C++ Anti-aliased line for beginner to SDL - c++

Question

Original question:
I've been asked prior to a job interview to understand how an
anti-aliased line is drawn in a framebuffer, using C or C++. I haven't
used C, and it's been a few years for me since last using C++. I am a
complete beginner when it comes to graphics. My C++ experience has
mostly been in simple command-line programs and sorting methods. The
company does not care if I grab the code online, they want me to
understand it but still have a working executable.
I've used this tutorial to set up SDL libraries in MS VC++ 2012
Express, and this algorithm for the actual anti-aliasing. I have
a good understanding of the algorithm, though I'm currently having
trouble getting it to compile. I just want a line to be drawn, and
then I can go forward with setting the code up to the skeleton class
definitions I was given. This is what I have included aside from what
is on that page with the algorithm:
#include <cmath>
#include <math.h>
#include "conio.h"
#include "stdlib.h"
#include "stdio.h"
#include "SDL.h"
const double HEIGHT = 240;
const double WIDTH = 320;
const double X0 = 25.6;
const double X1 = 64.7;
const double Y0 = 30;
const double Y1 = 42;
int round(double number)
{
return number < 0.0 ? ceil(number - 0.5) : floor(number + 0.5);
}
void main()
{
Uint32 pixelColor = 00000000000000000000000000000000;
SDL_Surface* myScreen = SDL_CreateRGBSurface(SDL_ALPHA_OPAQUE,WIDTH,HEIGHT,32, 0x000000FF,
0x0000FF00, 0x00FF0000, 0xFF000000);
WULinesAlpha(X0, X1, Y0, Y1,pixelColor,myScreen);
return;
}
I'm getting the following errors:
Error 21 error LNK2019: unresolved external symbol _SDL_main
referenced in function _main Error 22 error LNK1120: 1 unresolved
externals
I've seen a few code examples saying the main function has to look
like this:
int main(int argc, char *argv[])
{
}
Again, graphics stuff is unfamiliar to me so I know my main function
is likely very wrong; I'm anticipating some shaking heads. Can someone
explain what is happening/what I need to do?
New:
I have now replaced my main function with the following code, based on NomNomNom069's YouTube video: "C++ SDL Tutorial 2 Creating a Screen and Handling Basic Input"
#include "SDL.h"
int main(int argc, char * args[])
{
bool running = true;
//initialize SDL
if (SDL_Init(SDL_INIT_EVERYTHING) == -1)
{
running = false;
}
//set up screen
SDL_Surface *screen;
screen = SDL_SetVideoMode(WIDTH, HEIGHT, 32, SDL_HWSURFACE);
if (screen == NULL)
{
running = false;
}
SDL_Event occur;
//main application loop
while (running)
{
SDL_PollEvent(&occur);
if (occur.type == SDL_QUIT)
{
running = false;
}
//drawing occurs here
SDL_FillRect(screen, NULL, 0);
SDL_Flip(screen);
}
//quit SDL
SDL_Quit();
return 0;
}
No errors, and I get a window to pop up. Awesome.
My question now is regarding how/where to call WuLinesAlpha. This function calls for 4 doubles, a Uint32 variable, and an SDL_Surface*. I have my doubles, I set the Uint32 to 0x000000FF, and I assume that the SDL_Surface I have set up as screen is the one passed in.
I've toyed around with where the WuLinesAlpha function call goes and I keep getting the black screen. I thought, as explained in the video, it would go in the loop but nothing has happened. Are there any more SDL commands I should be calling?

Answer 1

Fix your main declaration first. This does need to be int main(int argc, char *argv[]). Especially on Windows, since I believe SDL.h actually renames your main to some other name, and takes over main for the library itself.
Next, make sure you link against SDL properly. In my own SDL 1.2.x based project I have these lines in my Makefile:
SDL_CFLAGS := $(shell sdl-config --cflags)
SDL_LFLAGS := $(shell sdl-config --libs)
I then later append those flags to my actual CFLAGS and LFLAGS. Note that if you use make and Makefiles, you want to use := there, otherwise make will invoke the $(shell ...) command every time it expands $(CFLAGS).
I can't help you set up Microsoft's GUI products. This tutorial, for a slightly older MSVC product (2010), looks pretty good, and may put you on the right track: http://lazyfoo.net/SDL_tutorials/lesson01/windows/msvsnet2010e/index.php
And finally, don't forget to call SDL_Init() at some point, preferably before you start creating surfaces.
Good luck!