[Render/RenderSystem] The camera's transform is used for XR views

- If it exists, its position & orientation are added to the XR device's views before rendering

- It probably isn't useful in a real scenario, but can help a lot for debugging purposes

examples/xrDemo.cpp

@@ -1,5 +1,7 @@
 #include "RaZ/RaZ.hpp"
 
+#include "DemoUtils.hpp"
+
 using namespace std::literals;
 
 int main() {
@@ -20,8 +22,11 @@ int main() {
     auto& xr = world.addSystem<Raz::XrSystem>("RaZ - XR demo");
     render.enableXr(xr);
 
-    // The camera parameters aren't technically used for XR rendering, but its transform may be later
-    world.addEntityWithComponent<Raz::Transform>().addComponent<Raz::Camera>(window.getWidth(), window.getHeight());
+    // In an XR workflow, the camera is optional; its parameters aren't technically used, but its transform is
+    auto& camera = world.addEntityWithComponent<Raz::Transform>();
+    camera.addComponent<Raz::Camera>(window.getWidth(), window.getHeight());
+
+    DemoUtils::setupCameraControls(camera, window);
 
     world.addEntityWithComponent<Raz::Transform>(Raz::Vec3f(0.f, -1.f, -5.f), Raz::Quaternionf(90_deg, Raz::Axis::Y), Raz::Vec3f(0.01f))
       .addComponent<Raz::MeshRenderer>(Raz::MeshFormat::load(RAZ_ROOT "assets/meshes/crytek_sponza.obj").second);

include/RaZ/XR/XrSession.hpp

@@ -32,7 +32,7 @@ struct ViewFov {
   Radiansf angleUp;
   Radiansf angleDown;
 };
-using ViewRenderFunc = std::function<std::pair<const Texture2D&, const Texture2D&>(const Vec3f&, const Quaternionf&, const ViewFov&)>;
+using ViewRenderFunc = std::function<std::pair<const Texture2D&, const Texture2D&>(Vec3f, Quaternionf, ViewFov)>;
 
 class XrSession {
   friend class XrSystem;

src/RaZ/Render/RenderSystem.cpp

@@ -297,7 +297,13 @@ void RenderSystem::renderXrFrame() {
   ZoneScopedN("RenderSystem::renderXrFrame");
   TracyGpuZone("RenderSystem::renderXrFrame")
 
-  m_xrSystem->renderFrame([this] (const Vec3f& position, const Quaternionf& rotation, const ViewFov& viewFov) {
+  m_xrSystem->renderFrame([this] (Vec3f position, Quaternionf rotation, ViewFov viewFov) {
+    if (m_cameraEntity) {
+      const auto& camTransform = m_cameraEntity->getComponent<Transform>();
+      position = camTransform.getRotation() * position + camTransform.getPosition();
+      rotation = camTransform.getRotation() * rotation;
+    }
+
     Mat4f invViewMat = rotation.computeMatrix();
     invViewMat.getElement(3, 0) = position.x();
     invViewMat.getElement(3, 1) = position.y();