[sdf] Added the subdivision and bounding box optimization.
* src/sdf/ftsdf.c (sdf_generate_bounding_box): Added function to generate SDF by only checking grid point around the bounding box of any edge. * src/sdf/ftsdf.c (sdf_generate_subdivision): Added function to generate SDF by splitting the shape into a number of line segments and then only checking grid points around the neighborhood of the lines.
This commit is contained in:
Anuj Verma
parent
596bcfd340
commit
5cee930937
292
src/sdf/ftsdf.c
292
src/sdf/ftsdf.c
@ -2801,4 +2801,296 @@
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#endif
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/**************************************************************************
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*
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* @Function:
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* sdf_generate_bounding_box
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*
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* @Description:
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* This function does basically the same thing as the above
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* `sdf_generate' but more efficiently.
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* Instead of checking all the pixels against all the edges, we loop
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* through all the edges and only check the pixels around the control
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* box of the edge, the control box is increased by the spread in all
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* all the directions. Anything outside the control box will naturally
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* be more than the `spread' and shouldn't be computed.
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* Lastly to determine the sign of unchecked pixels we do a single pass
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* of all the rows starting with a '+' sign and flipping when we come
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* across a '-' sign and continue.
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* This also eliminate the chance of overflow because we only check the
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* proximity of the curve. Therefore we can use squared distanced
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* safely.
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*
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* @Input:
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* internal_params ::
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* Internal parameters and properties required by the rasterizer.
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* See `SDF_Params' for the actual parameters.
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*
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* shape ::
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* A complete shape which is used to generate SDF.
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*
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* spread ::
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* Maximum distances to be allowed inthe output bitmap.
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*
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* @Return
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* bitmap ::
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* The output bitmap which will contain the SDF information.
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*
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* FT_Error ::
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* FreeType error, 0 means success.
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*
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*/
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static FT_Error
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sdf_generate_bounding_box( const SDF_Params internal_params,
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const SDF_Shape* shape,
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FT_UInt spread,
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const FT_Bitmap* bitmap )
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{
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FT_Error error = FT_Err_Ok;
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FT_Memory memory = NULL;
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FT_UInt width, rows, i, j;
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FT_UInt sp_sq; /* max value to check */
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SDF_Contour* contours; /* list of all contours */
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FT_Short* buffer; /* the bitmap buffer */
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/* This buffer has the same size in indices as the */
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/* bitmap buffer. When we check a pixel position for */
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/* shortest distance we keep it in this buffer. */
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/* This way we check find out which pixel is set, */
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/* and also determine the signs properly. */
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SDF_Signed_Distance* dists = NULL;
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if ( !shape || !bitmap )
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{
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error = FT_THROW( Invalid_Argument );
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goto Exit;
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}
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if ( spread < MIN_SPREAD || spread > MAX_SPREAD )
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{
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error = FT_THROW( Invalid_Argument );
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goto Exit;
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}
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memory = shape->memory;
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if ( !memory ){
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error = FT_THROW( Invalid_Argument );
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goto Exit;
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}
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contours = shape->contours;
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width = bitmap->width;
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rows = bitmap->rows;
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buffer = (FT_Short*)bitmap->buffer;
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if ( SDF_ALLOC( dists, width * rows * sizeof( *dists ) ) )
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goto Exit;
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FT_MEM_ZERO( dists, width * rows * sizeof(*dists) );
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if ( USE_SQUARED_DISTANCES )
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sp_sq = FT_INT_16D16( spread * spread );
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else
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sp_sq = FT_INT_16D16( spread );
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if ( width == 0 || rows == 0 )
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{
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FT_TRACE0(( "[sdf] sdf_generate:\n"
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" Cannot render glyph with width/height == 0\n"
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" (width, height provided [%d, %d])", width, rows ));
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error = FT_THROW( Cannot_Render_Glyph );
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goto Exit;
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}
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/* loop through all the contours */
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while ( contours ) {
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SDF_Edge* edges = contours->edges;
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/* loop through all the edges */
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while ( edges )
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{
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FT_CBox cbox;
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FT_Int x, y;
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/* get the control box and increase by `spread' */
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cbox = get_control_box( *edges );
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cbox.xMin = ( cbox.xMin - 63 ) / 64 - ( FT_Pos )spread;
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cbox.xMax = ( cbox.xMax + 63 ) / 64 + ( FT_Pos )spread;
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cbox.yMin = ( cbox.yMin - 63 ) / 64 - ( FT_Pos )spread;
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cbox.yMax = ( cbox.yMax + 63 ) / 64 + ( FT_Pos )spread;
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/* now loop the pixels in the control box. */
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for ( y = cbox.yMin; y < cbox.yMax; y++ )
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{
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for ( x = cbox.xMin; x < cbox.xMax; x++ )
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{
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FT_26D6_Vec grid_point = zero_vector;
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SDF_Signed_Distance dist = max_sdf;
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FT_UInt index = 0;
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if ( x < 0 || x >= width ) continue;
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if ( y < 0 || y >= rows ) continue;
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grid_point.x = FT_INT_26D6( x );
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grid_point.y = FT_INT_26D6( y );
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/* This `grid_point' is at the corner, but we */
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/* use the center of the pixel. */
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grid_point.x += FT_INT_26D6( 1 ) / 2;
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grid_point.y += FT_INT_26D6( 1 ) / 2;
