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//! Triangle scanline intersections iterator.
use crate::{
geometry::Point,
primitives::{
common::{LineJoin, PointType, Scanline, StrokeOffset, ThickSegment},
Triangle,
},
};
#[derive(Clone, Eq, PartialEq, Hash, Debug)]
struct LineConfig {
first: Scanline,
second: Scanline,
internal: Scanline,
internal_type: PointType,
}
/// Triangle scanline intersections iterator.
#[derive(Clone, Eq, PartialEq, Hash, Debug)]
pub struct ScanlineIntersections {
lines: LineConfig,
triangle: Triangle,
stroke_width: u32,
stroke_offset: StrokeOffset,
has_fill: bool,
is_collapsed: bool,
}
impl ScanlineIntersections {
/// Create a new thick segments iterator.
pub fn new(
triangle: &Triangle,
stroke_width: u32,
stroke_offset: StrokeOffset,
has_fill: bool,
scanline_y: i32,
) -> Self {
// Special case: If thick strokes completely fill the triangle interior and the stroke is
// inside the triangle, the normal triangle shape can be used to detect the intersection,
// with the line type being marked as Border so, when rendered, the correct color is used.
let is_collapsed = triangle.is_collapsed(stroke_width, stroke_offset)
&& stroke_offset == StrokeOffset::Right;
let mut self_ = Self {
has_fill,
triangle: *triangle,
stroke_offset,
stroke_width,
is_collapsed,
..Self::empty()
};
self_.reset_with_new_scanline(scanline_y);
self_
}
/// Empty.
pub const fn empty() -> Self {
Self {
lines: LineConfig {
first: Scanline::new_empty(0),
second: Scanline::new_empty(0),
internal: Scanline::new_empty(0),
internal_type: PointType::Fill,
},
has_fill: false,
triangle: Triangle::new(Point::zero(), Point::zero(), Point::zero()),
stroke_width: 0,
stroke_offset: StrokeOffset::None,
is_collapsed: false,
}
}
/// Reset with a new scanline.
pub fn reset_with_new_scanline(&mut self, scanline_y: i32) {
if let Some(lines) = self.generate_lines(scanline_y) {
self.lines = lines
}
}
fn edge_intersections(&self, scanline_y: i32) -> impl Iterator<Item = Scanline> + '_ {
let mut idx = 0;
let mut left = Scanline::new_empty(scanline_y);
let mut right = Scanline::new_empty(scanline_y);
core::iter::from_fn(move || {
if self.stroke_width == 0 {
return None;
}
while idx < 3 {
let start = LineJoin::from_points(
self.triangle.vertices[idx % 3],
self.triangle.vertices[(idx + 1) % 3],
self.triangle.vertices[(idx + 2) % 3],
self.stroke_width,
self.stroke_offset,
);
let end = LineJoin::from_points(
self.triangle.vertices[(idx + 1) % 3],
self.triangle.vertices[(idx + 2) % 3],
self.triangle.vertices[(idx + 3) % 3],
self.stroke_width,
self.stroke_offset,
);
idx += 1;
let scanline = ThickSegment::new(start, end).intersection(scanline_y);
if !left.is_empty() {
if left.try_extend(&scanline) {
continue;
}
} else {
left = scanline;
continue;
}
if !right.is_empty() {
right.try_extend(&scanline);
} else {
right = scanline;
}
}
// Merge any overlap between final left/right results
if left.try_extend(&right) {
right = Scanline::new_empty(scanline_y);
}
left.try_take().or_else(|| right.try_take())
})
}
fn generate_lines(&self, scanline_y: i32) -> Option<LineConfig> {
let mut edge_intersections = self.edge_intersections(scanline_y);
if self.is_collapsed {
Some(LineConfig {
internal: self.triangle.scanline_intersection(scanline_y),
internal_type: PointType::Stroke,
first: Scanline::new_empty(0),
second: Scanline::new_empty(0),
})
} else {
let first = edge_intersections.next();
// For scanlines that are parallel with and are inside one edge, this should be None.
let second = edge_intersections.next();
// If there are two intersections, this must mean we've traversed across the center of the
// triangle (assuming the edge line merging logic is correct). In this case, we need a
// scanline between the two edge intersections.
let internal = if self.has_fill {
match (&first, &second) {
// Triangle stroke is non-zero, so the fill line is between the insides of each
// stroke.
(Some(first), Some(second)) => {
let start_x = first.x.end.min(second.x.end);
let end_x = first.x.start.max(second.x.start);
Scanline {
x: start_x..end_x,
y: scanline_y,
}
}
// Triangles with no stroke intersections and a fill color.
(None, None) => self.triangle.scanline_intersection(scanline_y),
// Because a triangle is a closed shape, a single intersection here likely means
// we're inside one of the borders, so no fill should be returned for this
// scanline.
_ => Scanline::new_empty(scanline_y),
}
} else {
Scanline::new_empty(scanline_y)
};
Some(LineConfig {
first: first.unwrap_or(Scanline::new_empty(scanline_y)),
second: second.unwrap_or(Scanline::new_empty(scanline_y)),
internal,
internal_type: PointType::Fill,
})
}
}
}
impl Iterator for ScanlineIntersections {
type Item = (Scanline, PointType);
fn next(&mut self) -> Option<Self::Item> {
if let Some(internal) = self.lines.internal.try_take() {
Some((internal, self.lines.internal_type))
} else if let Some(first) = self.lines.first.try_take() {
Some((first, PointType::Stroke))
} else if let Some(second) = self.lines.second.try_take() {
Some((second, PointType::Stroke))
} else {
None
}
}
}