Text Flickering on Window Resize in SDL2 && SDL3

[rjopek]

I raised this issue on the discourse.libsdl.org forum, but there wasn't much interest in helping me. The example shows that the text loses precision, or perhaps I am not using the correct functions to handle it properly.

#include <stdio.h>
#include <stdbool.h>
#include <string.h>
#include <stddef.h>

#include <SDL3/SDL.h>
#include <SDL3_ttf/SDL_ttf.h>

#define LEN( n ) ( sizeof( n ) / sizeof( ( n ) [ 0 ] ) )

static size_t iUtf8Len( const char *szUtf8String )
{
   size_t iLen = 0;
   while( *szUtf8String )
   {
      unsigned char cByte = *szUtf8String;

      if( ( cByte & 0x80 ) == 0 )         // ASCII (0xxxxxxx)
         szUtf8String += 1;
      else if( ( cByte & 0xE0 ) == 0xC0 ) // (110xxxxx)
         szUtf8String += 2;
      else if( ( cByte & 0xF0 ) == 0xE0 ) // (1110xxxx)
         szUtf8String += 3;
      else if( ( cByte & 0xF8 ) == 0xF0 ) // (11110xxx)
         szUtf8String += 4;
      else
         szUtf8String += 1;

      iLen++;
   }

   return iLen;
}

void calculateFontCellSize( TTF_Font *pFont, int *iFontCellWidth, int *iFontCellHeight )
{
   const char *szTestChar = "M";
   int iMeasuredWidth = 0;
   size_t iMeasuredLength = 0;

   TTF_MeasureString( pFont, szTestChar, 0, 0, &iMeasuredWidth, &iMeasuredLength );

   *iFontCellWidth = iMeasuredWidth;
   *iFontCellHeight = TTF_GetFontHeight( pFont );
}

void drawText( TTF_Font *pFont, SDL_Renderer *pRenderer, float fX, float fY, const char *szText, SDL_Color sFg, SDL_Color sBg )
{
   int iFontCellWidth, iFontCellHeight;

   calculateFontCellSize( pFont, &iFontCellWidth, &iFontCellHeight );

   fX *= iFontCellWidth;
   fY *= iFontCellHeight;

   size_t iLen = iUtf8Len( szText );
   if( iLen == 0 )
   {
      SDL_FRect sRect = { fX, fY, ( float ) iFontCellWidth, ( float ) iFontCellHeight };
      SDL_SetRenderDrawColor( pRenderer, sBg.r, sBg.g, sBg.b, sBg.a );
      SDL_RenderFillRect( pRenderer, &sRect );
      return;
   }

   SDL_Surface *pSurface = TTF_RenderText_Shaded( pFont, szText, 0, sFg, sBg );
   if( pSurface )
   {
      SDL_Texture *pTextTexture = SDL_CreateTextureFromSurface( pRenderer, pSurface );
      SDL_DestroySurface( pSurface );

      if( pTextTexture )
      {
         SDL_FRect sTextRect = { fX, fY, ( float ) iFontCellWidth * iLen, ( float ) iFontCellHeight };
         SDL_RenderTexture( pRenderer, pTextTexture, NULL, &sTextRect );
         SDL_DestroyTexture( pTextTexture );
      }
      else
      {
         fprintf( stderr, "Error creating texture: %s\n", SDL_GetError() );
      }
   }
   else
   {
      fprintf( stderr, "Error rendering text: %s\n", SDL_GetError() );
   }
}

