| Name |
| |
| MESA_configless_context |
| |
| Name Strings |
| |
| EGL_MESA_configless_context |
| |
| Contact |
| |
| Neil Roberts <neil.s.roberts@intel.com> |
| |
| 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| Superseded by the functionally identical EGL_KHR_no_config_context |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 <config> 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) |