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Move numerical robustness into tiling
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Change representation to tile-relative coordinates for segment endpoints.
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@raphlinus
raphlinus committed Nov 1, 2023
1 parent faf288a commit 6f2a83e
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Showing 6 changed files with 118 additions and 90 deletions.
4 changes: 2 additions & 2 deletions crates/encoding/src/path.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -207,8 +207,8 @@ pub struct SegmentCount {
#[derive(Clone, Copy, Debug, Zeroable, Pod, Default)]
#[repr(C)]
pub struct PathSegment {
pub origin: [f32; 2],
pub delta: [f32; 2],
pub point0: [f32; 2],
pub point1: [f32; 2],
pub y_edge: f32,
pub _padding: u32,
}
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84 changes: 32 additions & 52 deletions shader/fine.wgsl
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Original file line number Diff line number Diff line change
Expand Up @@ -162,29 +162,18 @@ fn fill_path_ms(fill: CmdFill, local_id: vec2<u32>, result: ptr<function, array<
// TODO: might save a register rewriting this in terms of limit
if th_ix < slice_size {
let segment = segments[seg_off];
let xy0 = segment.origin;
let xy1 = xy0 + segment.delta;
let xy0 = segment.point0;
let xy1 = segment.point1;
var y_edge_f = f32(TILE_HEIGHT);
var delta = select(-1, 1, xy1.x <= xy0.x);
if xy0.x == 0.0 && xy1.x == 0.0 {
if xy0.y == 0.0 {
y_edge_f = 0.0;
} else if xy1.y == 0.0 {
y_edge_f = 0.0;
delta = -delta;
}
} else {
if xy0.x == 0.0 {
if xy0.y != 0.0 {
y_edge_f = xy0.y;
}
} else if xy1.x == 0.0 && xy1.y != 0.0 {
y_edge_f = xy1.y;
}
// discard horizontal lines aligned to pixel grid
if !(xy0.y == xy1.y && xy0.y == floor(xy0.y)) {
count = span(xy0.x, xy1.x) + span(xy0.y, xy1.y) - 1u;
}
if xy0.x == 0.0 {
y_edge_f = xy0.y;
} else if xy1.x == 0.0 {
y_edge_f = xy1.y;
}
// discard horizontal lines aligned to pixel grid
if !(xy0.y == xy1.y && xy0.y == floor(xy0.y)) {
count = span(xy0.x, xy1.x) + span(xy0.y, xy1.y) - 1u;
}
let y_edge = u32(ceil(y_edge_f));
if y_edge < TILE_HEIGHT {
Expand Down Expand Up @@ -222,8 +211,8 @@ fn fill_path_ms(fill: CmdFill, local_id: vec2<u32>, result: ptr<function, array<
let seg_off = fill.seg_data + batch * WG_SIZE + el_ix;
let segment = segments[seg_off];
// Coordinates are relative to tile origin
let xy0_in = segment.origin;
let xy1_in = xy0_in + segment.delta;
let xy0_in = segment.point0;
let xy1_in = segment.point1;
let is_down = xy1_in.y >= xy0_in.y;
let xy0 = select(xy1_in, xy0_in, is_down);
let xy1 = select(xy0_in, xy1_in, is_down);
Expand Down Expand Up @@ -514,27 +503,17 @@ fn fill_path_ms_evenodd(fill: CmdFill, local_id: vec2<u32>, result: ptr<function
if th_ix < slice_size {
let segment = segments[seg_off];
// Coordinates are relative to tile origin
let xy0 = segment.origin;
let xy1 = xy0 + segment.delta;
let xy0 = segment.point0;
let xy1 = segment.point1;
var y_edge_f = f32(TILE_HEIGHT);
if xy0.x == 0.0 && xy1.x == 0.0 {
if xy0.y == 0.0 {
y_edge_f = 0.0;
