sdltest.c

#include <SDL.h>
#include <stdio.h>



#if SDL_BYTEORDER == SDL_BIG_ENDIAN
#define rmask  0xff000000
#define gmask  0x00ff0000
#define bmask  0x0000ff00
#define amask  0x000000ff

#define rshift 24
#define gshift 16
#define bshift 8
#define ashift 0

#else
#define rmask  0x000000ff
#define gmask  0x0000ff00
#define bmask  0x00ff0000
#define amask  0xff000000

#define rshift 0
#define gshift 8
#define bshift 16
#define ashift 24

#endif

void PutPixel32( SDL_Surface *surface, int x, int y, Uint32 pixel )
{
    //Convert the pixels to 32 bit
    Uint32 *pixels = (Uint32 *)surface->pixels;
    //Set the pixel
    pixels[ ( y * surface->w ) + x ] = pixel;
}

int main(int argc, char ** argv)
{
    SDL_Window * window=NULL;
    SDL_Renderer *ren;
    SDL_Surface * Smain,*s1,*s2;
    SDL_Texture * Tmain,*t1,*t2;
    int x,y;
    SDL_Rect r;

    //Initialize SDL
    if( SDL_Init( SDL_INIT_VIDEO ) < 0 )
    {
        return -1;
    }
    //create windows and renderer
    window = SDL_CreateWindow( "test", SDL_WINDOWPOS_UNDEFINED, SDL_WINDOWPOS_UNDEFINED, 500, 500, SDL_WINDOW_SHOWN );
    ren=SDL_CreateRenderer(window,-1, SDL_RENDERER_ACCELERATED | SDL_RENDERER_PRESENTVSYNC);

    //create the main surfaces
    Smain= SDL_CreateRGBSurface(0,500,500,32,rmask,gmask,bmask,amask);
    s1= SDL_CreateRGBSurface(0,500,500,32,rmask,gmask,bmask,amask);
    s2= SDL_CreateRGBSurface(0,500,500,32,rmask,gmask,bmask,amask);

    //white background
    SDL_FillRect(Smain,NULL,0xffffffff);
    Tmain=SDL_CreateTextureFromSurface(ren,Smain);

    //create surface 1 with varied opacity with red color
    for(x=0;x<256;x++)
    {
        for(y=0;y<500;y++)
        {
            PutPixel32(s1,x,y,rmask| (x<<ashift));
        }
    }

    //fill the rest of red color,  opacity 100%
    r.x=256;
    r.y=0;
    r.w=500-r.x;
    r.h=500;
    SDL_FillRect(s1,&r,rmask|amask);

    //blit surface when it should have the bug
    SDL_BlitSurface(s1,NULL,s2,NULL);


    //create the rest of texture
    t1=SDL_CreateTextureFromSurface(ren,s1);
    t2=SDL_CreateTextureFromSurface(ren,s2);
    while (1)
    {
        //render t1
        SDL_RenderClear(ren);
        SDL_RenderCopy(ren,Tmain,NULL,NULL);
        SDL_RenderCopy(ren,t1,NULL,NULL);
        SDL_RenderPresent(ren);
        puts("t1");
        SDL_Delay(500);//wait


        //render t2
        SDL_RenderClear(ren);
        SDL_RenderCopy(ren,Tmain,NULL,NULL);
        SDL_RenderCopy(ren,t2,NULL,NULL);
        SDL_RenderPresent(ren);
        puts("t2");
        SDL_Delay(500);//wait


    }

    SDL_DestroyWindow(window);
    SDL_Quit();
    return 0;
}