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Name
MESA_image_dma_buf_export
Name Strings
EGL_MESA_image_dma_buf_export
Contributors
Dave Airlie
Contact
Dave Airlie (airlied 'at' redhat 'dot' com)
Status
Complete, shipping.
Version
Version 3, May 5, 2015
Number
EGL Extension #87
Dependencies
Requires EGL 1.4 or later. This extension is written against the
wording of the EGL 1.4 specification.
EGL_KHR_base_image is required.
The EGL implementation must be running on a Linux kernel supporting the
dma_buf buffer sharing mechanism.
Overview
This extension provides entry points for integrating EGLImage with the
dma-buf infrastructure. The extension allows creating a Linux dma_buf
file descriptor or multiple file descriptors, in the case of multi-plane
YUV image, from an EGLImage.
It is designed to provide the complementary functionality to
EGL_EXT_image_dma_buf_import.
IP Status
Open-source; freely implementable.
New Types
This extension uses the 64-bit unsigned integer type EGLuint64KHR
first introduced by the EGL_KHR_stream extension, but does not
depend on that extension. The typedef may be reproduced separately
for this extension, if not already present in eglext.h.
typedef khronos_uint64_t EGLuint64KHR;
New Procedures and Functions
EGLBoolean eglExportDMABUFImageQueryMESA(EGLDisplay dpy,
EGLImageKHR image,
int *fourcc,
int *num_planes,
EGLuint64KHR *modifiers);
EGLBoolean eglExportDMABUFImageMESA(EGLDisplay dpy,
EGLImageKHR image,
int *fds,
EGLint *strides,
EGLint *offsets);
New Tokens
None
Additions to the EGL 1.4 Specification:
To mirror the import extension, this extension attempts to return
enough information to enable an exported dma-buf to be imported
via eglCreateImageKHR and EGL_LINUX_DMA_BUF_EXT token.
Retrieving the information is a two step process, so two APIs
are required.
The first entrypoint
EGLBoolean eglExportDMABUFImageQueryMESA(EGLDisplay dpy,
EGLImageKHR image,
int *fourcc,
int *num_planes,
EGLuint64KHR *modifiers);
is used to retrieve the pixel format of the buffer, as specified by
drm_fourcc.h, the number of planes in the image and the Linux
drm modifiers. <fourcc>, <num_planes> and <modifiers> may be NULL,
in which case no value is retrieved.
The second entrypoint retrieves the dma_buf file descriptors,
strides and offsets for the image. The caller should pass
arrays sized according to the num_planes values retrieved previously.
Passing arrays of the wrong size will have undefined results.
If the number of fds is less than the number of planes, then
subsequent fd slots should contain -1.
EGLBoolean eglExportDMABUFImageMESA(EGLDisplay dpy,
EGLImageKHR image,
int *fds,
EGLint *strides,
EGLint *offsets);
<fds>, <strides>, <offsets> can be NULL if the infomatation isn't
required by the caller.
Issues
1. Should the API look more like an attribute getting API?
ANSWER: No, from a user interface pov, having to iterate across calling
the API up to 12 times using attribs seems like the wrong solution.
2. Should the API take a plane and just get the fd/stride/offset for that
plane?
ANSWER: UNKNOWN,this might be just as valid an API.
3. Does ownership of the file descriptor remain with the app?
ANSWER: Yes, the app is responsible for closing any fds retrieved.
4. If number of planes and number of fds differ what should we do?
ANSWER: Return -1 for the secondary slots, as this avoids having
to dup the fd extra times to make the interface sane.
Revision History
Version 3, May, 2015
Just use the KHR 64-bit type.
Version 2, March, 2015
Add a query interface (Dave Airlie)
Version 1, June 3, 2014
Initial draft (Dave Airlie)
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