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Address review comments
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@armansito
armansito committed Nov 13, 2023
1 parent 3df413a commit eded0a1
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Showing 3 changed files with 56 additions and 40 deletions.
76 changes: 46 additions & 30 deletions crates/encoding/src/path.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -444,10 +444,10 @@ impl<'a> PathEncoder<'a> {
/// segment tells the GPU stroker whether to draw a cap or a join based on the topology of the
/// path:
///
/// 1. This marker segment is encoded as a `quad-to` for an open path and a `line-to` for a
/// closed path. An open path gets drawn with a start and end cap. A closed path gets drawn
/// with a single join in place of the caps where the subpath's start and end control points
/// meet.
/// 1. This marker segment is encoded as a `quad-to` (2 additional points) for an open path and
/// a `line-to` (1 additional point) for a closed path. An open path gets drawn with a start
/// and end cap. A closed path gets drawn with a single join in place of the caps where the
/// subpath's start and end control points meet.
///
/// 2. The marker segment tells the GPU flattening stage how to render caps and joins while
/// processing each path segment in parallel. All subpaths end with the marker segment which
Expand Down Expand Up @@ -523,15 +523,13 @@ impl<'a> PathEncoder<'a> {
self.move_to(self.first_point[0], self.first_point[1]);
}
if self.state == PathState::MoveTo {
let x0 = self.first_point[0];
let y0 = self.first_point[1];
let p0 = (self.first_point[0], self.first_point[1]);
// Ensure that we don't end up with a zero-length start tangent.
const EPS: f32 = 1e-12;
if (x - x0).abs() < EPS && (y - y0).abs() < EPS {
let Some((x, y)) = start_tangent_for_curve(p0, (x, y), p0, p0) else {
// Drop the segment if its length is zero
// TODO: do this for all not segments, not just start?
// TODO: do this for all not segments, not just start.
return;
}
};
self.first_start_tangent_end = [x, y];
}
let buf = [x, y];
Expand All @@ -552,17 +550,11 @@ impl<'a> PathEncoder<'a> {
self.move_to(self.first_point[0], self.first_point[1]);
}
if self.state == PathState::MoveTo {
let x0 = self.first_point[0];
let y0 = self.first_point[1];
let p0 = (self.first_point[0], self.first_point[1]);
// Ensure that we don't end up with a zero-length start tangent.
const EPS: f32 = 1e-12;
let (x, y) = if (x1 - x0).abs() > EPS || (y1 - y0).abs() > EPS {
(x1, y1)
} else if (x2 - x0).abs() > EPS || (y2 - y0).abs() > EPS {
(x2, y2)
} else {
let Some((x, y)) = start_tangent_for_curve(p0, (x1, y1), (x2, y2), p0) else {
// Drop the segment if its length is zero
// TODO: do this for all not segments, not just start?
// TODO: do this for all not segments, not just start.
return;
};
self.first_start_tangent_end = [x, y];
Expand All @@ -585,19 +577,11 @@ impl<'a> PathEncoder<'a> {
self.move_to(self.first_point[0], self.first_point[1]);
}
if self.state == PathState::MoveTo {
let x0 = self.first_point[0];
let y0 = self.first_point[1];
let p0 = (self.first_point[0], self.first_point[1]);
// Ensure that we don't end up with a zero-length start tangent.
const EPS: f32 = 1e-12;
let (x, y) = if (x1 - x0).abs() > EPS || (y1 - y0).abs() > EPS {
(x1, y1)
} else if (x2 - x0).abs() > EPS || (y2 - y0).abs() > EPS {
(x2, y2)
} else if (x3 - x0).abs() > EPS || (y3 - y0).abs() > EPS {
(x3, y3)
} else {
let Some((x, y)) = start_tangent_for_curve(p0, (x1, y1), (x2, y2), (x3, y3)) else {
// Drop the segment if its length is zero
// TODO: do this for all not segments, not just start?
// TODO: do this for all not segments, not just start.
return;
};
self.first_start_tangent_end = [x, y];
Expand Down Expand Up @@ -739,6 +723,38 @@ impl fello::scale::Pen for PathEncoder<'_> {
}
}

// Returns the end point of the start tangent of a curve starting at `(x0, y0)`, or `None` if the
// curve is degenerate / has zero-length. The inputs are a sequence of control points that can
// represent a line, a quadratic Bezier, or a cubic Bezier. Lines and quadratic Beziers can be
// passed to this function by simply setting the invalid control point degrees equal to `(x0, y0)`.
fn start_tangent_for_curve(
p0: (f32, f32),
p1: (f32, f32),
p2: (f32, f32),
p3: (f32, f32),
) -> Option<(f32, f32)> {
debug_assert!(!p0.0.is_nan());
debug_assert!(!p0.1.is_nan());
debug_assert!(!p1.0.is_nan());
debug_assert!(!p1.1.is_nan());
debug_assert!(!p2.0.is_nan());
debug_assert!(!p2.1.is_nan());
debug_assert!(!p3.0.is_nan());
debug_assert!(!p3.1.is_nan());

const EPS: f32 = 1e-12;
let pt = if (p1.0 - p0.0).abs() > EPS || (p1.1 - p0.1).abs() > EPS {
p1
} else if (p2.0 - p0.0).abs() > EPS || (p2.1 - p0.1).abs() > EPS {
p2
} else if (p3.0 - p0.0).abs() > EPS || (p3.1 - p0.1).abs() > EPS {
p3
} else {
return None;
};
Some(pt)
}

