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[sdf] Add utility functions for contours. 

* src/sdf/ftsdf.c (get_control_box, get_contour_orientation): New
functions.
(split_conic, split_cubic, split_sdf_conic, split_sdf_cubic,
split_sdf_shape): New functions.
This commit is contained in:
Anuj Verma 2020-08-18 10:14:20 +05:30 committed by Werner Lemberg
parent 2de1b5630d
commit cd4138458a
2 changed files with 479 additions and 0 deletions
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ChangeLog
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@ -1,3 +1,12 @@
2020-08-18 Anuj Verma <anujv@iitbhilai.ac.in>
[sdf] Add utility functions for contours.
* src/sdf/ftsdf.c (get_control_box, get_contour_orientation): New
functions.
(split_conic, split_cubic, split_sdf_conic, split_sdf_cubic,
split_sdf_shape): New functions.
2020-08-17 Anuj Verma <anujv@iitbhilai.ac.in>
[sdf] Add functions to decompose `FT_Outline`.

470
src/sdf/ftsdf.c
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@ -842,4 +842,474 @@
return error;
}
/**************************************************************************
*
* utility functions
*
*/
/* Return the control box of a edge. The control box is a rectangle */
/* in which all the control points can fit tightly. */
static FT_CBox
get_control_box( SDF_Edge edge )
{
FT_CBox cbox;
FT_Bool is_set = 0;
switch ( edge.edge_type )
{
case SDF_EDGE_CUBIC:
cbox.xMin = edge.control_b.x;
cbox.xMax = edge.control_b.x;
cbox.yMin = edge.control_b.y;
cbox.yMax = edge.control_b.y;
is_set = 1;
/* fall through */
case SDF_EDGE_CONIC:
if ( is_set )
{
cbox.xMin = edge.control_a.x < cbox.xMin
? edge.control_a.x
: cbox.xMin;
cbox.xMax = edge.control_a.x > cbox.xMax
? edge.control_a.x
: cbox.xMax;
cbox.yMin = edge.control_a.y < cbox.yMin
? edge.control_a.y
: cbox.yMin;
cbox.yMax = edge.control_a.y > cbox.yMax
? edge.control_a.y
: cbox.yMax;
}
else
{
cbox.xMin = edge.control_a.x;
cbox.xMax = edge.control_a.x;
cbox.yMin = edge.control_a.y;
cbox.yMax = edge.control_a.y;
is_set = 1;
}
/* fall through */
case SDF_EDGE_LINE:
if ( is_set )
{
cbox.xMin = edge.start_pos.x < cbox.xMin
? edge.start_pos.x
: cbox.xMin;
cbox.xMax = edge.start_pos.x > cbox.xMax
? edge.start_pos.x
: cbox.xMax;
cbox.yMin = edge.start_pos.y < cbox.yMin
? edge.start_pos.y
: cbox.yMin;
cbox.yMax = edge.start_pos.y > cbox.yMax
? edge.start_pos.y
: cbox.yMax;
}
else
{
cbox.xMin = edge.start_pos.x;
cbox.xMax = edge.start_pos.x;
cbox.yMin = edge.start_pos.y;
cbox.yMax = edge.start_pos.y;
}
cbox.xMin = edge.end_pos.x < cbox.xMin
? edge.end_pos.x
: cbox.xMin;
cbox.xMax = edge.end_pos.x > cbox.xMax
? edge.end_pos.x
: cbox.xMax;
cbox.yMin = edge.end_pos.y < cbox.yMin
? edge.end_pos.y
: cbox.yMin;
cbox.yMax = edge.end_pos.y > cbox.yMax
? edge.end_pos.y
: cbox.yMax;
break;
default:
break;
}
return cbox;
}
/* Return orientation of a single contour. */
/* Note that the orientation is independent of the fill rule! */
/* So, for TTF a clockwise-oriented contour has to be filled */
/* and the opposite for OTF fonts. */
static SDF_Contour_Orientation
get_contour_orientation ( SDF_Contour* contour )
{
SDF_Edge* head = NULL;
FT_26D6 area = 0;
/* return none if invalid parameters */
if ( !contour || !contour->edges )
return SDF_ORIENTATION_NONE;
head = contour->edges;
/* Calculate the area of the control box for all edges. */
while ( head )
{
switch ( head->edge_type )
{
case SDF_EDGE_LINE:
