Pop-Up Menus

Glenn G. ChappellCHAPPELLG@member.ams.org

U. of Alaska Fairbanks

CS 381 Lecture NotesFriday, September 26, 2003

26 Sep 2003 CS 381 2

Review:Reshape Callback [1/2] The GLUT reshape callback function is called:

When the window is first created, before any other callback. Later, whenever the window size/shape changes. Not when the window is merely moved.

Reshape has 2 parameters: New width of window, in pixels. New height of window, in pixels.

In the reshape function, we handle things related to the size/shape of the window. This is relevant to mouse handling (right?). If you need information on the window size somewhere else

in your program, save it in the reshape function.

26 Sep 2003 CS 381 3

Review:Reshape Callback [2/2] Example reshape function:

void reshape(int w, int h)

{

// Set up the viewport

glViewport(0, 0, w, h);

// Save the window width & height in globals

winw = w;

winh = h;

// Set up the projection (now we do *not* need to do this in init)

glMatrixMode(GL_PROJECTION);

glLoadIdentity();

gluOrtho2D(0.0, 1.0, 0.0, 1.0); // left, right, bottom, top

glMatrixMode(GL_MODELVIEW); // Always go back to model/view mode

}

26 Sep 2003 CS 381 4

Review:Mouse-Related Callbacks GLUT has two main mouse-handling callbacks.

The mouse function.• Called when any mouse button is pressed or released.

• Unless there is a pop-up menu attached to that button.• 4 parameters:

• Which button (GLUT_LEFT_BUTTON, GLUT_MIDDLE_BUTTON, or GLUT_RIGHT_BUTTON).

• Button state (GLUT_UP or GLUT_DOWN).• Mouse x (in pixels from left)• Mouse y (in pixels from top)

The motion function.• This is called (possibly repeatedly) whenever the mouse

moves while any of the buttons is pressed.• 2 parameters: mouse x, y, as in mouse function.

Mouse is always called before motion is called.

26 Sep 2003 CS 381 5

Review:Converting Coordinates

GLUT gives mouse coordinates in pixels from the upper-left corner of the window.

OpenGL deals with coordinates set by the projection. May not be in pixels. Based at the lower-left corner of the viewport.

You’ll need to convert between the two. Lirp!

Note: Converting between coordinate systems is a theme that runs all through 3-D CG.

26 Sep 2003 CS 381 6

Mouse-Related Callbacks:Example

Write a program the uses the mouse and motion callbacks. Modified bmptext.cpp to make a purple

square appear at the mouse position, and follow the mouse, when the left button is down. A similar program is on the web page: simplemouse.cpp.

26 Sep 2003 CS 381 7

Menus in General:Introduction The next piece in our discussion of GUI’s is menus.

Menus are a common user-interface feature. Menus predate GUI’s. Advantages of Menus (over other GUI concepts):

• Easy for the user: Many commands all work alike, and new ones work the same as the old ones they already know how to use. No need to memorize command names (“grep”), keypresses (ctrl-alt-F4), etc.

• Easy for the programmer, if menuing is included in the libraries being used.

• Pop-up style menus use little or no screen/window space. Disadvantages of Menus:

• Using a menu takes time and interrupts user’s train of thought.• They are “too easy”; overuse can lead to a poorly designed user

interface.

26 Sep 2003 CS 381 8

Menus in General:Specification

To design a menu, we need to specify: What entries does the menu have? When/where does the menu appear?

• In a dialog box• In a menu bar• Pop-up on mouse click• Submenu of other menu

How are entries in the menu chosen?• Mouse actions• Key combinations

What happens when a menu entry is selected?

26 Sep 2003 CS 381 9

Using GLUT Menus:Introduction

GLUT provides simple mouse-controlled pop-up menus. GLUT menus are

not full-featured, but they provide a nice introduction.

Here is the window and menu from creature.cpp.

26 Sep 2003 CS 381 10

Using GLUT Menus:Overview What we can do with menus:

We can create (and destroy) menu data structures. We can add entries (and submenus) to a previously

created menu. We can attach a previously created menu to a mouse

button (and we can also detach it). We can change the entries of a menu.

The first three above are illustrated in creature.cpp. We will look at these in detail shortly.

Each menu has a callback associated with it: the handler function. This function is called when the user selects an entry in that menu.

26 Sep 2003 CS 381 11

Using GLUT Menus:Menu Creation

Creating a Menu Creating a menu means creating a data structure in

memory; nothing is displayed yet.• GLUT manages the data structure.

When we create a menu, we also register the handler callback function.

The initialization function (“init”) is a good place to create your menus.

To create a menu, call glutCreateMenu.• This function takes one parameter:

• A pointer to the handler callback function for this menu.

• A menu handler function takes one int parameter and returns void; more on this later.

• Example: glutCreateMenu(handle_menu);

26 Sep 2003 CS 381 12

Using GLUT Menus:Adding Entries

Adding Entries to a Menu We can add entries to the end of the current menu.

• What is the current menu? For now, if you have created one menu, then it is the current menu (similarly, if you have one window, then it is the current window).

