CARE AtLeast Larger 4 EGL_HEIGHT EGL_DONT_CARE AtLeast Larger 5 EGL_MODE_ID_MESA EGL_DONT_CARE Exact Smaller 6 EGLBoolean eglGetModesMESA(EGLDisplay dpy, EGLScreenMESA screen, EGLModeMESA *modes, EGLint modes_size, EGLint *num_modes) Like eglGetConfigs, returns a list of all modes supported by the given screen. The returned modes will be sorted in the same manner as for eglChooseModeMESA(). EGLBoolean eglGetModeAttribMESA(EGLDisplay dpy, EGLModeMESA mode, EGLint attrib, EGLint *value) Used to query mode attributes. The following attributes are supported: Name Return value description --------------------- ---------------------------------------------- EGL_OPTIMAL_MESA 1 indicates an optimal mode, 0 otherwise EGL_INTERLACED_MESA 1 indicates an interlaced mode, 0 otherwise EGL_REFRESH_RATE_MESA The mode's refresh rate, multiplied by 1000 EGL_WIDTH Mode width (resolution) EGL_HEIGHT Mode height (resolution) EGL_MODE_ID_MESA A unique small integer identifier for the mode Any other token will generate the error EGL_BAD_ATTRIBUTE. EGLBoolean eglGetScreensMESA(EGLDisplay dpy, EGLScreenMESA *screens, EGLint screens_size, EGLint *num_screens) This function returns an array of all available screen handles. is the maximum number of screens to return in the array. will return the number of screen handles placed in the array, even if is NULL. The number of screens and the availability of each may change over time (hot-plugging). Screen handles will not be reused. When a screen handle becomes invalid, function calls which reference an invalid handle will generate EGL_BAD_SCREEN_MESA. The first screen handle returned will be considered to be the primary one. EGLSurface eglCreateScreenSurfaceMESA(EGLDisplay dpy, EGLConfig config, const EGLint *attrib_list) Create a surface that can be displayed on a screen. is an array of token/value pairs terminated with EGL_NONE. Valid tokens include: Name Description ---------------- -------------------------------- EGL_WIDTH desired surface width in pixels EGL_HEIGHT desired surface height in pixels Any other token will generate the error EGL_BAD_ATTRIBUTE. The default width and height are zero. EGLBoolean eglShowSurfaceMESA(EGLDisplay dpy, EGLScreenMESA screen, EGLSurface surface, EGLModeMESA mode) This function causes a screen to show the given surface (or more precisely, the surface's front color buffer) with the given mode. If the surface is in any way incompatible with the mode, the error EGL_BAD_MATCH will be generated, EGL_FALSE will be returned, and the previous screen state will remain in effect. This might occur when the bandwidth of the video-out subsystem is exceeded, or if the mode specifies a width or height that's greater than the width or height of the surface. To disable a screen, the values EGL_NO_SURFACE and EGL_NO_MODE_MESA be passed as the and parameters. The values of EGL_SCREEN_POSITION_MESA are clamped to the new valid range computed from the screen size and surface size. If the new surface is EGL_NO_SURFACE, EGL_SCREEN_POSITION_MESA is set to [0, 0]. Attempting to delete a screen surface which is currently being displayed will result in the error EGL_BAD_ACCESS being generated. EGLBoolean eglScreenPositionMESA(EGLDisplay dpy, EGLScreenMESA screen, EGLint x, EGLint y) Specifies the origin of the screen's view into the surface, if the surface is larger than the screen. Valid values for x and y are [0, surfaceWidth - screenWidth] and [0, surfaceHeight - screenHeight], respectively. The x and y values are also constrained to be integer multiples of the EGL_SCREEN_POSITION_GRANULARITY_MESA values. EGLBoolean eglQueryScreenMESA(EGLDisplay dpy, EGLScreenMESA screen, EGLint attrib, EGLint *value); Used to query screen attributes. may be one of the following: Name Return value description ------------------------ --------------------------------------------- EGL_SCREEN_POSITION_MESA x, y position of the screen's origin with respect to the surface. If no surface is attached to the screen, [0, 0] is returned. EGL_SCREEN_POSITION_GRANULARITY_MESA Returns the granularity, in pixels, for which the screen position is constrained. Any other token will generate the error EGL_BAD_ATTRIBUTE. EGLBoolean eglQueryScreenSurfaceMESA(EGLDisplay dpy, EGLScreenMESA screen, EGLSurface *surface) Returns the surface currently displayed on the given screen. may be EGL_NO_SURFACE if the screen isn't currently showing any surface. EGLBoolean eglQueryScreenModeMESA(EGLDisplay dpy, EGLScreenMESA screen, EGLModeMESA *mode) Returns the given screen's current display mode. The mode may be EGL_NO_MODE_MESA if the screen is currently disabled. const char *eglQueryModeStringMESA(EGLDisplay dpy, EGLModeMESA mode); Returns a human-readable string for the given mode. The string is a zero-terminated C string which the user should not attempt to free. There is no standard syntax for mode strings. Applications should not directly rely on mode strings. Version History 1. 15 March 2005 - BrianP Initial version 2. 16 March 2005 - BrianP Removed EGL_DEPTH_MESA Added EGL_PHYSICAL_WIDTH_MESA, EGL_PHYSICAL_HEIGHT_MESA queries Added EGL_OPTIMAL_MESA for width/height/refresh rate selection Added possible eglQueryModeStringMESA() function More details of the new functions explained. 3. 18 March 2005 - BrianP Added screen_number to eglChooseModeMESA(). Fix off by one mistake in value range for ORIGIN attributes Added Issues section 4. 21 March 2005 - BrianP Removed eglScreenAttribsMESA(). Added eglScreenPositionMESA() to set screen origin. Replaced EGL_SCREEN_X/Y_OFFSET_MESA with EGL_SCREEN_POSITION_MESA. Replaced EGL_PHYSICAL_WIDTH/HEIGHT_MESA with EGL_PHYSICAL_SIZE_MESA. Use EGL_OPTIMAL_MESA as a new mode attribute. (Michel Danzer) Added a few more issues. 5. 6 April 2005 - BrianP More language for eglGetModeStringMESA(). Added issues 10, 11, 12, 13, 14. Updated issue 3 discussion about mode sorting. 6. 22 April 2005 - BrianP Fixed "LDC" typo. Added issues 15, 16. Changed dependency on EGL 1.1 to EGL 1.0 s/EGL_NUM_SCREENS_MESA/EGL_SCREEN_COUNT_MESA/ Added eglQueryDisplayMESA() to New Functions section. Clarified language for the EGL_SCREEN_COUNT_MESA query. 7. 29 April 2005 - BrianP Added EGLScreenMESA type and eglGetScreensMESA() function. [J. Smirl]. Replaced EGLint screen_number parameters with EGLScreenMESA screen. Added issue 17 (pixel-accurate panning) 8. 2 May 2005 - BrianP Removed eglQueryDisplayMESA. Fixed a few more EGLint -> EGLScreenMESA changes. 9. 20 May 2005 - BrianP Fixed a few typos. Updated some open issues text. 10. 10 August 2005 - BrianP Added EGL_SCREEN_POSITION_GRANULARITY_MESA. 11. 27 January 2006 - BrianP EGL_PHYSICAL_SIZE_MESA removed since EGL 1.2 has a similar feature.