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FT_CALL( sdf_edge_get_min_distance( edges,
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grid_point,
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&dist ) );
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if ( internal_params.orientation == FT_ORIENTATION_FILL_LEFT )
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dist.sign = -dist.sign;
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/* ignore if the distance is greater than spread */
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/* otherwise it creates artifacts due to wrong sign */
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if ( dist.distance > sp_sq ) continue;
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/* square_root the values and fit in a 6.10 fixed point */
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if ( USE_SQUARED_DISTANCES )
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dist.distance = square_root( dist.distance );
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if ( internal_params.flip_y )
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index = y * width + x;
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else
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index = ( rows - y - 1 ) * width + x;
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/* check weather the pixel is set or not */
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if ( dists[index].sign == 0 )
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dists[index] = dist;
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else if ( dists[index].distance > dist.distance )
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dists[index] = dist;
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else if ( FT_ABS(dists[index].distance - dist.distance ) < CORNER_CHECK_EPSILON )
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dists[index] = resolve_corner( dists[index], dist );
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}
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}
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edges = edges->next;
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}
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contours = contours->next;
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}
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/* final pass */
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for ( j = 0; j < rows; j++ )
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{
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/* We assume the starting pixel of each row */
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/* will be outside. */
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FT_Char current_sign = -1;
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FT_UInt index;
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if ( internal_params.overload_sign != 0 )
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current_sign = internal_params.overload_sign < 0 ? -1 : 1;
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for ( i = 0; i < width; i++ )
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{
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index = j * width + i;
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/* if the pixel is not set that means it's */
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/* shortest distance is more than spread */
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if ( dists[index].sign == 0 )
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dists[index].distance = FT_INT_16D16( spread );
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else
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current_sign = dists[index].sign;
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/* clamp the values */
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if ( dists[index].distance > FT_INT_16D16( spread ) )
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dists[index].distance = FT_INT_16D16( spread );
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/* convert from 16.16 to 6.10 */
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dists[index].distance /= 64;
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if ( internal_params.flip_sign )
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buffer[index] = (FT_Short)dists[index].distance * -current_sign;
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else
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buffer[index] = (FT_Short)dists[index].distance * current_sign;
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}
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}
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Exit:
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SDF_FREE( dists );
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return error;
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}
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/**************************************************************************
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*
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* @Function:
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* sdf_generate_subdivision
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*
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* @Description:
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* This function subdivide the shape into a number of straight lines
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* and then simply use the above `sdf_generate_bounding_box' to generate
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* the SDF.
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* Note: After calling this function the `shape' will no longer have the
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* original edges, it will only contain lines.
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*
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* @Input:
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* internal_params ::
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* Internal parameters and properties required by the rasterizer.
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* See `SDF_Params' for the actual parameters.
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*
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* shape ::
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* A complete shape which is used to generate SDF.
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*
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* spread ::
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* Maximum distances to be allowed inthe output bitmap.
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*
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* @Return
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* bitmap ::
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* The output bitmap which will contain the SDF information.
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*
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* FT_Error ::
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* FreeType error, 0 means success.
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*
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*/
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static FT_Error
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sdf_generate_subdivision( const SDF_Params internal_params,
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SDF_Shape* shape,
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FT_UInt spread,
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const FT_Bitmap* bitmap )
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{
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/* Thanks to Alexei for providing the idea of this optimization. */
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/* */
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/* This optimiztion mode take advantage of two facts: */
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/* */
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/* - Computing shortest distance froma point to a line segment */
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/* is super fast. */
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/* - We don't have to compute shortest distance for the entire */
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/* 2D grid. */
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/* */
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/* This is how it works: */
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/* */
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/* - We split the outlines into a number of line segments. */
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/* */
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/* - For each line segment we only process the neighborhood of */
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/* the line segment. */
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/* */
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/* - Now, only for the neighborhood grid points we compute the */
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/* closest distance to the line. */
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/* */
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/* - This way we do not have to check all grid points against */
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/* all the edges. Instead for each line's neighborhood we */
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/* only compute shortest distance for that one line only. */
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/* */
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/* All in all, it reduces the number of grid point to edge check */
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/* */
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FT_Error error = FT_Err_Ok;
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FT_CALL( split_sdf_shape( shape ) );
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FT_CALL( sdf_generate_bounding_box( internal_params,
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shape, spread, bitmap ) );
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Exit:
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return error;
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}
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/* END */
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