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[bsdf] Added function to find edge pixels given a grid of alpha values. 

* src/sdf/ftbsdf.c (bsdf_is_edge): The function find the edge pixel in a distance map
  which is basically a 2D array of alpha values which represent coverage in the
  original input bitmap.
This commit is contained in:
Anuj Verma 2020-08-20 09:20:26 +05:30
parent 2aeee74c0c
commit 44e9d12f0f
1 changed files with 111 additions and 0 deletions
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111
src/sdf/ftbsdf.c
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@ -123,5 +123,116 @@
static
const ED zero_ed = { 0, { 0, 0 }, 0 };
/**************************************************************************
*
* rasterizer functions
*
*/
#ifdef CHECK_NEIGHBOR
#undef CHECK_NEIGHBOR
#endif
/* Use the macro only in `bsdf_is_edge' function. */
#define CHECK_NEIGHBOR( x_offset, y_offset ) \
if ( x + x_offset >= 0 && x + x_offset < w && \
y + y_offset >= 0 && y + y_offset < r ) \
{ \
num_neighbour++; \
to_check = dm + y_offset * w + x_offset; \
if ( to_check->alpha == 0 ) \
{ \
is_edge = 1; \
goto Done; \
} \
}
/**************************************************************************
*
* @Function:
* bsdf_is_edge
*
* @Description:
* This function checks weather a pixel is an edge pixel. A pixel
* is edge bixel if it surrounded by a completely black pixel ( 0
* alpha ) and the current pixel is not a completely black pixel.
*
* @Input:
* dm ::
* Array of distances. The parameter must point to the current
* pixel i.e. the pixel that is to be checked for edge.
*
* x ::
* The x position of the current pixel.
*
* y ::
* The y position of the current pixel.
*
* w ::
* Width of the bitmap.
*
* r ::
* Number of rows in the bitmap.
*
* @Return:
* FT_Bool ::
* 1 if the current pixel is an edge pixel, 0 otherwise.
*
*/
static FT_Bool
bsdf_is_edge( ED* dm, /* distance map */
FT_Int x, /* x index of point to check */
FT_Int y, /* y index of point to check */
FT_Int w, /* width */
FT_Int r ) /* rows */
{
FT_Bool is_edge = 0;
ED* to_check = NULL;
FT_Int num_neighbour = 0;
if ( dm->alpha == 0 )
goto Done;
if ( dm->alpha > 0 && dm->alpha < 255 )
{
is_edge = 1;
goto Done;
}
/* up */
CHECK_NEIGHBOR( 0, -1 );
/* down */
CHECK_NEIGHBOR( 0, 1 );
/* left */
CHECK_NEIGHBOR( -1, 0 );
/* right */
CHECK_NEIGHBOR( 1, 0 );
/* up left */
CHECK_NEIGHBOR( -1, -1 );
/* up right */
CHECK_NEIGHBOR( 1, -1 );
/* down left */
CHECK_NEIGHBOR( -1, 1 );
/* down right */
CHECK_NEIGHBOR( 1, 1 );
if ( num_neighbour != 8 )
is_edge = 1;
Done:
return is_edge;
}
#undef CHECK_NEIGHBOR
/* END */