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* src/sdf/ftsdf.c (sdf_generate_coarse_grid): Comments. 

Add more comments explaining the step by step
process of using coarse grid to increase the
performance of nearest distance search.
This commit is contained in:
Anuj Verma 2020-07-11 10:50:24 +05:30 committed by anujverma
parent 2afa0cb369
commit 2045c7d9b3
2 changed files with 37 additions and 9 deletions
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8
[GSoC]ChangeLog
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@ -1,3 +1,11 @@
2020-07-11 Anuj Verma <anujv@iitbhilai.ac.in>
* src/sdf/ftsdf.c (sdf_generate_coarse_grid): Comments.
Add more comments explaining the step by step
process of using coarse grid to increase the
performance of nearest distance search.
2020-07-11 Anuj Verma <anujv@iitbhilai.ac.in>
* src/sdf/ftsdf.c (sdf_generate_coarse_grid): Memory leak.

38
src/sdf/ftsdf.c
View File

@ -2723,7 +2723,7 @@
* dimension is determined by the COARSE_GRID_DIV). Then for each
* coarse grid, it checks which edges a relevant. An edge is relevant
* if it's shortest distance from the coarse grid is less than `spread'
* + `COARSE_GRID_DIV'.
* + coarse grid max dimension in the x/y axis.
* After we have all the relevant edges we only check those edges for
* the pixels inside the coarse grid.
*
@ -2741,14 +2741,15 @@
FT_Error error = FT_Err_Ok;
FT_Memory memory;
FT_UInt width, rows, i, j;
FT_UInt c_width, c_rows;
FT_16D16 sp_sq; /* max value to check */
FT_16D16 cg_sq; /* max value to check for coarse grid */
FT_UInt width, rows; /* width and rows of the bitmap */
FT_UInt i, j; /* iterators */
FT_UInt c_width, c_rows; /* coarse grid dimensions */
FT_16D16 sp_sq; /* max value to check */
FT_16D16 cg_sq; /* max value to check for coarse grid */
FT_16D16 cg_max;
SDF_Contour* contours; /* list of all contours */
FT_Short* buffer; /* the bitmap buffer */
SDF_Contour* contours; /* list of all contours */
FT_Short* buffer; /* the bitmap buffer */
/* coarse grid to hold the list of edges */
SDF_Edge* coarse_grid[ CG_DIMEN * CG_DIMEN ];
@ -2787,10 +2788,12 @@
cg_max = c_width > c_rows ? c_width : c_rows;
/* `cg_sq' is the max value for which we add an edge */
/* to the coarse grid list. */
if ( USE_SQUARED_DISTANCES )
{
sp_sq = FT_INT_16D16( spread * spread );
cg_sq = sp_sq * 2;
cg_sq = sp_sq + FT_INT_16D16( cg_max * cg_max ) / 4;
}
else
{
@ -2806,6 +2809,8 @@
goto Exit;
}
/* Loop through the coarse grid and buildup the list */
/* of edges for further checking. */
for ( j = 0; j < CG_DIMEN; j++ )
{
for ( i = 0; i < CG_DIMEN; i++ )
@ -2815,14 +2820,19 @@
SDF_Edge* edge;
FT_26D6_Vec cpoint;
coarse_grid[cindex] = NULL;
/* we check from the center of the coarse grid */
cpoint.x = FT_INT_26D6( i * c_width ) + FT_INT_26D6( c_width / 2 );
cpoint.y = FT_INT_26D6( j * c_rows ) + FT_INT_26D6( c_rows / 2 );
/* for all contours */
while ( cont )
{
edge = cont->edges;
/* for all edges */
while ( edge )
{
SDF_Signed_Distance dist;
@ -2831,7 +2841,7 @@
FT_CALL( sdf_edge_get_min_distance( edge, cpoint, &dist ) );
/* if the distance is more than `cg_sq' than discard it */
if ( dist.distance < cg_sq )
{
FT_CALL( sdf_edge_new( memory, &temp ) );
@ -2849,6 +2859,11 @@
}
}
/* Now that we have the list of edges relevant for the pixels */
/* inside a coarse grid, we only need to check those pixels */
/* against the list of edges. */
/* again loop through the coarse grid */
for ( j = 0; j < CG_DIMEN; j++ )
{
for ( i = 0; i < CG_DIMEN; i++ )
@ -2859,12 +2874,14 @@
if ( !coarse_grid[j * CG_DIMEN + i] ) continue;
/* this gives the pixels inside the coarse grid */
sample_region.xMin = i * c_width;
sample_region.xMax = sample_region.xMin + c_width;
sample_region.yMin = j * c_rows;
sample_region.yMax = sample_region.yMin + c_rows;
/* for all the pixes inside the coarse grid */
for ( y = sample_region.yMin; y < sample_region.yMax; y++ )
{
for ( x = sample_region.xMin; x < sample_region.xMax; x++ )
@ -2877,9 +2894,11 @@
if ( x < 0 || x >= width ) continue;
if ( y < 0 || y >= rows ) continue;
/* we check from the center of a pixel */
current_pos.x = FT_INT_26D6( x ) + FT_INT_26D6( 1 ) / 2;
current_pos.y = FT_INT_26D6( y ) + FT_INT_26D6( 1 ) / 2;
/* check the pixels only against the relevant edges */
while ( edges )
{
SDF_Signed_Distance dist;
@ -2894,6 +2913,7 @@
edges = edges->next;
}
/* finally truncate and assign the values */
if ( min_dist.distance > sp_sq )
min_dist.distance = sp_sq;