area += MUL_26D6( ( head->end_pos.x - head->start_pos.x ),
( head->end_pos.y + head->start_pos.y ) );
break;
case SDF_EDGE_CONIC:
area += MUL_26D6( head->control_a.x - head->start_pos.x,
head->control_a.y + head->start_pos.y );
area += MUL_26D6( head->end_pos.x - head->control_a.x,
head->end_pos.y + head->control_a.y );
break;
case SDF_EDGE_CUBIC:
area += MUL_26D6( head->control_a.x - head->start_pos.x,
head->control_a.y + head->start_pos.y );
area += MUL_26D6( head->control_b.x - head->control_a.x,
head->control_b.y + head->control_a.y );
area += MUL_26D6( head->end_pos.x - head->control_b.x,
head->end_pos.y + head->control_b.y );
break;
default:
return SDF_ORIENTATION_NONE;
}
head = head->next;
}
/* Clockwise contours cover a positive area, and anti-clockwise */
/* contours cover a negative area. */
if ( area > 0 )
return SDF_ORIENTATION_CW;
else
return SDF_ORIENTATION_ACW;
}
/* This function is exactly the same as the one */
/* in the smooth renderer. It splits a conic */
/* into two conics exactly half way at t = 0.5. */
static void
split_conic( FT_26D6_Vec* base )
{
FT_26D6 a, b;
base[4].x = base[2].x;
a = base[0].x + base[1].x;
b = base[1].x + base[2].x;
base[3].x = b / 2;
base[2].x = ( a + b ) / 4;
base[1].x = a / 2;
base[4].y = base[2].y;
a = base[0].y + base[1].y;
b = base[1].y + base[2].y;
base[3].y = b / 2;
base[2].y = ( a + b ) / 4;
base[1].y = a / 2;
}
/* This function is exactly the same as the one */
/* in the smooth renderer. It splits a cubic */
/* into two cubics exactly half way at t = 0.5. */
static void
split_cubic( FT_26D6_Vec* base )
{
FT_26D6 a, b, c;
base[6].x = base[3].x;
a = base[0].x + base[1].x;
b = base[1].x + base[2].x;
c = base[2].x + base[3].x;
base[5].x = c / 2;
c += b;
base[4].x = c / 4;
base[1].x = a / 2;
a += b;
base[2].x = a / 4;
base[3].x = ( a + c ) / 8;
base[6].y = base[3].y;
a = base[0].y + base[1].y;
b = base[1].y + base[2].y;
c = base[2].y + base[3].y;
base[5].y = c / 2;
c += b;
base[4].y = c / 4;
base[1].y = a / 2;
a += b;
base[2].y = a / 4;
base[3].y = ( a + c ) / 8;
}
/* Split a conic Bezier curve into a number of lines */
/* and add them to `out'. */
/* */
/* This function uses recursion; we thus need */
/* parameter `max_splits' for stopping. */
static FT_Error
split_sdf_conic( FT_Memory memory,
FT_26D6_Vec* control_points,
FT_Int max_splits,
SDF_Edge** out )
{
FT_Error error = FT_Err_Ok;
FT_26D6_Vec cpos[5];
SDF_Edge* left,* right;
if ( !memory || !out )
{
error = FT_THROW( Invalid_Argument );
goto Exit;
}
/* split conic outline */
cpos[0] = control_points[0];
cpos[1] = control_points[1];
cpos[2] = control_points[2];
split_conic( cpos );
/* If max number of splits is done */
/* then stop and add the lines to */
/* the list. */
if ( max_splits <= 2 )
goto Append;
/* Otherwise keep splitting. */
FT_CALL( split_sdf_conic( memory, &cpos[0], max_splits / 2, out ) );
FT_CALL( split_sdf_conic( memory, &cpos[2], max_splits / 2, out ) );
/* [NOTE]: This is not an efficient way of */
/* splitting the curve. Check the deviation */
/* instead and stop if the deviation is less */
/* than a pixel. */
goto Exit;
Append:
/* Do allocation and add the lines to the list. */
FT_CALL( sdf_edge_new( memory, &left ) );
FT_CALL( sdf_edge_new( memory, &right ) );
left->start_pos = cpos[0];
left->end_pos = cpos[2];
left->edge_type = SDF_EDGE_LINE;
right->start_pos = cpos[2];
right->end_pos = cpos[4];
right->edge_type = SDF_EDGE_LINE;
