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Pop-Up Menus

Pop-Up Menus. Glenn G. Chappell CHAPPELLG@member.ams.org U. of Alaska Fairbanks CS 381 Lecture Notes Friday, September 26, 2003. Review: Reshape Callback [1/2]. The GLUT reshape callback function is called: When the window is first created, before any other callback.

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Pop-Up Menus

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

  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. 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 } 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. 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. 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. 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. 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? 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. 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. 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); 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); 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. 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. 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 menu void 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. 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. 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. 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. 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. CS 381

  20. More on Menus:What are Submenus For? • There are many bad uses for submenus. Here are three good ones. • 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., program-configuration commands). • Have a submenu corresponding to a list of objects, with the entries being the objects (e.g., a “recently-opened files” submenu). 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? CS 381

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