Fix Cursive positioning
Test case: "مرا" rendered using IranNastaliq.
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Behdad Esfahbod
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aefdb64689
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ea22c749c7
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@ -826,123 +826,6 @@ struct CursivePosFormat1
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inline bool apply (hb_apply_context_t *c) const
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inline bool apply (hb_apply_context_t *c) const
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{
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{
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TRACE_APPLY ();
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TRACE_APPLY ();
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/* Now comes the messiest part of the whole OpenType
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specification. At first glance, cursive connections seem easy
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to understand, but there are pitfalls! The reason is that
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the specs don't mention how to compute the advance values
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resp. glyph offsets. I was told it would be an omission, to
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be fixed in the next OpenType version... Again many thanks to
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Andrei Burago <andreib@microsoft.com> for clarifications.
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Consider the following example:
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| xadv1 |
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+---------+
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+-----+--+ 1 |
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| | .| |
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| 0+--+------+
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| 2 |
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0+--------+
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| xadv2 |
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glyph1: advance width = 12
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anchor point = (3,1)
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glyph2: advance width = 11
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anchor point = (9,4)
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LSB is 1 for both glyphs (so the boxes drawn above are glyph
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bboxes). Writing direction is R2L; `0' denotes the glyph's
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coordinate origin.
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Now the surprising part: The advance width of the *left* glyph
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(resp. of the *bottom* glyph) will be modified, no matter
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whether the writing direction is L2R or R2L (resp. T2B or
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B2T)! This assymetry is caused by the fact that the glyph's
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coordinate origin is always the lower left corner for all
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writing directions.
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Continuing the above example, we can compute the new
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(horizontal) advance width of glyph2 as
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9 - 3 = 6 ,
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and the new vertical offset of glyph2 as
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1 - 4 = -3 .
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Vertical writing direction is far more complicated:
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a) Assuming that we recompute the advance height of the lower glyph:
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--
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+---------+
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-- | |
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+-----+--+ 1 | yadv1
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| | .| |
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yadv2 | 0+--+------+ -- BSB1 --
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| 2 | -- -- y_offset
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BSB2 -- 0+--------+ --
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-- --
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glyph1: advance height = 6
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anchor point = (3,1)
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glyph2: advance height = 7
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anchor point = (9,4)
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TSB is 1 for both glyphs; writing direction is T2B.
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BSB1 = yadv1 - (TSB1 + ymax1)
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BSB2 = yadv2 - (TSB2 + ymax2)
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y_offset = y2 - y1
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vertical advance width of glyph2
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= y_offset + BSB2 - BSB1
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= (y2 - y1) + (yadv2 - (TSB2 + ymax2)) - (yadv1 - (TSB1 + ymax1))
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= y2 - y1 + yadv2 - TSB2 - ymax2 - (yadv1 - TSB1 - ymax1)
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= y2 - y1 + yadv2 - TSB2 - ymax2 - yadv1 + TSB1 + ymax1
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b) Assuming that we recompute the advance height of the upper glyph:
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-- --
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+---------+ -- TSB1
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-- -- | |
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TSB2 -- +-----+--+ 1 | yadv1 ymax1
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yadv2 | 0+--+------+ -- --
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ymax2 | 2 | -- y_offset
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-- 0+--------+ --
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--
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glyph1: advance height = 6
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anchor point = (3,1)
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glyph2: advance height = 7
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anchor point = (9,4)
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TSB is 1 for both glyphs; writing direction is T2B.
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y_offset = y2 - y1
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vertical advance width of glyph2
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= TSB1 + ymax1 + y_offset - (TSB2 + ymax2)
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= TSB1 + ymax1 + y2 - y1 - TSB2 - ymax2
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Comparing a) with b) shows that b) is easier to compute. I'll wait
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for a reply from Andrei to see what should really be implemented...
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Since horizontal advance widths or vertical advance heights
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can be used alone but not together, no ambiguity occurs. */
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struct hb_ot_layout_context_t::info_t::gpos_t *gpi = &c->layout->info.gpos;
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struct hb_ot_layout_context_t::info_t::gpos_t *gpi = &c->layout->info.gpos;
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hb_codepoint_t last_pos = gpi->last;
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hb_codepoint_t last_pos = gpi->last;
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gpi->last = HB_OT_LAYOUT_GPOS_NO_LAST;
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gpi->last = HB_OT_LAYOUT_GPOS_NO_LAST;
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@ -965,15 +848,14 @@ struct CursivePosFormat1
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/* TODO vertical */
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/* TODO vertical */
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/* Align the exit anchor of the left glyph with the entry anchor of the right glyph. */
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if (c->buffer->props.direction == HB_DIRECTION_RTL)
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if (c->buffer->props.direction == HB_DIRECTION_RTL)
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{
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{
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/* advance is absolute, not relative */
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c->buffer->pos[c->buffer->i].x_advance = c->buffer->pos[c->buffer->i].x_offset + entry_x - gpi->anchor_x;
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c->buffer->pos[c->buffer->i].x_advance = entry_x - gpi->anchor_x;
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}
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}
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else
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else
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{
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{
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/* advance is absolute, not relative */
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c->buffer->pos[last_pos].x_advance = c->buffer->pos[last_pos].x_advance + gpi->anchor_x - entry_x;
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c->buffer->pos[last_pos].x_advance = gpi->anchor_x - entry_x;
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}
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}
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if (c->lookup_flag & LookupFlag::RightToLeft)
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if (c->lookup_flag & LookupFlag::RightToLeft)
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