SDL2笔记03_使用SDL_Renderer在SDL_Texture上画矩形01

1. clion新建项目，并编写代码main.cpp

    #include <iostream>
    #include "SDL.h"
    #include "SDL_image.h"
   
    void drawMyRect(SDL_Renderer *sdlRenderer, SDL_Texture *sdlTexture, SDL_Rect &rect) {// SDL_Texture填充透明色（没有生效）
        SDL_SetRenderDrawBlendMode(sdlRenderer, SDL_BLENDMODE_BLEND);
        SDL_SetTextureBlendMode(sdlTexture, SDL_BLENDMODE_BLEND);
   
        SDL_RenderFillRect(sdlRenderer, &rect);
        // SDL_画红色矩形  缺点：闪烁
        SDL_SetRenderDrawColor(sdlRenderer, 0xff, 0, 0, 255);
        rect.x++;
        rect.x %= rect.w;
        SDL_RenderDrawRect(sdlRenderer, &rect);
    }
   
    SDL_Rect drawBackGround(SDL_Renderer *sdlRenderer, unsigned char r, unsigned char g) {// 重新把sdl_renderer指向window
        SDL_SetRenderTarget(sdlRenderer, nullptr);
        SDL_SetRenderDrawBlendMode(sdlRenderer, SDL_BLENDMODE_NONE);
   
        SDL_SetRenderDrawColor(sdlRenderer, r, g, 255, 0);
        SDL_Rect srect = {0, 0, 640, 480};
        return srect;
    }
   
    int main(int argc, char *argv[]) {
   
        SDL_Init(SDL_INIT_EVERYTHING);
   
        SDL_Window *sdlWindow = SDL_CreateWindow("sdl_draw_on_texture", 0, 0, 640, 480, SDL_WINDOW_ALWAYS_ON_TOP);
        SDL_Renderer *sdlRenderer = SDL_CreateRenderer(sdlWindow, -1, SDL_RENDERER_ACCELERATED | SDL_RENDERER_PRESENTVSYNC);
        // 创建一个SDL_Texture, 等下把图形画到texture上，再贴到window上
        SDL_Texture *sdlTexture = SDL_CreateTexture(sdlRenderer, SDL_PIXELFORMAT_RGBA32, SDL_TEXTUREACCESS_TARGET, 400,
                                                    320);
   
        SDL_Event event;
        int quit = false, delayMs = 1000 / 24;
        SDL_Rect winRect = {0, 0, 400, 320}, texRect = {0, 0, 400, 320};
        SDL_Rect rect = {100, 100, 150, 150};
   
        while (!quit) {
            uint32_t startTime = SDL_GetTicks();
            while (SDL_PollEvent(&event) > 0) {
                if (event.type == SDL_QUIT) {
                    quit = true;
                }
            }
   
            // 设置画到SDL_Texture上
            SDL_SetRenderTarget(sdlRenderer, sdlTexture);
            unsigned char r, g, b, a;
            // 先保存rgba
            SDL_GetRenderDrawColor(sdlRenderer, &r, &g, &b, &a);
            SDL_SetRenderDrawColor(sdlRenderer, 0, 0, 0, 0xff);
            drawMyRect(sdlRenderer, sdlTexture, rect);
   
            SDL_Rect srect = drawBackGround(sdlRenderer, r, g);
   
            // window填充蓝色
            SDL_RenderFillRect(sdlRenderer, &srect);
            SDL_RenderCopy(sdlRenderer, sdlTexture, &winRect, &texRect);
            SDL_RenderPresent(sdlRenderer);
   
            uint32_t endTime = SDL_GetTicks();
            if (endTime - startTime < delayMs) {
                SDL_Log("delay %d
   ", delayMs - (endTime - startTime));
                SDL_Delay(delayMs - (endTime - startTime));
            }
        }
   
   
        return 0;
    }
   
   
   

2. 运行后就行啦

   • 问题：alpha透明度没有生效