mirror of https://github.com/freetype/freetype
[autofit] Add tilde-unflattening algorithm.
* src/autofit/aflatin.c (af_find_highest_contour, af_remove_segments_containing_point, af_latin_remove_tilde_points_from_edges, af_latin_stretch_tildes, af_latin_align_tildes): New functions. (af_latin_hints_apply): Call tilde-unflatting code if necessary.
This commit is contained in:
Craig White
Werner Lemberg
parent
1e5e193adb
commit
adf5129ad9
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@ -2776,6 +2776,300 @@
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}
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static FT_Int
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af_find_highest_contour( AF_GlyphHints hints )
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{
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FT_Int highest_contour = -1;
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FT_Pos highest_min_y = 0;
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FT_Pos current_min_y = 0;
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FT_Int contour;
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for ( contour = 0; contour < hints->num_contours; contour++ )
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{
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AF_Point point = hints->contours[contour];
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AF_Point first_point = point;
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if ( !point )
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continue;
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current_min_y = point->y;
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do
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{
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if ( point->y < current_min_y )
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current_min_y = point->y;
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point = point->next;
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} while ( point != first_point );
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if ( highest_contour == -1 || current_min_y > highest_min_y )
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{
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highest_min_y = current_min_y;
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highest_contour = contour;
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}
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}
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return highest_contour;
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}
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static void
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af_remove_segments_containing_point( AF_GlyphHints hints,
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AF_Point point )
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{
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AF_AxisHints axis = &hints->axis[AF_DIMENSION_VERT];
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AF_Segment segments = axis->segments;
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FT_UInt i;
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for ( i = 0; i < axis->num_segments; i++ )
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{
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AF_Segment seg = &segments[i];
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AF_Point p = seg->first;
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FT_Bool remove = 0;
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while ( 1 )
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{
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if ( p == point )
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{
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remove = 1;
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break;
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}
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if ( p == seg->last )
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break;
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p = p->next;
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}
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if ( remove )
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{
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/* First, check the first and last segment of the edge. */
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AF_Edge edge = seg->edge;
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if ( edge->first == seg && edge->last == seg )
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{
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/* The edge only consists of the segment to be removed. */
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/* Remove the edge. */
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*edge = axis->edges[--axis->num_edges];
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}
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else
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{
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if ( edge->first == seg )
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edge->first = seg->edge_next;
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if ( edge->last == seg )
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{
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edge->last = edge->first;
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while ( edge->last->edge_next != seg )
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edge->last = edge->last->edge_next;
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}
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}
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/* Now, delete the segment. */
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*seg = axis->segments[--axis->num_segments];
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i--; /* We have to check the new segment at this position. */
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}
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}
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}
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/* Remove all segments containing points on the tilde contour. */
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static void
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af_latin_remove_tilde_points_from_edges( AF_GlyphHints hints )
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{
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FT_Int highest_contour = af_find_highest_contour( hints );
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AF_Point first_point = hints->contours[highest_contour];
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AF_Point p = first_point;
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do
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{
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p = p->next;
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af_remove_segments_containing_point( hints, p );
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} while ( p != first_point );
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}
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/*
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The tilde-unflattening algorithm sometimes goes too far and makes an
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unusually high tilde, where decreasing the ppem will increase the height
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instead of a steady decrease in height as less pixels are used.
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For example, the 'n tilde' glyph from 'Times New Roman', with forced
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autofitting on, exhibits this behaviour in the font size range 16.5 to
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18 ppem.
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*/
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static void
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af_latin_stretch_tildes( AF_GlyphHints hints )
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{
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FT_Int highest_contour = af_find_highest_contour( hints );
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AF_Point p = hints->contours[highest_contour];
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AF_Point first_point = p;
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FT_Pos min_y, max_y;
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FT_Short min_fy, max_fy;
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FT_Pos min_measurement;
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FT_Pos height;
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FT_Pos target_height;
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min_y = max_y = p->y;
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min_fy = max_fy = p->fy;
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do
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{
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p = p->next;
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if ( p->y < min_y )
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min_y = p->y;
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if ( p->y > max_y )
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max_y = p->y;
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if ( p->fy < min_fy )
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min_fy = p->fy;
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if ( p->fy > max_fy )
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max_fy = p->fy;
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} while ( p != first_point );
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min_measurement = 32000;
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do
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{
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p = p->next;
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if ( !( p->flags & AF_FLAG_CONTROL ) &&
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p->prev->y == p->y && p->next->y == p->y &&
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p->y != min_y && p->y != max_y &&
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p->prev->flags & AF_FLAG_CONTROL &&
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p->next->flags & AF_FLAG_CONTROL )
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{
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/* This point could be a candidate. Find the next and previous */
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/* on-curve points, and make sure they are both either above or */
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/* below the point, then make the measurement. */
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AF_Point prevOn = p->prev;
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AF_Point nextOn = p->next;
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FT_Pos measurement;
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while ( prevOn->flags & AF_FLAG_CONTROL )
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prevOn = prevOn->prev;
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while ( nextOn->flags & AF_FLAG_CONTROL )
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nextOn = nextOn->next;
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if ( nextOn->y > p->y && prevOn->y > p->y )
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measurement = p->y - min_y;
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else if ( nextOn->y < p->y && prevOn->y < p->y )
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measurement = max_y - p->y;
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else
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continue;
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if ( measurement < min_measurement )
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min_measurement = measurement;
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}
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} while ( p != first_point );
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/* touch all points */
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p = first_point;
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do
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{
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p = p->next;
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if ( !( p->flags & AF_FLAG_CONTROL ) )
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p->flags |= AF_FLAG_TOUCH_Y;
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} while ( p != first_point );
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height = max_y - min_y;
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target_height = min_measurement + 64;
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if ( height >= target_height )
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return;
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p = first_point;
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do
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{
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p = p->next;
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p->y = ( ( p->y - min_y ) * target_height / height ) + min_y;
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p->fy = ( ( p->fy - min_fy ) * target_height / height ) + min_fy;
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p->oy = p->y;
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} while ( p != first_point );
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}
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/*
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As part of `af_latin_stretch_tildes`, all points in the tilde are marked
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as touched, so the existing grid fitting will leave the tilde misaligned
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with the grid.
