ref: 1010f2c39c5522e384ba093e82878ffc74424a02
parent: 986d3108ac9fd0d7344bc83b20ccd64d433a02b3
author: Anuj Verma <[email protected]>
date: Wed Aug 19 12:25:08 EDT 2020
[sdf] Add subdivision and bounding box optimization. * src/sdf/ftsdf.c (sdf_generate_bounding_box): New function, which is an optimized version of `sdf_generate`. (sdf_generate_subdivision): New function.
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,5 +1,13 @@
2020-08-19 Anuj Verma <[email protected]>
+ [sdf] Add subdivision and bounding box optimization.
+
+ * src/sdf/ftsdf.c (sdf_generate_bounding_box): New function, which
+ is an optimized version of `sdf_generate`.
+ (sdf_generate_subdivision): New function.
+
+2020-08-19 Anuj Verma <[email protected]>
+
[sdf] Add function to generate SDF.
* src/sdf/ftsdf.c (sdf_generate): New function, currently disabled.
--- a/src/sdf/ftsdf.c
+++ b/src/sdf/ftsdf.c
@@ -3049,4 +3049,307 @@
#endif /* 0 */
+
+ /**************************************************************************
+ *
+ * @Function:
+ * sdf_generate_bounding_box
+ *
+ * @Description:
+ * This function does basically the same thing as `sdf_generate` above
+ * but more efficiently.
+ *
+ * Instead of checking all pixels against all edges, we loop over all
+ * edges and only check pixels around the control box of the edge; the
+ * control box is increased by the spread in all directions. Anything
+ * outside of the control box that exceeds `spread` doesn't need to be
+ * computed.
+ *
+ * Lastly, to determine the sign of unchecked pixels, we do a single
+ * pass of all rows starting with a '+' sign and flipping when we come
+ * across a '-' sign and continue. This also eliminates the possibility
+ * of overflow because we only check the proximity of the curve.
+ * Therefore we can use squared distanced safely.
+ *
+ * @Input:
+ * internal_params ::
+ * Internal parameters and properties required by the rasterizer.
+ * See @SDF_Params for more.
+ *
+ * shape ::
+ * A complete shape which is used to generate SDF.
+ *
+ * spread ::
+ * Maximum distances to be allowed in the output bitmap.
+ *
+ * @Output:
+ * bitmap ::
+ * The output bitmap which will contain the SDF information.
+ *
+ * @Return:
+ * FreeType error, 0 means success.
+ *
+ */
+ static FT_Error
+ sdf_generate_bounding_box( const SDF_Params internal_params,
+ const SDF_Shape* shape,
+ FT_UInt spread,
+ const FT_Bitmap* bitmap )
+ {+ FT_Error error = FT_Err_Ok;
+ FT_Memory memory = NULL;
+
+ FT_Int width, rows, i, j;
+ FT_Int sp_sq; /* max value to check */
+
+ SDF_Contour* contours; /* list of all contours */
+ FT_Short* buffer; /* the bitmap buffer */
+
+ /* This buffer has the same size in indices as the */
+ /* bitmap buffer. When we check a pixel position for */
+ /* a shortest distance we keep it in this buffer. */
+ /* This way we can find out which pixel is set, */
+ /* and also determine the signs properly. */
+ SDF_Signed_Distance* dists = NULL;
+
+
+ if ( !shape || !bitmap )
+ {+ error = FT_THROW( Invalid_Argument );
+ goto Exit;
+ }
+
+ if ( spread < MIN_SPREAD || spread > MAX_SPREAD )
+ {+ error = FT_THROW( Invalid_Argument );
+ goto Exit;
+ }
+
+ memory = shape->memory;
+ if ( !memory )
+ {+ error = FT_THROW( Invalid_Argument );
+ goto Exit;
+ }
+
+ contours = shape->contours;
+ width = (FT_Int)bitmap->width;
+ rows = (FT_Int)bitmap->rows;
+ buffer = (FT_Short*)bitmap->buffer;
+
+ if ( SDF_ALLOC( dists, width * rows * sizeof ( *dists ) ) )
+ goto Exit;
+
+ FT_MEM_ZERO( dists, width * rows * sizeof ( *dists ) );
+
+ if ( USE_SQUARED_DISTANCES )
+ sp_sq = FT_INT_16D16( spread * spread );
+ else
+ sp_sq = FT_INT_16D16( spread );
+
+ if ( width == 0 || rows == 0 )
+ {+ FT_TRACE0(( "sdf_generate:"
+ " Cannot render glyph with width/height == 0\n" ));
+ FT_TRACE0(( " "
+ " (width, height provided [%d, %d])", width, rows ));
+
+ error = FT_THROW( Cannot_Render_Glyph );
+ goto Exit;
+ }
+
+ /* loop over all contours */
+ while ( contours )
+ {+ SDF_Edge* edges = contours->edges;
+
+
+ /* loop over all edges */
+ while ( edges )
+ {+ FT_CBox cbox;
+ FT_Int x, y;
+
+
+ /* get the control box and increase it by `spread' */
+ cbox = get_control_box( *edges );
+
+ cbox.xMin = ( cbox.xMin - 63 ) / 64 - ( FT_Pos )spread;
+ cbox.xMax = ( cbox.xMax + 63 ) / 64 + ( FT_Pos )spread;
+ cbox.yMin = ( cbox.yMin - 63 ) / 64 - ( FT_Pos )spread;
+ cbox.yMax = ( cbox.yMax + 63 ) / 64 + ( FT_Pos )spread;
