On Tue, Sep 19, 2017 at 4:13 AM Nicolas Jinchereau <
[email protected]> 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.
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