SDL入门教程（五）：6、对C++异常机制的思考，代码重写

作者：龙飞

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::DisplaySurface(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;
}