On 2021-02-16 05:55, Richard Gaskin via use-livecode wrote:
My expectation was almost beyond anything reasonable, but it would
seem useful if there was some way to make it happen: imagine if each
segment within a list of discontiguous points was rendered as though
it's a separate object, back to front.
It's not going to kill me to use separate graphics to hide the
portions of the vertices I need covered, but it sure would have been
nifty if I'd found a way to have a single poly object render as though
it were many.
So the even-odd fill rule will not give you what you want - overlapping
regions alternate.
The non-zero fill rule can give you what you want - but you need to make
sure that all your sub-polygons go 'in the same direction'. (NB: Fixed
width font ASCII art follows):
These two overlapping rects both go clock-wise so everything is filled.
|--->---|
|.......|
|...|--->---|
^...|...|...|
|...|...|...|
|-- |---|...v
|.......|
|-------|
The left rect goes anti-clockwise and the right rect goes clockwise:
|---<---|
|.......|
|...|--->---|
v...| |...|
|...| |...|
|-- |---|...v
|.......|
|-------|
Notionally:
- the non-zero winding rule works by starting on the left of each
scanline and scanning to the right
- there is a winding counter which starts at 0.
- at any pixel, if the winding counter is non-zero the pixel is
filled.
- if an edge is crossed which goes 'down', the winding counter is
decreased
- if an edge is crossed which goes 'up', the winding counter is
increased
Hope this helps!
Warmest Regards,
Mark.
--
Mark Waddingham ~ m...@livecode.com ~ http://www.livecode.com/
LiveCode: Everyone can create apps
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