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authorKristian Høgsberg <krh@bitplanet.net>2010-06-04 14:28:59 -0400
committerKristian Høgsberg <krh@bitplanet.net>2010-08-25 09:17:47 -0400
commitb7a8893a2413adfddf4dc836676a19463fb6ffd7 (patch)
treeea03799b61f31600f49601c27bbe40ce8a18d9b1 /docs
parent29bcbf5e797a18430285c75abb8a9300c8defe1d (diff)
egl: Add EGL_MESA_drm_image extension
Create EGLImages from DRM buffer handles.
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+Name
+
+ MESA_drm_image
+
+Name Strings
+
+ EGL_MESA_drm_image
+
+Contact
+
+ Kristian Høgsberg <krh@bitplanet.net>
+
+Status
+
+ Proposal
+
+Version
+
+ Version 2, August 25, 2010
+
+Number
+
+ EGL Extension #not assigned
+
+Dependencies
+
+ Reguires EGL 1.4 or later. This extension is written against the
+ wording of the EGL 1.4 specification.
+
+ EGL_KHR_base_image is required.
+
+Overview
+
+ This extension provides entry points for integrating EGLImage with the
+ Linux DRM mode setting and memory management drivers. The extension
+ lets applications create EGLImages without a client API resource and
+ lets the application get the DRM buffer handles.
+
+IP Status
+
+ Open-source; freely implementable.
+
+New Procedures and Functions
+
+ EGLImageKHR eglCreateDRMImageMESA(EGLDisplay dpy,
+ const EGLint *attrib_list);
+
+ EGLBoolean eglExportDRMImageMESA(EGLDisplay dpy,
+ EGLImageKHR image,
+ EGLint *name,
+ EGLint *handle,
+ EGLint *stride);
+
+New Tokens
+
+ Accepted in the <attrib_list> parameter of eglCreateDRMImageMESA:
+
+ EGL_DRM_BUFFER_FORMAT_MESA 0x31D0
+ EGL_DRM_BUFFER_USE_MESA 0x31D1
+
+ Accepted as values for the EGL_IMAGE_FORMAT_MESA attribute:
+
+ EGL_DRM_BUFFER_FORMAT_ARGB32_MESA 0x31D2
+
+ Bits accepted in EGL_DRM_BUFFER_USE_MESA:
+
+ EGL_DRM_BUFFER_USE_SCANOUT_MESA 0x0001
+ EGL_DRM_BUFFER_USE_SHARE_MESA 0x0002
+
+ Accepted in the <target> parameter of eglCreateImageKHR:
+
+ EGL_DRM_BUFFER_MESA 0x31D3
+
+ Use when importing drm buffer:
+
+ EGL_DRM_BUFFER_STRIDE_MESA 0x31D4
+ EGL_DRM_BUFFER_FORMAT_MESA 0x31D0
+
+Additions to the EGL 1.4 Specification:
+
+ To create a DRM EGLImage, call
+
+ EGLImageKHR eglCreateDRMImageMESA(EGLDisplay dpy,
+ const EGLint *attrib_list);
+
+ In the attribute list, pass EGL_WIDTH, EGL_EIGHT and format and
+ use in the attrib list using EGL_DRM_BUFFER_FORMAT_MESA and
+ EGL_DRM_BUFFER_USE_MESA. The only format specified by this
+ extension is EGL_DRM_BUFFER_FORMAT_ARGB32_MESA, where each pixel
+ is a CPU-endian, 32-bit quantity, with alpha in the upper 8 bits,
+ then red, then green, then blue. The bit values accepted by
+ EGL_DRM_BUFFER_USE_MESA are EGL_DRM_BUFFER_USE_SCANOUT_MESA and
+ EGL_DRM_BUFFER_USE_SHARE_MESA. EGL_DRM_BUFFER_USE_SCANOUT_MESA
+ requests that the created EGLImage should be usable as a scanout
+ buffer with the DRM kernel modesetting API. The
+ EGL_DRM_BUFFER_USE_SHARE_MESA bit requests that the EGLImage can
+ be shared with other processes by passing the underlying DRM
+ buffer name.
+
+ To create a process local handle or a global DRM name for a
+ buffer, call
+
+ EGLBoolean eglExportDRMImageMESA(EGLDisplay dpy,
+ EGLImageKHR image,
+ EGLint *name,
+ EGLint *handle,
+ EGLint *stride);
+
+ If <name> is non-NULL, a global name is assigned to the image and
+ written to <name>, the handle (local to the DRM file descriptor,
+ for use with DRM kernel modesetting API) is written to <handle> if
+ non-NULL and the stride (in bytes) is written to <stride>, if
+ non-NULL.
+
+ Import a shared buffer by calling eglCreateImageKHR with
+ EGL_DRM_BUFFER_MESA as the target, using EGL_WIDTH, EGL_HEIGHT,
+ EGL_DRM_BUFFER_FORMAT_MESA, EGL_DRM_BUFFER_STRIDE_MESA
+ in the attrib list.
+
+Issues
+
+ 1. Why don't we use eglCreateImageKHR with a target that
+ indicates that we want to create an EGLImage from scratch?
+
+ RESOLVED: The eglCreateImageKHR entry point is reserved for
+ creating an EGLImage from an already existing client API
+ resource. This is fine when we're creating the EGLImage from
+ an existing DRM buffer name, it doesn't seem right to overload
+ the function to also allocate the underlying resource.
+
+ 2. Why don't we use an eglQueryImageMESA type functions for
+ querying the DRM EGLImage attributes (name, handle, and stride)?
+
+ RESOLVED: The eglQueryImage function has been proposed often,
+ but it goes against the EGLImage design. EGLImages are opaque
+ handles to a 2D array of pixels, which can be passed between
+ client APIs. By referenceing an EGLImage in a client API, the
+ EGLImage target (a texture, a renderbuffer or such) can be
+ used to query the attributes of the EGLImage. We don't have a
+ full client API for creating and querying DRM buffers, though,
+ so we use a new EGL extension entry point instead.
+
+Revision History
+
+ Version 1, June 3, 2010
+ Initial draft (Kristian Høgsberg)
+ Version 2, August 25, 2010
+ Flesh out the extension a bit, add final EGL tokens, capture
+ some of the original discussion in the issues section.