twn_amalgam.c: a way for single unit compilation, controlled with -DTWN_USE_AMALGAM in cmake

CMakeLists.txt

@@ -24,6 +24,7 @@ set(TWN_ROOT_DIR ${CMAKE_CURRENT_SOURCE_DIR} CACHE INTERNAL "")
 
 # feature configuration, set them with -DFEATURE=ON/OFF in cli
 option(TWN_FEATURE_DYNLIB_GAME  "Enable dynamic library loading support" ON)
+option(TWN_USE_AMALGAM  "Enable use of twn_amalgam.c as a single compilation unit" ON)
 
 # todo: figure out how to compile for dynamic linking instead
 if(EMSCRIPTEN)
@@ -88,7 +89,8 @@ set(TWN_THIRD_PARTY_SOURCE_FILES
         third-party/tomlc99/toml.c
         $<$<NOT:$<BOOL:${EMSCRIPTEN}>>:third-party/glad/src/glad.c>)
 
-set(TWN_SOURCE_FILES
+set(TWN_NONOPT_SOURCE_FILES
+        src/twn_stb.c
         src/twn_loop.c
         src/twn_main.c
         src/twn_context.c include/twn_context.h
@@ -104,7 +106,10 @@ set(TWN_SOURCE_FILES
         src/rendering/twn_triangles.c
         src/rendering/twn_circles.c
         src/rendering/twn_skybox.c
-        src/rendering/twn_fog.c
+        src/rendering/twn_fog.c)
+
+set(TWN_SOURCE_FILES
+        $<IF:$<BOOL:${TWN_USE_AMALGAM}>,src/twn_amalgam.c src/twn_stb.c,${TWN_NONOPT_SOURCE_FILES}>
 
         # for dynamic load based solution main is compiled in a separate target
         $<$<NOT:$<BOOL:${TWN_FEATURE_DYNLIB_GAME}>>:src/twn_main.c
@@ -113,6 +118,7 @@ set(TWN_SOURCE_FILES
         ${SYSTEM_SOURCE_FILES})
 
 list(TRANSFORM TWN_SOURCE_FILES PREPEND ${TWN_ROOT_DIR}/)
+source_group(TREE ${TWN_ROOT_DIR} FILES ${TWN_NONOPT_SOURCE_FILES})
 
 add_library(twn_third_parties STATIC ${TWN_THIRD_PARTY_SOURCE_FILES})
 
@@ -123,8 +129,6 @@ else()
         add_library(${TWN_TARGET} STATIC ${TWN_SOURCE_FILES} ${twn_third_parties})
 endif()
 
-source_group(TREE ${TWN_ROOT_DIR} FILES ${TWN_SOURCE_FILES})
-
 set_target_properties(${TWN_TARGET} PROPERTIES
                                     C_STANDARD 11
                                     C_STANDARD_REQUIRED ON