查看“EGL backends”的源代码

{{ReviewsComments|PCO (W803) : please avoid "br"}}
{{ReviewsComments|PCO (W803) : maybe improve the summary by simply adding the names of possible backends}}

The EGL backend is the EGL low level interface to define how buffer will be allocated and how display will be done.<br>

==Supported backends==
To be integrated into OpenSTLinux, GPU software stack should supports '''DRM/GBM''' and '''Wayland''' backends.<br>

The GPU userland library dynamically selects the currently running EGL backend according to the information given by the application thanks to the support of the '''eglGetPlatformDisplayEXT''' extension:
* EGL_PLATFORM_GBM_KHR (selects DRM backend based on GBM) => choice made by weston compositor 
* EGL_PLATFORM_WAYLAND_KHR (selects Wayland backend) => choice made by a wayland client application

{{Info | Only one of the DRM backend and Wayland backends runs at a time}}

==EGL focus==
{{ReviewsComments|PCO (W803) : please add a legend for colors, use the official template maybe}}
[[File:egl-focus.png|center|800px]]

==DRM/GBM backend==
'''DRM/GBM backend''' is based on the Graphic Buffer Management interfaced ('''GBM''') to handle buffer/surface creation. <br>
'''GBM''' is itself based on dmabuf DRM/KMS allocator (using DRM_IOCTL_MODE_CREATE_DUMB). <br>

The application need to set the display mode using the KMS mode setting of the DRM/KMS protocol and then should drop the DRM master token.<br>
So that, the '''DRM/GBM backend''' could take the DRM master token and perform EGL rendering directly on the the display selected set by the KMS mode setting (done by the application).

==Wayland backend==
The '''Wayland backend''' implements Wayland EGL extensions:
* eglBindWaylandDisplayWL
* eglUnbindWaylandDisplayWL
* eglQueryWaylandBufferWL
* support of EGL_WAYLAND_BUFFER_WL in eglCreateKHRImage interface.

The '''wayland backend''' is used by the egl wayland clients (means application that want to display EGL surface in a wayland windows). <br>
This back end is responsible of allocating output buffer for the GL rendering but it is up to wayland client protocol to display it. <br>
The Wayland client uses a wl_display (recovered by wl_display_connect) to initialize EGL. <br>
__egl_swap_buffer uses the attached/commit/flush wayland API to display the result in a wayland window.
{{ReviewsComments|PCO (W803) : explanations are pretty complex, we can discuss about what we should explain and what is too complex}}

==Wayland/Weston EGL architecture==
{{ReviewsComments|PCO (W803) : please add a legend for colors, use the official template maybe}}
[[File:egl_wayland_weston_architecture.png|center|800px]]

Wayland/Weston uses both DRM and Wayland backends. <br>
*'''Weston compositor''' (through the gl-renderer) relies on the '''DRM backend''' (EGL_PLATFORM_GBM_KHR) to render surfaces that could not be assigned to a plane.
** DMABUF native buffers are rendered using egl_image_create in EGL_LINUX_DMA_BUF_EXT mode (texture 0-copy path)
** Wayland buffers (wl_buffer) issued by an EGL wayland application are rendered using egl_image_create in  EGL_WAYLAND_BUFFER_WL mode (texture 0-copy path.
** SHM buffers are rendered using the glImage2D interface (low performance because texture is copied)
*'''EGL Wayland applications''' rely on the '''Wayland backend''' (EGL_PLATFORM_WAYLAND_KHR) to render their 3D EGL animation/UI into a wl_surface that will be then commit to weston compositor

<noinclude>
[[Category:GPU]]
</noinclude>