SDL透明背景实现问题

比如这样，直接把文字也给透明了，怎么才能让字不透明呢

图片透明
SDL_SetSurfaceBlendMode(s,SDL_BLENDMODE_BLEND);//透明度模式
SDL_SetSurfaceAlphaMod(s,100);//设置透明度

window = SDL_CreateWindow("Test",SDL_WINDOWPOS_CENTERED,SDL_WINDOWPOS_CENTERED,640,480,SDL_WINDOW_SHOWN);
winSurface = SDL_GetWindowSurface(window); SDL_SetSurfaceBlendMode(winSurface,SDL_BLENDMODE_BLEND); SDL_SetSurfaceAlphaMod (winSurface,100);
while(!quit) {
SDL_UpdateWindowSurface(window);
SDL_Delay(1000/60);
}
@liuhaitian520是这样吗，好像不顶用

#include <SDL2/SDL.h>
int main(int args,char*argv[])
{
SDL_Init(SDL_INIT_VIDEO);
SDL_Window*w=SDL_CreateWindow("",0,0,720,1280,0);
SDL_Renderer*r=SDL_CreateRenderer(w,-1,0);
SDL_RenderClear(r);
SDL_SetRenderDrawColor(r,255,255,255,255);
SDL_Rect box={0,0,720,1280};
SDL_RenderFillRect(r,&box);
SDL_Surface*s=SDL_CreateRGBSurface(0, 500, 500, 32, 0, 0, 0, 0);
SDL_FillRect(s,NULL,0x00000000);
SDL_SetSurfaceBlendMode(s,SDL_BLENDMODE_BLEND);//透明度模式
SDL_SetSurfaceAlphaMod(s,200);//设置透明度，200为透明程度
SDL_Texture*t=SDL_CreateTextureFromSurface(r,s);
box.w=500;
box.h=500;
SDL_RenderCopy(r,t,NULL,&box);
SDL_RenderPresent(r);
SDL_Delay(2000);
SDL_FreeSurface(s);
SDL_DestroyRenderer(r);
SDL_DestroyRenderer(r);
SDL_DestroyWindow(w);
SDL_Quit();
}

需要窗口背景透明，可以看到窗口后边的其他程序，图中的效果是使用了SDL_SetWindowOpacity函数，但这个函数会使整个窗口透明，比如你在上边渲染一个图片，图片也会变成透明

#include <SDL2/SDL.h>
#include <SDL2/SDL_image.h>
#include <SDL2/SDL_ttf.h>
int main(int args,char*argv[])
{
SDL_Init(SDL_INIT_VIDEO);
SDL_Window*w=SDL_CreateWindow("",0,0,720,1280,0);
SDL_Renderer*r=SDL_CreateRenderer(w,-1,0);
SDL_RenderClear(r);
//图片转纹理
SDL_Texture*t=IMG_LoadTexture(r,"a.png");
SDL_RenderCopy(r,t,NULL,NULL);
SDL_DestroyTexture(t);
t=NULL;
SDL_SetRenderDrawBlendMode(r,SDL_BLENDMODE_BLEND);//设置renderer透明度
SDL_SetRenderDrawColor(r,0,0,0,200);
SDL_Rect box={100,200,520,520};
SDL_RenderFillRect(r,&box);
t=IMG_LoadTexture(r,"../../Window/显示图片/ball.png");
box.x=200; box.y=250;
box.w=100; box.h=100;
SDL_RenderCopy(r,t,NULL,&box);
SDL_DestroyTexture(t);
t=NULL;
TTF_Init();
TTF_Font*f=TTF_OpenFont("../文字/方正黑体简体.ttf",100);
SDL_Color c={200,200,200,0};
SDL_Surface*sur=TTF_RenderUTF8_Blended(f,"宁静致远",c);
box={200,400,sur->w,sur->h};
TTF_CloseFont(f);
f=NULL;
TTF_Quit();
t=SDL_CreateTextureFromSurface(r,sur);
SDL_RenderCopy(r,t,NULL,&box);
SDL_FreeSurface(sur);
SDL_RenderPresent(r);
SDL_Delay(5000);
SDL_DestroyTexture(t);
SDL_DestroyRenderer(r);
SDL_DestroyWindow(w);
SDL_Quit();
}