Set BUILD_RENDERER_VULKAN default to OFF

The Vulkan renderer currently only builds and works on Linux. It has
not been tested on macOS, Windows, OpenBSD, or Emscripten. Setting the
default to OFF prevents CI failures on unsupported platforms.

Author: runlevel5

CMakeLists.txt

@@ -15,7 +15,7 @@ option(BUILD_SERVER "Build dedicated server" ON)
 option(BUILD_CLIENT "Build client" ON)
 option(BUILD_RENDERER_GL1 "Build GL1 renderer" ON)
 option(BUILD_RENDERER_GL2 "Build GL2 renderer" ON)
-option(BUILD_RENDERER_VULKAN "Build Vulkan renderer" ON)
+option(BUILD_RENDERER_VULKAN "Build Vulkan renderer" OFF)
 option(BUILD_GAME_LIBRARIES "Build game module libraries" ON)
 option(BUILD_GAME_QVMS "Build game module qvms" ON)
 option(BUILD_STANDALONE "Build binaries for standalone games" OFF)

README.md

@@ -163,7 +163,7 @@ The following CMake variables may be set, using `-D` on the command line.
   BUILD_CLIENT            - build the 'ioquake3' client binary
   BUILD_RENDERER_OPENGL1  - build the opengl1 client / renderer library
   BUILD_RENDERER_OPENGL2  - build the opengl2 client / renderer library
-  BUILD_RENDERER_VULKAN   - build the vulkan client / renderer library
+  BUILD_RENDERER_VULKAN   - build the vulkan client / renderer library (default OFF)
   BUILD_GAME_LIBRARIES    - build the game shared libraries
   BUILD_GAME_QVMS         - build the game qvms
   BUILD_STANDALONE        - build binaries suited for stand-alone games

docs/vulkan-readme.md

@@ -28,11 +28,11 @@ graphics API path while maintaining compatibility with existing Quake 3 content.
   BUILDING
 -------------------------------------------------------------------------------
 
-The Vulkan renderer is enabled by default.  To disable it, pass
-`-DBUILD_RENDERER_VULKAN=OFF` to CMake.
+The Vulkan renderer is not built by default.  To enable it, pass
+`-DBUILD_RENDERER_VULKAN=ON` to CMake.
 
     mkdir build && cd build
-    cmake .. -DCMAKE_BUILD_TYPE=Release
+    cmake .. -DCMAKE_BUILD_TYPE=Release -DBUILD_RENDERER_VULKAN=ON
     make renderer_vulkan
 
 This produces `renderer_vulkan_<arch>.so` (Linux), `renderer_vulkan_<arch>.dll`