Coordinates are relative to the glyph origin, using the Y-upwards convention.
If the glyph has been loaded with FT_LOAD_NO_SCALE, `bbox_mode' must be set to `FT_GLYPH_BBOX_UNSCALED' to get unscaled font units in 26.6 pixel format. The value `FT_GLYPH_BBOX_SUBPIXELS' is another name for this constant.
Note that the maximum coordinates are exclusive, which means that one can compute the width and height of the glyph image (be it in integer or 26.6 pixels) as:
width = bbox.xMax - bbox.xMin; height = bbox.yMax - bbox.yMin;
Note also that for 26.6 coordinates, if `bbox_mode' is set to `FT_GLYPH_BBOX_GRIDFIT', the coordinates will also be grid-fitted, which corresponds to:
bbox.xMin = FLOOR(bbox.xMin); bbox.yMin = FLOOR(bbox.yMin); bbox.xMax = CEILING(bbox.xMax); bbox.yMax = CEILING(bbox.yMax);
To get the bbox in pixel coordinates, set `bbox_mode' to `FT_GLYPH_BBOX_TRUNCATE'.
To get the bbox in grid-fitted pixel coordinates, set `bbox_mode' to `FT_GLYPH_BBOX_PIXELS'.