[linux] Added OSMesa headless backend

platform/default/headless_backend_osmesa.cpp

@@ -0,0 +1,47 @@
+#include <mbgl/platform/default/headless_backend.hpp>
+#include <mbgl/platform/log.hpp>
+
+namespace mbgl {
+
+gl::glProc HeadlessBackend::initializeExtension(const char* name) {
+    return OSMesaGetProcAddress(name);
+}
+
+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");
+        }
+    }
+
+    if (glContext == nullptr) {
+        throw std::runtime_error("Error creating GL context object.");
+    }
+}
+
+void HeadlessBackend::destroyContext() {
+    if (glContext) {
+        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 HeadlessBackend::deactivateContext() {
+    // no-op.
+}
+
+} // namespace mbgl

platform/linux/config.cmake

@@ -1,4 +1,5 @@
 mason_use(glfw VERSION 3.2.1)
+mason_use(mesa VERSION 13.0.0)
 mason_use(boost_libprogram_options VERSION 1.60.0)
 mason_use(sqlite VERSION 3.14.2)
 mason_use(libuv VERSION 1.9.1)
@@ -11,7 +12,34 @@ mason_use(benchmark VERSION 1.0.0)
 
 include(cmake/loop-uv.cmake)
 
+macro(use_glx_backend _TARGET)
+    target_sources(${_TARGET}
+        PRIVATE platform/default/headless_backend_glx.cpp
+    )
+
+    target_link_libraries(${_TARGET}
+        PUBLIC -lGL
+        PUBLIC -lX11
+    )
+endmacro()
+
+macro(use_osmesa_backend _TARGET)
+    target_sources(${_TARGET}
+        PRIVATE platform/default/headless_backend_osmesa.cpp
+    )
+
+    target_add_mason_package(${_TARGET}
+        PUBLIC mesa
+    )
+endmacro()
+
 macro(mbgl_platform_core)
+    if (WITH_OSMESA)
+        use_osmesa_backend(mbgl-core)
+    else()
+        use_glx_backend(mbgl-core)
+    endif()
+
     target_sources(mbgl-core
         # File source
         PRIVATE platform/default/asset_file_source.cpp
@@ -41,7 +69,6 @@ macro(mbgl_platform_core)
         PRIVATE platform/default/webp_reader.cpp
 
         # Headless view
-        PRIVATE platform/default/headless_backend_glx.cpp
         PRIVATE platform/default/headless_backend.cpp
         PRIVATE platform/default/headless_display.cpp
         PRIVATE platform/default/offscreen_view.cpp
@@ -63,8 +90,6 @@ macro(mbgl_platform_core)
     target_link_libraries(mbgl-core
         PUBLIC -lz
         PUBLIC -lcurl
-        PUBLIC -lGL
-        PUBLIC -lX11
     )
 endmacro()