[Freetype] text appears clipped on small rasters

[John Hunter]

When I render characters at small raster sizes (eg 80 dpi, 12 point),
the right hand side of the character often appears as if it has been
clipped off.  I suspect I am not handling something properly.

Below is code modified from example1.c in the tutorial that
illustrates the problem.  When I print the raster for "0" to a string
with show image, I get

  0   0   0   0   0   0   0   0   0   0
  0   0   0   0   0   0   0   0   0   0
  0  10 160 240 233 128   0   0   0   0
  0 149 191  13  28 221  98   0   0   0
  4 243  68   0   0 112 197   0   0   0
 37 255  21   0   0  66 243   0   0   0
 49 255  10   0   0  54 255   1   0   0
 37 255  21   0   0  66 243   0   0   0
  4 243  67   0   0 112 198   0   0   0
  0 150 189  13  28 221  98   0   0   0
  0  10 161 240 234 129   0   0   0   0
  0   0   0   0   0   0   0   0   0   0
  0   0   0   0   0   0   0   0   0   0

                              ^
                  raster appears clipped here

I ran this code with Vera.ttf.

Any advice?

Thanks,
John Hunter

#include <stdio.h>
#include <string.h>
#include <math.h>

#include <ft2build.h>
#include FT_FREETYPE_H

#define WIDTH   10
#define HEIGHT  13


/* origin is the upper left corner */
unsigned char image[HEIGHT][WIDTH];


/* Replace this function with something useful. */

void
draw_bitmap( FT_Bitmap*  bitmap,
             FT_Int      x,
             FT_Int      y)
{
  FT_Int  i, j, p, q;
  FT_Int  x_max = x + bitmap->width;
  FT_Int  y_max = y + bitmap->rows;


  for ( i = x, p = 0; i < x_max; i++, p++ )
  {
    for ( j = y, q = 0; j < y_max; j++, q++ )
      {
      if ( i >= WIDTH || j >= HEIGHT )
        continue;

      image[j][i] |= bitmap->buffer[q * bitmap->width + p];

    }
  }
}


void
show_image( void )
{
  int  i, j;
  
  

  for ( i = 0; i < HEIGHT; i++ )
  {
    for ( j = 0; j < WIDTH; j++ ) {
      printf("%3u ",image[i][j]);
      //putchar(image[i][j]);

    }
    printf("\n");
  }
}


int
main( int     argc,
      char**  argv )
{
  FT_Library    library;
  FT_Face       face;

  FT_GlyphSlot  slot;
  FT_Matrix     matrix;                 /* transformation matrix */
  FT_UInt       glyph_index;
  FT_Vector     pen;                    /* untransformed origin  */
  FT_Error      error;

  char*         filename;
  char*         text;

  int           target_height;
  int           n, num_chars;


  filename      = argv[1];                           /* first argument     */
  text          = "0";                           /* second argument    */
  num_chars     = strlen( text );
  target_height = HEIGHT;

  error = FT_Init_FreeType( &library );              /* initialize library */
  /* error handling omitted */

  error = FT_New_Face( library, argv[1], 0, &face ); /* create face object */
  /* error handling omitted */

  /* use 50pt at 100dpi */
  error = FT_Set_Char_Size( face, 12 * 64, 0,
                            80, 0 );                /* set character size */
  /* error handling omitted */

  slot = face->glyph;

  /* the pen position in 26.6 cartesian space coordinates; */
  /* start at (300,200) relative to the upper left corner  */
  pen.x = 0;
  pen.y = 0;

  for ( n = 0; n < num_chars; n++ )
  {
    /* set transformation */
    FT_Set_Transform( face, 0, &pen );

    /* load glyph image into the slot (erase previous one) */
    error = FT_Load_Char( face, text[n], FT_LOAD_RENDER );
    if ( error )
      continue;                 /* ignore errors */

    /* now, draw to our target surface (convert position) */
    draw_bitmap( &slot->bitmap,
                 slot->bitmap_left,
                 target_height-2 - slot->bitmap_top );

    /* increment pen position */
    pen.x += slot->advance.x;
    pen.y += slot->advance.y;
  }

  show_image();
  FT_Done_Face    ( face );
  FT_Done_FreeType( library );

  return 0;
}

/* EOF */