Font Rendering: Multiple FT_Faces and baselines

[takase1121]

Hi,

I'm working on a renderer using FreeType. The renderer creates a list of 
FT_Faces, and query each face to find a suitable glyph for a given codepoint. 
This glyph is then rendered into a bitmap and stored for later use. When text 
is rendered, the renderer calculates the position of the bitmap with the 
following formula:
// font->size is the intended height of the face, passed into 
FT_Set_Pixel_Sizes()
baseline = (face->ascender / (float) face->units_per_EM) * font->size;
target_y = y - face->glyph->bitmap_top + baseline;

My problem arises when different faces have different baselines, and some faces 
(especially CJK) has weird baselines as CJK scripts technically don't have a 
concept of baselines. This causes the text using different faces to be 
offsetted vertically. I've thought of choosing the lowest baseline or 
calculating the average baseline for the entire run, but all of them would 
potentially mess up the text. What would be a good way to solve this?

Any help is appreciated.

Thanks,
Kelvin