Implement EGL_KHR_surfaceless_context for D3D, GL and NULL backends.

src/libANGLE/Config.cpp

@@ -218,6 +218,11 @@ std::vector<const Config*> ConfigSet::filter(const AttributeMap &attributeMap) c
             EGLAttrib attributeKey   = attribIter->first;
             EGLAttrib attributeValue = attribIter->second;
 
+            if (attributeValue == EGL_DONT_CARE)
+            {
+                continue;
+            }
+
             switch (attributeKey)
             {
               case EGL_BUFFER_SIZE:               match = config.bufferSize >= attributeValue;                        break;

src/libANGLE/renderer/d3d/d3d11/Renderer11.cpp

@@ -1145,6 +1145,9 @@ void Renderer11::generateDisplayExtensions(egl::DisplayExtensions *outExtensions
 
     // getSyncValues requires direct composition.
     outExtensions->getSyncValues = outExtensions->directComposition;
+
+    // D3D11 can be used without a swap chain
+    outExtensions->surfacelessContext = true;
 }
 
 gl::Error Renderer11::flush()

src/libANGLE/renderer/d3d/d3d9/Renderer9.cpp

@@ -566,6 +566,9 @@ void Renderer9::generateDisplayExtensions(egl::DisplayExtensions *outExtensions)
 
     // Contexts are virtualized so textures can be shared globally
     outExtensions->displayTextureShareGroup = true;
+
+    // D3D9 can be used without an output surface
+    outExtensions->surfacelessContext = true;
 }
 
 void Renderer9::startScene()

src/libANGLE/renderer/gl/glx/DisplayGLX.cpp

@@ -776,6 +776,8 @@ void DisplayGLX::generateExtensions(egl::DisplayExtensions *outExtensions) const
 
     // Contexts are virtualized so textures can be shared globally
     outExtensions->displayTextureShareGroup = true;
+
+    outExtensions->surfacelessContext = true;
 }
 
 void DisplayGLX::generateCaps(egl::Caps *outCaps) const
@@ -783,6 +785,13 @@ void DisplayGLX::generateCaps(egl::Caps *outCaps) const
     outCaps->textureNPOT = true;
 }
 
+egl::Error DisplayGLX::makeCurrentSurfaceless(gl::Context *context)
+{
+    // Nothing to do because GLX always uses the same context and the previous surface can be left
+    // current.
+    return egl::NoError();
+}
+
 int DisplayGLX::getGLXFBConfigAttrib(glx::FBConfig config, int attrib) const
 {
     int result;

src/libANGLE/renderer/gl/glx/DisplayGLX.h

@@ -97,6 +97,8 @@ class DisplayGLX : public DisplayGL
     void generateExtensions(egl::DisplayExtensions *outExtensions) const override;
     void generateCaps(egl::Caps *outCaps) const override;
 
+    egl::Error makeCurrentSurfaceless(gl::Context *context) override;
+
     int getGLXFBConfigAttrib(glx::FBConfig config, int attrib) const;
     egl::Error createContextAttribs(glx::FBConfig,
                                     const Optional<gl::Version> &version,

src/libANGLE/renderer/gl/wgl/DisplayWGL.cpp

@@ -617,6 +617,8 @@ void DisplayWGL::generateExtensions(egl::DisplayExtensions *outExtensions) const
 
     // Contexts are virtualized so textures can be shared globally
     outExtensions->displayTextureShareGroup = true;
+
+    outExtensions->surfacelessContext = true;
 }
 
 void DisplayWGL::generateCaps(egl::Caps *outCaps) const
@@ -624,6 +626,13 @@ void DisplayWGL::generateCaps(egl::Caps *outCaps) const
     outCaps->textureNPOT = true;
 }
 
+egl::Error DisplayWGL::makeCurrentSurfaceless(gl::Context *context)
+{
+    // Nothing to do because WGL always uses the same context and the previous surface can be left
+    // current.
+    return egl::NoError();
+}
+
 egl::Error DisplayWGL::waitClient() const
 {
     // Unimplemented as this is not needed for WGL

src/libANGLE/renderer/gl/wgl/DisplayWGL.h

@@ -72,6 +72,8 @@ class DisplayWGL : public DisplayGL
     void generateExtensions(egl::DisplayExtensions *outExtensions) const override;
     void generateCaps(egl::Caps *outCaps) const override;
 
+    egl::Error makeCurrentSurfaceless(gl::Context *context) override;
+
     HGLRC initializeContextAttribs(const egl::AttributeMap &eglAttributes) const;
     HGLRC createContextAttribs(const gl::Version &version, int profileMask) const;
 

src/libANGLE/renderer/null/DisplayNULL.cpp

@@ -203,6 +203,7 @@ void DisplayNULL::generateExtensions(egl::DisplayExtensions *outExtensions) cons
     outExtensions->createContextWebGLCompatibility    = true;
     outExtensions->createContextBindGeneratesResource = true;
     outExtensions->swapBuffersWithDamage              = true;
+    outExtensions->surfacelessContext                 = true;
 }
 
 void DisplayNULL::generateCaps(egl::Caps *outCaps) const