#[cfg(test)]
mod tests {
use super::*;
Expand Down
14 changes: 7 additions & 7 deletions shader/flatten.wgsl
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Original file line number Diff line number Diff line change
Expand Up @@ -153,7 +153,7 @@ fn flatten_cubic(cubic: Cubic) {

// HACK: this increase subdivision count as function of the stroke width for shitty strokes.
var tol = sqrt(REM_ACCURACY);
if cubic.flags == 1u {
if cubic.flags == CUBIC_IS_STROKE {
tol *= min(1000., dot(cubic.stroke, cubic.stroke));
}
let params = estimate_subdiv(qp0, qp1, qp2, tol);
Expand Down Expand Up @@ -302,7 +302,7 @@ fn read_path_segment(tag: PathTagData, transform: Transform, is_stroke: bool) ->

var seg_type = tag.tag_byte & PATH_TAG_SEG_TYPE;
let pathseg_offset = tag.monoid.pathseg_offset;
let is_stroke_cap_marker = is_stroke && (tag.tag_byte & PATH_TAG_SUBPATH_END_BIT) != 0u;
let is_stroke_cap_marker = is_stroke && (tag.tag_byte & PATH_TAG_SUBPATH_END) != 0u;
let is_open = seg_type == PATH_TAG_QUADTO;

if (tag.tag_byte & PATH_TAG_F32) != 0u {
Expand Down Expand Up @@ -331,7 +331,7 @@ fn read_path_segment(tag: PathTagData, transform: Transform, is_stroke: bool) ->
// is ignored.
//
// This is encoded this way because encoding this as a lineto would require adding a moveto,
// which would terminate the subpath too early (by setting the SUBPATH_END_BIT on the
// which would terminate the subpath too early (by setting the SUBPATH_END on the
// segment preceding the cap marker). This scheme is only used for strokes.
p0 = transform_apply(transform, p1);
p1 = transform_apply(transform, p2);
Expand Down Expand Up @@ -374,7 +374,7 @@ fn read_neighboring_segment(ix: u32) -> NeighboringSegment {
let pts = read_path_segment(tag, transform, true);

let is_closed = (tag.tag_byte & PATH_TAG_SEG_TYPE) == PATH_TAG_LINETO;
let is_stroke_cap_marker = (tag.tag_byte & PATH_TAG_SUBPATH_END_BIT) != 0u;
let is_stroke_cap_marker = (tag.tag_byte & PATH_TAG_SUBPATH_END) != 0u;
let do_join = !is_stroke_cap_marker || is_closed;
let p0 = pts.p0;
let tangent = cubic_start_tangent(pts.p0, pts.p1, pts.p2, pts.p3);
Expand All @@ -397,15 +397,15 @@ fn main(
let out = &path_bboxes[path_ix];
let style_flags = scene[config.style_base + style_ix];
// The fill bit is always set to 0 for strokes which represents a non-zero fill.
let draw_flags = select(DRAW_INFO_FLAGS_FILL_RULE_BIT, 0u, (style_flags & STYLE_FLAGS_FILL_BIT) == 0u);
let draw_flags = select(DRAW_INFO_FLAGS_FILL_RULE_BIT, 0u, (style_flags & STYLE_FLAGS_FILL) == 0u);
if (tag.tag_byte & PATH_TAG_PATH) != 0u {
(*out).draw_flags = draw_flags;
(*out).trans_ix = trans_ix;
}
// Decode path data
let seg_type = tag.tag_byte & PATH_TAG_SEG_TYPE;
if seg_type != 0u {
let is_stroke = (style_flags & STYLE_FLAGS_STYLE_BIT) != 0u;
let is_stroke = (style_flags & STYLE_FLAGS_STYLE) != 0u;
let transform = read_transform(config.transform_base, trans_ix);
let pts = read_path_segment(tag, transform, is_stroke);
var bbox = vec4(min(pts.p0, pts.p1), max(pts.p0, pts.p1));
Expand All @@ -421,7 +421,7 @@ fn main(
stroke = 0.5 * linewidth * vec2(length(transform.mat.xz), length(transform.mat.yw));
bbox += vec4(-stroke, stroke);
let is_open = (tag.tag_byte & PATH_TAG_SEG_TYPE) != PATH_TAG_LINETO;
let is_stroke_cap_marker = (tag.tag_byte & PATH_TAG_SUBPATH_END_BIT) != 0u;
let is_stroke_cap_marker = (tag.tag_byte & PATH_TAG_SUBPATH_END) != 0u;
if is_stroke_cap_marker {
if is_open {
let n = cubic_start_normal(pts.p0, pts.p1, pts.p2, pts.p3) * stroke;
Expand Down
6 changes: 3 additions & 3 deletions shader/shared/pathtag.wgsl
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Original file line number Diff line number Diff line change
Expand Up @@ -21,12 +21,12 @@ let PATH_TAG_TRANSFORM = 0x20u;
let PATH_TAG_PATH = 0x10u;
let PATH_TAG_STYLE = 0x40u;
#endif
let PATH_TAG_SUBPATH_END_BIT = 4u;
let PATH_TAG_SUBPATH_END = 4u;

// Size of the `Style` data structure in words
let STYLE_SIZE_IN_WORDS: u32 = 2u;
let STYLE_FLAGS_STYLE_BIT: u32 = 0x80000000u;
let STYLE_FLAGS_FILL_BIT: u32 = 0x40000000u;
let STYLE_FLAGS_STYLE: u32 = 0x80000000u;
let STYLE_FLAGS_FILL: u32 = 0x40000000u;

// TODO: Declare the remaining STYLE flags here.

Expand Down

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