SDL入门教程（五）：6、对C++异常机制的思考，代码重写

woaidaima2016

6.1：用bool作为命令是不是画蛇添足了？

        不知道为什么，我总觉得总是用if结构来调用命令让人读起程序来很不连贯。所以，我决定重新修改下，并且异常抛出改为使用类对象，这样是不是更C++一点呢？

6.2：修改后的代码。
//FileName: SurfaceClass.h

#ifndef SURFACE_CLASS_H
#define SURFACE_CLASS_H

#include <iostream>
#include <string>
#include "SDL/SDL.h"

using std::string;

class ScreenSurface
{
private:
    static int screenNum;
    int width;
    int height;
    int bpp;
    Uint32 flags;
    SDL_Surface* pScreen;
public:
    ScreenSurface();
    ScreenSurface(int w, int h, int b = 0, Uint32 f = 0);
    ~ScreenSurface();
    SDL_Surface* point() const;
    void flip() const;
};

class DisplaySurface
{
private:
    string fileName;
    SDL_Surface* pSurface;
    SDL_Surface* pScreen;
public:
    DisplaySurface(string file_name, const ScreenSurface& screen);
    ~DisplaySurface();
    SDL_Surface* point() const;
    void blit() const;
    void blit(int at_x, int at_y) const;
    void blit(int at_x, int at_y,
                int from_x, int from_y, int w, int h,
                int delta_x = 2, int delta_y = 2) const;
    void blitToSurface(const DisplaySurface& dst_surface,
                        int at_x = 0, int at_y = 0) const;
    void blitToSurface(const DisplaySurface& dst_surface,
                        int at_x, int at_y,
                        int from_x, int from_y, int w, int h,
                        int delta_x = 2, int delta_y = 2) const;
};

class ErrorInfo
{
private:
    string info;
public:
    ErrorInfo():info("Unknown ERROR!")
    {}
    ErrorInfo(const char* c_str)
    {
        info = string(c_str);
    }
    ErrorInfo(const string& str):info(str)
    {}
    void show() const
    {
        std::cerr << info << std::endl;
    }
};

#endif

#include "SurfaceClass.h"

//VVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVV
//class ScreenSurface

int ScreenSurface::screenNum = 0;

ScreenSurface::ScreenSurface():
width(640), height(480), bpp(32), flags(0)
{
    if ( screenNum > 0 )
        throw ErrorInfo("DONOT create more than ONE screen!");
    if ( SDL_Init(SDL_INIT_VIDEO < 0 ) )
        throw ErrorInfo(SDL_GetError());
    pScreen = SDL_SetVideoMode(width, height, bpp, flags);
    screenNum++;
}

ScreenSurface::ScreenSurface(int w, int h, int b, Uint32 f):
width(w), height(h), bpp(b), flags(f)
{
    if ( screenNum > 0 )
        throw ErrorInfo("DONOT create more than ONE screen!");
    if ( SDL_Init(SDL_INIT_VIDEO < 0 ) )
        throw ErrorInfo(SDL_GetError());
    pScreen = SDL_SetVideoMode(width, height, bpp, flags);
    screenNum++;
}

ScreenSurface::~ScreenSurface()
{
    SDL_Quit();
}

SDL_Surface* ScreenSurface::point() const
{
    return pScreen;
}

void ScreenSurface::flip() const
{
    if ( SDL_Flip(pScreen) < 0 )
        throw ErrorInfo(SDL_GetError());
}

//AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA

//VVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVV
//class DisplaySurface

DisplaySurface:isplaySurface(std::string file_name, const ScreenSurface& screen):
fileName(file_name)
{
    pSurface = SDL_LoadBMP(file_name.c_str());
    if ( pSurface == 0 )
        throw ErrorInfo(SDL_GetError());
    pScreen = screen.point();
}

DisplaySurface::~DisplaySurface()
{
    SDL_FreeSurface(pSurface);
}

SDL_Surface* DisplaySurface::point() const
{
    return pSurface;
}

void DisplaySurface::blit() const
{
    if ( SDL_BlitSurface(pSurface, 0, pScreen, 0) < 0 )
        throw ErrorInfo(SDL_GetError());
}


void DisplaySurface::blit(int at_x, int at_y) const
{
    SDL_Rect offset;
    offset.x = at_x;
    offset.y = at_y;

    if ( SDL_BlitSurface(pSurface, 0, pScreen, &offset) < 0 )
        throw ErrorInfo(SDL_GetError());
}

void DisplaySurface::blit(int at_x, int at_y,
                          int from_x, int from_y, int w, int h,
                          int delta_x, int delta_y) const
{
    SDL_Rect offset;
    offset.x = at_x - delta_x;
    offset.y = at_y - delta_y;