int main()
{
   SDL_Window *pWindow = NULL;
   SDL_Renderer *pRenderer = NULL;
   TTF_Font *pFont = NULL;
   SDL_Event sEvent;
   bool lQuit = false;
   SDL_Color sFg = { 0, 0, 0, 255 };
   SDL_Color sBg = { 255, 255, 255, 255 };
   const char *szText[] =
   {
      "",
      "Mathematics and sciences:",
      "",
      "  ∮ E⋅da = Q,  n → ∞, ∑ f(i) = ∏ g(i),      ⎧⎡⎛┌─────┐⎞⎤⎫",
      "                                            ⎪⎢⎜│a²+b³ ⎟⎥⎪",
      "  ∀x∈ℝ: ⌈x⌉ = −⌊−x⌋, α ∧ ¬β = ¬(¬α ∨ β),    ⎪⎢⎜│───── ⎟⎥⎪",
      "                                            ⎪⎢⎜⎷ c₈   ⎟⎥⎪",
      "  ℕ ⊆ ℕ₀ ⊂ ℤ ⊂ ℚ ⊂ ℝ ⊂ ℂ,                   ⎨⎢⎜       ⎟⎥⎬",
      "                                            ⎪⎢⎜ ∞     ⎟⎥⎪",
      "  ⊥ < a ≠ b ≡ c ≤ d ≪ ⊤ ⇒ (⟦A⟧ ⇔ ⟪B⟫),      ⎪⎢⎜ ⎲     ⎟⎥⎪",
      "                                            ⎪⎢⎜ ⎳aⁱ-bⁱ⎟⎥⎪",
      "  2H₂ + O₂ ⇌ 2H₂O, R = 4.7 kΩ, ⌀ 200 mm     ⎩⎣⎝i=1    ⎠⎦⎭",
      "",
      "Linguistics and dictionaries:",
      "",
      "  ði ıntəˈnæʃənəl fəˈnɛtık əsoʊsiˈeıʃn",
      "  Y [ˈʏpsilɔn], Yen [jɛn], Yoga [ˈjoːgɑ]",
      "",
      "APL:",
      "",
      "  ((V⍳V)=⍳⍴V)/V←,V    ⌷←⍳→⍴∆∇⊃‾⍎⍕⌈"
   };

   int iLines = LEN( szText );

   SDL_SetHint( SDL_HINT_SHUTDOWN_DBUS_ON_QUIT, "1" );

   if( !SDL_Init( SDL_INIT_VIDEO ) )
   {
      fprintf( stderr, "Error initializing SDL: %s\n", SDL_GetError() );
      return 1;
   }

   if( !TTF_Init() )
   {
      fprintf( stderr, "Error initializing SDL_ttf: %s\n", SDL_GetError() );
      SDL_Quit();
      return 1;
   }

   pWindow = SDL_CreateWindow( "Simple SDL3 Text", 800, 600, SDL_WINDOW_RESIZABLE );
   if( pWindow == NULL )
   {
      fprintf( stderr, "Error creating SDL window: %s\n", SDL_GetError() );
      SDL_Quit();
      return 1;
   }

   pRenderer = SDL_CreateRenderer( pWindow, NULL );
   if( pRenderer == NULL )
   {
      fprintf( stderr, "Error creating SDL renderer: %s\n", SDL_GetError() );
      SDL_DestroyWindow( pWindow );
      SDL_Quit();
      return 1;
   }

   pFont = TTF_OpenFont( "../../docs/assets/font/9x18.pcf.gz", 18 );
   if( pFont == NULL )
   {
      fprintf( stderr, "Error opening SDL_ttf font: %s\n", SDL_GetError() );
      SDL_DestroyRenderer( pRenderer );
      SDL_DestroyWindow( pWindow );
      SDL_Quit();
      return 1;
   }

   while( !lQuit )
   {
      while( SDL_PollEvent( &sEvent ) )
      {
         switch( sEvent.type )
         {
         case SDL_EVENT_QUIT:
            lQuit = true;
            break;
         case SDL_EVENT_WINDOW_CLOSE_REQUESTED:
            lQuit = true;
            break;
         }

      }

      SDL_SetRenderDrawColor( pRenderer, 50, 50, 50, 255 );
      SDL_RenderClear( pRenderer );

      for( int i = 0; i < iLines; i++ )
      {
         drawText( pFont, pRenderer, 1, i, szText[ i ], sFg, sBg );
      }

      SDL_RenderPresent( pRenderer );
   }

   TTF_CloseFont( pFont );
   SDL_DestroyRenderer( pRenderer );
   SDL_DestroyWindow( pWindow );
   TTF_Quit();
   SDL_Quit();

   return 0;
}