CS60 Lecture 20
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Announce
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- proj4 
- hw14 posted, due mon

Today
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- proj4
- review virtual funcs
- file IO
- C++ strings
- OpenGL

Proj4
-------------------

- questions?
- y * width gives the rigth row
- + x gives the right column
- *3 since each el is 3 bytes
- +0,+1,+2 for r, g, b respectively

Review Virtual Functions
--------------------------

- know about inheritance

- some problems arise
	- constructors, destructors, copy const, assign op
	- solve by implementing these special funcs for ALL classes

- some more problems
	- base function uses another member func only defed in child
	- solution is to use virtual functions

- base class has a virtual function defned and uses in member func

- child class use of base class member uses child class version of
virtual func

- base has 'center()' which uses 'draw()'
- base has virtual function draw()
- child has virtual function draw()
- child instance.center() gets child draw()

- if we never plan on using base class, declare PURE virtual functions
	- virtual <func prototype> = 0;


C++ File IO
-----------------------

- in C, we had file descriptors and FILE pointers

- fd IO set: read, write, open, close
- FILE IO set: fprintf, fscanf, fopen, fclose

- IO channels generic (files, devices, screen, keyboard)

- C++ uses streams, which are also generic

- inheritance hierarchy

fstream
|	\
ostream	istream
|		\
ofstream 	ifstream

- anything that is an output stream is of type 'ostream' like cout
- input is 'istream' like cin

- cout and cin are instances of 'ostream' and 'istream' objects

- file IO happens through derived classes ifstream and ofstream

- *fstream have member functions:

- open
- close
- flush
- overloaded ops << and >> .. like cout/cin!

Ex:

ofstream ofile;
int a=10;

ofile.open("/tmp/out.txt");

ofile << "A is = " << a << endl;

ofile.close();

- similarly, ifstream objects work like cin

- remember out cin works, though, ignores whitespace, newlines, etc

- to do character output, use member functions:

- get
- put
- eof

char tmp;

ifile.open("/tmp/foo.txt");

ifile.get(tmp);
while(!ifile.eof()) {
	cout << tmp;
	ifile.get(tmp);
}
ifile.close();

- to check for failure, use 'fail' member function

ofile.open("/etc/passwd");
if (ofile.fail()) {
	cout << "doh!\n";
	exit(1);
}


- good for simple IO, also have functionality we're more familiar with:

fstream 

- member functions are all above, but also 'read' and 'write'

- TWO seeks, one for read (get), one for write (put) (seekp, seekg)

- constants defined in ios class for IO flags
	- ios::in
	- ios::out	
	- ios::app

- OR them together just like we did with O_RDONLY, O_WRONLY, etc


C++ Strings
---------------------

- C strings work the same way

- C++ has a standard string class

- pretty nice actually

- #include <string> using namespace std;

- string a, b, c, z;

- initializing
	string d(" world");

	a = "hello";

	b = d;

- modifying/accessing

	c = a + b;
	c[0] = 'H';

	int i = c.find("world");
	z = c.substr(i, c.length(c));

- comparing
	if (a == b) ...

- other
	- a.length()
	- a.empty();


OpenGL
--------------------

- we have been using OpenGL for project4

- OpenGL developed by SGI as a portable 3d graphics standard

- Other standard is DirectX by microsoft

- glut (gl utility toolkit) implements an eventloop and gives us an
OpenGL context

- openGL is a stateful programming model where you set a state,
perform some operations while in that state, then leave the state

- ex: drawing a square

glColor3f(255.0, 0.0, 0.0);

glBegin(GL_QUADS);
glVertex3f(0.0, 0.0, 0.0);
glVertex3f(0.0, 1.0, 0.0);
glVertex3f(1.0, 1.0, 0.0);
glVertex3f(1.0, 0.0, 0.0);
glEnd();

- above draws a 2d rectangle in 3d space, can rotate and scale with
simple functions

- can add textures to surfaces with simple function, textures scale,
rotate, etc with the surface they're attached to

- this is how 3d video games are created!

- great tutorials at http://nehe.gamedev.net

- OpenGL very low level 3d primitives, higher level libraries have
been created to do common operations

- libSDL: Simple DirectMedia Layer

- portable game/graphics library for UNIX/Windows/Mac

- programming interface for graphics, sound, image manipulation, GUI,
etc

- tons of open source and commercial games use it: www.libsdl.org