Added key input to quick tutorial.

docs/quick.dox

@@ -194,6 +194,24 @@ useful if you want to interpret other kinds of input as closing the window, like
 for example pressing the escape key.
 
 
+@section quick_key_input Receiving input events
+
+Each window has a large number of callbacks that can be set to receive all the
+various kinds of events.  To receive key press and release events, a
+[key callback](@ref GLFWkeyfun) is set using @ref glfwSetKeyCallback.
+
+@code
+static void key_callback(GLFWwindow* window, int key, int scancode, int action, int mods)
+{
+    if (key == GLFW_KEY_ESCAPE && action == GLFW_PRESS)
+        glfwSetWindowShouldClose(window, GL_TRUE);
+}
+@endcode
+
+For event callbacks to actually be called when an event occurs, you need to
+process events as described below.
+
+
 @section quick_render Rendering with OpenGL
 
 Once you have a current OpenGL context, you can use OpenGL normally.  In this

examples/simple.c

@@ -34,6 +34,12 @@ static void error_callback(int error, const char* description)
     fputs(description, stderr);
 }
 
+static void key_callback(GLFWwindow* window, int key, int scancode, int action, int mods)
+{
+    if (key == GLFW_KEY_ESCAPE && action == GLFW_PRESS)
+        glfwSetWindowShouldClose(window, GL_TRUE);
+}
+
 int main(void)
 {
     GLFWwindow* window;
@@ -52,6 +58,8 @@ int main(void)
 
     glfwMakeContextCurrent(window);
 
+    glfwSetKeyCallback(window, key_callback);
+
     while (!glfwWindowShouldClose(window))
     {
         float ratio;