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Add some documentation for the shaping algorithm

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Kovid Goyal 2018-01-13 11:35:25 +05:30
parent 4a17a946fb
commit 67308f2ca1
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1 changed files with 13 additions and 1 deletions
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kitty/fonts.c
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@ -681,7 +681,19 @@ shape_run(Cell *first_cell, index_type num_cells, Font *font) {
printf("\n%s\n", (char*)canvas);
clear_canvas();
#endif
// Now distribute the glyphs into groups of cells
/* Now distribute the glyphs into groups of cells
* Considerations to keep in mind:
* Group sizes should be as small as possible for best performance
* Combining chars can result in multiple glyphs rendered into a single cell
* Emoji and East Asian wide chars can cause a single glyph to be rendered over multiple cells
* Ligature fonts, take two common approaches:
* 1. ABC becomes EMPTY, EMPTY, WIDE GLYPH this means we have to render N glyphs in N cells (example Fira Code)
* 2. ABC becomes WIDE GLYPH this means we have to render one glyph in N cells (example Operator Mono Lig)
*
* We rely on the cluster numbers from harfbuzz to tell us how many unicode codepoints a glyph corresponds to.
* Then we check if the glyph is a ligature glyph (is_special_glyph) and if it is an empty glyph. These three
* datapoints give us enough information to satisfy the constraint above, for a wide variety of fonts.
*/
uint32_t cluster, next_cluster;
bool add_to_current_group;
#define G(x) (group_state.x)