egl: EGL_KHR_surfaceless_* extensions

These extensions allow an application to make a context current by
passing EGL_NO_SURFACE for the write and read surface in the call to
eglMakeCurrent.  The motivation is that applications that only want to
render to client API targets (such as OpenGL framebuffer objects)
should not need to create a throw-away EGL surface just to get a
current context.

src/egl/main/eglapi.c

@@ -379,7 +379,11 @@ eglCreateContext(EGLDisplay dpy, EGLConfig config, EGLContext share_list,
    _EGLContext *context;
    EGLContext ret;
 
-   _EGL_CHECK_CONFIG(disp, conf, EGL_NO_CONTEXT, drv);
+   if (config)
+      _EGL_CHECK_CONFIG(disp, conf, EGL_NO_CONTEXT, drv);
+   else
+      drv = _eglCheckDisplay(disp, __FUNCTION__);
+
    if (!share && share_list != EGL_NO_CONTEXT)
       RETURN_EGL_ERROR(disp, EGL_BAD_CONTEXT, EGL_NO_CONTEXT);
 

src/egl/main/eglcontext.c

@@ -83,7 +83,7 @@ _eglParseContextAttribList(_EGLContext *ctx, const EGLint *attrib_list)
       }
    }
 
-   if (err == EGL_SUCCESS) {
+   if (err == EGL_SUCCESS && ctx->Config) {
       EGLint renderable_type, api_bit;
 
       renderable_type = GET_CONFIG_ATTRIB(ctx->Config, EGL_RENDERABLE_TYPE);
@@ -220,45 +220,49 @@ _eglBindContextToSurfaces(_EGLContext *newCtx,
     * surface (oldDraw), the old bindings are broken first and the new one is
     * created.
     */
-   oldCtx = newDraw->CurrentContext;
-   if (newCtx != oldCtx) {
-      if (oldCtx) {
-         assert(oldCtx->DrawSurface == newDraw);
-         oldCtx->DrawSurface = NULL;
+   if (newDraw) {
+      oldCtx = newDraw->CurrentContext;
+      if (newCtx != oldCtx) {
+	 if (oldCtx) {
+	    assert(oldCtx->DrawSurface == newDraw);
+	    oldCtx->DrawSurface = NULL;
+	 }
+      
+	 newDraw->CurrentContext = newCtx;
       }
+   }
 
-      if (newCtx) {
-         _EGLSurface *oldDraw = newCtx->DrawSurface;
-         if (oldDraw)
-            oldDraw->CurrentContext = NULL;
+   if (newCtx) {
+      _EGLSurface *oldDraw = newCtx->DrawSurface;
+      if (oldDraw)
+	 oldDraw->CurrentContext = NULL;
 
-         newCtx->DrawSurface = newDraw;
-         *draw = oldDraw;
-      }
-
-      newDraw->CurrentContext = newCtx;
+      newCtx->DrawSurface = newDraw;
+      *draw = oldDraw;
    }
 
    /* likewise */
-   if (newRead != newDraw)
+   if (newRead && newRead != newDraw) {
       oldCtx = newRead->CurrentContext;
-   if (newCtx != oldCtx) {
-      if (oldCtx) {
-         assert(oldCtx->ReadSurface == newRead);
-         oldCtx->ReadSurface = NULL;
+      if (newCtx != oldCtx) {
+	 if (oldCtx) {
+	    assert(oldCtx->ReadSurface == newRead);
+	    oldCtx->ReadSurface = NULL;
+	 }
+
+	 newRead->CurrentContext = newCtx;
       }
-
-      if (newCtx) {
-         _EGLSurface *oldRead = newCtx->ReadSurface;
-         if (oldRead)
-            oldRead->CurrentContext = NULL;
-
-         newCtx->ReadSurface = newRead;
-         *read = oldRead;
-      }
-
-      newRead->CurrentContext = newCtx;
    }
+
+   if (newCtx) {
+      _EGLSurface *oldRead = newCtx->ReadSurface;
+      if (oldRead)
+	 oldRead->CurrentContext = NULL;
+
+      newCtx->ReadSurface = newRead;
+      *read = oldRead;
+   }
+
 }
 
