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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_HEIGHT 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.
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