Fun Day 11 21 2007 1 Opening Discussion Let s look at solutions to the interclass problem Vote was 7 for ASCII 10 for X11 Do you have any questions about the assignment 2 Full Terminal Control The ncurses library provides you with functions that allow you to write any ASCII character that you want to any point on the screen This can allow you to do ASCII animations It also includes functions for doing non blocking input and input of non character keys Normal scanf and getchar functions only read from a terminal once enter has been pressed Note that this isn t portable code It won t work on a Windows box unless perhaps you have something like Cygwin 3 Setup In order to set up a window so that you can use curses function with it you need to initialize it You do this with the WINDOW initscr function Let s look at the man page for this function The WINDOW that is returned needs to be remembered because it has to be passed to most of the functions that will draw out characters for us 4 Drawing Functions There are number of different functions that can output to the screen I m not going to type them all up here but I ll give a little list We can look at a web page for a more complete list mvaddch win y x ch mvwaddstr win y x str mvwaddchstr win y x chstr After calling one of these call refresh win to see the change You can use the See Also section of the man pages to find more related functions 5 Input Functions There are a number of functions for getting input in curses The simplest is wgetch win Unless you set other options this will work just like getchar blocking the program and printing to screen The following lines will allow non blocking nonprinted input that doesn t print keypad win 1 wtimeout win 0 necho 6 X Windows and X11 Linux and Unix boxes use a windowing system called X windows This is a very general graphical system that allows a lot of flexibility One of the most significant features of X windows is the ability to display windows remotely Cygwin can give you X windows under Windows but by default you can t use it there 7 Windows There are several steps in getting an X window Get a display XOpenDisplay Get a screen number on the display XDefaultScreen Create the window XCreateSimpleWindow Here again the man pages can help us get more information 8 Events Most GUI environments use events for user input That s because you can t block the thread and there are many different event types key presses mouse actions exposures etc The is a big union called XEvent that has the different events Every structure in it shares certain elements at the beginning The XNextEvent function will return the next event to you You switch on the type of the event to determine what you should do about it For X programs the event handling likely belongs in a loop 9 Exposures One type of event that is particular to the X system is exposures They tell you that some part of the window has been exposed and that you need to redraw it By default X windows don t remember what is drawn in them so the refresh has to be done manually 10 Graphics Context The graphics context in X is a struct that tells X how to draw things You can create multiple instances of this structure and set them up to draw in different ways You can think of each one as being like a pencil or brush with a different color width etc The struct is called XGCValues 11 Drawing and Colors There are a bunch of drawing functions in X11 that begin with XDraw and XFill They are fairly simply to master and running a command like man k XDraw will list them Colors are more challenging The XAllocNamedColor will give you a color from a set of named colors For more variety you need to use XCreateColormap to make a full color map This makes X applications more cross platform compatible but harder to work with 12 Minute Essay What are you doing for Thanksgiving Interclass Problem Write a little program to use one of these two libraries 13
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