When the bounding boxes of a path and its clip are disjoint (i.e. they
do not intersect) the result of their intersection is a negative
rectangle.
When calculating the intersection of the bboxes, the binning stage
ensures that the bbox is non-negative. It then normalizes the
coordinates to bin dimensions and rounds the top-left corner down
to the neareast integer and the bottom-right corner up.
However this rounding causes zero-area bounding boxes to have a non-zero
area and sends the bottom-right corner to the placed in the next bin.
This causes fully clipped out draw objects to be included in binning,
with an incorrect clip bounding box that causes them to be erroneously
drawn with partial clipping.
`binning` now takes care around this logic to make sure that a zero-area
intersected-bbox gets skipped and clipped out. `tile_alloc`, also takes
care in its logic.
Fixes#286 and #333
Fixed several other shader validation errors caught when running
vello_shaders natively on Metal.
These were primarily caused by reading an invalid drawtag while
accessing the scene buffer. Scene buffer access in the offending
pipelines now initialize the draw tag to DRAWTAG_NOP if an
invocation ID would land beyond the valid index range of encoded draw
objects.
* Add counts to offsets when comparing against buffer size limits
* Remove multiplication by 4 in blend buffer allocation (we use units of u32)
* Move buffer sizes from BumpAllocators to Config
* Add comments about early exit
* Move the vello crate to the root of the crate
* Add warning that README is work in progress
* Add newline in warning
* Move the unlicense into the shader folder
* Fixup wgsl-analyzer include paths
