Rendering text over video

SDL Development
1

Hello folks,

I’ve got a small SDL2-based program which renders YUV video at up to 30 frames per second, which is working smoothly. I am now trying to render some text info over the video, like frame number or video quality figures (PSNR or whatever). I’ve followed the Lazy Foo production tutorial on TTF (http://lazyfoo.net/SDL_tutorials/lesson07/) and I’ve managed to make it work, but the text is blinking and seem it can’t keep up with the video. I’m not sure if I’m doing something wrong or is just a limitation.

The skeleton of the code is the following:

Code:

// the renderer
if (NULL == (renderer = SDL_CreateRenderer(window, -1, SDL_RENDERER_PRESENTVSYNC|SDL_RENDERER_ACCELERATED)))
    error(ESDL, "Failed to create renderer: %s\n", SDL_GetError());

// the video
if (NULL == (video = SDL_CreateTexture(renderer, SDL_PIXELFORMAT_IYUV, SDL_TEXTUREACCESS_STREAMING, p->width, p->height)))
    error(ESDL, "Failed to create texture: %s\n", SDL_GetError());

// the text
surface = TTF_RenderText_Solid(font, "blended", color);
text = SDL_CreateTextureFromSurface(renderer, surface);


for ( frame = 0; frame <= last_frame; frame++)
{
    ...

    if (display_info)
    {
       // render text
       SDL_RenderCopy(renderer, text, NULL, &text_rect);
       SDL_RenderPresent(renderer);
   }

    ...

    // render video
    SDL_RenderCopy(renderer, video, NULL, &video_rect);
    SDL_RenderPresent(renderer);

   ...
 }

Any suggestions?

Thanks

2

I think you must do something like this steps:

  1. Clear (or not, if you fill all target rect) rendering target.
  2. Render video frame.
  3. Render text (info or what you want).

Maybe you clear render target after rendering text? Or variable “display_info” changes its value on different frames? That’s why it blinking.

3

Indeed. This solved the blinking

Code:

    ...

    // render video
    SDL_RenderCopy(renderer, video, NULL, &video_rect);

    if (display_info)
    {
       // render text
       SDL_RenderCopy(renderer, text, NULL, &text_rect);
   }

   SDL_RenderPresent(renderer);

Thanks Rang