From 836e7269f6055bd01e5d7df258190d403a726b6e Mon Sep 17 00:00:00 2001
From: Quinn Elara <128988672+Quinn-Elara@users.noreply.github.com>
Date: Sat, 5 Sep 2026 18:41:39 +0100
Subject: [PATCH] render: guard generateImpostor against degenerate fov/aspect

When an avatar's spatial extents project to zero in the camera's up axis
(collapsed bounding box, extreme distance, or a lookAt singularity when
the avatar is directly above or below the camera), tdim.mV[1] is zero.
This produces fov=0 and aspect=NaN, which assert-crash inside
glm::perspectiveRH_NO before the perspective matrix is written.

Add a finite/positive check on fov and aspect before the GL matrix push.
On failure, restore pushRenderTypeMask, sUseOcclusion, sShadowRender and
sImpostorRender and return early. Move the MM_PROJECTION pushMatrix to
after the guard so no pop is needed on the early-out path and the normal
path has exactly one push.

Fixes a reproducible crash when impostoring a distant avatar (>3km) while
the viewer window is in the background.
---
 indra/newview/pipeline.cpp | 23 +++++++++++++++++++++--
 1 file changed, 21 insertions(+), 2 deletions(-)

diff --git a/indra/newview/pipeline.cpp b/indra/newview/pipeline.cpp
index f24b2ad60a5..3d8aa4ed20b 100644
--- a/indra/newview/pipeline.cpp
+++ b/indra/newview/pipeline.cpp
@@ -12546,13 +12546,32 @@ void LLPipeline::generateImpostor(LLVOAvatar* avatar, bool preview_avatar, bool
         tdim.mV[0] = half_height.dot3(left).getF32();
         tdim.mV[1] = half_height.dot3(up).getF32();
 
-        gGL.matrixMode(LLRender::MM_PROJECTION);
-        gGL.pushMatrix();
 
         F32 distance = (pos-camera.getOrigin()).length();
         F32 fov = atanf(tdim.mV[1]/distance)*2.f*RAD_TO_DEG;
         F32 aspect = tdim.mV[0]/tdim.mV[1];
 
+        // Guard against degenerate geometry: the avatar's bounding box can project
+        // to zero in one or both axes (collapsed extents, extreme distance, or a
+        // lookAt singularity when the avatar is directly above/below the camera).
+        // fov==0 or non-finite aspect both produce an unusable projection matrix
+        // and assert-crash inside glm::perspectiveRH_NO.
+        if (fov <= 0.f || !std::isfinite(aspect) || aspect <= 0.f)
+        {
+            LL_WARNS_ONCE("AvatarRenderPipeline") << "generateImpostor: degenerate fov/aspect for avatar "
+                << avatar->getID() << " (fov=" << fov << " aspect=" << aspect
+                << " distance=" << distance << " tdim=" << tdim.mV[0] << "," << tdim.mV[1]
+                << ") -- skipping impostor bake this frame" << LL_ENDL;
+            popRenderTypeMask();
+            sUseOcclusion   = occlusion;
+            sShadowRender   = saved_shadow_render;
+            sImpostorRender = saved_impostor_render;
+            return;
+        }
+
+        gGL.matrixMode(LLRender::MM_PROJECTION);
+        gGL.pushMatrix();
+
         // Clip planes bracketing the subject instead of a hardcoded 1..256.
         //
         // Impostoring is chosen by rank, not distance (LLVOAvatar::shouldImpostor), so an