To add an entry, call glutAddMenuEntry.• This function takes two parameters:

• A char* (C-style string) that gives the text of the entry.• If you are using the C++ string class, you can pass a C-

style string using the .c_str() member function.• An int that is passed to the handler function when the user

selects this entry.

• Example: glutAddMenuEntry("Toggle eye color", 1);

26 Sep 2003 CS 381 13

Using GLUT Menus:Attaching Attaching a Menu to a Mouse Button

We can attach the current menu to a mouse button in the current window.

To attach a menu, call glutAttachMenu.• This function takes one parameter:

• An int indicating which mouse button to attach to.• Example: glutAttachMenu(GLUT_RIGHT_BUTTON);

Once we attach a menu, the user can use it.• Whenever they want, the user pops up the menu with the

appropriate mouse action.• We do not draw the menu; GLUT does this for us.• When a menu entry is selected, the handler function is

called, with the proper number as a parameter. Since a menu is attached in the current window, do not

attach a menu until you have created a window.

26 Sep 2003 CS 381 14

Using GLUT Menus: Example (creature.cpp) [1/2] The following is called in function init.

void make_main_menu()

{

glutCreateMenu(handle_main_menu);

glutAddMenuEntry("Toggle eye color", 1);

glutAddMenuEntry("Toggle mouth motion", 2);

glutAddMenuEntry("Quit", 3);

glutAddMenuEntry("------------------------", 999);

… glutAddMenuEntry("for CS 381, fall 2003", 999);

glutAttachMenu(GLUT_RIGHT_BUTTON);

}

Value passed to handler callback can be the same for multiple entries.

26 Sep 2003 CS 381 15

Using GLUT Menus: Example (creature.cpp) [2/2] Here is part of the handler callback function (declared before make_main_menu!).

// handle_main_menu// Menu handling callback function for our menuvoid handle_main_menu(int value){ switch (value) { case 1: // Toggle eye color blueeyes = !blueeyes; glutPostRedisplay(); break;… case 3: // Quit exit(0); break; case 999: // Other menu items do nothing break; Menu handlers, like keyboard functions, typically consist of one switch statement.

26 Sep 2003 CS 381 16

More on Menus:Overview

Now, we quickly look at a few more advanced topics. We will discuss some of these in more detail later on. GLUT Menus:

• The “current menu”.• Submenus.• Changing menu entries.

Thoughts on menus in general:• What are submenus for?• On changing menus.

26 Sep 2003 CS 381 17

More on Menus: GLUT — The Current Menu Some GLUT menuing commands (e.g., glutAddMenuEntry,

glutAttachMenu) deal with the current menu. If you have just one menu, then it is the current menu. glutCreateMenu sets the current menu to the menu created. In a menu handler, the current menu is the one handled. Function glutCreateMenu returns an int identifying the

menu created. If you have multiple menus, save this value.

int menu_x = glutCreateMenu(handle_menu_x);

You can set the current menu yourself using glutSetMenu. There is also a “current window”. It is dealt with similarly.

26 Sep 2003 CS 381 18

More on Menus: GLUT — Submenus A submenu is a menu that is an item in another menu. To make a submenu (in the “main” menu):

Create the submenu (as an ordinary menu, but do not attach it). Create the main menu. Use glutAddSubMenu to make submenu an item in the main menu.

int superduper_menu =

glutCreateMenu(handle_superduper_menu);

…int rightmouse_menu =

glutCreateMenu(handle_rightmouse_menu);

glutAddSubMenu("Super-Duper Stuff", superduper_menu);

The submenu does not need to be attached.

26 Sep 2003 CS 381 19

More on Menus:GLUT — Changing Menu Entries To change the text or return value of a menu entry:

Set the the current menu, by passing the proper ID to glutSetMenu.• If you are in the menu handler, this is unnecessary.

glutSetMenu(superduper_menu);

Use glutChangeToMenuEntry to set the new text & return value. This function takes 3 parameters:

• The entry number (int): count from the top of the menu, starting at 1.• The new text (char*).• The new return value (int).

glutChangeToMenuEntry(1, the_entry.c_str(), 1);

You can also change submenus, using glutChangeToSubMenu; see the GLUT documentation.

26 Sep 2003 CS 381 20

More on Menus:What are Submenus For?

There are many bad uses for submenus. Here are three good ones.

1. Write a submenu corresponding to a single variable or option, with its entries being the possible values (e.g., a “color” submenu; entries are colors).

2. Put rarely-used commands that belong together in a submenu (e.g., program-configuration commands).

3. Have a submenu corresponding to a list of objects, with the entries being the objects (e.g., a “recently-opened files” submenu).

26 Sep 2003 CS 381 21

More on Menus:On Changing Menus

Changing a menu item can be a useful way to indicate state information to the user.

But be sure to differentiate clearly between “current state” and “what this menu item does”. Bad example: a menu item reading “Super-

Duper Mode: ON”. Does this mean that super mode is currently on, or that selecting this entry turns super mode on?