NVIDIA DRIVE 5.0 Linux SDK API Reference

5.0.5.0 Release

 All Data Structures Files Functions Variables Typedefs Enumerations Enumerator Macros Groups Pages
EGL_KHR_config_attribs
Name

    KHR_config_attribs

Name Strings

    EGL_KHR_config_attribs

Contributors

    Jon Leech

Contacts

    Jon Leech (jon 'at' alumni.caltech.edu)

Status

    Complete

Version

    Version 5, April 5, 2007

Number

    EGL Extension #1

Dependencies

    Requires EGL 1.2

    Some of the extended config attributes defined by this extension are
    only relevant when specific client APIs are supported.

    This extension is written against the wording of the EGL 1.2
    Specification. It exists for backwards compatibility with
    functionality introduced in EGL 1.3.

Overview

    This extension adds new EGL config attributes and attribute bits
    that express limitations of configs on a per-API basis, including
    whether client APIs created with respect to a config are expected to
    pass conformance, and which optional OpenVG color space and alpha
    mask format attributes are valid at surface creation time.

New Types

    None

New Procedures and Functions

    None

New Tokens

    New EGLConfig bitmask attribute name:

	EGL_CONFORMANT_KHR		    0x3042

    Valid bitfields in the EGL_SURFACE_TYPE bitmask attribute
    of EGLConfig:

	EGL_VG_COLORSPACE_LINEAR_BIT_KHR    0x0020
	EGL_VG_ALPHA_FORMAT_PRE_BIT_KHR     0x0040

Additions to Chapter 3 of the EGL 1.2 Specification (EGL Functions and Errors)

    Add to table 3.1, "EGLConfig attributes":

	Attribute	    Type	Notes
	---------	    ----	-----
	EGL_CONFORMANT_KHR  bitmask	whether contexts created with
					this config are conformant

    Add to table 3.2, "Types of surfaces supported by an EGLConfig":

	EGL Token Name			Description
	--------------			-----------
	EGL_VG_COLORSPACE_LINEAR_BIT_KHR EGLConfig supports OpenVG rendering
					in linear colorspace
	EGL_VG_ALPHA_FORMAT_PRE_BIT_KHR EGLConfig supports OpenVG rendering
					with premultiplied alpha

    Add following the second paragraph of "Other EGLConfig Attribute
    Descriptions" in section 3.4 on p. 16:

       "If EGL_VG_COLORSPACE_LINEAR_BIT_KHR is set in EGL_SURFACE_TYPE,
	then the EGL_COLORSPACE attribute may be set to
	EGL_COLORSPACE_LINEAR when creating a window, pixmap, or pbuffer
	surface (see section 3.5)."

       "If EGL_VG_ALPHA_FORMAT_PRE_BIT_KHR is set in EGL_SURFACE_TYPE,
	then the EGL_ALPHA_FORMAT attribute may be set to
	EGL_ALPHA_FORMAT_PRE when creating a window, pixmap, or pbuffer
	surface (see section 3.5)."

    Add at the end of the fourth paragraph (description of
    EGL_CONFIG_CAVEAT) on p. 17:

       "... required OpenGL ES conformance tests (note that
	EGL_NON_CONFORMANT_CONFIG is obsolete, and the same information
	can be obtained from the EGL_CONFORMANT_KHR attribute on a
	per-client-API basis, not just for OpenGL ES."

       "EGL_CONFORMANT_KHR is a mask indicating if a client API context
	created with respect to the corresponding EGLConfig will pass
	the required conformance tests for that API. The valid bit
	settings are the same as for EGL_RENDERABLE_TYPE, as defined in
	table 3.3, but the presence or absence of each client API bit
	determines whether the corresponding context will be conformant
	or non-conformant(fn1)."

       "(fn1) most EGLConfigs should be conformant for all supported
	client APIs. Conformance requirements limit the number of
	non-conformant configs that an implementation can define."

    Add to the last paragraph of section 3.5.1 on p. 24 (describing
    eglCreateWindowSurface):

       "If <config> does not support the colorspace or alpha format
	attributes specified in <attrib_list> (e.g. if EGL_COLORSPACE is
	specified as EGL_COLORSPACE_LINEAR but the EGL_SURFACE_TYPE
	attribute of <config> does not include
	EGL_VG_COLORSPACE_LINEAR_BIT_KHR, or if EGL_ALPHA_FORMAT is
	specified as EGL_ALPHA_FORMAT_PRE but EGL_SURFACE_TYPE does not
	include EGL_VG_ALPHA_FORMAT_PRE_BIT_KHR), an EGL_BAD_MATCH error
	is generated."

