examples: add CMake build + run.sh for the standalone dRICH example

Gives examples/drich the standalone CMakeLists.txt (find_package eic-opticks +
Geant4 gdml) and run.sh that the sibling examples carry, so the no-DD4hep dRICH
driver builds the canonical way. Compiling it serves as a build-smoke for the
standalone GDML flow; README gains the CMake recipe.

Author: ggalgoczi

examples/drich/CMakeLists.txt

@@ -0,0 +1,27 @@
+cmake_minimum_required(VERSION 3.20)
+
+project(drich_gdml LANGUAGES CXX)
+
+set(CMAKE_CXX_STANDARD 17)
+set(CMAKE_CXX_STANDARD_REQUIRED ON)
+set(CMAKE_CXX_EXTENSIONS OFF)
+
+find_package(eic-opticks REQUIRED)
+find_package(Geant4 REQUIRED gdml)   # gdml component pulls G4GDMLParser + xerces-c
+
+# Standalone (no-DD4hep) Geant4 + Opticks dRICH driver. Builds against an
+# installed eic-opticks the same way as the sibling examples; compiling it
+# serves as a build-smoke for the standalone GDML flow.
+add_executable(drich_gdml_main drich_gdml_main.cc)
+target_link_libraries(drich_gdml_main
+    eic-opticks::gphox
+    eic-opticks::G4CX
+    eic-opticks::U4
+    eic-opticks::QUDARap
+    eic-opticks::CSG
+    eic-opticks::CSGOptiX
+    eic-opticks::SysRap
+    ${Geant4_LIBRARIES}
+)
+
+install(TARGETS drich_gdml_main)

examples/drich/README.md

@@ -20,6 +20,20 @@ carry, wavelength-linear lookup) live in `__device__` headers compiled into the
 PTX, so the PTX must be regenerated — not just the host libraries.
 
 ## Build
+
+### CMake (preferred)
+This directory is a standalone CMake project, like the other `examples/`:
+
+```
+cmake -S examples/drich -B build/drich -DCMAKE_PREFIX_PATH=${OPTICKS_PREFIX}
+cmake --build build/drich
+```
+
+It builds `drich_gdml_main` against an installed eic-opticks/simphony and Geant4
+(gdml component); compiling it doubles as a build-smoke for the standalone flow.
+`run.sh` runs it (`./run.sh`, or `GDML_FILE=… MULT=… SEED=… NEVENTS=… ./run.sh`).
+
+### Manual g++
 Adjust `-I/-L` to your install layout. NOTE: the project was renamed
 `eic-opticks` → `simphony`, so installed headers may live under
 `include/simphony/...` (the recipe below used the old `eic-opticks` prefix).

examples/drich/run.sh

@@ -0,0 +1,43 @@
+#!/bin/bash
+# run.sh — run the standalone (no-DD4hep) dRICH GDML example.
+#
+# Runs the Geant4 + Opticks driver side-by-side and prints per-event
+# "gpu_hits=N cpu_hits=M ..." so the GPU/G4 hit ratio can be checked.
+# Build first via CMake (find_package(eic-opticks)); see README.md.
+#
+# Usage:
+#   ./run.sh                                            # drich_ag02.gdml, 1 event
+#   GDML_FILE=drich_ag02.gdml MULT=100 SEED=12345 NEVENTS=5 ./run.sh
+#
+# Env (see drich_gdml_main.cc): GDML_FILE MULT SEED NEVENTS PHI_DEG ETA
+#   KILL_OPTICAL (1=GPU-only, skips CPU optical transport) CUDA_VISIBLE_DEVICES
+set -e
+
+SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
+cd "$SCRIPT_DIR"
+
+GDML_FILE="${GDML_FILE:-drich_ag02.gdml}"
+if [ ! -f "$GDML_FILE" ]; then
+    echo "ERROR: $SCRIPT_DIR/$GDML_FILE not found"
+    exit 1
+fi
+
+# Locate the built binary (installed/on PATH, or a sibling build dir).
+BIN="${BIN:-drich_gdml_main}"
+if ! command -v "$BIN" >/dev/null 2>&1 && [ ! -x "$BIN" ]; then
+    echo "ERROR: '$BIN' not found — build it first (see README.md) or set BIN=/path/to/drich_gdml_main"
+    exit 1
+fi
+
+echo "=== standalone dRICH GDML example ==="
+echo "GDML:    $GDML_FILE"
+echo "events:  ${NEVENTS:-1}   MULT: ${MULT:-1}   SEED: ${SEED:-1}   PHI_DEG: ${PHI_DEG:-30}   ETA: ${ETA:-2.0}"
+echo ""
+
+GDML_FILE="$GDML_FILE" \
+MULT="${MULT:-1}" SEED="${SEED:-1}" NEVENTS="${NEVENTS:-1}" \
+PHI_DEG="${PHI_DEG:-30}" ETA="${ETA:-2.0}" \
+"$BIN"
+
+echo ""
+echo "=== Done ==="