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// Copyright 2025 Lars Brubaker
// License: SGI Free Software License B (MIT-compatible)
//
//! The sweep-line event driver.
//!
//! Core of `tess/sweep.rs` (libtess2 sweep.c): `sweep_event` dispatches
//! each event to the connect / dirty-region machinery, while
//! `add_right_edges` and `finish_left_regions` splice the new and
//! finished edges into the active region structure around it.
use crate::geom::{vert_leq};
use crate::mesh::{EdgeIdx, INVALID, VertIdx};
use super::{Tessellator, RegionIdx};
impl Tessellator {
pub(super) fn finish_left_regions(&mut self, reg_first: RegionIdx, reg_last: RegionIdx) -> EdgeIdx {
let mut reg_prev = reg_first;
let mut e_prev = self.region(reg_first).e_up;
while reg_prev != reg_last {
self.region_mut(reg_prev).fix_upper_edge = false;
let reg = self.region_below(reg_prev);
if reg == INVALID {
break;
}
let mut e = self.region(reg).e_up;
let e_org = if e != INVALID {
self.mesh.as_ref().unwrap().edges[e as usize].org
} else {
INVALID
};
let ep_org = if e_prev != INVALID {
self.mesh.as_ref().unwrap().edges[e_prev as usize].org
} else {
INVALID
};
if e_org != ep_org {
if !self.region(reg).fix_upper_edge {
self.finish_region(reg_prev);
break;
}
let ep_lprev = if e_prev != INVALID {
self.mesh.as_ref().unwrap().lprev(e_prev)
} else {
INVALID
};
let e_sym = if e != INVALID { e ^ 1 } else { INVALID };
let new_e = if ep_lprev != INVALID && e_sym != INVALID {
self.mesh.as_mut().unwrap().connect(ep_lprev, e_sym)
} else {
None
};
if let Some(ne) = new_e {
if !self.fix_upper_edge(reg, ne) {
return INVALID;
}
// C: `e = tessMeshConnect(...)` — the relink splice below must
// operate on the newly connected edge, not the old `e`. Not
// reassigning here spliced the wrong edge, corrupting the mesh
// topology (found by differential test vs. the C reference).
e = ne;
}
}
if e_prev != INVALID && e != INVALID {
let ep_onext = self.mesh.as_ref().unwrap().edges[e_prev as usize].onext;
if ep_onext != e {
let e_oprev = self.mesh.as_ref().unwrap().oprev(e);
self.mesh.as_mut().unwrap().splice(e_oprev, e);
self.mesh.as_mut().unwrap().splice(e_prev, e);
}
}
self.finish_region(reg_prev);
e_prev = self.region(reg).e_up;
reg_prev = reg;
}
e_prev
}
pub(super) fn add_right_edges(
&mut self,
reg_up: RegionIdx,
e_first: EdgeIdx,
e_last: EdgeIdx,
e_top_left: EdgeIdx,
clean_up: bool,
) {
// Insert right-going edges into the dictionary. Guard: the
// onext ring must contain e_last; if it doesn't (degenerate
// mesh), break early rather than looping forever. libtess2's
// C original asserts `VertLeq(e->Org, e->Dst)` — i.e., `e` is
// right-going from the event vertex — and our previous Rust
// port silently accepted any orientation, so a degenerate
// input could push an edge whose SYM was already an active
// region's `e_up` into the ring. `add_region_below` then
// bound both halves of the same edge pair to two different
// regions; `walk_dirty_regions`'s degenerate-2-edge-loop
// branch later `delete_edge`d the pair from under one of
// them, leaving its e_up dangling and producing the wasm-only
// `mesh.verts[INVALID]` panic in `check_for_right_splice` /
// `walk_dirty_regions`. See `tests/wasm_glyph_repro.rs`.
let max_edge_iters = self.mesh.as_ref().unwrap().edges.len() + 2;
let mut e = e_first;
let mut edge_iter = 0usize;
loop {
// Right-going invariant + duplicate-pair guard. Either
// condition means the edge isn't a fresh right-going
// edge of the event vertex and must be skipped.
