How to blit a text surface on SDL_Overlay? - sdl

Question

I'm a newbie in sdl. this is my question: I create a text surface use sdl_ttf.dll.
like this
TTF_Font* myFont = TTF_OpenFont(szFontPath, text.m_iFontSize);
SDL_Surface *textSurface = TTF_RenderUNICODE_Blended(myFont, (const
Uint16*)text.m_wstrFilePath.c_str(), textColor);
This works fine and the textsurface is ok if I blit on my screen,which is used to play a video.
SDL_BlitSurface(textSurface , null, screen, offset);
But the problem is the text on the screen keep blinking in every 3 /4 seconds, even I set the
screen with SDL_DOUBLEBUF and SDL_HWSURFACE, it will not help. so it went another way.I decide to blit the text on the screen before it display. i use this function:
blitSurface2YUV(text, vp->bmp, &rectOffset); //vp->bmp is the sdl_overlay
display it: SDL_DisplayYUVOverlay(vp->bmp, &rcRView); //rcView is the offset to the screen
"blitSurface2YUV" is defined here:
int blitSurface2YUV(SDL_Surface *src, SDL_Overlay *dst, SDL_Rect *dstrect)
{
Uint8 r, g, b;
int y1,u1,v1;
int y,x;
int height = src->h < dstrect->h ? src->h: dstrect->h;
int width = src->w < dstrect->w ? src->w: dstrect->w;
int uv_off = 0;
Uint32 pixel;
if(dst->format != SDL_YV12_OVERLAY)
return 1;
for(y = 0; y < height; ++y)
{
for(x = 0; x < width; ++x)
{
switch(src->format->BitsPerPixel)
{
case 8:
pixel = *((Uint8*)src->pixels + y*src->pitch + x);
break;
case 16:
pixel = *((Uint16*)src->pixels + y*src->pitch/2 + x);
break;
case 32:
pixel = *((Uint32*)src->pixels + y*src->pitch/4 + x);
break;
default:
return -1;
}
SDL_GetRGB(pixel, src->format, &r, &g, &b);
rgb2yuv(r, g, b, &y1, &u1, &v1);
memset(dst->pixels[0] + (dstrect->y + y) * dst->pitches[0] + (dstrect->x + x),
(Uint8)y1, 1);
if((x%2 == 0 ) && (y%2 == 0 ))
{
memset(dst->pixels[1] + (uv_off + dstrect->y /2) * dst->pitches[1] + (dstrect->x/2 + x/2),
(Uint8)v1, 1);
memset(dst->pixels[2] + (uv_off + dstrect->y /2) * dst->pitches[2] + (dstrect->x/2 + x/2),
(Uint8)u1, 1);
}
}
if(y%2 == 0)++uv_off;
}
return 0;
}
This can solve the blink problem. but the text on the screen has a black background, which is supposed to be empty.
so can someone tell me what is the problem?

Answer 1

This is not really an answer but definitely too long for a comment.
I think you're trying to solve the wrong problem. Your initial problem is that your text, generated using TTF_RenderUNICODE_Blended "blinks" at an interval when calling SDL_BlitSurface on your screen surface. This is supposed to work, and has worked in all of my SDL projects.
This means that there has to be something wrong with either your rendering loop or your text, if you could post more code about this it would be helpful!

Answer 2

You may add this into the loop. And than black pixels won't process.
if(pixel == 0 )
continue;
Here is corrected function.
int blitSurface2YUV(SDL_Surface *src, SDL_Overlay *dst, SDL_Rect *dstrect)
{
Uint8 r, g, b;
int y1,u1,v1;
int y,x;
int height = src->h < dstrect->h ? src->h: dstrect->h;
int width = src->w < dstrect->w ? src->w: dstrect->w;
int uv_off = 0;
Uint32 pixel;
if(dst->format != SDL_YV12_OVERLAY)
return 1;
for(y = 0; y < height; ++y)
{
for(x = 0; x < width; ++x)
{
switch(src->format->BitsPerPixel)
{
case 8:
pixel = *((Uint8*)src->pixels + y*src->pitch + x);
break;
case 16:
pixel = *((Uint16*)src->pixels + y*src->pitch/2 + x);
break;
case 32:
pixel = *((Uint32*)src->pixels + y*src->pitch/4 + x);
break;
default:
return -1;
}
if(pixel == 0 )
continue;
SDL_GetRGB(pixel, src->format, &r, &g, &b);
rgb2yuv(r, g, b, y1, u1, v1);
memset(dst->pixels[0] + (dstrect->y + y) * dst->pitches[0] + (dstrect->x + x),
(Uint8)y1, 1);
if((x%2 == 0 ) && (y%2 == 0 ))
{
memset(dst->pixels[1] + (uv_off + dstrect->y /2) * dst->pitches[1] + (dstrect->x/2 + x/2),
(Uint8)v1, 1);
memset(dst->pixels[2] + (uv_off + dstrect->y /2) * dst->pitches[2] + (dstrect->x/2 + x/2),
(Uint8)u1, 1);
}
}
if(y%2 == 0) ++uv_off;
}
return 0;
}