build(rhi): make SDL3 optional so CI builds without it

SDL3 is only available on dev machines with local installs.
When SDL3 is not found, RHI sources and tests are excluded
from the build. Defines CF_HAS_SDL3=1 when available.

Author: LyeZinho

CMakeLists.txt

@@ -12,25 +12,36 @@ if(CMAKE_BUILD_TYPE STREQUAL "Debug")
     add_compile_definitions(CF_DEBUG)
 endif()
 
-# ── SDL3 ────────────────────────────────────────────────────────
-find_package(SDL3 REQUIRED CONFIG)
+# ── SDL3 (optional – RHI is only built when SDL3 is available) ──
+find_package(SDL3 CONFIG QUIET)
 
 add_library(Caffeine
     src/core/Timer.cpp
     src/core/GameLoop.cpp
     src/input/InputManager.cpp
     src/debug/LogSystem.cpp
     src/debug/Profiler.cpp
-    src/rhi/RenderDevice.cpp
-    src/rhi/CommandBuffer.cpp
 )
 
+if(SDL3_FOUND)
+    target_sources(Caffeine PRIVATE
+        src/rhi/RenderDevice.cpp
+        src/rhi/CommandBuffer.cpp
+    )
+endif()
+
 target_include_directories(Caffeine PUBLIC 
     $<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}/src>
     $<INSTALL_INTERFACE:include>
 )
 
-target_link_libraries(Caffeine PUBLIC SDL3::SDL3)
+if(SDL3_FOUND)
+    target_link_libraries(Caffeine PUBLIC SDL3::SDL3)
+    target_compile_definitions(Caffeine PUBLIC CF_HAS_SDL3=1)
+    message(STATUS "SDL3 found – RHI module enabled")
+else()
+    message(STATUS "SDL3 not found – RHI module disabled")
+endif()
 
 target_compile_features(Caffeine PUBLIC cxx_std_20)
 

tests/CMakeLists.txt

@@ -1,6 +1,6 @@
 cmake_minimum_required(VERSION 3.20)
 
-add_executable(CaffeineTest
+set(CAFFEINE_TEST_SOURCES
     test_allocators.cpp
     test_containers.cpp
     test_math.cpp
@@ -9,9 +9,14 @@ add_executable(CaffeineTest
     test_gameloop.cpp
     test_input.cpp
     test_debug.cpp
-    test_rhi.cpp
 )
 
+if(SDL3_FOUND)
+    list(APPEND CAFFEINE_TEST_SOURCES test_rhi.cpp)
+endif()
+
+add_executable(CaffeineTest ${CAFFEINE_TEST_SOURCES})
+
 target_link_libraries(CaffeineTest PRIVATE Caffeine)
 target_include_directories(CaffeineTest PRIVATE ${CMAKE_CURRENT_SOURCE_DIR} ${CMAKE_CURRENT_SOURCE_DIR}/Catch2)
 if(MSVC)
@@ -23,10 +28,10 @@ endif()
 enable_testing()
 add_test(NAME CaffeineTest COMMAND CaffeineTest)
 
-if(WIN32)
+if(SDL3_FOUND AND WIN32)
     add_custom_command(TARGET CaffeineTest POST_BUILD
         COMMAND ${CMAKE_COMMAND} -E copy_if_different
             $<TARGET_FILE:SDL3::SDL3>
             $<TARGET_FILE_DIR:CaffeineTest>
     )
-endif()
+endif()