在SDL中显示PNG

Displaying a PNG in SDL?

本文关键字：PNG 显示 SDL      更新时间：2023-10-16

我正在试着让一个骑马的骑士(名字很不吉利的"家伙")跑过屏幕。骑士目前以2 .png文件的形式存在于我的目录中，以模拟一些动画效果不佳的驰骋。当他是。bmp的时候，我可以让他出现，但我想利用png文件的透明度——我也试过打开tif文件，但失败了。我怎样才能改变我的代码，以让他出现从一个。png加载到SDL正确?

这是我的。cpp文件:

#include "SDL/SDL.h"
#include <iostream>
#include "source_sdl.h"
# include <string>
using namespace std;
int source_sdl( int argc, char* args[] ) {
int switch = 1;
int running = 1;
// surface & rect declarations
SDL_Surface* ground = NULL;
SDL_Surface* guy = NULL;
SDL_Surface* guy2 = NULL;
SDL_Rect guylocationRect;
SDL_Rect groundlocationRect;
// initialize SDL & the screen
SDL_Init( SDL_INIT_EVERYTHING );
screen = SDL_SetVideoMode( 875, 625, 32, SDL_SWSURFACE );
// open .png files
SDL_RWops* guy_rwop;
SDL_RWops* guy2_rwop;
guy_rwop = SDL_RWFromFile("tiffKnight.png", "rb");
guy2_rwop = SDL_RWFromFile("tiffKnight2.png", "rb");
guy = IMG_LoadPNG_RW(guy_rwop);
guy2 = IMG_LoadPNG_RW(guy2_rwop);
guylocationRect.x = 300;
guylocationRect.y = 300;
groundlocationRect.x = 300;
groundlocationRect.y = 300;
SDL_Event occur;
// animation loop (currently endless)
while (running == 1){
    SDL_Flip( screen );
    SDL_Delay( 300 );
    if (gallop > 89) gallop=0;
    // draw the ground
    for( int yu = 0; yu<35; yu++){
         groundlocationRect.x=25*yu;
         groundlocationRect.y=5*25;
         SDL_BlitSurface( ground, NULL, screen, &groundlocationRect );
    }
    // draw the gallopping
    guylocationRect.x=10*gallop;
    guylocationRect.y=5*25;
    if( switch ){
        SDL_BlitSurface( guy, NULL, screen, &guylocationRect );
    }else{
        SDL_BlitSurface( guy2, NULL, screen, &guylocationRect );
    }
    gallop++;
    switch = (switch+1)%2;
    for(int u = 6; u < 25; u++){
        for(int yu = 0; yu < 35; yu++){ 
            groundlocationRect.x = 25*yu;
            groundlocationRect.y = 25*u;
            SDL_BlitSurface( ground, NULL, screen, &groundlocationRect );
        }
    }
}
SDL_FreeSurface( guy );
SDL_FreeSurface( guy2 );
SDL_FreeSurface( ground );
}

就像我目前拥有的那样，骑士没有出现，我也没有收到任何错误(SDL屏幕打开的结果?)失败检查，如

if(!guy) {
    cout << "IMG_LoadPNG_RW: %sn" << IMG_GetError();
}

也没有结果。我的。h文件很简单:

#include "SDL/SDL.h"
#include <iostream>
using namespace std;
 int source_sdl( int argc, char* args[] );

And my main.cpp:

#include "SDL/SDL.h"
#include <iostream>
#include "source_sdl.h"
using namespace std;
int main( int argc, char* args[] ){
    source_sdl( argc, args );
}

如果您真的想坚持使用c++中的SDL，我建议您使用SDL_image库并使用如下函数:

SDL_Surface * loadImage(std::string const & filename)
{
    SDL_Surface * img = nullptr;
    SDL_Surface * tmp = IMG_Load(filename.c_str());
    if (tmp)
    {
        img = SDL_DisplayFormatAlpha(tmp);
        SDL_FreeSurface(tmp);
    }
    return img;
}

一个更现代和安全的方法的例子是这样的:

using SurfacePtr = std::unique_ptr<SDL_Surface, decltype(&SDL_FreeSurface)>;
SurfacePtr loadImage(std::string const & filename)
{
    SurfacePtr img { nullptr,                    &SDL_FreeSurface };
    SurfacePtr tmp { IMG_Load(filename.c_str()), &SDL_FreeSurface };
    if (tmp)
        img.reset(SDL_DisplayFormatAlpha(tmp.get()));
    return img;
}

或者更好，使用现有的c++绑定，如libSDL2pp(我与它们无关)。

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