    SDL_Rect dest;
    dest.x = from_x - delta_x;
    dest.y = from_y - delta_y;
    dest.w = w + delta_x*2;
    dest.h = h + delta_y*2;

    if ( SDL_BlitSurface(pSurface, &dest, pScreen, &offset) < 0 )
        throw ErrorInfo(SDL_GetError());
}

void DisplaySurface::blitToSurface(const DisplaySurface& dst_surface, int at_x, int at_y) const
{
    SDL_Rect offset;
    offset.x = at_x;
    offset.y = at_y;

    if ( &dst_surface == this )
        throw ErrorInfo("Cannot blit surface to itself!");

    if ( SDL_BlitSurface(pSurface, 0, dst_surface.point(), &offset) < 0 )
        throw ErrorInfo(SDL_GetError());
}

void DisplaySurface::blitToSurface(const DisplaySurface& dst_surface,
                                    int at_x, int at_y,
                                    int from_x, int from_y, int w, int h,
                                    int delta_x, int delta_y) const
{
    SDL_Rect offset;
    offset.x = at_x - delta_x;
    offset.y = at_y - delta_y;

    SDL_Rect dest;
    dest.x = from_x - delta_x;
    dest.y = from_y - delta_y;
    dest.w = w + delta_x*2;
    dest.h = h + delta_y*2;

    if ( &dst_surface == this )
        throw ErrorInfo("Cannot blit surface to itself!");

    if ( SDL_BlitSurface(pSurface, &dest, dst_surface.point(), &offset) < 0 )
        throw ErrorInfo(SDL_GetError());
}

//AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA

#include "SurfaceClass.h"

int game(int argc, char* argv[]);
int main(int argc ,char* argv[])
{
    int mainRtn = 0;
    try {
        mainRtn = game(argc, argv);
    }
    catch ( const ErrorInfo& info ) {
        info.show();
        return -1;
    }
   
    return mainRtn;
}

int game(int argc ,char* argv[])
{
    //Create a SDL screen.
    const int SCREEN_WIDTH = 640;
    const int SCREEN_HEIGHT = 480;
    ScreenSurface screen(SCREEN_WIDTH, SCREEN_HEIGHT);

    //Create 2 SDL surface for the screen that just created.
    DisplaySurface backGround("bg.bmp", screen);
    DisplaySurface frontImage("image.bmp", screen);
    //VVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVV
    //way2: If use blitToSurface, must get a copy of backGround.
/*
    DisplaySurface backGroundCopy("bg.bmp", screen);
*/
    //AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA

    //Blit backGround surface to screen and flip the screen.
    backGround.blit();
    screen.flip();

    //variable for main loop.
    //key event for up, down, left and right.
    Uint8* keys;
    //moving image's coordinate.
    int xpos = 0;
    int ypos = 0;
    //moving image's size.
    const int IMG_WIDTH = 128;
    const int IMG_HEIGHT = 128;
    //main loop.
    bool gameOver = false;
    while( gameOver == false ){
        //press ESC or click X to quit.
        SDL_Event gameEvent;
        while ( SDL_PollEvent(&gameEvent) != 0 ){
            if ( gameEvent.type == SDL_QUIT ){
                gameOver = true;
            }
            if ( gameEvent.type == SDL_KEYUP ){
                if ( gameEvent.key.keysym.sym == SDLK_ESCAPE ){
                    gameOver = true;
                }
            }
        }
        //key event to move image.
        keys = SDL_GetKeyState(0);
        if ( keys[SDLK_UP] || keys[SDLK_w] ){
            ypos -= 1;
        }
        if ( keys[SDLK_DOWN]|| keys[SDLK_s] ){
            ypos += 1;
        }
        if ( keys[SDLK_LEFT]|| keys[SDLK_a] ){
            xpos -= 1;
        }
        if ( keys[SDLK_RIGHT]|| keys[SDLK_d] ){
            xpos += 1;
        }

        //Hold moving image on the backGround area.
        if ( xpos <= 0 )
            xpos = 0;
        if ( xpos >= SCREEN_WIDTH - IMG_WIDTH )
            xpos = SCREEN_WIDTH - IMG_WIDTH;
        if ( ypos <= 0 )
            ypos = 0;
        if ( ypos >= SCREEN_HEIGHT - IMG_HEIGHT )
            ypos = SCREEN_HEIGHT - IMG_HEIGHT;

        //VVVVVVVVVVVVVVVVVVVVVVVVVVVVVV
        //way1: blit surface to screen
        //Blit a part of backGround ( a rectangular area ) to screen,
        //then the original blitted backGround can be "cleaned".
        backGround.blit(xpos, ypos, xpos, ypos, IMG_WIDTH, IMG_HEIGHT);
        //Blit the image to screen.
        frontImage.blit(xpos, ypos);
        //Flip the screen
        screen.flip();
        //AAAAAAAAAAAAAAAAAAAAAAAAAAAAAA

        //VVVVVVVVVVVVVVVVVVVVVVVVVVVVVV
        //way2: blit surface to surface, then blit the last surface to screen
/*
        backGroundCopy.blitToSurface(backGround, xpos, ypos, xpos, ypos, IMG_WIDTH, IMG_HEIGHT);
        frontImage.blitToSurface(backGround, xpos, ypos);
        backGround.blit();
        screen.flip();
*/
        //AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA
    }

    return 0;
}