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This function moves the tilde contour down to be grid-fitted. We assume
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that if moving the tilde down would cause it to touch or overlap another
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countour, the vertical adjustment step will fix it.
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Because the vertical adjustment step comes after all other grid-fitting
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steps, the top edge of the contour under the tilde is usually aligned
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with a horizontal grid line. The vertical gap enforced by the vertical
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adjustment is exactly one pixel, so if the top edge of the contour below
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the tilde is on a grid line, the resulting tilde contour will also be
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grid-aligned.
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But in cases where the gap is already big enough so that the vertical
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adjustment does nothing, this function ensures that even without the
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intervention of the vertical adjustment step, the tilde will be
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grid-aligned.
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*/
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static void
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af_latin_align_tildes( AF_GlyphHints hints )
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{
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FT_Int highest_contour = af_find_highest_contour( hints );
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AF_Point p = hints->contours[highest_contour];
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AF_Point first_point = p;
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FT_Pos min_y, max_y;
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FT_Pos min_y_rounded;
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FT_Pos delta;
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do
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{
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p = p->next;
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if ( p->y < min_y )
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min_y = p->y;
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if ( p->y > max_y )
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max_y = p->y;
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} while ( p != first_point );
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// mid_y = ( min_y + max_y ) / 2;
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min_y_rounded = FT_PIX_ROUND( min_y );
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delta = min_y_rounded - min_y;
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do
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{
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p = p->next;
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p->y += delta;
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} while ( p != first_point );
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}
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/* Return 1 if the given contour overlaps horizontally with the bounding */
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/* box of all other contours combined. This is a helper for function */
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/* `af_glyph_hints_apply_vertical_separation_adjustments`. */
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@ -2934,6 +3228,9 @@
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adjustment_amount = 64 - ( highest_min_y - max_y );
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}
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FT_TRACE4(( " Calculated adjustment amount: %d\n",
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adjustment_amount ));
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if ( adjustment_amount > 64 )
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FT_TRACE4(( " Calculated adjustment amount %d"
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" was more than threshold of 64. Not adjusting\n",
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@ -3860,6 +4157,47 @@
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}
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#ifdef FT_DEBUG_LEVEL_TRACE
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/* Print the height of the topmost contour for debugging purposes. */
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/* TODO: remove this once the tilde unflattening works. */
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static void
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af_latin_trace_height( FT_UInt num,
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AF_GlyphHints hints )
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{
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AF_Point p = hints->contours[af_find_highest_contour(hints)];
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AF_Point first_point = p;
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FT_Pos min_y, max_y;
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min_y = max_y = p->y;
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do
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{
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p = p->next;
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if ( !(p->flags & AF_FLAG_CONTROL) )
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{
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if ( p->y < min_y )
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min_y = p->y;
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if ( p->y > max_y )
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max_y = p->y;
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}
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} while ( p != first_point );
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FT_TRACE4(( "height %d: %ld\n", num, max_y - min_y ));
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}
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#else
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static void
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af_latin_trace_height( FT_UInt num,
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AF_GlyphHints hints )
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{
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FT_UNUSED( num );
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FT_UNUSED( hints );
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}
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#endif
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/* Apply the complete hinting algorithm to a latin glyph. */
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static FT_Error
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@ -3894,11 +4232,26 @@
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if ( AF_HINTS_DO_VERTICAL( hints ) )
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{
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FT_Bool is_tilde = af_lookup_tilde_correction_type(
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metrics->root.reverse_charmap, glyph_index );
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if ( is_tilde )
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{
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af_latin_trace_height(0, hints );
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af_latin_stretch_tildes( hints );
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af_latin_align_tildes( hints );
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af_latin_trace_height(1, hints );
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}
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axis = &metrics->axis[AF_DIMENSION_VERT];
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error = af_latin_hints_detect_features( hints,
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axis->width_count,
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axis->widths,
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AF_DIMENSION_VERT );
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if ( is_tilde )
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af_latin_remove_tilde_points_from_edges( hints );
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if ( error )
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goto Exit;
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@ -3914,14 +4267,19 @@
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( dim == AF_DIMENSION_VERT && AF_HINTS_DO_VERTICAL( hints ) ) )
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{
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af_latin_hint_edges( hints, (AF_Dimension)dim );
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af_latin_trace_height(2, hints );
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af_glyph_hints_align_edge_points( hints, (AF_Dimension)dim );
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af_latin_trace_height(3, hints );
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af_glyph_hints_align_strong_points( hints, (AF_Dimension)dim );
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af_latin_trace_height(4, hints );
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af_glyph_hints_align_weak_points( hints, (AF_Dimension)dim );
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af_latin_trace_height(5, hints );
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af_glyph_hints_apply_vertical_separation_adjustments(
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hints,
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(AF_Dimension)dim,
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glyph_index,
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metrics->root.reverse_charmap );
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af_latin_trace_height(6, hints );
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}
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}
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