pixel_size = point_size * resolution / 72
pixel_size = point_size * resolution / 72
pixel_coord = grid_coord * pixel_size / EM_size
pixel_size
computed in the above formula does not directly relate to the size of characters on the screen. It simply is the size of the EM square if it was to be displayed. Each font designer is free to place its glyphs as it pleases him within the square. This explains why the letters of the following text have not the same height, even though they are displayed at the same point size with distinct fonts:grid-fitting scheme | advantages | disadvantages |
---|---|---|
explicit | Quality. Excellent results at small sizes are possible. This is very important for screen display. Consistency. All renderers produce the same glyph bitmaps (at least in theory). | Speed. Interpreting bytecode can be slow if the glyph programs are complex. Size. Glyph programs can be long. Technical difficulty. It is extremely difficult to write good hinting programs. Very few tools available. |
implicit | Size. Hints are usually much smaller than explicit glyph programs. Speed. Grid-fitting is usually a fast process. | Quality. Often questionable at small sizes. Better with anti-aliasing though. Inconsistency. Results can vary between different renderers, or even distinct versions of the same engine. |
automatic | Size. No need for control information, resulting in smaller font files. Speed. Depends on the grid-fitting algorithm. Usually faster than explicit grid-fitting. | Quality. Often questionable at small sizes. Better with anti-aliasing though. Speed. Depends on the grid-fitting algorithm. Inconsistency. Results can vary between different renderers, or even distinct versions of the same engine. |