[core] Refactor HeadlessBackend

2 files changed, 54 insertions, 31 deletions

diff --git a/platform/default/headless_backend.cpp b/platform/default/headless_backend.cpp
index 279a7973c9..30ce8d2230 100644
--- a/platform/default/headless_backend.cpp
+++ b/platform/default/headless_backend.cpp
@@ -3,15 +3,16 @@
 
 #include <cassert>
 #include <stdexcept>
+#include <type_traits>
 
 namespace mbgl {
 
-HeadlessBackend::HeadlessBackend() : display(std::make_shared<HeadlessDisplay>()) {
+HeadlessBackend::HeadlessBackend() {
     activate();
 }
 
 HeadlessBackend::HeadlessBackend(std::shared_ptr<HeadlessDisplay> display_)
-    : display(std::move(display_)) {
+        : display(std::move(display_)) {
     activate();
 }
 
@@ -23,8 +24,8 @@ HeadlessBackend::~HeadlessBackend() {
 void HeadlessBackend::activate() {
     active = true;
 
-    if (!glContext) {
-        if (!display) {
+    if (!hasContext()) {
+        if (!hasDisplay()) {
             throw std::runtime_error("Display is not set");
         }
         createContext();
@@ -47,6 +48,21 @@ void HeadlessBackend::invalidate() {
     assert(false);
 }
 
+void HeadlessBackend::destroyContext() {
+    assert(hasContext());
+    impl.reset();
+}
+
+void HeadlessBackend::activateContext() {
+    assert(hasContext());
+    impl->activateContext();
+}
+
+void HeadlessBackend::deactivateContext() {
+    assert(hasContext());
+    impl->deactivateContext();
+}
+
 void HeadlessBackend::notifyMapChange(MapChange change) {
     if (mapChangeCallback) {
         mapChangeCallback(change);
diff --git a/platform/default/headless_backend_osmesa.cpp b/platform/default/headless_backend_osmesa.cpp
index e0e385fcc6..04709d4a1b 100644
--- a/platform/default/headless_backend_osmesa.cpp
+++ b/platform/default/headless_backend_osmesa.cpp
@@ -1,47 +1,54 @@
 #include <mbgl/platform/default/headless_backend.hpp>
 #include <mbgl/platform/log.hpp>
 
-namespace mbgl {
+#include <GL/osmesa.h>
 
-gl::glProc HeadlessBackend::initializeExtension(const char* name) {
-    return OSMesaGetProcAddress(name);
-}
+#include <cassert>
 
-void HeadlessBackend::createContext() {
-    if (glContext == nullptr) {
-#if OSMESA_MAJOR_VERSION * 100 + OSMESA_MINOR_VERSION >= 305
-        glContext = OSMesaCreateContextExt(OSMESA_RGBA, 16, 0, 0, nullptr);
-#else
-        glContext = OSMesaCreateContext(OSMESA_RGBA, nullptr);
-#endif
-        if (glContext == nullptr) {
-            Log::Error(Event::OpenGL, "failed to create OSMesa context");
-        }
-    }
+namespace mbgl {
 
-    if (glContext == nullptr) {
-        throw std::runtime_error("Error creating GL context object.");
+struct OSMesaImpl : public HeadlessBackend::Impl {
+    OSMesaImpl(OSMesaContext glContext_) : glContext(glContext_) {
     }
-}
 
-void HeadlessBackend::destroyContext() {
-    if (glContext) {
+    ~OSMesaImpl() {
         if (glContext != OSMesaGetCurrentContext()) {
             activateContext();
         }
         OSMesaDestroyContext(glContext);
-        glContext = nullptr;
     }
-}
 
-void HeadlessBackend::activateContext() {
-    if (!OSMesaMakeCurrent(glContext, &fakeBuffer, GL_UNSIGNED_BYTE, 1, 1)) {
-        throw std::runtime_error("Switching OpenGL context failed.\n");
+    void activateContext() final {
+        if (!OSMesaMakeCurrent(glContext, &fakeBuffer, GL_UNSIGNED_BYTE, 1, 1)) {
+            throw std::runtime_error("Switching OpenGL context failed.\n");
+        }
     }
+
+    OSMesaContext glContext = nullptr;
+    GLubyte fakeBuffer = 0;
+};
+
+gl::glProc HeadlessBackend::initializeExtension(const char* name) {
+    return OSMesaGetProcAddress(name);
 }
 
-void HeadlessBackend::deactivateContext() {
-    // no-op.
+bool HeadlessBackend::hasDisplay() {
+    return true;
+};
+
+void HeadlessBackend::createContext() {
+    assert(!hasContext());
+
+#if OSMESA_MAJOR_VERSION * 100 + OSMESA_MINOR_VERSION >= 305
+    OSMesaContext glContext = OSMesaCreateContextExt(OSMESA_RGBA, 16, 0, 0, nullptr);
+#else
+    OSMesaContext glContext = OSMesaCreateContext(OSMESA_RGBA, nullptr);
+#endif
+    if (glContext == nullptr) {
+        throw std::runtime_error("Error creating GL context object.");
+    }
+
+    impl.reset(new OSMesaImpl(glContext));
 }
 
 } // namespace mbgl