+
+ /* now loop over the pixels in the control box. */
+ for ( y = cbox.yMin; y < cbox.yMax; y++ )
+ {+ for ( x = cbox.xMin; x < cbox.xMax; x++ )
+ {+ FT_26D6_Vec grid_point = zero_vector;
+ SDF_Signed_Distance dist = max_sdf;
+ FT_UInt index = 0;
+
+
+ if ( x < 0 || x >= width )
+ continue;
+ if ( y < 0 || y >= rows )
+ continue;
+
+ grid_point.x = FT_INT_26D6( x );
+ grid_point.y = FT_INT_26D6( y );
+
+ /* This `grid_point` is at the corner, but we */
+ /* use the center of the pixel. */
+ grid_point.x += FT_INT_26D6( 1 ) / 2;
+ grid_point.y += FT_INT_26D6( 1 ) / 2;
+
+ FT_CALL( sdf_edge_get_min_distance( edges,
+ grid_point,
+ &dist ) );
+
+ if ( internal_params.orientation == FT_ORIENTATION_FILL_LEFT )
+ dist.sign = -dist.sign;
+
+ /* ignore if the distance is greater than spread; */
+ /* otherwise it creates artifacts due to the wrong sign */
+ if ( dist.distance > sp_sq )
+ continue;
+
+ /* square_root the values and fit in a 6.10 fixed-point */
+ if ( USE_SQUARED_DISTANCES )
+ dist.distance = square_root( dist.distance );
+
+ if ( internal_params.flip_y )
+ index = y * width + x;
+ else
+ index = ( rows - y - 1 ) * width + x;
+
+ /* check whether the pixel is set or not */
+ if ( dists[index].sign == 0 )
+ dists[index] = dist;
+ else if ( dists[index].distance > dist.distance )
+ dists[index] = dist;
+ else if ( FT_ABS( dists[index].distance - dist.distance )
+ < CORNER_CHECK_EPSILON )
+ dists[index] = resolve_corner( dists[index], dist );
+ }
+ }
+
+ edges = edges->next;
+ }
+
+ contours = contours->next;
+ }
+
+ /* final pass */
+ for ( j = 0; j < rows; j++ )
+ {+ /* We assume the starting pixel of each row is outside. */
+ FT_Char current_sign = -1;
+ FT_UInt index;
+
+
+ if ( internal_params.overload_sign != 0 )
+ current_sign = internal_params.overload_sign < 0 ? -1 : 1;
+
+ for ( i = 0; i < width; i++ )
+ {+ index = j * width + i;
+
+ /* if the pixel is not set */
+ /* its shortest distance is more than `spread` */
+ if ( dists[index].sign == 0 )
+ dists[index].distance = FT_INT_16D16( spread );
+ else
+ current_sign = dists[index].sign;
+
+ /* clamp the values */
+ if ( dists[index].distance > (FT_Int)FT_INT_16D16( spread ) )
+ dists[index].distance = FT_INT_16D16( spread );
+
+ /* convert from 16.16 to 6.10 */
+ dists[index].distance /= 64;
+
+ if ( internal_params.flip_sign )
+ buffer[index] = (FT_Short)dists[index].distance * -current_sign;
+ else
+ buffer[index] = (FT_Short)dists[index].distance * current_sign;
+ }
+ }
+
+ Exit:
+ SDF_FREE( dists );
+ return error;
+ }
+
+
+ /**************************************************************************
+ *
+ * @Function:
+ * sdf_generate_subdivision
+ *
+ * @Description:
+ * Subdivide the shape into a number of straight lines, then use the
+ * above `sdf_generate_bounding_box` function to generate the SDF.
+ *
+ * Note: After calling this function `shape` no longer has the original
+ * edges, it only contains lines.
+ *
+ * @Input:
+ * internal_params ::
+ * Internal parameters and properties required by the rasterizer.
+ * See @SDF_Params for more.
+ *
+ * shape ::
+ * A complete shape which is used to generate SDF.
+ *
+ * spread ::
+ * Maximum distances to be allowed inthe output bitmap.
+ *
+ * @Output:
+ * bitmap ::
+ * The output bitmap which will contain the SDF information.
+ *
+ * @Return:
+ * FreeType error, 0 means success.
+ *
+ */
+ static FT_Error
+ sdf_generate_subdivision( const SDF_Params internal_params,
+ SDF_Shape* shape,
+ FT_UInt spread,
+ const FT_Bitmap* bitmap )
+ {+ /*
+ * Thanks to Alexei for providing the idea of this optimization.
+ *
+ * We take advantage of two facts.
+ *
+ * (1) Computing the shortest distance from a point to a line segment is
+ * very fast.
+ * (2) We don't have to compute the shortest distance for the entire
+ * two-dimensional grid.
+ *
+ * Both ideas lead to the following optimization.
+ *
+ * (1) Split the outlines into a number of line segments.
+ *
+ * (2) For each line segment, only process its neighborhood.
+ *
+ * (3) Compute the closest distance to the line only for neighborhood
+ * grid points.
+ *
+ * This greatly reduces the number of grid points to check.
+ */
+
+ FT_Error error = FT_Err_Ok;
+
+
+ FT_CALL( split_sdf_shape( shape ) );
+ FT_CALL( sdf_generate_bounding_box( internal_params,
+ shape, spread, bitmap ) );
+
+ Exit:
+ return error;
+ }
+
/* END */