Messy hacks, but actually working with SteamVR on linux, at least.

Maekfile.js

@@ -21,7 +21,7 @@ const maek = init_maek();
 //======================================================================
 
 const NEST_LIBS = `../nest-libs/${maek.OS}`;
-const OPENXR_SDK = `../openxr-sdk-source`;
+const OPENXR_SDK = `../openxr-sdk`;
 
 //set compile flags (these can also be overridden per-task using the "options" parameter):
 if (maek.OS === "windows") {
@@ -58,7 +58,8 @@ if (maek.OS === "windows") {
  //linker flags for nest libraries:
  `-L${NEST_LIBS}/SDL2/lib`, `-lSDL2`, `-lm`, `-ldl`, `-lasound`, `-lpthread`, `-lX11`, `-lXext`, `-lpthread`, `-lrt`, `-lGL`, //the output of sdl-config --static-libs
  `-L${NEST_LIBS}/libpng/lib`, `-lpng`,
- `-L${NEST_LIBS}/zlib/lib`, `-lz`
+ `-L${NEST_LIBS}/zlib/lib`, `-lz`,
+ `-L${OPENXR_SDK}/build/linux/src/loader`, `-lopenxr_loader`,
  );
 } else if (maek.OS === "macos") {
  maek.options.CPPFlags.push(
@@ -87,6 +88,9 @@ let copies = [
 if (maek.OS === 'windows') {
  copies.push( maek.COPY(`${NEST_LIBS}/SDL2/dist/SDL2.dll`, `dist/SDL2.dll`) );
 }
+if (maek.OS === 'linux') {
+ copies.push( maek.COPY(`${OPENXR_SDK}/build/linux/src/loader/libopenxr_loader.so.1`, `dist/libopenxr_loader.so.1`) );
+}
 
 //call rules on the maek object to specify tasks.
 // rules generally look like:
@@ -99,8 +103,9 @@ if (maek.OS === 'windows') {
 const game_names = [
  maek.CPP('PlayMode.cpp'),
  maek.CPP('main.cpp'),
- maek.CPP('LitColorTextureProgram.cpp')
+ maek.CPP('LitColorTextureProgram.cpp'),
  //, maek.CPP('ColorTextureProgram.cpp') //not used right now, but you might want it
+ maek.CPP('XR.cpp')
 ];
 
 const common_names = [

PlayMode.cpp

@@ -1,4 +1,6 @@
 #include "PlayMode.hpp"
+#include "XR.hpp"
+#include "xr_linear.h" //for projection matrix building helper
 
 #include "LitColorTextureProgram.hpp"
 
@@ -9,6 +11,7 @@
 #include "data_path.hpp"
 
 #include <glm/gtc/type_ptr.hpp>
+#include <glm/gtx/string_cast.hpp>
 
 #include <random>
 
@@ -168,9 +171,9 @@ void PlayMode::update(float elapsed) {
 }
 
 void PlayMode::draw(glm::uvec2 const &drawable_size) {
- //update camera aspect ratio for drawable:
+ //update window's camera aspect ratio for drawable:
  camera->aspect = float(drawable_size.x) / float(drawable_size.y);
-
+ 
  //set up light type and position for lit_color_texture_program:
  // TODO: consider using the Light(s) in the scene to do this
  glUseProgram(lit_color_texture_program->program);
@@ -179,16 +182,8 @@ void PlayMode::draw(glm::uvec2 const &drawable_size) {
  glUniform3fv(lit_color_texture_program->LIGHT_ENERGY_vec3, 1, glm::value_ptr(glm::vec3(1.0f, 1.0f, 0.95f)));
  glUseProgram(0);
 
- glClearColor(0.5f, 0.5f, 0.5f, 1.0f);
- glClearDepth(1.0f); //1.0 is actually the default value to clear the depth buffer to, but FYI you can change it.
- glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
-
- glEnable(GL_DEPTH_TEST);
- glDepthFunc(GL_LESS); //this is the default depth comparison function, but FYI you can change it.
-
- GL_ERRORS(); //print any errors produced by this setup code
-
- scene.draw(*camera);
+ //main scene drawing into the window:
+ draw_helper(camera->make_projection() * glm::mat4(camera->transform->make_world_to_local()));
 
