[ft] FreeType Library Question

[Ivailo Stoianov]

Hello FreeType Team,

I am Ivailo Stoianov, and I am trying to use The FreeType Library (ver. 2.4.2) to use TrueType fonts.

I have some issues about that, so I would like to ask you for help!

My first question is about glyph size. When I specify exact pixel size for the glyph, the generated bitmap has smaller dimensions. For example: if I execute the folowing code (I am using standart Windows Arial font in all examples):

    FT_Library library;
    FT_Error result;
    FT_Face face;
    FT_Matrix matrix;
    FT_Vector delta;

    result = FT_Init_FreeType(&library);
    result = FT_New_Face(library, "arial.ttf", 0, &face);

    result = FT_Set_Pixel_Sizes(face, 250, 250);

    delta.x = 0 * 64;
    delta.y = 0 * 64;

    matrix.xx = 0x10000L;
    matrix.xy = 0x0000L;
    matrix.yx = 0x0000L;
    matrix.yy = 0x10000L;

    FT_Set_Transform(face, &matrix, &delta);

    result = FT_Load_Char(face, 'D' , FT_LOAD_RENDER | FT_LOAD_MONOCHROME);

the 'face' object has the following fields:

  FACE:

     NUM. FACES(face->num_faces): '1'

     FACE INDEX(face->face_index): '0'

     FACE FLAGS(face->face_flags): '00000A59'

     STYLE FLAGS(face->style_flags): '00000000'

     NUM. GLYPHS(face->num_glyphs): '3415'

     FAMILY NAME(face->family_name): 'Arial'

     STYLE NAME(face->style_name): 'Regular'

     NUM. CHARMAPS(face->num_charmaps): '3'

   BBOX:

     X MIN(face->bbox.xMin): '-1361'

     X MAX(face->bbox.xMax): '4096'

     Y MIN(face->bbox.yMin): '-665'

     Y MAX(face->bbox.yMax): '2060'

     UNITS PER EM(face->units_per_EM): '2048'

     HEIGHT(face->height): '2355'

     MAX ADVANCE WIDTH(face->max_advance_width): '4096'

     MAX ADVANCE HEIGHT(face->max_advance_height): '2355'

     UNDERLINE POSITION(face->underline_position): '-292'

     UNDERLINE THICKNESS(face->underline_thickness): '150'

   METRICS:

     HEIGHT(face->glyph->metrics.height): '11456'

     WIDTH(face->glyph->metrics.width): '9536'

     HORIZONTAL ADVANCE(face->glyph->metrics.horiAdvance): '11584'

     HORIZONTAL BEARING X(face->glyph->metrics.horiBearingX): '1280'

     HORIZONTAL BEARING Y(face->glyph->metrics.horiBearingY): '11456'

     LINEAR HORIZONTAL ADVANCE(face->glyph->linearHoriAdvance): '11832000'

     LINEAR VERTICAL ADVANCE(face->glyph->linearVertAdvance): '15376000'

     ADVANCE X(face->glyph->advance.x): '11584'

     ADVANCE Y(face->glyph->advance.y): '0'

     FORMAT(face->glyph->format): '62697473'

   BITMAP:

     ROWS(face->glyph->bitmap.rows): '179'

     WIDTH(face->glyph->bitmap.width): '149'

     PITCH(face->glyph->bitmap.pitch): '20'

     BITMAP LEFT(face->glyph->bitmap_left): '20'

     BITMAP TOP(face->glyph->bitmap_top): '179'

The output bitmap has smaller dimensions than these specified in the ' FT_Set_Pixel_Sizes' function. Specified size is 250x250, but the generated bitmap has this size - 149x179.

Even if I use 'FT_Set_Char_Size' instead of ' FT_Set_Pixel_Sizes' the output size is not the expected by me. In the code above if I replace the row "result = FT_Set_Pixel_Sizes(face, 250, 250);" with "result = FT_Set_Char_Size(face, 50*64, 0, 96, 0);" (96 is the dpi of my monitor), the 'face' object has the following fields:

   FACE:

     NUM. FACES(face->num_faces): '1'

     FACE INDEX(face->face_index): '0'

     FACE FLAGS(face->face_flags): '00000A59'

     STYLE FLAGS(face->style_flags): '00000000'

     NUM. GLYPHS(face->num_glyphs): '3415'

     FAMILY NAME(face->family_name): 'Arial'

     STYLE NAME(face->style_name): 'Regular'

     NUM. CHARMAPS(face->num_charmaps): '3'

   BBOX:

     X MIN(face->bbox.xMin): '-1361'

     X MAX(face->bbox.xMax): '4096'

     Y MIN(face->bbox.yMin): '-665'

     Y MAX(face->bbox.yMax): '2060'

     UNITS PER EM(face->units_per_EM): '2048'