 
@@ -297,7 +301,9 @@ static EGLBoolean
 _eglCheckMakeCurrent(_EGLContext *ctx, _EGLSurface *draw, _EGLSurface *read)
 {
    _EGLThreadInfo *t = _eglGetCurrentThread();
+   _EGLDisplay *dpy = ctx->Resource.Display;
    EGLint conflict_api;
+   EGLBoolean surfaceless;
 
    if (_eglIsCurrentThreadDummy())
       return _eglError(EGL_BAD_ALLOC, "eglMakeCurrent");
@@ -309,8 +315,22 @@ _eglCheckMakeCurrent(_EGLContext *ctx, _EGLSurface *draw, _EGLSurface *read)
       return EGL_TRUE;
    }
 
-   /* ctx/draw/read must be all given */
-   if (draw == NULL || read == NULL)
+   switch (_eglGetContextAPIBit(ctx)) {
+   case EGL_OPENGL_ES_BIT:
+      surfaceless = dpy->Extensions.KHR_surfaceless_gles1;
+      break;
+   case EGL_OPENGL_ES2_BIT:
+      surfaceless = dpy->Extensions.KHR_surfaceless_gles2;
+      break;
+   case EGL_OPENGL_BIT:
+      surfaceless = dpy->Extensions.KHR_surfaceless_opengl;
+      break;
+   default:
+      surfaceless = EGL_FALSE;
+      break;
+   }
+
+   if (!surfaceless && (draw == NULL || read == NULL))
       return _eglError(EGL_BAD_MATCH, "eglMakeCurrent");
 
    /* context stealing from another thread is not allowed */
@@ -331,12 +351,13 @@ _eglCheckMakeCurrent(_EGLContext *ctx, _EGLSurface *draw, _EGLSurface *read)
     *
     * The latter is more restrictive so we can check only the latter case.
     */
-   if ((draw->CurrentContext && draw->CurrentContext != ctx) ||
-       (read->CurrentContext && read->CurrentContext != ctx))
+   if ((draw && draw->CurrentContext && draw->CurrentContext != ctx) ||
+       (read && read->CurrentContext && read->CurrentContext != ctx))
       return _eglError(EGL_BAD_ACCESS, "eglMakeCurrent");
 
    /* simply require the configs to be equal */
-   if (draw->Config != ctx->Config || read->Config != ctx->Config)
+   if ((draw && draw->Config != ctx->Config) ||
+       (read && read->Config != ctx->Config))
       return _eglError(EGL_BAD_MATCH, "eglMakeCurrent");
 
    switch (ctx->ClientAPI) {
@@ -387,7 +408,6 @@ _eglBindContext(_EGLContext **ctx, _EGLSurface **draw, _EGLSurface **read)
 
       *draw = oldCtx->DrawSurface;
       *read = oldCtx->ReadSurface;
-      assert(*draw && *read);
 
       _eglBindContextToSurfaces(NULL, draw, read);
    }

src/egl/main/egldisplay.h

@@ -60,6 +60,9 @@ struct _egl_extensions
    EGLBoolean KHR_gl_texture_cubemap_image;
    EGLBoolean KHR_gl_texture_3D_image;
    EGLBoolean KHR_gl_renderbuffer_image;
+   EGLBoolean KHR_surfaceless_gles1;
+   EGLBoolean KHR_surfaceless_gles2;
+   EGLBoolean KHR_surfaceless_opengl;
    EGLBoolean NOK_swap_region;
    EGLBoolean NOK_texture_from_pixmap;
 

src/egl/main/eglmisc.c

@@ -97,6 +97,10 @@ _eglUpdateExtensionsString(_EGLDisplay *dpy)
    _EGL_CHECK_EXTENSION(KHR_gl_texture_3D_image);
    _EGL_CHECK_EXTENSION(KHR_gl_renderbuffer_image);
 
+   _EGL_CHECK_EXTENSION(KHR_surfaceless_gles1);
+   _EGL_CHECK_EXTENSION(KHR_surfaceless_gles2);
+   _EGL_CHECK_EXTENSION(KHR_surfaceless_opengl);
+
    _EGL_CHECK_EXTENSION(NOK_swap_region);
    _EGL_CHECK_EXTENSION(NOK_texture_from_pixmap);
 #undef _EGL_CHECK_EXTENSION