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[sdf] Add '8-point sequential Euclidean distance mapping' algorithm.

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* src/sdf/ftbsdf.c (compare_neighbor, first_pass, second_pass,
edt8): New functions.
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Anuj Verma 2020-08-20 21:19:32 -07:00 committed by Werner Lemberg
parent 6b9a8044be
commit e2ae96b978
2 changed files with 257 additions and 1 deletions
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ChangeLog
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@ -1,3 +1,10 @@
2020-08-20 Anuj Verma <anujv@iitbhilai.ac.in>
[sdf] Add '8-point sequential Euclidean distance mapping' algorithm.
* src/sdf/ftbsdf.c (compare_neighbor, first_pass, second_pass,
edt8): New functions.
2020-08-20 Anuj Verma <anujv@iitbhilai.ac.in>
[sdf] Add function to copy source bitmap to distance map.

251
src/sdf/ftbsdf.c
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@ -303,7 +303,7 @@
* non-axis-aligned edges.
*
* (3) The only remaining piece of information that we cannot
* approximate directly from the alpha is the direction of the edge.
* approximate directly from the alpha is the direction of the edge.
* This is where we use Sobel's operator to compute the gradient of
* the pixel. The gradient give us a pretty good approximation of
* the edge direction. We use a 3x3 kernel filter to compute the
@ -695,4 +695,253 @@
}
/**************************************************************************
*
* @Function:
* compare_neighbor
*
* @Description:
* Compare neighbor pixel (which is defined by the offset) and update
* `current` distance if the new distance is shorter than the original.
*
* @Input:
* x_offset ::
* X offset of the neighbor to be checked. The offset is relative to
* the `current`.
*
* y_offset ::
* Y offset of the neighbor to be checked. The offset is relative to
* the `current`.
*
* width ::
* Width of the `current` array.
*
* @InOut:
* current ::
* Pointer into array of distances. This parameter must point to the
* position whose neighbor is to be checked. The array is treated as
* a two-dimensional array.
*
*/
static void
compare_neighbor( ED* current,
FT_Int x_offset,
FT_Int y_offset,
FT_Int width )
{
ED* to_check;
FT_16D16 dist;
FT_16D16_Vec dist_vec;
to_check = current + ( y_offset * width ) + x_offset;
/*
* While checking for the nearest point we first approximate the
* distance of `current` by adding the deviation (which is sqrt(2) at
* most). Only if the new value is less than the current value we
* calculate the actual distances using `FT_Vector_Length`. This last
* step can be omitted by using squared distances.
*/
/*
* Approximate the distance. We subtract 1 to avoid precision errors,
* which could happen because the two directions can be opposite.
*/
dist = to_check->dist - ONE;
if ( dist < current->dist )
{
dist_vec = to_check->near;
dist_vec.x += x_offset * ONE;
dist_vec.y += y_offset * ONE;
dist = VECTOR_LENGTH_16D16( dist_vec );
if ( dist < current->dist )
{
current->dist = dist;
current->near = dist_vec;
}
}
}
/**************************************************************************
*
* @Function:
* first_pass
*
* @Description:
* First pass of the 8SED algorithm. Loop over the bitmap from top to
* bottom and scan each row left to right, updating the distances in
* `worker->distance_map`.
*
* @InOut:
* worker::
* Contains all the relevant parameters.
*
*/
static void
first_pass( BSDF_Worker* worker )
{
FT_Int i, j; /* iterators */
FT_Int w, r; /* width, rows */
ED* dm; /* distance map */
dm = worker->distance_map;
w = worker->width;
r = worker->rows;
/* Start scanning from top to bottom and sweep each */
/* row back and forth comparing the distances of the */
/* neighborhood. Leave the first row as it has no top */
/* neighbor; it will be covered in the second scan of */
/* the image (from bottom to top). */
for ( j = 1; j < r; j++ )
{
FT_Int index;
ED* current;
/* Forward pass of rows (left -> right). Leave the first */
/* column, which gets covered in the backward pass. */
for ( i = 1; i < w; i++ )
{
index = j * w + i;
current = dm + index;
/* left-up */
compare_neighbor( current, -1, -1, w );
/* up */
compare_neighbor( current, 0, -1, w );
/* up-right */
compare_neighbor( current, 1, -1, w );
/* left */
compare_neighbor( current, -1, 0, w );
}
/* Backward pass of rows (right -> left). Leave the last */
/* column, which was already covered in the forward pass. */
for ( i = w - 2; i >= 0; i-- )
{
index = j * w + i;
current = dm + index;
/* right */
compare_neighbor( current, 1, 0, w );
}
}
}
/**************************************************************************
*
* @Function:
* second_pass
*
* @Description:
* Second pass of the 8SED algorithm. Loop over the bitmap from bottom
* to top and scan each row left to right, updating the distances in
* `worker->distance_map`.
*
* @InOut:
* worker::
* Contains all the relevant parameters.
*
*/
static void
second_pass( BSDF_Worker* worker )
{
FT_Int i, j; /* iterators */
FT_Int w, r; /* width, rows */
ED* dm; /* distance map */
dm = worker->distance_map;
w = worker->width;
r = worker->rows;
/* Start scanning from bottom to top and sweep each */
/* row back and forth comparing the distances of the */
/* neighborhood. Leave the last row as it has no down */
/* neighbor; it is already covered in the first scan */
/* of the image (from top to bottom). */
for ( j = r - 2; j >= 0; j-- )
{
FT_Int index;
ED* current;
/* Forward pass of rows (left -> right). Leave the first */
/* column, which gets covered in the backward pass. */
for ( i = 1; i < w; i++ )
{
index = j * w + i;
current = dm + index;
/* left-up */
compare_neighbor( current, -1, 1, w );
/* up */
compare_neighbor( current, 0, 1, w );
/* up-right */
compare_neighbor( current, 1, 1, w );
/* left */
compare_neighbor( current, -1, 0, w );
}
/* Backward pass of rows (right -> left). Leave the last */
/* column, which was already covered in the forward pass. */
for ( i = w - 2; i >= 0; i-- )
{
index = j * w + i;
current = dm + index;
/* right */
compare_neighbor( current, 1, 0, w );
}
}
}
/**************************************************************************
*
* @Function:
* edt8
*
* @Description:
* Compute the distance map of the a bitmap. Execute both first and
* second pass of the 8SED algorithm.
*
* @InOut:
* worker::
* Contains all the relevant parameters.
*
* @Return:
* FreeType error, 0 means success.
*
*/
static FT_Error
edt8( BSDF_Worker* worker )
{
FT_Error error = FT_Err_Ok;
if ( !worker || !worker->distance_map )
{
error = FT_THROW( Invalid_Argument );
goto Exit;
}
/* first scan of the image */
first_pass( worker );
/* second scan of the image */
second_pass( worker );
Exit:
return error;
}
/* END */