SDL 教程 09 : 视口

示例代码

/**
 * Title: 视口
 * 有时，您只想为迷你地图之类的内容渲染屏幕的一部分。使用视口可以控制屏幕上的渲染位置。
 */

#include <SDL2/SDL.h>
#include <SDL2/SDL_image.h>
#include <stdio.h>

const int SCREEN_WIDTH = 640;
const int SCREEN_HEIGHT = 480;

#define sdlerror() { printf("error in line %d %s\n", __LINE__, SDL_GetError()); exit(-1); }

int main(int argc, char *argv[])
{
    // 初始化
    if(SDL_Init(SDL_INIT_VIDEO) < 0) sdlerror();
        
    // 创建窗口和渲染器
    SDL_Window *window = SDL_CreateWindow( "SDL Tutorial", SDL_WINDOWPOS_UNDEFINED, 
        SDL_WINDOWPOS_UNDEFINED, SCREEN_WIDTH, SCREEN_HEIGHT, SDL_WINDOW_SHOWN );
    SDL_Renderer* render = SDL_CreateRenderer(window, -1, SDL_RENDERER_ACCELERATED);

    // 初始化 IMG 为 支持 PNG
    if(IMG_Init(IMG_INIT_PNG) != IMG_INIT_PNG) 
        sdlerror();
    // 加载图片
    SDL_Surface *pngSurface = IMG_Load("viewport.png");
    if(pngSurface == NULL) 
        sdlerror();
        
    // 从图片图层中创建纹理
    SDL_Texture *texture = SDL_CreateTextureFromSurface(render , pngSurface );
    SDL_FreeSurface( pngSurface );
    pngSurface = NULL;

    //清屏
    SDL_SetRenderDrawColor( render, 0xFF, 0xFF, 0xFF, 0xFF );
    SDL_RenderClear( render );

    //Top left corner viewport
    SDL_Rect topLeftViewport;
    topLeftViewport.x = 0;
    topLeftViewport.y = 0;
    topLeftViewport.w = SCREEN_WIDTH / 2;
    topLeftViewport.h = SCREEN_HEIGHT / 2;
    SDL_RenderSetViewport( render, &topLeftViewport );
    
    // 将纹理拷贝到渲染器
    SDL_RenderCopy( render, texture, NULL, NULL );

    // 首先，我们先渲染左上角，这与创建宽度/高度为屏幕一半的矩形并将此区域传递给 SDL_RenderDrawRect 一样简单。
    // 在该调用之后完成的任何渲染都将在给定视口定义的区域内渲染。它还将使用创建它的窗口的坐标系，
    // 因此我们创建的视图的底部仍然是y=480，而它距离顶部有240个像素
    SDL_Rect topRightViewport;
    topRightViewport.x = SCREEN_WIDTH / 2;
    topRightViewport.y = 0;
    topRightViewport.w = SCREEN_WIDTH / 2;
    topRightViewport.h = SCREEN_HEIGHT / 2;
    SDL_RenderSetViewport( render, &topRightViewport );
    
    // 将纹理拷贝到渲染器
    SDL_RenderCopy( render, texture, NULL, NULL );

    // 底部视窗
    SDL_Rect bottomViewport;
    bottomViewport.x = 0;
    bottomViewport.y = SCREEN_HEIGHT / 2;
    bottomViewport.w = SCREEN_WIDTH;
    bottomViewport.h = SCREEN_HEIGHT / 2;
    SDL_RenderSetViewport( render, &bottomViewport );

    // 将纹理拷贝到渲染器
    SDL_RenderCopy( render, texture, NULL, NULL );

    // 更新屏幕
    SDL_RenderPresent( render );
    SDL_Event event;
    while( SDL_PollEvent( &event ) != 0 || event.type != SDL_QUIT);

    SDL_DestroyTexture( texture );
    SDL_DestroyRenderer( render );
    SDL_DestroyWindow(window);
    IMG_Quit();
    SDL_Quit();
    return 0;
}

运行结果

运行结果.png

示例中的图片资源

viewport.png