rntviewer/src/mainloop.cpp

internal 
void glfw_error_callback(i32 error, const char *description) {
	fprintf(stderr, "GLFW error %d: %s\n", error, description);
}

internal 
GLFWwindow *init_glfw(i32 desired_win_width, i32 desired_win_height)
{
	glfwSetErrorCallback(glfw_error_callback);
	glfwInit();
	glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 4);
	// glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 3);
	glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE);
	glfwWindowHint(GLFW_DOUBLEBUFFER, GLFW_TRUE);
	glfwWindowHint(GLFW_RESIZABLE, GLFW_TRUE);
	glfwWindowHint(GLFW_DECORATED, GLFW_TRUE);
	glfwWindowHint(GLFW_DEPTH_BITS, 32);
#ifndef NDEBUG
	glfwWindowHint(GLFW_OPENGL_DEBUG_CONTEXT, true);
#endif

	GLFWwindow *window = glfwCreateWindow(
			desired_win_width, desired_win_height,
			"RNTuple Viewer",
			nullptr,
			nullptr
			);

	glfwMakeContextCurrent(window);

	return window;
}

internal
void monitor_key(GLFWwindow *window, u8 *key_state, i32 glfw_key, Input_Key key) {
	u8 &state = key_state[key];
	if (glfwGetKey(window, glfw_key) == GLFW_PRESS) {
		if (!(state & KEY_STATE_IS_DOWN)) state |= KEY_STATE_JUST_PRESSED;
		state |= KEY_STATE_IS_DOWN;
	} else if (glfwGetKey(window, glfw_key) == GLFW_RELEASE) {
		if (state & KEY_STATE_IS_DOWN) state |= KEY_STATE_JUST_RELEASED;
		state &= ~KEY_STATE_IS_DOWN;
	}
}

internal 
void run_main_loop(GLFWwindow *window, Arena *arena, App_State &app)
{
  f32 delta_time_ms;
  chr::time_point last_saved_time = chr::high_resolution_clock::now();

  app.delta_time_accum.max = 100;
  app.delta_time_accum.base = arena_push_array<f32>(arena, app.delta_time_accum.max);
  
  b8 running = true;
  while (running) {
		chr::time_point frame_start = chr::high_resolution_clock::now();
		u64 time_since_prev_frame_us = chr::duration_cast<chr::microseconds>(frame_start - last_saved_time).count();
		delta_time_ms = time_since_prev_frame_us * 0.001f;
		last_saved_time = frame_start;

		glfwPollEvents();

		// Update window size
		{
			Window_Data &wdata = app.win_data;

			i32 prev_width = wdata.width;
			i32 prev_height = wdata.height;

			glfwGetWindowSize(window, &wdata.width, &wdata.height);

			wdata.size_just_changed = prev_width != wdata.width || prev_height != wdata.height;
		}

		ImGui_ImplOpenGL3_NewFrame();
		ImGui_ImplGlfw_NewFrame();
		ImGui::NewFrame();

		// Check if the inspected file changed
		{
			char buf[sizeof(inotify_event) + NAME_MAX + 1];
			ssize_t nbytes = read(app.inspected_file.inot, buf, sizeof(buf));
			if (nbytes)
				app.inspected_file.size = file_size(app.inspected_file.stream);		
		}

		if (glfwGetKey(window, GLFW_KEY_ESCAPE) == GLFW_PRESS || glfwWindowShouldClose(window)) {
			running = false;
			break;
		}

		b32 focused = glfwGetWindowAttrib(window, GLFW_FOCUSED);
		if (focused) {
			// Update keyboard
			u8 *key_state = app.user_input.key_state;
			monitor_key(window, key_state, GLFW_KEY_Q, KEY_Q);
			monitor_key(window, key_state, GLFW_KEY_UP, KEY_UP);
			monitor_key(window, key_state, GLFW_KEY_DOWN, KEY_DOWN);
			monitor_key(window, key_state, GLFW_KEY_LEFT, KEY_LEFT);
			monitor_key(window, key_state, GLFW_KEY_RIGHT, KEY_RIGHT);
			monitor_key(window, key_state, GLFW_KEY_LEFT_ALT, KEY_ALT);
			monitor_key(window, key_state, GLFW_KEY_TAB, KEY_TAB);

			// Update mouse
			f64 mposx, mposy;
			glfwGetCursorPos(window, &mposx, &mposy);

			app.user_input.mouse_pos.x = static_cast<i32>(mposx);
			app.user_input.mouse_pos.y = static_cast<i32>(mposy);
		}

		update_and_render(arena, app, delta_time_ms);

		ImGui::Render();
		ImGui_ImplOpenGL3_RenderDrawData(ImGui::GetDrawData());

		glfwSwapBuffers(window);
  }  
}