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LIBGL_FIX.md

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libOpenGL.so Missing - Root Cause & Fix

Problem Summary

Build fails with:

error: cannot find -lOpenGL
/usr/bin/ld: cannot find -lOpenGL: No such file or directory

Despite OpenGL libraries being installed in the Pixi environment.

Root Cause Analysis

The Pixi environment had:

  • ✅ libOpenGL.so.0 (versioned symlink → libOpenGL.so.0.0.0)
  • ✅ libOpenGL.so.0.0.0 (actual library file)
  • ❌ libOpenGL.so (unversioned symlink) - MISSING

Why this broke:

  • CMake's find_package(OpenGL) explicitly looks for the unversioned libOpenGL.so
  • Conda packages libgl-devel includes only versioned .so.0 files
  • The unversioned symlink must be created manually

The Fix

Immediate Fix (Manual)

ln -sf libOpenGL.so.0 $CONDA_PREFIX/lib/libOpenGL.so

Permanent Fix (Script Changes)

Modified scripts/build-deps.sh to create OpenGL symlinks before building (not just during Pangolin):

Added at line 106-120:

# Ensure OpenGL symlinks exist BEFORE building anything
# This is critical for CMake to find libOpenGL.so (unversioned)
echo "Ensuring OpenGL/EGL symlinks in Pixi environment..."
ensure_gl_symlink() {
    local link_path="$1"
    local target_path="$2"
    if [ ! -e "$link_path" ] && [ -e "$target_path" ]; then
        ln -s "$(basename "$target_path")" "$link_path"
        echo "  Created: $(basename "$link_path") -> $(basename "$target_path")"
    elif [ -e "$link_path" ]; then
        echo "  OK: $(basename "$link_path") already exists"
    else
        echo "  WARNING: Target $(basename "$target_path") not found"
    fi
}

ensure_gl_symlink "$CONDA_PREFIX/lib/libOpenGL.so" "$CONDA_PREFIX/lib/libOpenGL.so.0"
ensure_gl_symlink "$CONDA_PREFIX/lib/libEGL.so" "$CONDA_PREFIX/lib/libEGL.so.1"

Removed duplicate: Pangolin section (lines 179-191) no longer redefines ensure_gl_symlink

Technical Details

Symlink Chain

Before fix:

libOpenGL.so         (MISSING)
libOpenGL.so.0  ──→  libOpenGL.so.0.0.0 (✓ exists)

After fix:

libOpenGL.so   ──→  libOpenGL.so.0 ──→  libOpenGL.so.0.0.0 (✓)

Why GLVND?

The CMakeLists use set(OpenGL_GL_PREFERENCE GLVND) which:

  • Looks for separate libGL.so and libOpenGL.so (NVIDIA GLVND model)
  • NOT the legacy unified libGL.so approach
  • Both must be present for proper linking

Related Files

File Change
scripts/build-deps.sh Added early symlink creation, removed duplicate function
scripts/check-opengl-symlinks.sh NEW: Diagnostic script to verify symlinks
lib/iridescence/CMakeLists.txt Line 19: set(OpenGL_GL_PREFERENCE GLVND)
lib/Pangolin/cmake/* Uses find_package(OpenGL) which requires unversioned symlinks

Verification

After fix, verify with:

pixi shell
bash scripts/check-opengl-symlinks.sh

Expected output:

✓ libOpenGL.so → libOpenGL.so.0
✓ libEGL.so → libEGL.so.1.1.0

Timeline

  1. Environment setup: Pixi installs libgl-devel with versioned libraries only
  2. Before fix: Building Pangolin or Iridescence would fail at CMake configuration stage
  3. With fix: Symlinks are created early in build-deps.sh, before any CMake invocation

Prevention

  • Always run pixi run build-deps before pixi run build
  • Check symlinks with bash scripts/check-opengl-symlinks.sh after pixi shell
  • The fixed script now prevents this automatically