一个SDL2.0程序的分析

//把图片加载到SDL_Texture
SDL_Texture* loadTexture(const std::string &file, SDL_Renderer *ren){
        SDL_Texture *texture = nullptr;
        SDL_Surface *loadedImage = SDL_LoadBMP(file.c_str());
        texture = SDL_CreateTextureFromSurface(ren, loadedImage);
        SDL_FreeSurface(loadedImage);
        return texture;
}
//渲染纹理（渲染图片）
void renderTexture(SDL_Texture *tex, SDL_Renderer *ren, int x, int y){
        SDL_Rect dst;
        dst.x = x;
        dst.y = y;
        SDL_QueryTexture(tex, NULL, NULL, &dst.w, &dst.h);//获取图像的宽、高
        SDL_RenderCopy(ren, tex, NULL, &dst);//纹理复制给渲染器
}
int main()
{

//初始化SDL、Window、前景、后景
SDL_Init(SDL_INIT_VIDEO)
SDL_CreateWindow("Lesson 2", 100, 100, SCREEN_WIDTH, SCREEN_HEIGHT, SDL_WINDOW_SHOWN);
SDL_CreateRenderer(window, -1, SDL_RENDERER_ACCELERATED | SDL_RENDERER_PRESENTVSYNC)
SDL_Texture *background = loadTexture(resPath + "background.bmp", renderer);
SDL_Texture *image = loadTexture(resPath + "image.bmp", renderer);
while(1){

SDL_RenderClear(renderer);

SDL_QueryTexture(background, NULL, NULL, &bW, &bH);//获取背景的宽、高

renderTexture(background, renderer, 0, 0);

renderTexture(background, renderer, bW, 0);

renderTexture(background, renderer, 0, bH);

renderTexture(background, renderer, bW, bH);

SDL_QueryTexture(image, NULL, NULL, &iW, &iH);//获取前景的宽、高

renderTexture(image, renderer, x, y);

SDL_RenderPresent(renderer);//渲染

SDL_Delay(1000);

}

}

最后的效果图

完整代码如下

#include <iostream>#include <SDL.h>#include "res_path.h"#include "cleanup.h"/* * Lesson 2: Don't Put Everything in Main *///Screen attributesconst int SCREEN_WIDTH  = 640;const int SCREEN_HEIGHT = 480;/* * Log an SDL error with some error message to the output stream of our choice * @param os The output stream to write the message too * @param msg The error message to write, format will be msg error: SDL_GetError()        os << msg << " error: " << SDL_GetError() << std::endl;}/* * Loads a BMP image into a texture on the rendering device * @param file The BMP image file to load */SDL_Texture* loadTexture(const std::string &file, SDL_Renderer *ren){        SDL_Texture *texture = nullptr;        //Load the image        SDL_Surface *loadedImage = SDL_LoadBMP(file.c_str());        //If the loading went ok, convert to texture and return the texture        if (loadedImage != nullptr){                texture = SDL_CreateTextureFromSurface(ren, loadedImage);                SDL_FreeSurface(loadedImage);                //Make sure converting went ok too                if (texture == nullptr){                        logSDLError(std::cout, "CreateTextureFromSurface");                }        }        else {                logSDLError(std::cout, "LoadBMP");        }        return texture;}/* * Draw an SDL_Texture to an SDL_Renderer at position x, y, preserving * the texture's width and height * @param tex The source texture we want to draw * @param ren The renderer we want to draw too * @param x The x coordinate to draw too * @param y The y coordinate to draw too */void renderTexture(SDL_Texture *tex, SDL_Renderer *ren, int x, int y){        //Setup the destination rectangle to be at the position we want        SDL_Rect dst;        dst.x = x;        dst.y = y;        //Query the texture to get its width and height to use        SDL_QueryTexture(tex, NULL, NULL, &dst.w, &dst.h);        SDL_RenderCopy(ren, tex, NULL, &dst);}int main(int, char**){        //Start up SDL and make sure it went ok        if (SDL_Init(SDL_INIT_VIDEO) != 0){                logSDLError(std::cout, "SDL_Init");                return 1;        }        //Setup our window and renderer        if (window == nullptr){                logSDLError(std::cout, "CreateWindow");                SDL_Quit();                return 1;        }        SDL_Renderer *renderer = SDL_CreateRenderer(window, -1, SDL_RENDERER_ACCELERATED | SDL_RENDERER_PRESENTVSYNC);        if (renderer == nullptr){                logSDLError(std::cout, "CreateRenderer");                cleanup(window);                SDL_Quit();                return 1;        }        //The textures we'll be using        const std::string resPath = getResourcePath("Lesson2");        SDL_Texture *background = loadTexture(resPath + "background.bmp", renderer);        SDL_Texture *image = loadTexture(resPath + "image.bmp", renderer);        //Make sure they both loaded ok        if (background == nullptr || image == nullptr){                cleanup(background, image, renderer, window);                SDL_Quit();                return 1;        }        //A sleepy rendering loop, wait for 3 seconds and render and present the screen each time        for (int i = 0; i < 3; ++i){                //Clear the window                SDL_RenderClear(renderer);                //Get the width and height from the texture so we know how much to move x,y by                //to tile it correctly                int bW, bH;                SDL_QueryTexture(background, NULL, NULL, &bW, &bH);                //We want to tile our background so draw it 4 times                renderTexture(background, renderer, 0, 0);                renderTexture(background, renderer, bW, 0);                renderTexture(background, renderer, 0, bH);                renderTexture(background, renderer, bW, bH);                //Draw our image in the center of the window                //We need the foreground image's width to properly compute the position                //of it's top left corner so that the image will be centered                int iW, iH;                SDL_QueryTexture(image, NULL, NULL, &iW, &iH);                int x = SCREEN_WIDTH / 2 - iW / 2;                int y = SCREEN_HEIGHT / 2 - iH / 2;                renderTexture(image, renderer, x, y);                //Update the screen                SDL_RenderPresent(renderer);                //Take a quick break after all that hard work                SDL_Delay(1000);        }