left->next = right;
right->next = (*out);
*out = left;
Exit:
return error;
}
/* Split a cubic Bezier curve into a number of lines */
/* and add them to `out`. */
/* */
/* This function uses recursion; we thus need */
/* parameter `max_splits' for stopping. */
static FT_Error
split_sdf_cubic( FT_Memory memory,
FT_26D6_Vec* control_points,
FT_Int max_splits,
SDF_Edge** out )
{
FT_Error error = FT_Err_Ok;
FT_26D6_Vec cpos[7];
SDF_Edge* left,* right;
if ( !memory || !out )
{
error = FT_THROW( Invalid_Argument );
goto Exit;
}
/* split the conic */
cpos[0] = control_points[0];
cpos[1] = control_points[1];
cpos[2] = control_points[2];
cpos[3] = control_points[3];
split_cubic( cpos );
/* If max number of splits is done */
/* then stop and add the lines to */
/* the list. */
if ( max_splits <= 2 )
goto Append;
/* Otherwise keep splitting. */
FT_CALL( split_sdf_cubic( memory, &cpos[0], max_splits / 2, out ) );
FT_CALL( split_sdf_cubic( memory, &cpos[3], max_splits / 2, out ) );
/* [NOTE]: This is not an efficient way of */
/* splitting the curve. Check the deviation */
/* instead and stop if the deviation is less */
/* than a pixel. */
goto Exit;
Append:
/* Do allocation and add the lines to the list. */
FT_CALL( sdf_edge_new( memory, &left) );
FT_CALL( sdf_edge_new( memory, &right) );
left->start_pos = cpos[0];
left->end_pos = cpos[3];
left->edge_type = SDF_EDGE_LINE;
right->start_pos = cpos[3];
right->end_pos = cpos[6];
right->edge_type = SDF_EDGE_LINE;
left->next = right;
right->next = (*out);
*out = left;
Exit:
return error;
}
/* Subdivide an entire shape into line segments */
/* such that it doesn't look visually different */
/* from the original curve. */
static FT_Error
split_sdf_shape( SDF_Shape* shape )
{
FT_Error error = FT_Err_Ok;
FT_Memory memory;
SDF_Contour* contours;
SDF_Contour* new_contours = NULL;
if ( !shape || !shape->memory )
{
error = FT_THROW( Invalid_Argument );
goto Exit;
}
contours = shape->contours;
memory = shape->memory;
/* for each contour */
while ( contours )
{
SDF_Edge* edges = contours->edges;
SDF_Edge* new_edges = NULL;
SDF_Contour* tempc;
/* for each edge */
while ( edges )
{
SDF_Edge* edge = edges;
SDF_Edge* temp;
switch ( edge->edge_type )
{
case SDF_EDGE_LINE:
/* Just create a duplicate edge in case */
/* it is a line. We can use the same edge. */
FT_CALL( sdf_edge_new( memory, &temp ) );
ft_memcpy( temp, edge, sizeof ( *edge ) );
temp->next = new_edges;
new_edges = temp;
break;
case SDF_EDGE_CONIC:
/* Subdivide the curve and add it to the list. */
{
FT_26D6_Vec ctrls[3];
ctrls[0] = edge->start_pos;
ctrls[1] = edge->control_a;
ctrls[2] = edge->end_pos;
error = split_sdf_conic( memory, ctrls, 32, &new_edges );
}
break;
case SDF_EDGE_CUBIC:
/* Subdivide the curve and add it to the list. */
{
FT_26D6_Vec ctrls[4];
ctrls[0] = edge->start_pos;
ctrls[1] = edge->control_a;
ctrls[2] = edge->control_b;
ctrls[3] = edge->end_pos;
error = split_sdf_cubic( memory, ctrls, 32, &new_edges );
}
break;
default:
error = FT_THROW( Invalid_Argument );
goto Exit;
}
edges = edges->next;
}
/* add to the contours list */
FT_CALL( sdf_contour_new( memory, &tempc ) );
tempc->next = new_contours;
tempc->edges = new_edges;
new_contours = tempc;
new_edges = NULL;
/* deallocate the contour */
tempc = contours;
contours = contours->next;
sdf_contour_done( memory, &tempc );
}
shape->contours = new_contours;
Exit:
return error;
}
/* END */