More notes on font rendering

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Francesco Abbate 2020-05-30 15:19:33 +02:00
parent 155e76df5f
commit d9dea5d122
1 changed files with 82 additions and 1 deletions

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@ -73,6 +73,87 @@ float s = ScaleForMappingEmToPixels(1) / ScaleForPixelHeight(1);
so 's' is actually equal to (ascent - descent) / unitsPerEm. so 's' is actually equal to (ascent - descent) / unitsPerEm.
Then BakeFontBitmap is called and `font->size * s` is used for the pixel_height argument. Then BakeFontBitmap is called and `font->size * s` is used for the pixel_height argument.
So BakeFontBitmap gets, for pixel_height, (ascent - descent) * font->size / unitsPerEm. So BakeFontBitmap gets
```c
pixel_height = (ascent - descent) * font->size / unitsPerEm;
```
This is equal almost equal to font->height except the 0.5, the missing linegap calculation This is equal almost equal to font->height except the 0.5, the missing linegap calculation
and the fact that this latter is an integer instead of a float. and the fact that this latter is an integer instead of a float.
## AGG Font Engine
Calls
FT_Init_FreeType (initialize the library)
In load_font() method:
FT_New_Face or FT_New_Memory_Face (use FT_Done_Face when done)
FT_Attach_File
FT_Select_Charmap
In update_char_size() method:
FT_Set_Char_Size or FT_Set_Pixel_Sizes
In prepare_glyph() method:
FT_Get_Char_Index
FT_Load_Glyph
FT_Render_Glyph (if glyph_render_native_mono or native_gray8)
in add_kerning() method
FT_Get_Kerning
FT_Done_FreeType (end with library)
## Freetype2's metrics related function and structs
FT_New_Face
```c
typedef struct FT_FaceRec_
{
FT_Long num_faces;
FT_Long face_index;
FT_Long face_flags;
FT_Long style_flags;
FT_Long num_glyphs;
FT_String* family_name;
FT_String* style_name;
FT_Int num_fixed_sizes;
FT_Bitmap_Size* available_sizes;
FT_Int num_charmaps;
FT_CharMap* charmaps;
FT_Generic generic;
/*# The following member variables (down to `underline_thickness`) */
/*# are only relevant to scalable outlines; cf. @FT_Bitmap_Size */
/*# for bitmap fonts. */
FT_BBox bbox;
FT_UShort units_per_EM;
FT_Short ascender;
FT_Short descender;
FT_Short height;
FT_Short max_advance_width;
FT_Short max_advance_height;
FT_Short underline_position;
FT_Short underline_thickness;
FT_GlyphSlot glyph;
FT_Size size;
FT_CharMap charmap;
/* private part omitted. */
} FT_FaceRec;
```