[linux] Added OSMesa headless backend

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()