[英]Why won't my image render?
所以我正在用SDL学习C ++(在Visual Studio 2013上)。 我正在关注Lazy Foo的教程(特别是: http : //lazyfoo.net/tutorials/SDL/02_getting_an_image_on_the_screen/index.php )。
我的图像无法渲染。 与本教程相反(有效),我没有全局表面变量。 相反,我在主体中声明了它们并传递了指针。
码:
#include <SDL.h>
#include <SDL_image.h>
#include <stdio.h>
#include <string>
const int SCREEN_WIDTH = 600;
const int SCREEN_HEIGHT = 480;
//SDL init.
bool initialiseSDL(SDL_Window* gWindow, SDL_Surface* gWindowSurface)
{
bool success = true;
/*SDL_Init() initisalises SDL library. Returning 0 or less signifies an error.
SDL_INIT_VIDEO flag refers to graphics sub system.*/
if (SDL_Init(SDL_INIT_VIDEO) < 0)
{
printf("SDL could not initialise. SDL Error: %s\n", SDL_GetError());
success = false;
}
else
{
//Create the window
gWindow = SDL_CreateWindow("Asteroids", SDL_WINDOWPOS_UNDEFINED, SDL_WINDOWPOS_UNDEFINED, SCREEN_WIDTH, SCREEN_HEIGHT, SDL_WINDOW_SHOWN);
if (gWindow == NULL)
{
printf("Could not create window. SDL Error: %s\n", SDL_GetError());
success = false;
}
else
{
//Get the window surface.
gWindowSurface = SDL_GetWindowSurface(gWindow);
}
}
return success;
}
bool loadMedia(SDL_Surface* surface, std::string path)
{
//Success flag
bool success = true;
surface = SDL_LoadBMP(path.c_str());
if (surface == NULL)
{
printf("SDL surface failed to load. SDL Error: %s\n", SDL_GetError());
success = false;
}
return success;
}
void close()
{
}
int main(int argc, char* argv[])
{
SDL_Window* gWindow = NULL;
SDL_Surface* gWindowSurface = NULL;
SDL_Surface* gImageSurface = NULL;
if (!initialiseSDL(gWindow, gWindowSurface))
{
printf("Failed to initialise.\n");
}
else
{
if (!loadMedia(gImageSurface, "hw.bmp"))
{
printf("Failed to load inital media.");
}
else
{
//Apply the image
SDL_BlitSurface(gImageSurface, NULL, gWindowSurface, NULL);
//Update the surface
SDL_UpdateWindowSurface(gWindow);
//Wait two seconds
SDL_Delay(2000);
}
}
return 0;
}
您的程序表现出未定义的行为 ,因为main
函数内部的指针未初始化。
当您将它们传递给initialiseSDL
函数时,将按值传递它们,这意味着它们将被复制,并且该函数仅对副本进行操作,而不对原始指针进行操作,原始指针在调用后仍将未初始化。
您需要做的是通过引用传递指针:
bool initialiseSDL(SDL_Window*& gWindow, SDL_Surface*& gWindowSurface)
当然,您需要对loadMedia
函数执行相同的loadMedia
。
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