Update which backends are enabled by default

This changes the Vulkan backend to be enabled by default on Windows and
Linux as well as changes the OpenGL backend to be disabled by default on
OSX.

.travis.yml

@@ -58,14 +58,11 @@ script:
  # Use the more recent compilers we just installed
  - if [ "$TRAVIS_OS_NAME" == "linux" ] && [ "$CXX" == "clang++" ]; then export CXX="clang++-5.0" CC="clang-5.0"; fi
 
- # Build the Vulkan backend on Linux
- - if [ "$TRAVIS_OS_NAME" == "linux" ]; then export BUILD_VULKAN=1; else export BUILD_VULKAN=0; fi
-
  # Build
  - mkdir -p build
  - cd build
  - cmake --version
- - cmake -G "Ninja" -DCMAKE_BUILD_TYPE=$BUILD_TYPE -DDAWN_USE_WERROR=1 -DDAWN_ENABLE_VULKAN=$BUILD_VULKAN ..
+ - cmake -G "Ninja" -DCMAKE_BUILD_TYPE=$BUILD_TYPE -DDAWN_USE_WERROR=1 ..
  - cmake --build .
 
  # Test

CMakeLists.txt

@@ -40,17 +40,24 @@ option(DAWN_USE_WERROR "Treat warnings as error (useful for CI)" 0)
 # Default values for the backend-enabling options
 set(ENABLE_D3D12 OFF)
 set(ENABLE_METAL OFF)
+set(ENABLE_OPENGL OFF)
+set(ENABLE_VULKAN OFF)
 if (WIN32)
     set(ENABLE_D3D12 ON)
+    set(ENABLE_OPENGL ON)
+    set(ENABLE_VULKAN ON)
 elseif(APPLE)
     set(ENABLE_METAL ON)
+elseif(UNIX)
+    set(ENABLE_OPENGL ON)
+    set(ENABLE_VULKAN ON)
 endif()
 
 option(DAWN_ENABLE_D3D12 "Enable compilation of the D3D12 backend" ${ENABLE_D3D12})
 option(DAWN_ENABLE_METAL "Enable compilation of the Metal backend" ${ENABLE_METAL})
 option(DAWN_ENABLE_NULL "Enable compilation of the Null backend" ON)
-option(DAWN_ENABLE_OPENGL "Enable compilation of the OpenGL backend" ON)
-option(DAWN_ENABLE_VULKAN "Enable compilation of the Vulkan backend" OFF)
+option(DAWN_ENABLE_OPENGL "Enable compilation of the OpenGL backend" ${ENABLE_OPENGL})
+option(DAWN_ENABLE_VULKAN "Enable compilation of the Vulkan backend" ${ENABLE_VULKAN})
 option(DAWN_ALWAYS_ASSERT "Enable assertions on all build types" OFF)
 option(DAWN_USE_CPP17 "Use some optional C++17 features for compile-time checks" OFF)