Previously, drawing an opaque, scaled component with CoreGraphics could
lead to visible artefacts around the edge of the component.
When drawing the parent of an opaque component, the area covered by the
opaque component is excluded from the clip region. If the clip region is
non-integral when transformed into device space, anti-aliasing will be
applied on the edges of the clip region. Similarly, when drawing the
opaque component itself, anti-aliasing will be applied at the edges of
the component. When the two drawings are superimposed, the foreground
anti-aliased pixels will be blended with the background anti-aliased
pixels, leading to a noticeable border around the component. Ideally,
only the foreground anti-aliasing should be applied, and the background
should not be anti-aliased around its edges.
Occasionally, on Linux, Address Sanitizer can complain about a memory
region overlap in the arguments to memcpy, originating in
EdgeTable::intersectWithEdgeTableLine. I haven't been able to reproduce
this personally.
The final memcpy call in this function requires there to be
"srcNum1 * 2" valid entries after the current "src1" ptr, and none of
those entries may overlap with the area starting at "temp".
On inspection, I think that the memory region being read is too large.
At the point of the call, src1 will point to a LineItem::level, not
LineItem::x, so there will actually be (srcNum1 * 2 - 1) valid items
following it.
All this pointer arithmetic is very difficult to understand. In an
effort to make this function slightly more understandable, I've switched
to using Spans to delineate lines of the table, which makes it easier to
keep track of the size of each line.
Previously, if the PathFlatteningIterator returned a line segment with
very large x or y positions, the result of
roundToInt (iter.y1 * 256.0f)
could be incorrect, if the result was too large to fit in an int.
Using int64_t to store intermediate results, converting to int when
updating the edge table itself produces accurate results for a wider
range of inputs.
