Question

我已经开始研究SDL了。我有一个基本程序的麻烦，每次我编译它我没有错误，但程序是完全空白的。 Build Succeeds，应用程序图标弹出到我的Dock中，但在没有窗口的情况下保持打开状态5秒。代码如下：

    //
//  main.cpp
//  HelloSDL
//
//  Created by Liam Tan
//  Copyright 2014 Liam Tan. All rights reserved.
//

#include <stdlib.h>
#include <SDL/SDL.h>
#include <string>
#include <iostream>
const int SCREEN_WIDTH = 640;
const int SCREEN_HEIGHT = 480;
const int SCREEN_BPP = 32;
//Declares surfaces
SDL_Surface* message = NULL;
SDL_Surface* background = NULL;
SDL_Surface* screen = NULL;

SDL_Surface *load_image( std::string filename) {
    //declaration
    SDL_Surface* loadedImage = NULL;
    SDL_Surface* optimizedImage = NULL;
    //takes arguement and loads that BMP
    loadedImage = SDL_LoadBMP(filename.c_str() );
    //Checks, swaps opti with loaded then frees loaded
    if (loadedImage!= NULL) {
        optimizedImage = SDL_DisplayFormat (loadedImage);
        SDL_FreeSurface(loadedImage);
    }
    return optimizedImage;
}
void apply_surface(int x, int y, SDL_Surface* source, SDL_Surface* destination) {
    //temporary rectangle to hold offsets
    SDL_Rect offset;
    offset.x = x;
    offset.y = y;
    SDL_BlitSurface(source, NULL, destination, NULL);
}

int SDL_main (int argc, char **argv) {
    const std::string errorMsg = "failed to initialize. ";
    //Initialise
    if( SDL_Init(SDL_INIT_EVERYTHING) == -1 ) {
        std::cout << "SDL " << errorMsg << std::endl;
        SDL_GetError();
        return 1;
    }
    screen = SDL_SetVideoMode(SCREEN_WIDTH, SCREEN_HEIGHT, SCREEN_BPP, SDL_SWSURFACE);
    if (screen == NULL) {
        std::cout << "Video mode " << errorMsg << std::endl;
        SDL_GetError();
        return 1;
    }
    SDL_WM_SetCaption("Programming", NULL);
    //loads message
    message = load_image("textures/hello.bmp");
    //loads background
    background = load_image("textures/background.bmp");
    //blits 4 times!
    apply_surface(0,0,background,screen);
    apply_surface( 320, 0, background, screen );
    apply_surface( 0, 240, background, screen );
    apply_surface( 320, 240, background, screen );
    SDL_Delay(5000);
    SDL_Quit();
    return 0;
}

我正在使用Xcode 5和SDL 1.2。

Answer 1

我在您的代码中看到了一些问题。它们可能不是全部错误。

1）当您对图像进行blit时，它不会直接进入屏幕。它会保留在缓冲区中，直到您拨打SDL_Flip(screen);

所以最后几行应该是那样的

...
apply_surface( 320, 240, background, screen );
SDL_Flip(screen);//Display the results of the blits
SDL_Delay(5000);
SDL_Quit();
return 0;

2）当您对图像进行blit时，不要使用Rect offset。它将始终显示在0,0位置。

//temporary rectangle to hold offsets
SDL_Rect offset;
offset.x = x;
offset.y = y;
SDL_BlitSurface(source, NULL, destination, NULL);

3）你永远不会释放你加载的图像。你需要在SDL_Quit之前添加一些SDL_FreeSurface(...);。

4）您加载但从不使用hello.bmp

另外，我不明白为什么你将表面声明为全局。但也许你有充分的理由。

您也可以尝试将SDL_Delay(5000);替换为

bool done = false;
while (!done)//we wait until done == true
{

    SDL_Event event;
    while (SDL_WaitEvent(&event))//we get all the events
    {
        switch (event.type) //we look what type of event we received
        {
        case SDL_QUIT:  //We received a quit event
            done = true;//we want to exit the loop
        break;
        }
    }
}

因为SDL_Delay告诉您的计算机您的应用程序不需要更新一段时间。

无法构建SDL项目

1 个答案: