面向 SDL 初学者的 C++ 抗锯齿线

Question

原始问题:

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?

新:

根据 NomNomNom069 的 YouTube 视频“C++ SDL 教程 2 创建屏幕和处理基本输入”，我现在已将我的主要功能替换为以下代码

#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;
}

没有错误，我会弹出一个窗口。太棒了。

我现在的问题是关于如何/在何处调用 WuLinesAlpha。此函数调用 4 个 double、一个 Uint32 变量和一个 SDL_Surface*。我有我的double，我将Uint32设置为0x000000FF，我假设我设置的SDL_Surface up as screen 是传入的。

我一直在研究 WuLinesAlpha 函数调用的去向，但总是出现黑屏。我以为，正如视频中所解释的那样，它会进入循环，但什么也没发生。我应该调用更多 SDL 命令吗？

Answer 1

首先修正你的 main 声明。这确实需要是 int main(int argc, char *argv[])。特别是在 Windows 上，因为我相信 SDL.h 实际上会将您的 main 重命名为其他名称，并接管 main 库本身。

接下来，确保正确链接到 SDL。在我自己的基于 SDL 1.2.x 的项目中，我的 Makefile 中有这些行:

SDL_CFLAGS := $(shell sdl-config --cflags)
SDL_LFLAGS := $(shell sdl-config --libs)

然后我将这些标志附加到我的实际 CFLAGS 和 LFLAGS 中。请注意，如果您使用 make 和 Makefile，您需要在那里使用 :=，否则 make 将调用每次扩展 $(CFLAGS) 时 $(shell ...) 命令。

我无法帮助您设置 Microsoft 的 GUI 产品。本教程针对稍旧的 MSVC 产品(2010 年)，看起来很不错，可能会让您走上正轨:http://lazyfoo.net/SDL_tutorials/lesson01/windows/msvsnet2010e/index.php

最后，不要忘记在某个时候调用 SDL_Init()，最好是在开始创建表面之前。

祝你好运!