130 lines
4.3 KiB
RPMSpec
130 lines
4.3 KiB
RPMSpec
Name
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MESA_configless_context
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Name Strings
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EGL_MESA_configless_context
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Contact
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Neil Roberts <neil.s.roberts@intel.com>
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Status
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Superseded by the functionally identical EGL_KHR_no_config_context
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extension.
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Version
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Version 2, September 9, 2016
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Number
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EGL Extension #not assigned
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Dependencies
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Requires EGL 1.4 or later. This extension is written against the
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wording of the EGL 1.4 specification.
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Overview
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This extension provides a means to use a single context to render to
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multiple surfaces which have different EGLConfigs. Without this extension
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the EGLConfig for every surface used by the context must be compatible
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with the one used by the context. The only way to render to surfaces with
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different formats would be to create multiple contexts but this is
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inefficient with modern GPUs where this restriction is unnecessary.
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IP Status
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Open-source; freely implementable.
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New Procedures and Functions
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None.
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New Tokens
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Accepted as <config> in eglCreateContext
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EGL_NO_CONFIG_MESA ((EGLConfig)0)
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Additions to the EGL Specification section "2.2 Rendering Contexts and Drawing
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Surfaces"
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Add the following to the 3rd paragraph:
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"EGLContexts can also optionally be created with respect to an EGLConfig
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depending on the parameters used at creation time. If a config is provided
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then additional restrictions apply on what surfaces can be used with the
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context."
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Replace the last sentence of the 6th paragraph with:
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"In order for a context to be compatible with a surface they both must have
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been created with respect to the same EGLDisplay. If the context was
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created without respect to an EGLConfig then there are no further
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constraints. Otherwise they are only compatible if:"
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Remove the last bullet point in the list of constraints.
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Additions to the EGL Specification section "3.7.1 Creating Rendering Contexts"
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Replace the paragraph starting "If config is not a valid EGLConfig..."
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with
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"The config argument can either be a valid EGLConfig or EGL_NO_CONFIG_MESA.
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If it is neither of these then an EGL_BAD_CONFIG error is generated. If a
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valid config is passed then the error will also be generated if the config
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does not support the requested client API (this includes requesting
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creation of an OpenGL ES 1.x context when the EGL_RENDERABLE_TYPE
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attribute of config does not contain EGL_OPENGL_ES_BIT, or creation of an
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OpenGL ES 2.x context when the attribute does not contain
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EGL_OPENGL_ES2_BIT).
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Passing EGL_NO_CONFIG_MESA will create a configless context. When a
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configless context is used with the OpenGL API it can be assumed that the
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initial values of the context's state will be decided when the context is
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first made current. In particular this means that the decision of whether
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to use GL_BACK or GL_FRONT for the initial value of the first output in
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glDrawBuffers will be decided based on the config of the draw surface when
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it is first bound."
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Additions to the EGL Specification section "3.7.3 Binding Contexts and
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Drawables"
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Replace the first bullet point with the following:
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"* If draw or read are not compatible with ctx as described in section 2.2,
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then an EGL_BAD_MATCH error is generated."
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Add a second bullet point after that:
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"* If draw and read are not compatible with each other as described in
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section 2.2, then an EGL_BAD_MATCH error is generated."
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Issues
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1. What happens when an OpenGL context with a double-buffered surface and
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draw buffer set to GL_BACK is made current with a single-buffered
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surface?
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NOT RESOLVED: There are a few options here. An implementation can
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raise an error, change the drawbuffer state to GL_FRONT or just do
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nothing, expecting the application to set GL_FRONT drawbuffer before
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drawing. However, this extension deliberately does not specify any
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required behavior in this corner case and applications should avoid
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mixing single- and double-buffered surfaces with configless contexts.
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Future extensions may specify required behavior in this case.
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Revision History
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Version 2, September 9, 2016
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Defer to EGL_KHR_no_config_context (Adam Jackson)
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Version 1, February 28, 2014
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Initial draft (Neil Roberts)
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