Name MESA_configless_context Name Strings EGL_MESA_configless_context Contact Neil Roberts Status Superseded by the functionally identical EGL_KHR_no_config_context extension.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