  { //use DrawLines to overlay some text:
  glDisable(GL_DEPTH_TEST);
@@ -211,4 +206,62 @@ void PlayMode::draw(glm::uvec2 const &drawable_size) {
  glm::vec3(H, 0.0f, 0.0f), glm::vec3(0.0f, H, 0.0f),
  glm::u8vec4(0xff, 0xff, 0xff, 0x00));
  }
+
+ //----------------------------------------------
+
+ if (xr && xr->next_frame.should_render) {
+ //set up a transform representing the stage's position in the world:
+ // NOTE: state's "up" direction is +Y.
+ Scene::Transform stage;
+ stage.rotation = glm::quat_cast(glm::mat3(
+ glm::vec3(1.0f, 0.0f, 0.0f),
+ glm::vec3(0.0f, 0.0f, 1.0f),
+ glm::vec3(0.0f,-1.0f, 0.0f)
+ ));
+ stage.position = glm::vec3(0.0f, 0.0f, 0.0f); //just center up for now
+ stage.scale = glm::vec3(10.0f); //let's make the player large!
+
+ for (auto const &view : xr->views) {
+ if (!view.current_framebuffer) continue; //weird bug but nothing to do, I guess
+
+ glBindFramebuffer(GL_DRAW_FRAMEBUFFER, view.current_framebuffer->fb);
+ glViewport(0, 0, xr->size.x, xr->size.y);
+
+ XrMatrix4x4f xr_proj;
+ XrMatrix4x4f_CreateProjectionFov(&xr_proj, GRAPHICS_OPENGL, view.fov, 0.1f, 0.0f);
+
+ glm::mat4 proj = glm::mat4(
+ xr_proj.m[0], xr_proj.m[1], xr_proj.m[2], xr_proj.m[3],
+ xr_proj.m[4], xr_proj.m[5], xr_proj.m[6], xr_proj.m[7],
+ xr_proj.m[8], xr_proj.m[9], xr_proj.m[10], xr_proj.m[11],
+ xr_proj.m[12], xr_proj.m[13], xr_proj.m[14], xr_proj.m[15]
+ );
+
+ Scene::Transform at;
+ at.parent = &stage;
+ at.position = glm::vec3(view.pose.position.x, view.pose.position.y, view.pose.position.z);
+ at.rotation = glm::quat(view.pose.orientation.w, view.pose.orientation.x, view.pose.orientation.y, view.pose.orientation.z);
+
+ draw_helper(proj * glm::mat4(at.make_world_to_local()));
+
+ glBindFramebuffer(GL_DRAW_FRAMEBUFFER, 0);
+ glViewport(0, 0, drawable_size.x, drawable_size.y);
+ }
+ }
+
+
+}
+void PlayMode::draw_helper(glm::mat4 const &world_to_clip) {
+
+ glClearColor(0.5f, 0.5f, 0.5f, 1.0f);
+ glClearDepth(1.0f); //1.0 is actually the default value to clear the depth buffer to, but FYI you can change it.
+ glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
+
+ glEnable(GL_DEPTH_TEST);
+ glDepthFunc(GL_LESS); //this is the default depth comparison function, but FYI you can change it.
+
+ GL_ERRORS(); //print any errors produced by this setup code
+
+ scene.draw(world_to_clip);
+
 }

PlayMode.hpp

@@ -16,6 +16,9 @@ struct PlayMode : Mode {
  virtual void update(float elapsed) override;
  virtual void draw(glm::uvec2 const &drawable_size) override;
 
+ //draw_helper called to draw both into game window and into VR views:
+ void draw_helper(glm::mat4 const &world_to_clip);
+
  //----- game state -----
 
  //input tracking:

README.md

@@ -45,12 +45,40 @@ $ cd ovr-openxr-sdk
 $ unzip ../downloads/ovr_openxr_mobile_sdk_57.0.zip #current version as of this writing
 ```
 
+For **desktop** VR use, grab Khronos's OpenXR loader: (see the README.md for more build info; like non-linux build instructions, required packages to install)
+```
+$ git clone https://github.com/KhronosGroup/OpenXR-SDK openxr-sdk
+$ cd openxr-sdk
+$ mkdir -p build/linux
+$ cd build/linux
+$ cmake -DDYNAMIC_LOADER=ON -DCMAKE_BUILD_TYPE=RelWithDebInfo ../..
+```
+
 Once all of that is done you should have these three as siblings:
 ```
 15466-f23-ndk-openxr #this folder
 android-sdk #android sdk, tools, etc
 ovr-openxr-sdk #Meta's OpenXR SDK stuff
+openxr-sdk #Knrono's OpenXR SDK (optional; for desktop use)
+```
+
+### SteamVR Linux Notes
+
+Getting "failed to determine active runtime file path for this environment":
+
+```
+$ mkdir -p .config/openxr/1
+$ ln -sf ~/.steam/steam/steamapps/common/SteamVR/steamxr_linux64.json ~/.config/openxr/1/active_runtime.json
+```
+
+Or you can just:
+```
+$ XR_RUNTIME_JSON=~/.steam/steam/steamapps/common/SteamVR/steamxr_linux64.json ./dist/game
 ```
+(As per https://community.khronos.org/t/openxr-loader-how-to-select-runtime/108524)
+
+
+I found that opening SteamVR, then closing SteamVR but leaving steam open resulted in OpenXR calls succeeding. But not having steam open at all or having steamvr open both resulted in CreateInstance failing.
 
 ### Hardware
 
@@ -76,5 +104,9 @@ $ ./platform-tools/adb shell
 
 ## Building
 
-
 ...
+
+
+## OpenXR Notes
+
+