    Add to the next-to-last paragraph of section 3.5.2 on p. 26
    (describing eglCreatePbufferSurface):

       "If <config> does not support the colorspace or alpha format
	attributes specified in <attrib_list> (as defined for
	eglCreateWindowSurface), an EGL_BAD_MATCH error is generated."

    Add to the last paragraph of section 3.5.4 on p. 29 (describing
    eglCreatePixmapSurface):

       "If <config> does not support the colorspace or alpha format
	attributes specified in <attrib_list> (as defined for
	eglCreateWindowSurface), an EGL_BAD_MATCH error is generated."

Issues

    1) How should colorspace and alpha format restrictions be specified?
       OpenVG implementations may not allow linear colorspace or
       premultiplied alpha rendering to all configs they support.

	RESOLVED: To maximize compatibility with EGL 1.3, we continue to
	specify the desired colorspace and alpha format at surface
	creation time. However, surface creation may fail if if the
	specified colorspace or alpha format are not supported.

	To allow apps to detect this situation, this extension adds
	EGLConfig attributes specifying *if* linear colorspace and/or
	premultiplied alpha formats are supported. If they are not
	supported, surface creation with the corresponding attributes
	set will fail with an EGL_BAD_MATCH error.

    2) How should the colorspace and alpha format capabilities be
       exposed in EGLConfigs?

	RESOLVED: as bitfields of the existing EGL_SURFACE_TYPE bitmask
	attribute.

	A separate bitmask might be more orthogonal, but there are
	plenty of unused bits in EGL_SURFACE_TYPE and this minimizes API
	and programming complexity.

    3) Are support for linear colorspace and and premultiplied alpha
       formats orthogonal?

	RESOLVED: Yes, according to the OpenVG Working Group. If they
	were not orthogonal, we could not specify them as independent
	bitfields.

    4) Should information about conformance be specified on a
       per-client-API basis?

	RESOLVED: Yes. This is needed for conformance testing and cannot
	be expressed by the EGL_CONFIG_CAVEAT attribute, which is OpenGL
	ES-specific.

    5) Should there also be a config attribute which specifies whether
       EGL_RENDER_BUFFER will be respected?

	UNRESOLVED: it would be consistent to add this attribute. but
	it's not clear if there's a requirement for doing so yet.

    6) Does this extension introduce a regression against EGL 1.2?

	RESOLVED: Yes. This is unavoidable, since we're allowing failure
	of surface creation that was required to succeed in the past.
	However, implementations that could not support the required
	colorspace or alpha mask format were effectively non-conformant
	(e.g. broken) in any event. The new EGL_SURFACE_TYPE attributes
	at least allow apps to know that their request will not be
	satisfied.

Dependencies on OpenGL ES

    If OpenGL ES is not supported, the EGL_OPENGL_ES_BIT in the
    EGL_CONFORMANT_KHR is irrelevant.

Dependencies on OpenVG

    If OpenVG is not supported, the EGL_OPENVG_BIT bit in
    EGL_CONFORMANT_KHR, and the EGL_VG_COLORSPACE_LINEAR_BIT_KHR and
    EGL_VG_ALPHA_FORMAT_PRE_BIT_KHR bits in EGL_SURFACE_TYPE, are
    irrelevant.

Revision History

    Version 5, 2007/04/05 - add enum values corresponding to EGL 1.3
	core features.
    Version 4, 2006/10/24 - prefix the bitfield names with "VG" to
	clarify that they only apply to OpenVG rendering to surfaces
	(although the corresponding core EGL_COLORSPACE and
	EGL_ALPHA_FORMAT attribute names do not currently include this
	prefix). Use "KHR" suffix instead of "OES".
    Version 3, 2006/10/15 - add new config attribute to express whether
	configs are conformant on a per-API basis. Correct sRGB
	terminology to linear (sRGB is the default, linear colorspace
	rendering may not be supported). Change extension name
	accordingly.
    Version 2, 2006/09/26 - add _OES extension suffix to bitfield names.
    Version 1, 2006/09/26 - first draft.