PopUp Menus Glenn G Chappell CHAPPELLGmember ams org

Pop-Up Menus Glenn G. Chappell CHAPPELLG@member. ams. org U. of Alaska Fairbanks CS 381 Lecture Notes Friday, September 26, 2003 26 Sep 2003 CS 381

Review: Reshape Callback [1/2] n The GLUT reshape callback function is called: n n Reshape has 2 parameters: n n n When the window is first created, before any other callback. Later, whenever the window size/shape changes. Not when the window is merely moved. 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. n n 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 2

Review: Reshape Callback [2/2] n Example reshape function: void reshape(int w, int h) { // Set up the viewport gl. Viewport(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) gl. Matrix. Mode(GL_PROJECTION); gl. Load. Identity(); glu. Ortho 2 D(0. 0, 1. 0, 0. 0, 1. 0); // left, right, bottom, top gl. Matrix. Mode(GL_MODELVIEW); // Always go back to model/view mode } 26 Sep 2003 CS 381 3

Review: Mouse-Related Callbacks n GLUT has two main mouse-handling callbacks. n 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) n 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. n Mouse is always called before motion is called. 26 Sep 2003 CS 381 4

Review: Converting Coordinates n n GLUT gives mouse coordinates in pixels from the upper-left corner of the window. Open. GL deals with coordinates set by the projection. n n n You’ll need to convert between the two. n n May not be in pixels. Based at the lower-left corner of the viewport. Lirp! Note: Converting between coordinate systems is a theme that runs all through 3 -D CG. 26 Sep 2003 CS 381 5

Mouse-Related Callbacks: Example n Write a program the uses the mouse and motion callbacks. n 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 6

Menus in General: Introduction n The next piece in our discussion of GUI’s is menus. n n n 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 -F 4), 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. n 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 7

Menus in General: Specification n To design a menu, we need to specify: n n What entries does the menu have? When/where does the menu appear? • • n 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 n What happens when a menu entry is selected? 26 Sep 2003 CS 381 8

Using GLUT Menus: Introduction n GLUT provides simple mousecontrolled pop-up menus. n n 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 9

Using GLUT Menus: Overview n What we can do with menus: n n n 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 10

Using GLUT Menus: Menu Creation n Creating a Menu n Creating a menu means creating a data structure in memory; nothing is displayed yet. • GLUT manages the data structure. n n n 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 glut. Create. Menu. • 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: glut. Create. Menu(handle_menu); 26 Sep 2003 CS 381 11

Using GLUT Menus: Adding Entries n Adding Entries to a Menu n 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). n To add an entry, call glut. Add. Menu. Entry. • 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: glut. Add. Menu. Entry("Toggle eye color", 1); 26 Sep 2003 CS 381 12

Using GLUT Menus: Attaching n Attaching a Menu to a Mouse Button n n We can attach the current menu to a mouse button in the current window. To attach a menu, call glut. Attach. Menu. • This function takes one parameter: • An int indicating which mouse button to attach to. • Example: glut. Attach. Menu(GLUT_RIGHT_BUTTON); n 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. n 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 13

Using GLUT Menus: Example (creature. cpp) [1/2] n The following is called in function init. void make_main_menu() { glut. Create. Menu(handle_main_menu); glut. Add. Menu. Entry("Toggle eye color", 1); glut. Add. Menu. Entry("Toggle mouth motion", 2); glut. Add. Menu. Entry("Quit", 3); glut. Add. Menu. Entry("------------", 999); … glut. Add. Menu. Entry("for CS 381, fall 2003", 999); glut. Attach. Menu(GLUT_RIGHT_BUTTON); } n Value passed to handler callback can be the same for multiple entries. 26 Sep 2003 CS 381 14

Using GLUT Menus: Example (creature. cpp) [2/2] n Here is part of the handler callback function (declared before make_main_menu!). // handle_main_menu // Menu handling callback function for our menu void handle_main_menu(int value) { switch (value) { case 1: // Toggle eye color blueeyes = !blueeyes; glut. Post. Redisplay(); break; … case 3: // Quit exit(0); break; case 999: // Other menu items do nothing break; n Menu handlers, like keyboard functions, typically consist of one switch statement. 26 Sep 2003 CS 381 15

More on Menus: Overview n Now, we quickly look at a few more advanced topics. We will discuss some of these in more detail later on. n GLUT Menus: • The “current menu”. • Submenus. • Changing menu entries. n Thoughts on menus in general: • What are submenus for? • On changing menus. 26 Sep 2003 CS 381 16

More on Menus: GLUT — The Current Menu n Some GLUT menuing commands (e. g. , glut. Add. Menu. Entry, glut. Attach. Menu) deal with the current menu. n n If you have just one menu, then it is the current menu. glut. Create. Menu sets the current menu to the menu created. In a menu handler, the current menu is the one handled. Function glut. Create. Menu returns an int identifying the menu created. If you have multiple menus, save this value. int menu_x = glut. Create. Menu(handle_menu_x); n n You can set the current menu yourself using glut. Set. Menu. There is also a “current window”. It is dealt with similarly. 26 Sep 2003 CS 381 17

More on Menus: GLUT — Submenus n n A submenu is a menu that is an item in another menu. To make a submenu (in the “main” menu): n n n Create the submenu (as an ordinary menu, but do not attach it). Create the main menu. Use glut. Add. Sub. Menu to make submenu an item in the main menu. int superduper_menu = glut. Create. Menu(handle_superduper_menu); … int rightmouse_menu = glut. Create. Menu(handle_rightmouse_menu); glut. Add. Sub. Menu("Super-Duper Stuff", superduper_menu); n The submenu does not need to be attached. 26 Sep 2003 CS 381 18

More on Menus: GLUT — Changing Menu Entries n To change the text or return value of a menu entry: n Set the current menu, by passing the proper ID to glut. Set. Menu. • If you are in the menu handler, this is unnecessary. glut. Set. Menu(superduper_menu); n Use glut. Change. To. Menu. Entry 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). glut. Change. To. Menu. Entry(1, the_entry. c_str(), 1); n You can also change submenus, using glut. Change. To. Sub. Menu; see the GLUT documentation. 26 Sep 2003 CS 381 19

More on Menus: What are Submenus For? n There are many bad uses for submenus. Here are three good ones. 1. 2. 3. 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). Put rarely-used commands that belong together in a submenu (e. g. , programconfiguration commands). 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 20

More on Menus: On Changing Menus n n 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”. n 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? 26 Sep 2003 CS 381 21