From 5c001a2c1078a88b9129a344e2e594aee12de69a Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Julian=20Gro=C3=9F?= <julian.g@posteo.de>
Date: Fri, 24 Jul 2026 12:03:54 +0200
Subject: [PATCH] Revert improved culling frustum in OpenVR. Fixes
 https://github.com/overte-org/overte/issues/2242 Reverts the OpenVR part of
 fcf5981e98a234fb1104f3053dda0fac30d059e9

---
 plugins/openvr/src/OpenVrDisplayPlugin.cpp | 69 ++++------------------
 1 file changed, 10 insertions(+), 59 deletions(-)

diff --git a/plugins/openvr/src/OpenVrDisplayPlugin.cpp b/plugins/openvr/src/OpenVrDisplayPlugin.cpp
index 76a2b5498ff..d24107978d1 100644
--- a/plugins/openvr/src/OpenVrDisplayPlugin.cpp
+++ b/plugins/openvr/src/OpenVrDisplayPlugin.cpp
@@ -362,67 +362,17 @@ glm::mat4 OpenVrDisplayPlugin::getEyeProjection(Eye eye, const glm::mat4& basePr
     }
 }
 
-inline static glm::mat4 fovToCullingProjection(const std::array<float, 4> fov, const float _near, const float _far) {
-    const float left = fov[0];
-    const float right = fov[1];
-    const float down = fov[2];
-    const float up = fov[3];
-
-    const float width = right - left;
-    const float height = up - down;
-
-    const float m11 = 2 / width;
-    const float m22 = 2 / height;
-    const float m33 = -(_far + _near) / (_far - _near);
-
-    const float m31 = (right + left) / width;
-    const float m32 = (up + down) / height;
-    const float m43 = -(_far * (_near + _near)) / (_far - _near);
-
-    // clang-format off
-    const float mat[16] = {
-        m11, 0  , 0  ,  0,
-        0  , m22, 0  ,  0,
-        m31, m32, m33, -1,
-        0  , 0  , m43,  0,
-    };
-    // clang-format on
-
-    return glm::make_mat4(mat);
-}
-
 glm::mat4 OpenVrDisplayPlugin::getCullingProjection(const glm::mat4& baseProjection) const {
-    if (!_system) {
+    if (_system) {
+        ViewFrustum baseFrustum;
+        baseFrustum.setProjection(baseProjection);
+        float baseNearClip = baseFrustum.getNearClip();
+        float baseFarClip = baseFrustum.getFarClip();
+        // FIXME Calculate the proper combined projection by using GetProjectionRaw values from both eyes
+        return toGlm(_system->GetProjectionMatrix((vr::EVREye)0, baseNearClip, baseFarClip));
+    } else {
         return baseProjection;
     }
-
-    std::array<std::array<float, 4>, 2> fovs;
-
-    for (auto i = 0; i < 2; i++) {
-        _system->GetProjectionRaw(
-            (vr::EVREye)i,
-            &fovs[i][0],
-            &fovs[i][1],
-            &fovs[i][2],
-            &fovs[i][3]
-        );
-    }
-
-    // FIXME: OpenVR gives us tan(angle), how can we clamp
-    // this to within ~170° when multiplied by margin?
-    // const float maxAngle = 0.9f * PI;
-    const float margin = 1.0f;
-
-    std::array<float, 4> fovMax = {
-        std::min(fovs[0][0], fovs[1][0]) * margin, // left
-        std::max(fovs[0][1], fovs[1][1]) * margin, // right
-        std::min(fovs[0][2], fovs[1][2]) * margin, // bottom (flipped)
-        std::max(fovs[0][3], fovs[1][3]) * margin, // top (flipped)
-    };
-
-    ViewFrustum frustum;
-    frustum.setProjection(baseProjection);
-    return fovToCullingProjection(fovMax, frustum.getNearClip(), frustum.getFarClip());
 }
 
 float OpenVrDisplayPlugin::getTargetFrameRate() const {
@@ -510,7 +460,8 @@ bool OpenVrDisplayPlugin::internalActivate() {
             _eyeOffsets[eye] = toGlm(_system->GetEyeToHeadTransform(eye));
             _eyeProjections[eye] = toGlm(_system->GetProjectionMatrix(eye, DEFAULT_NEAR_CLIP, DEFAULT_FAR_CLIP));
         });
-        _cullingProjection = getCullingProjection(_eyeProjections[0]);
+        // FIXME Calculate the proper combined projection by using GetProjectionRaw values from both eyes
+        _cullingProjection = _eyeProjections[0];
     });
 
     // enable async time warp