Re: [ft] bottom-row first pixel order?

[Joe Krahn]

Here is some sample code and results illustrating problems with a 
mat.yy=-1 transform. Somtimes it works OK, but even then, the hinter 
seems to malfunction, even though the transform does not intersect whole 
pixels.

Joe Krahn

/****** test.c ******/
#include <stdio.h>
#include <string.h>
#include <math.h>
#include <ft2build.h>
#include FT_FREETYPE_H

int main( int     argc, char**  argv ) {
  FT_Library    library;
  FT_Face       face;
  FT_Error      error;
  FT_Bitmap     *bitmap;
  unsigned char *buffer;
  int           x, y;
  FT_Matrix     mat={0x10000,0,0,0x10000};
  FT_Vector     vec={0,0};
  char *filename, ch;
  int target_height;

  if (argc<6) {
    printf("usage: %s <font_file> <char> <height> <y-scale> 
<y-shift>\n",argv[0]);
    exit(1);
  }

  filename = argv[1];
  ch = argv[2][0];
  target_height = atoi(argv[3]);
  mat.yy = (int)(atof(argv[4])*65536.0);
  vec.y = (int)(atof(argv[5])*64.0);

  printf ("Transform: M={0x%08lx,0x%08lx,0x%08lx,0x%08lx}, 
V={0x%08lx,0x%08lx}\n",
          mat.xx,mat.xy,mat.yx,mat.yy,vec.x,vec.y);

  FT_Init_FreeType( &library );
  error = FT_New_Face( library, filename, 0, &face );
  if (error) { printf("Error 0x%04x loading %s\n",error,filename); 
exit(error); }

  FT_Set_Pixel_Sizes( face,  0, target_height );
  FT_Set_Transform(face,&mat,&vec);

  error=FT_Load_Char( face, ch, FT_LOAD_RENDER | FT_LOAD_TARGET_MONO);
  if (error) { printf("Error 0x%04x loading character 
'%c'\n",error,ch); exit(error); }

  bitmap=&face->glyph->bitmap;
  buffer = (unsigned char *)bitmap->buffer;
  for(y=0;y<bitmap->rows;y++) {
    for(x=0;x<bitmap->width;x++) {
      putchar ( (buffer[y*bitmap->pitch+(x>>3)] & (0x80>>(x&7))) ? '#' 
: '.');
    }
    putchar('\n');
  }

  FT_Done_Face    ( face );
  FT_Done_FreeType( library );
  return 0;
}
/***** END test.c *****/

> rpm -q freetype-devel
freetype-devel-2.1.7-4

> gcc -Wall `freetype-config --cflags --libs` -o test test.c


Identity transform OK:
> ./test Courier.ttf W 16 1 0
Transform: M={0x00010000,0x00000000,0x00000000,0x00010000}, 
V={0x00000000,0x00000000}
###...###
#......#.
#...#..#.
#..#.#.#.
.#.#.#.#.
.#.#.#.#.
.##..#.#.
.##...##.
.##...##.


Negative Y gives an error:
> ./test Courier.ttf W 16 -1 0
Transform: M={0x00010000,0x00000000,0x00000000,0xffff0000}, 
V={0x00000000,0x00000000}
Error 0x0014 loading character 'W


Negative Y with a small Y shift works, but different shifts affect the 
scale:

> ./test Courier.ttf W 16 -1 -0.1
Transform: M={0x00010000,0x00000000,0x00000000,0xffff0000}, 
V={0x00000000,0xfffffffa}
.#######.

> ./test Courier.ttf W 16 -1 0.6
Transform: M={0x00010000,0x00000000,0x00000000,0xffff0000}, 
V={0x00000000,0x00000026}
.#.....#.
.##...##.
.##...##.
.##...##.
.##...##.
.##..#.#.
.#.#.#.#.
.#.#.#.#.
.#.#.#.#.
.#.#.#.#.
#..#.#.#.
#..##..#.
#...#..#.
#......#.
#......#.
###...###
.........

This one is shorter even though the Y scale is unchaged:
> ./test Courier.ttf W 16 -1 2.6
Transform: M={0x00010000,0x00000000,0x00000000,0xffff0000}, 
V={0x00000000,0x000000a6}
.........
.##...##.
.##...##.
.##...##.
.##..#.#.
.#.#.#.#.
.#.#.#.#.
.#.#.#.#.
#..##..#.
#......#.
#......#.
###...###
.........


For some fonts+sizes, Y-flipping works:
> ./test Symbol.ttf W 16 -1 0
Transform: M={0x00010000,0x00000000,0x00000000,0xffff0000}, 
V={0x00000000,0x00000000}
...###.
...#...
...#...
...#...
...#...
...#...
.######
xenon:~/Prog/gltext> ./test Symbol.ttf W 16 1 0
Transform: M={0x00010000,0x00000000,0x00000000,0x00010000}, 
V={0x00000000,0x00000000}
.######
...#...
...#...
...#...
...#...
...#...
...###.