Basic API usage

[Jan Bruns]

Pekka Paalanen wrote:

 >> Would they introduce
 >> structures named like
 >>
 >> VK_STRUCTURE_TYPE_WAYLAND_NOLIBWAYLAND_SURFACE_CREATE_INFO_KHR or
 >> VK_STRUCTURE_TYPE_DIRECTWAYLAND_SURFACE_CREATE_INFO_KHR, in addition to
 >> the existing VK_STRUCTURE_TYPE_WAYLAND_SURFACE_CREATE_INFO_KHR?
 >
 > I cannot guess what you are thinking here. If Vulkan didn't use
 > actually implemented types from *some* Wayland implementation in its
 > API, what could it use?


Assume there'd be some core wayland approved protocol like (roughly, 
just designed for this posting):

<protocol name="inheritance_v0.0.0.0.0.0">

   <interface name="wl_subwire_parent" version="1">
     <description summary="allow another connection to use our objects">
        Interface used to move wayland objects to other connections.
     </description>

     <event name="tellname">
       <description summary="A wayland-server chosen name.">
      Child connections use this name to identify the parent.
       </description>
       <arg name="name" type="string" />
     </event>

     <event name="authping">
       <description summary="Incoming request for alternate connection.">
       </description>
       <arg name="name" type="string" summary="the child's name"/>
       <arg name="secatt" type="string" summary="security attribute"/>
       <arg name="serial" type="int" summary="wayland-server chosen"/>
     </event>

     <request name="authpong">
       <description summary="Autenticate the alternate connection."> 
</description>
       <arg name="decision" type="int" enum="authresult" summary="enum 
to allow or deny"/>
       <arg name="serial" type="int" summary="serial from authping"/>
     </request>

     <enum name="authresult">
       <description summary="authentication result"> </description>
       <entry name="deny" value="0" summary="indicate denied request"/>
       <entry name="allow" value="1" summary="indicate allowed request"/>
     </enum>

     <request name="sendobj">
       <description summary="send an obj to child connection.">
      Allow the child connection to send request and/or receive events
          for the specified object.
          We'll uses pname to refer to the object for commincation 
beyond wayland protocol.
       </description>
       <arg name="sharemode" type="uint" enum="sharemode" 
summary="details about sharing"/>
       <arg name="type" type="string" summary="interface name of object 
becoming inherited on the other side"/>
       <arg name="obj" type="object" summary="obj to send"/>
       <arg name="pname" type="uint" summary="parent-chosen name"/>
     </request>

     <enum name="sharemode" bitfield="true">
       <description summary="how to share the obj">
       </description>
       <entry name="parent_req" value="1" summary="parent to still send 
requests"/>
       <entry name="parent_ev" value="2" summary="parent to still 
receive events"/>
       <entry name="child_req" value="4" summary="child to send requests"/>
       <entry name="child_ev" value="8" summary="child to receive events"/>
     </enum>
   </interface>

   <interface name="wl_subwire_child" version="1">
     <description summary="child-side connection">
        Interface used to inherit wayland objects from other connections.
     </description>

     <event name="tellname">
       <description summary="A wayland-server chosen name.">
      Parent connections use this name to identify the child.
       </description>
       <arg name="name" type="string" />
     </event>

     <request name="authenticate">
       <description summary="request authentication">
      Request to treat the active connection as a child.
       </description>
       <arg name="name" type="string" summary="the parent's name to 
inherit from"/>
       <arg name="secatt" type="string" summary="security attribute"/>
       <arg name="serial" type="int" summary="child-chosen id of request"/>
     </request>

     <event name="authentication_result">
       <description summary="Notification about the authentication 
outcome.">
       </description>
       <arg name="serial" type="int" summary="id used for authenticate 
request"/>
       <arg name="result" type="int" summary="authentication outcome"/>
     </event>

     <event name="parent_obj">
       <description summary="Receive an obj from parent.">
         Receive an obj from parent.
         The parent uses pname to refer to the object for commincation 
beyond wayland protocol.
       </description>
       <arg name="sender" type="string" summary="the sending parent's 
name."/>
       <arg name="type" type="string" summary="interface name of 
inherited object"/>
       <arg name="obj" type="new_id" summary="inherited object"/>
       <arg name="pname" type="uint" summary="parent-chosen name"/>
     </event>

   </interface>
</protocol>



The Vk-structure for passing the surrface to Vk would instead of


typedef struct VkWaylandSurfaceCreateInfoKHR {
     VkStructureType                   sType;
     const void*                       pNext;
     VkWaylandSurfaceCreateFlagsKHR    flags;
     struct wl_display*                display;
     struct wl_surface*                surface;
} VkWaylandSurfaceCreateInfoKHR;


would turn into something like

typedef struct VkRealYetUnrealWaylandSurfaceCreateInfoKHR {
     VkStructureType                   sType;
     const void*                       pNext;
     VkWaylandSurfaceCreateFlagsKHR    flags;
     char*                             wl_parent_name; // wayland server 
generated wl_subwire_parent.tellname.name
     uint                              display_name; // 
wl_subwire_parent.sendobj.pname;
     uint                              surface_name; // 
wl_subwire_parent.sendobj.pname;
} VkRealYetUnrealWaylandSurfaceCreateInfoKHR;


And the difference is that there'd only be references to the protocol, 
instead of secret references to specific implementations.

The Vk implementation as well as the application instanciating the Vk 
would then both be free to choose whatever implementation to talk 
wayland protocol.

 > For comparison, VkXcbSurfaceCreateInfoKHR uses libxcb types in the API,
 > so you are forced to use libxcb if you want to use that. Likewise in
 > EGL, you are forced to use libX11 if you want to use the EGL X11
 > platform, and libwayland-client if you want to use the EGL Wayland
 > platform.

XCB aims to be some specific protocol-talker implementation.
Isn't that very diffrent from what wayland should be?


 > In any case, Wayland per se is not tied to any particular
 > implementation, even through libwayland is the authoritative
 > implementation. You are free to write a Wayland protocol implementation
 > from scratch with your own language. If the implementation is correct,
 > it will have no trouble as a client communicating with a Wayland
 > compositor written in C and using libwayland-server, for instance. Or
 > vice versa, your own compositor in your own language can well accept
 > any existing client written in any language.
 >
 > It is also possible to replace libwayland in one process with a
 > completely different but ABI-compatible implementation. Just make sure
 > all pieces in the process use the same implementation. Between
 > processes, each process can use a totally different Wayland
 > implementation if you want to, as long as they all talk the same binary
 > wire format.

Well, isn't that yet still pretty much a sleeping dreamer...

Gruss

Jan Bruns