sys: add support for Kinc main loop callback

doc/examples/window.cpp

@@ -14,11 +14,27 @@
 #   include "config.h"
 #endif
 
+#include <kinc/graphics4/graphics.h>
 #include <lol/engine/sys>
+#include <cmath>
 
 int main(int argc, char **argv)
 {
+    int frame = 0;
+
+    // Open a simple window
     lol::sys::init(argc, argv, "window", 640, 480);
+
+    // Update routine: clear the background color
+    lol::sys::add_callback([&frame]() {
+        uint32_t alpha = uint32_t(127.0f + 127.0f * std::cos(++frame * 0.1f));
+        kinc_g4_begin(0);
+        kinc_g4_clear(KINC_G4_CLEAR_COLOR, 0x800000 | alpha * 0x0101, 0.f, 0);
+        kinc_g4_end(0);
+        kinc_g4_swap_buffers();
+        return true;
+    });
+
     lol::sys::run();
     return EXIT_SUCCESS;
 }

src/include/lol/engine/private/sys/init.h

@@ -17,6 +17,7 @@
 // -------------------------------
 //
 
+#include <functional> // std::function
 #include <string> // std::string
 
 //
@@ -52,13 +53,20 @@
 namespace lol::sys
 {
 
+// Initialise the system and automatically create a window.
 extern void init(int argc, char *argv[],
                  std::string const &name, int width, int height,
                  std::string const &projectdir = LOL_CONFIG_PROJECTDIR,
                  std::string const &solutiondir = LOL_CONFIG_SOLUTIONDIR,
                  std::string const &sourcesubdir = LOL_CONFIG_SOURCESUBDIR);
 
+// Register an update callback. The callback can return false to automatically unregister.
+extern void add_callback(std::function<bool()>);
+
+// Run the main loop.
 extern void run();
+
+// Stop the main loop.
 extern void stop();
 
 extern void add_data_dir(std::string const &dir);

src/sys/init.cpp

@@ -13,12 +13,13 @@
 #include <lol/engine/sys>
 #include <lol/msg>
 
-#include <vector> // std::vector
-#include <string> // std::string
+#include <algorithm> // std::erase_if
 #include <cctype>
 #if !defined _LIBCPP_HAS_NO_FILESYSTEM_LIBRARY
 #   include <filesystem> // std::filesystem::exists
 #endif
+#include <string> // std::string
+#include <vector> // std::vector
 
 #include <kinc/system.h>
 
@@ -29,6 +30,8 @@ namespace lol::sys
 static std::vector<std::filesystem::path> data_dir;
 #endif
 
+static std::vector<std::function<int()>> g_callbacks;
+
 void init(int argc, char *argv[],
           std::string const &name, int width, int height,
           std::string const &projectdir,
@@ -37,10 +40,6 @@ void init(int argc, char *argv[],
 {
     using namespace std;
 
-#if LOL_USE_KINC
-    kinc_init(name.c_str(), width, height, nullptr, nullptr);
-#endif
-
 #if !defined _LIBCPP_HAS_NO_FILESYSTEM_LIBRARY
     msg::debug("project dir: “%s”\n", std::filesystem::path(projectdir).generic_string().c_str());
     msg::debug("solution dir: “%s”\n", std::filesystem::path(solutiondir).generic_string().c_str());
@@ -115,6 +114,20 @@ void init(int argc, char *argv[],
         msg::debug("data dir %d/%d: “%s”\n", i + 1, int(data_dir.size()),
                    data_dir[i].generic_string().c_str());
 #endif
+
+#if LOL_USE_KINC
+    kinc_init(name.c_str(), width, height, nullptr, nullptr);
+
+    // Call all the registered callbacks and remove the ones that return false
+    kinc_set_update_callback([](void *){
+        std::erase_if(g_callbacks, [](auto fn) { return !fn(); });
+    } , nullptr);
+#endif
+}
+
+void add_callback(std::function<bool()> fn)
+{
+    g_callbacks.push_back(fn);
 }
 
 void run()