wayland: Add an extension to create wl_buffers from EGLImages

This adds an extension called EGL_WL_create_wayland_buffer_from_image
which adds the following single function:

struct wl_buffer *
eglCreateWaylandBufferFromImageWL(EGLDisplay dpy, EGLImageKHR image);

The function creates a wl_buffer which shares its contents with the given
EGLImage. The expected use case for this is in a nested Wayland compositor
which is using subsurfaces to present buffers from its clients. Using this
extension it can attach the client buffers directly to the subsurface without
having to blit the contents into an intermediate buffer. The compositing can
then be done in the parent compositor.

The extension is only implemented in the Wayland EGL platform because of
course it wouldn't make sense anywhere else.

1 files changed, 101 insertions, 0 deletions

diff --git a/docs/specs/WL_create_wayland_buffer_from_image.spec b/docs/specs/WL_create_wayland_buffer_from_image.spec
new file mode 100644
index 0000000..aa5eb4d
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+++ b/docs/specs/WL_create_wayland_buffer_from_image.spec
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+Name
+
+    WL_create_wayland_buffer_from_image
+
+Name Strings
+
+    EGL_WL_create_wayland_buffer_from_image
+
+Contributors
+
+    Neil Roberts
+    Axel Davy
+    Daniel Stone
+
+Contact
+
+    Neil Roberts <neil.s.roberts@intel.com>
+
+Status
+
+    Proposal
+
+Version
+
+    Version 2, October 25, 2013
+
+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.
+
+    EGL_KHR_base_image is required.
+
+Overview
+
+    This extension provides an entry point to create a wl_buffer which shares
+    its contents with a given EGLImage. The expected use case for this is in a
+    nested Wayland compositor which is using subsurfaces to present buffers
+    from its clients. Using this extension it can attach the client buffers
+    directly to the subsurface without having to blit the contents into an
+    intermediate buffer. The compositing can then be done in the parent
+    compositor.
+
+    The nested compositor can create an EGLImage from a client buffer resource
+    using the existing WL_bind_wayland_display extension. It should also be
+    possible to create buffers using other types of images although there is
+    no expected use case for that.
+
+IP Status
+
+    Open-source; freely implementable.
+
+New Procedures and Functions
+
+    struct wl_buffer *eglCreateWaylandBufferFromImageWL(EGLDisplay dpy,
+                                                        EGLImageKHR image);
+
+New Tokens
+
+    None.
+
+Additions to the EGL 1.4 Specification:
+
+    To create a client-side wl_buffer from an EGLImage call
+
+      struct wl_buffer *eglCreateWaylandBufferFromImageWL(EGLDisplay dpy,
+                                                          EGLImageKHR image);
+
+    The returned buffer will share the contents with the given EGLImage. Any
+    updates to the image will also be updated in the wl_buffer. Typically the
+    EGLImage will be generated in a nested Wayland compositor using a buffer
+    resource from a client via the EGL_WL_bind_wayland_display extension.
+
+    If there was an error then the function will return NULL. In particular it
+    will generate EGL_BAD_MATCH if the implementation is not able to represent
+    the image as a wl_buffer. The possible reasons for this error are
+    implementation-dependant but may include problems such as an unsupported
+    format or tiling mode or that the buffer is in memory that is inaccessible
+    to the GPU that the given EGLDisplay is using.
+
+Issues
+
+    1) Under what circumstances can the EGL_BAD_MATCH error be generated? Does
+       this include for example unsupported tiling modes?
+
+       RESOLVED: Yes, the EGL_BAD_MATCH error can be generated for any reason
+       which prevents the implementation from representing the image as a
+       wl_buffer. For example, these problems can be but are not limited to
+       unsupported tiling modes, inaccessible memory or an unsupported pixel
+       format.
+
+Revision History
+
+    Version 1, September 6, 2013
+        Initial draft (Neil Roberts)
+    Version 2, October 25, 2013
+        Added a note about more possible reasons for returning EGL_BAD_FORMAT.