let skip = {
let mesh = self.mesh.as_ref().unwrap();
let org = mesh.edges[e as usize].org;
let dst = mesh.dst(e);
let not_right_going = org != INVALID
&& dst != INVALID
&& !vert_leq(
mesh.verts[org as usize].s,
mesh.verts[org as usize].t,
mesh.verts[dst as usize].s,
mesh.verts[dst as usize].t,
);
let sym_already_bound =
mesh.edges[(e ^ 1) as usize].active_region != INVALID;
not_right_going || sym_already_bound
};
if !skip {
self.add_region_below(reg_up, e ^ 1);
}
e = self.mesh.as_ref().unwrap().edges[e as usize].onext;
if e == e_last {
break;
}
edge_iter += 1;
if edge_iter > max_edge_iters {
break; // degenerate onext ring — skip remaining edges
}
}
// Determine e_top_left
let e_top_left = if e_top_left == INVALID {
let reg_below = self.region_below(reg_up);
if reg_below == INVALID {
return;
}
let rb_e = self.region(reg_below).e_up;
if rb_e == INVALID {
return;
}
self.mesh.as_ref().unwrap().rprev(rb_e)
} else {
e_top_left
};
let mut reg_prev = reg_up;
let mut e_prev = e_top_left;
let mut first_time = true;
let max_reg_iters = self.regions.len() + 2;
let mut reg_iter2 = 0usize;
loop {
let reg = self.region_below(reg_prev);
if reg == INVALID {
break;
}
let e = {
let re = self.region(reg).e_up;
if re == INVALID {
break;
}
re ^ 1 // e = reg->eUp->Sym
};
let e_org = self.mesh.as_ref().unwrap().edges[e as usize].org;
let ep_org = if e_prev != INVALID {
self.mesh.as_ref().unwrap().edges[e_prev as usize].org
} else {
INVALID
};
if e_org != ep_org {
break;
}
reg_iter2 += 1;
if reg_iter2 > max_reg_iters {
break; // degenerate region chain
}
if e_prev != INVALID {
// C: if( e->Onext != ePrev ) { splice(e->Oprev, e); splice(ePrev->Oprev, e); }
let e_onext = self.mesh.as_ref().unwrap().edges[e as usize].onext;
if e_onext != e_prev {
let e_oprev = self.mesh.as_ref().unwrap().oprev(e);
self.mesh.as_mut().unwrap().splice(e_oprev, e);
let ep_oprev = self.mesh.as_ref().unwrap().oprev(e_prev);
self.mesh.as_mut().unwrap().splice(ep_oprev, e);
}
}
let above_winding = self.region(reg_prev).winding_number;
let e_winding = self.mesh.as_ref().unwrap().edges[e as usize].winding;
let new_winding = above_winding - e_winding;
let inside = self.is_winding_inside(new_winding);
self.region_mut(reg).winding_number = new_winding;
self.region_mut(reg).inside = inside;
if self.trace_enabled {
eprintln!("R ARE winding={new_winding} inside={}", inside as i32);
}
self.region_mut(reg_prev).dirty = true;
if !first_time {
let cfrs = self.check_for_right_splice(reg_prev);
if self.trace_enabled {
eprintln!("R ARE_CFRS={}", cfrs as i32);
}
if cfrs {
// AddWinding
let re = self.region(reg).e_up;
let rep = self.region(reg_prev).e_up;
if re != INVALID && rep != INVALID {
let w1 = self.mesh.as_ref().unwrap().edges[re as usize].winding;
let w2 = self.mesh.as_ref().unwrap().edges[(re ^ 1) as usize].winding;
let wp1 = self.mesh.as_ref().unwrap().edges[rep as usize].winding;
let wp2 = self.mesh.as_ref().unwrap().edges[(rep ^ 1) as usize].winding;
self.mesh.as_mut().unwrap().edges[re as usize].winding += wp1;
self.mesh.as_mut().unwrap().edges[(re ^ 1) as usize].winding += wp2;
}
self.delete_region(reg_prev);
if e_prev != INVALID {
self.mesh.as_mut().unwrap().delete_edge(e_prev);
}
}
}
first_time = false;
reg_prev = reg;
e_prev = e;
}
self.region_mut(reg_prev).dirty = true;
if clean_up {
self.walk_dirty_regions(reg_prev);
}
}
pub(super) fn sweep_event(&mut self, v_event: VertIdx) -> bool {
let an_edge = self.mesh.as_ref().unwrap().verts[v_event as usize].an_edge;
if an_edge == INVALID {
return true;
}
if self.trace_enabled {
let (vs, vt) = (
self.mesh.as_ref().unwrap().verts[v_event as usize].s,
self.mesh.as_ref().unwrap().verts[v_event as usize].t,
);
eprintln!(
"R SWEEP #{} s={:.6} t={:.6}",
self.sweep_event_num, vs, vt
);
self.sweep_event_num += 1;
}
// Walk through all edges at v_event (the onext ring).
// If ANY has active_region != INVALID, it's already in the dict -> "right vertex" case.
// If NONE has active_region set -> call connect_left_vertex (C: ConnectLeftVertex).
let e_start = an_edge;
let mut e = e_start;
let found_e = loop {
let ar = self.mesh.as_ref().unwrap().edges[e as usize].active_region;
if ar != INVALID {
break Some(e);
}
let next = self.mesh.as_ref().unwrap().edges[e as usize].onext;
e = next;
if e == e_start {
break None;
}
};
if found_e.is_none() {
if self.trace_enabled {
eprintln!("R PATH left");
}
self.connect_left_vertex(v_event);
return true;
}
// At least one edge is already in the dict.
let e = found_e.unwrap();
if self.trace_enabled {
eprintln!("R PATH right");
}
let reg_up = {
let ar = self.mesh.as_ref().unwrap().edges[e as usize].active_region;
self.top_left_region(ar)
};
if reg_up == INVALID {
return false;
}
let reg_lo = self.region_below(reg_up);
if reg_lo == INVALID {
return true;
}
let e_top_left = self.region(reg_lo).e_up;
let e_bottom_left = self.finish_left_regions(reg_lo, INVALID);
if e_bottom_left == INVALID {
return true;
}
let e_bottom_left_onext = self.mesh.as_ref().unwrap().edges[e_bottom_left as usize].onext;
if e_bottom_left_onext == e_top_left {
if self.trace_enabled {
eprintln!("R CONNECT_RIGHT");
}
self.connect_right_vertex(reg_up, e_bottom_left);
} else {
if self.trace_enabled {
eprintln!("R ADD_RIGHT_EDGES");
}
self.add_right_edges(reg_up, e_bottom_left_onext, e_top_left, e_top_left, true);
}
true
}
}