Blame - docs/specs/MESA_configless_context.spec - platform/external/mesa3d

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Neil Roberts	551d459	2014-03-07 18:05:47 +0000	[diff] [blame]	1	Name
				2
				3	MESA_configless_context
				4
				5	Name Strings
				6
				7	EGL_MESA_configless_context
				8
				9	Contact
				10
				11	Neil Roberts <neil.s.roberts@intel.com>
				12
				13	Status
				14
Adam Jackson	0cb1428	2016-09-09 12:25:35 -0400	[diff] [blame]	15	Superseded by the functionally identical EGL_KHR_no_config_context
				16	extension.
Neil Roberts	551d459	2014-03-07 18:05:47 +0000	[diff] [blame]	17
				18	Version
				19
Adam Jackson	0cb1428	2016-09-09 12:25:35 -0400	[diff] [blame]	20	Version 2, September 9, 2016
Neil Roberts	551d459	2014-03-07 18:05:47 +0000	[diff] [blame]	21
				22	Number
				23
				24	EGL Extension #not assigned
				25
				26	Dependencies
				27
				28	Requires EGL 1.4 or later. This extension is written against the
				29	wording of the EGL 1.4 specification.
				30
				31	Overview
				32
				33	This extension provides a means to use a single context to render to
				34	multiple surfaces which have different EGLConfigs. Without this extension
				35	the EGLConfig for every surface used by the context must be compatible
				36	with the one used by the context. The only way to render to surfaces with
				37	different formats would be to create multiple contexts but this is
				38	inefficient with modern GPUs where this restriction is unnecessary.
				39
				40	IP Status
				41
				42	Open-source; freely implementable.
				43
				44	New Procedures and Functions
				45
				46	None.
				47
				48	New Tokens
				49
				50	Accepted as <config> in eglCreateContext
				51
				52	EGL_NO_CONFIG_MESA ((EGLConfig)0)
				53
				54	Additions to the EGL Specification section "2.2 Rendering Contexts and Drawing
				55	Surfaces"
				56
				57	Add the following to the 3rd paragraph:
				58
				59	"EGLContexts can also optionally be created with respect to an EGLConfig
				60	depending on the parameters used at creation time. If a config is provided
				61	then additional restrictions apply on what surfaces can be used with the
				62	context."
				63
				64	Replace the last sentence of the 6th paragraph with:
				65
				66	"In order for a context to be compatible with a surface they both must have
				67	been created with respect to the same EGLDisplay. If the context was
				68	created without respect to an EGLConfig then there are no further
				69	constraints. Otherwise they are only compatible if:"
				70
				71	Remove the last bullet point in the list of constraints.
				72
				73	Additions to the EGL Specification section "3.7.1 Creating Rendering Contexts"
				74
				75	Replace the paragraph starting "If config is not a valid EGLConfig..."
				76	with
				77
				78	"The config argument can either be a valid EGLConfig or EGL_NO_CONFIG_MESA.
				79	If it is neither of these then an EGL_BAD_CONFIG error is generated. If a
				80	valid config is passed then the error will also be generated if the config
				81	does not support the requested client API (this includes requesting
				82	creation of an OpenGL ES 1.x context when the EGL_RENDERABLE_TYPE
				83	attribute of config does not contain EGL_OPENGL_ES_BIT, or creation of an
				84	OpenGL ES 2.x context when the attribute does not contain
				85	EGL_OPENGL_ES2_BIT).
				86
				87	Passing EGL_NO_CONFIG_MESA will create a configless context. When a
				88	configless context is used with the OpenGL API it can be assumed that the
				89	initial values of the context's state will be decided when the context is
				90	first made current. In particular this means that the decision of whether
				91	to use GL_BACK or GL_FRONT for the initial value of the first output in
				92	glDrawBuffers will be decided based on the config of the draw surface when
				93	it is first bound."
				94
				95	Additions to the EGL Specification section "3.7.3 Binding Contexts and
				96	Drawables"
				97
				98	Replace the first bullet point with the following:
				99
				100	"* If draw or read are not compatible with ctx as described in section 2.2,
				101	then an EGL_BAD_MATCH error is generated."
				102
				103	Add a second bullet point after that:
				104
				105	"* If draw and read are not compatible with each other as described in
				106	section 2.2, then an EGL_BAD_MATCH error is generated."
				107
				108	Issues
				109
				110	1. What happens when an OpenGL context with a double-buffered surface and
				111	draw buffer set to GL_BACK is made current with a single-buffered
				112	surface?
				113
				114	NOT RESOLVED: There are a few options here. An implementation can
				115	raise an error, change the drawbuffer state to GL_FRONT or just do
				116	nothing, expecting the application to set GL_FRONT drawbuffer before
				117	drawing. However, this extension deliberately does not specify any
				118	required behavior in this corner case and applications should avoid
				119	mixing single- and double-buffered surfaces with configless contexts.
				120
				121	Future extensions may specify required behavior in this case.
				122
				123	Revision History
				124
Adam Jackson	0cb1428	2016-09-09 12:25:35 -0400	[diff] [blame]	125	Version 2, September 9, 2016
				126	Defer to EGL_KHR_no_config_context (Adam Jackson)
				127
Neil Roberts	551d459	2014-03-07 18:05:47 +0000	[diff] [blame]	128	Version 1, February 28, 2014
				129	Initial draft (Neil Roberts)