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FreeType: Round glyph advances

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The old code would simply add advances and store as a float with
individual glyph positioning using floor() based on the advance +
offset. This breaks rendering of infinite length ligatures at some font
sizes as they either under or overflow. Rounding the advances seems to
fix it. Dont know if it will have other ill-effects for non infinite
length ligatures. If it does we can test total ligature length and
use rounding only for long ligatures.

Fixes #3896
This commit is contained in:
Kovid Goyal 2021-08-04 08:35:51 +05:30
parent 8a6b51441c
commit 55319cd6d6
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GPG Key ID: 06BC317B515ACE7C
2 changed files with 13 additions and 1 deletions
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2
docs/changelog.rst
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@ -15,6 +15,8 @@ To update |kitty|, :doc:`follow the instructions <binary>`.
windows, allowing individual tabs/windows to have their own titles, even when
the OS Window has a fixed overall title (:iss:`3893`)
- Linux: Fix some very long ligatures being rendered incorrectly at some font
sizes (:iss:`3896`)
0.22.2 [2021-08-02]
----------------------

12
kitty/freetype.c
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@ -566,6 +566,8 @@ copy_color_bitmap(uint8_t *src, pixel* dest, Region *src_rect, Region *dest_rect
}
}
static const bool debug_placement = false;
static void
place_bitmap_in_canvas(pixel *cell, ProcessedBitmap *bm, size_t cell_width, size_t cell_height, float x_offset, float y_offset, size_t baseline, unsigned int glyph_num) {
// We want the glyph to be positioned inside the cell based on the bearingX
@ -575,6 +577,7 @@ place_bitmap_in_canvas(pixel *cell, ProcessedBitmap *bm, size_t cell_width, size
// Calculate column bounds
int32_t xoff = (int32_t)(x_offset + bm->bitmap_left);
if (debug_placement) printf(" bitmap_left: %d xoff: %d", bm->bitmap_left, xoff);
if (xoff < 0) src.left += -xoff;
else dest.left = xoff;
// Move the dest start column back if the width overflows because of it, but only if we are not in a very long/infinite ligature
@ -629,10 +632,17 @@ render_glyphs_in_cells(PyObject *f, bool bold, bool italic, hb_glyph_info_t *inf
}
x_offset = x + (float)positions[i].x_offset / 64.0f;
y = (float)positions[i].y_offset / 64.0f;
if (debug_placement) printf("%d: x=%f canvas: %u", i, x_offset, canvas_width);
if ((*was_colored || self->face->glyph->metrics.width > 0) && bm.width > 0) {
place_bitmap_in_canvas(canvas, &bm, canvas_width, cell_height, x_offset, y, baseline, i);
}
x += (float)positions[i].x_advance / 64.0f;
if (debug_placement) printf(" adv: %f\n", (float)positions[i].x_advance / 64.0f);
// the roundf() below is needed for infinite length ligatures, for a test case
// use: kitty --config None -o 'font_family Fira Code' -o 'font_size 4.5' sh -c
// "echo '|---|--------|-------|-------------|-------------|HH'; read"
// if this causes issues with non-infinite ligatures, we could choose this behavior
// based on num_glyphs and/or num_cells
x += roundf((float)positions[i].x_advance / 64.0f);
free_processed_bitmap(&bm);
}