     HEIGHT(face->height): '2355'

     MAX ADVANCE WIDTH(face->max_advance_width): '4096'

     MAX ADVANCE HEIGHT(face->max_advance_height): '2355'

     UNDERLINE POSITION(face->underline_position): '-292'

     UNDERLINE THICKNESS(face->underline_thickness): '150'

   METRICS:

     HEIGHT(face->glyph->metrics.height): '3072'

     WIDTH(face->glyph->metrics.width): '2560'

     HORIZONTAL ADVANCE(face->glyph->metrics.horiAdvance): '3072'

     HORIZONTAL BEARING X(face->glyph->metrics.horiBearingX): '320'

     HORIZONTAL BEARING Y(face->glyph->metrics.horiBearingY): '3072'

     LINEAR HORIZONTAL ADVANCE(face->glyph->linearHoriAdvance): '3155447'

     LINEAR VERTICAL ADVANCE(face->glyph->linearVertAdvance): '4100587'

     ADVANCE X(face->glyph->advance.x): '3072'

     ADVANCE Y(face->glyph->advance.y): '0'

     FORMAT(face->glyph->format): '62697473'

   BITMAP:

     ROWS(face->glyph->bitmap.rows): '48'

     WIDTH(face->glyph->bitmap.width): '40'

     PITCH(face->glyph->bitmap.pitch): '6'

     BITMAP LEFT(face->glyph->bitmap_left): '5'

     BITMAP TOP(face->glyph->bitmap_top): '48'

If I use the formula "pixel_size = point_size * resolution / 72" from The FreeType Conventions the calculated size is 67 pixels, but the output size of the bitmap is smaller - 40x48 pixels. When I use 203 dpi in the function above (203 is the dpi of my target device), the 'face' object has the following fields:

   FACE:

     NUM. FACES(face->num_faces): '1'

     FACE INDEX(face->face_index): '0'

     FACE FLAGS(face->face_flags): '00000A59'

     STYLE FLAGS(face->style_flags): '00000000'

     NUM. GLYPHS(face->num_glyphs): '3415'

     FAMILY NAME(face->family_name): 'Arial'

     STYLE NAME(face->style_name): 'Regular'

     NUM. CHARMAPS(face->num_charmaps): '3'

   BBOX:

     X MIN(face->bbox.xMin): '-1361'

     X MAX(face->bbox.xMax): '4096'

     Y MIN(face->bbox.yMin): '-665'

     Y MAX(face->bbox.yMax): '2060'

     UNITS PER EM(face->units_per_EM): '2048'

     HEIGHT(face->height): '2355'

     MAX ADVANCE WIDTH(face->max_advance_width): '4096'

     MAX ADVANCE HEIGHT(face->max_advance_height): '2355'

     UNDERLINE POSITION(face->underline_position): '-292'

     UNDERLINE THICKNESS(face->underline_thickness): '150'

   METRICS:

     HEIGHT(face->glyph->metrics.height): '6464'

     WIDTH(face->glyph->metrics.width): '5376'

     HORIZONTAL ADVANCE(face->glyph->metrics.horiAdvance): '6528'

     HORIZONTAL BEARING X(face->glyph->metrics.horiBearingX): '704'

     HORIZONTAL BEARING Y(face->glyph->metrics.horiBearingY): '6464'

     LINEAR HORIZONTAL ADVANCE(face->glyph->linearHoriAdvance): '6671769'

     LINEAR VERTICAL ADVANCE(face->glyph->linearVertAdvance): '8670142'

     ADVANCE X(face->glyph->advance.x): '6528'

     ADVANCE Y(face->glyph->advance.y): '0'

     FORMAT(face->glyph->format): '62697473'

   BITMAP:

     ROWS(face->glyph->bitmap.rows): '101'

     WIDTH(face->glyph->bitmap.width): '84'

     PITCH(face->glyph->bitmap.pitch): '12'

     BITMAP LEFT(face->glyph->bitmap_left): '11'

     BITMAP TOP(face->glyph->bitmap_top): '101'

When I make the calculations again - the size expected by me is 141 pixels, but the generated image is smaller - 84x101 pixels.

So, as a conclusion, my question is - Is it possible to generate birmap image with the size, desired by me? - for example if I want letter with size 200x200 pixels, the output bitmap image to be with this size or with size near to the desired one.

My second qustion is - Is it possible to generate "outline letters" - letter only with outlines, without fill? - like this one Outline letter.

If you need any additional information about my code(field data of other objects, return values of functions or something else), please, send me an e-mail and I will answer it as soon as possible.

Thank you for the time spent on reading my mail! I look forward to your reply. Thanks in advance!

Best regards!

-- 
Ivailo Stoianov - Firmware Engineer, DATECS LTD. Firmware Deparment