79 lines
2.1 KiB
Markdown
79 lines
2.1 KiB
Markdown
|
```c
|
||
|
|
stbtt_InitFont
|
||
|
|
|
||
|
|
stbtt_ScaleForMappingEmToPixels x 3
|
||
|
|
stbtt_ScaleForPixelHeight
|
||
|
|
stbtt_BakeFontBitmap
|
||
|
|
stbtt_GetFontVMetrics x 2
|
||
|
|
|
||
|
|
typedef struct {
|
||
|
|
unsigned short x0, y0, x1, y1; // coordinates of bbox in bitmap
|
||
|
|
float xoff, yoff, xadvance;
|
||
|
|
} stbtt_bakedchar;
|
||
|
|
|
||
|
|
struct RenImage {
|
||
|
|
RenColor *pixels;
|
||
|
|
int width, height;
|
||
|
|
};
|
||
|
|
|
||
|
|
typedef struct {
|
||
|
|
RenImage *image;
|
||
|
|
stbtt_bakedchar glyphs[256];
|
||
|
|
} GlyphSet;
|
||
|
|
|
||
|
|
struct RenFont {
|
||
|
|
void *data;
|
||
|
|
stbtt_fontinfo stbfont;
|
||
|
|
GlyphSet *sets[MAX_GLYPHSET];
|
||
|
|
float size;
|
||
|
|
int height;
|
||
|
|
};
|
||
|
|
|
||
|
|
```
|
||
|
|
|
||
|
|
The function stbtt_BakeFontBitmap is used to write bitmap data into set->image->pixels (where set is a GlyphSet).
|
||
|
|
Note that set->image->pixels need data in RGB format. After stbtt_BakeFontBitmap call the bitmap data are converted into RGB.
|
||
|
|
With a single call many glyphs corresponding to a range of codepoints, all in a
|
||
|
|
single image.
|
||
|
|
|
||
|
|
## STB truetype font metrics
|
||
|
|
|
||
|
|
stbtt_ScaleForPixelHeight takes a float 'height' and returns height / (ascent - descent).
|
||
|
|
|
||
|
|
stbtt_ScaleForMappingEmToPixels take a float 'pixels' and returns pixels / unitsPerEm.
|
||
|
|
|
||
|
|
### Computing RenFont
|
||
|
|
|
||
|
|
When loading a font, in renderer.c, the font->height is determined as:
|
||
|
|
|
||
|
|
```c
|
||
|
|
int ascent, descent, linegap;
|
||
|
|
stbtt_GetFontVMetrics(&font->stbfont, &ascent, &descent, &linegap);
|
||
|
|
float scale = stbtt_ScaleForMappingEmToPixels(&font->stbfont, font->size);
|
||
|
|
font->height = (ascent - descent + linegap) * scale + 0.5;
|
||
|
|
```
|
||
|
|
|
||
|
|
so, mathematically
|
||
|
|
|
||
|
|
```c
|
||
|
|
font->height = (ascent - descent + linegap) * font->size / unitsPerEm + 0.5;
|
||
|
|
```
|
||
|
|
|
||
|
|
**TO DO**: find out for what font->height is actually used.
|
||
|
|
|
||
|
|
### Call to BakeFontBitmap
|
||
|
|
|
||
|
|
In the same file, renderer.c, to create the glyphset image it computes:
|
||
|
|
|
||
|
|
```c
|
||
|
|
// Using stbtt functions
|
||
|
|
float s = ScaleForMappingEmToPixels(1) / ScaleForPixelHeight(1);
|
||
|
|
```
|
||
|
|
|
||
|
|
so 's' is actually equal to (ascent - descent) / unitsPerEm.
|
||
|
|
|
||
|
|
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.
|
||
|
|
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.
|