Re: [ft-devel] glyph metrics don't match bitmap size (2.8.1)

[Nicolas Jinchereau]

Thanks for the quick responses.

I've managed to render text correctly now using LCD filtering (the new 2.8.1 version). I was able to do it by ignoring the glyph metrics and using the bitmap size itself. This works well enough for now, and the text looks great, but I would like to be able to retrieve final dimensions of the bitmap without actually rendering/allocating anything, so I can calculate the layout of a bitmap-font/texture-atlas, and blit the glyphs afterward. I've been doing this for while and only ran into a problem when I tried the new LCD filtering.

I understand why the padding would be needed, but why wouldn't it be included in the glyph metrics (width/height)?

Is there any way to determine the final bitmap size without rendering it, or could it be added in a future version?

Thanks,

   Nick

On Mon, Sep 18, 2017 at 11:18 PM, Jan Alexander Steffens <address@hidden> wrote:

On Tue, Sep 19, 2017 at 4:13 AM Nicolas Jinchereau <address@hidden> wrote:

When using FT_LOAD_TARGET_LCD, the size of the rendered bitmap doesn't seem to match the size in the metrics. It's usually off by 1~2 units - is this normal?

Example:

#include <ft2build.h>

#include FT_FREETYPE_H

#include FT_LCD_FILTER_H

int main()

{

    FT_Library _library;

    FT_Init_FreeType(&_library);

    FT_Library_SetLcdFilter(_library, FT_LCD_FILTER_DEFAULT);

    FT_Face face;

    FT_New_Face(_library, "arial.ttf", 0, &face);

    FT_Set_Pixel_Sizes(face, 0, 14);

    

    FT_Int32 flags = 0;

    flags |= FT_LOAD_TARGET_LCD;

    flags |= FT_LOAD_RENDER;

    string sample = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz";

    for(char c : sample)

    {

        FT_Load_Char(face, (int)c, flags);

        cout << (face->glyph->bitmap.width / 3) << " ==? ";

        cout << (face->glyph->metrics.width >> 6) << endl;

    }

    FT_Done_Face(face);

    return 0;

}

Any help with this would be appreciated

I assume you used to build 2.8 and earlier without subpixel rendering. In that case, FT_LOAD_TARGET_LCD doesn't really do LCD rendering and just gives you bitmaps three times wider without increasing the resolution.

With "subpixel rendering" enabled, glyphs are rendered at higher resolution with LCD filtering which blurs the image horizontally. This requires up to one pixel (three bitmap columns) of padding at each side.

With "subpixel rendering" disabled, 2.8.1 now includes a patent-free LCD rendering technique which does not use filters but effectively multisamples the outline. It has similar padding requirements.