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 attributes
const 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);
        }