add init draw and frame buffer size callback

src/main.c

@@ -2,6 +2,18 @@
 #include <GLFW/glfw3.h>
 #include <stdio.h>
 
+void init(void) {
+	glClearColor(0.1f, 0.1f, 0.1f, 1.0f);
+}
+
+void draw(void) {
+	glClear(GL_COLOR_BUFFER_BIT);
+}
+
+void framebuffer_size_callback(GLFWwindow* window, int width, int height) {
+	glViewport(0, 0, width, height);
+}
+
 int main(int argc, char const *argv[])
 {
 	glfwInit();
@@ -15,9 +27,16 @@ int main(int argc, char const *argv[])
 		glfwTerminate();
 		return 1;
 	}
+	glfwSetFramebufferSizeCallback(window, framebuffer_size_callback);
 	glfwMakeContextCurrent(window);
 	
+	glewInit();
+
+	init();
+
 	while (!glfwWindowShouldClose(window)) {
+		draw();
+
 		glfwSwapBuffers(window);
 		glfwPollEvents();
 	}