- // We need to make sure that the SVP we now have bounds an area (i.e. the
- // source line wound anticlockwise) rather than excludes an area (i.e. the
- // line wound clockwise). It seems that PDF (or xpdf) is less strict about
- // this for bitmaps than it is for fill areas.
- //
- // To check this, we'll sum the cross products of all pairs of adjacent
- // lines. If the result is positive, the direction is correct; if not, we
- // need to reverse the sense of the SVP generated. The easiest way to do
- // this is to flip the up/down flags of all the segments.
- //
- // This is approximate; since the gfxline_t structure can contain any
- // combination of moveTo, lineTo and splineTo in any order, not all pairs
- // of lines in the shape that share a point need be described next to each
- // other in the sequence. For ease, we'll consider only pairs of lines
- // stored as lineTos and splineTos without intervening moveTos.
- //
- // TODO is this a valid algorithm? My vector maths is rusty.
- //
- // It may be more correct to instead reverse the line before we feed it
- // into gfxfilltoSVP. However, this seems equivalent and is easier to
- // implement!
- double total_cross_product = 0.0;
- gfxline_t* cursor = line;
- if (cursor != NULL)
- {
- double x_last = cursor->x;
- double y_last = cursor->y;
- cursor = cursor->next;
-
- while((cursor != NULL) && (cursor->next != NULL))
- {
- if (((cursor->type == gfx_lineTo) || (cursor->type == gfx_splineTo))
- && ((cursor->next->type == gfx_lineTo) || (cursor->next->type == gfx_splineTo)))
- {
- // Process these lines
- //
- // In this space (x right, y down) the cross-product is
- // (x1 * y0) - (x0 * y1)
- double x0 = cursor->x - x_last;
- double y0 = cursor->y - y_last;
- double x1 = cursor->next->x - cursor->x;
- double y1 = cursor->next->y - cursor->y;
- total_cross_product += (x1 * y0) - (x0 * y1);
- }
-
- x_last = cursor->x;
- y_last = cursor->y;
- cursor = cursor->next;
- }
- }
- if (total_cross_product < 0.0)
- {
- int i = 0;
- for(; i < svp->n_segs; ++i)
- {
- if (svp->segs[i].dir != 0)
- svp->segs[i].dir = 0;
- else
- svp->segs[i].dir = 1;
- }
- }
-