} else if xy1.y == 0.0 {
y_edge_f = 0.0;
}
} else {
if xy0.x == 0.0 {
if xy0.y != 0.0 {
y_edge_f = xy0.y;
}
} else if xy1.x == 0.0 && xy1.y != 0.0 {
y_edge_f = xy1.y;
}
// discard horizontal lines aligned to pixel grid
if !(xy0.y == xy1.y && xy0.y == floor(xy0.y)) {
count = span(xy0.x, xy1.x) + span(xy0.y, xy1.y) - 1u;
}
if xy0.x == 0.0 {
y_edge_f = xy0.y;
} else if xy1.x == 0.0 {
y_edge_f = xy1.y;
}
// discard horizontal lines aligned to pixel grid
if !(xy0.y == xy1.y && xy0.y == floor(xy0.y)) {
count = span(xy0.x, xy1.x) + span(xy0.y, xy1.y) - 1u;
}
let y_edge = u32(ceil(y_edge_f));
if y_edge < TILE_HEIGHT {
Expand Down Expand Up @@ -571,8 +550,8 @@ fn fill_path_ms_evenodd(fill: CmdFill, local_id: vec2<u32>, result: ptr<function
let sub_ix = i - select(0u, sh_count[el_ix - 1u], el_ix > 0u);
let seg_off = fill.seg_data + batch * WG_SIZE + el_ix;
let segment = segments[seg_off];
let xy0_in = segment.origin;
let xy1_in = xy0_in + segment.delta;
let xy0_in = segment.point0;
let xy1_in = segment.point1;
let is_down = xy1_in.y >= xy0_in.y;
let xy0 = select(xy1_in, xy0_in, is_down);
let xy1 = select(xy0_in, xy1_in, is_down);
Expand Down Expand Up @@ -807,17 +786,18 @@ fn fill_path(fill: CmdFill, xy: vec2<f32>, result: ptr<function, array<f32, PIXE
for (var i = 0u; i < n_segs; i++) {
let seg_off = fill.seg_data + i;
let segment = segments[seg_off];
let y = segment.origin.y - xy.y;
let y = segment.point0.y - xy.y;
let delta = segment.point1 - segment.point0;
let y0 = clamp(y, 0.0, 1.0);
let y1 = clamp(y + segment.delta.y, 0.0, 1.0);
let y1 = clamp(y + delta.y, 0.0, 1.0);
let dy = y0 - y1;
if dy != 0.0 {
let vec_y_recip = 1.0 / segment.delta.y;
let vec_y_recip = 1.0 / delta.y;
let t0 = (y0 - y) * vec_y_recip;
let t1 = (y1 - y) * vec_y_recip;
let startx = segment.origin.x - xy.x;
let x0 = startx + t0 * segment.delta.x;
let x1 = startx + t1 * segment.delta.x;
let startx = segment.point0.x - xy.x;
let x0 = startx + t0 * delta.x;
let x1 = startx + t1 * delta.x;
let xmin0 = min(x0, x1);
let xmax0 = max(x0, x1);
for (var i = 0u; i < PIXELS_PER_THREAD; i += 1u) {
Expand All @@ -831,7 +811,7 @@ fn fill_path(fill: CmdFill, xy: vec2<f32>, result: ptr<function, array<f32, PIXE
area[i] += a * dy;
}
}
let y_edge = sign(segment.delta.x) * clamp(xy.y - segment.y_edge + 1.0, 0.0, 1.0);
let y_edge = sign(delta.x) * clamp(xy.y - segment.y_edge + 1.0, 0.0, 1.0);
for (var i = 0u; i < PIXELS_PER_THREAD; i += 1u) {
area[i] += y_edge;
}
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41 changes: 32 additions & 9 deletions shader/path_tiling.wgsl
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Original file line number Diff line number Diff line change
Expand Up @@ -120,19 +120,42 @@ fn main(
xy1 = vec2(x_clip, yt);
}
}
// See comments in CPU version of shader
var y_edge = 1e9;
if xy0.x == tile_xy.x && xy1.x != tile_xy.x && xy0.y != tile_xy.y {
y_edge = xy0.y;
} else if xy1.x == tile_xy.x && xy1.y != tile_xy.y {
y_edge = xy1.y;
// Apply numerical robustness logic
var p0 = xy0 - tile_xy;
var p1 = xy1 - tile_xy;
// When we move to f16, this will be f16::MIN_POSITIVE
let EPSILON = 1e-6;
if p0.x == 0.0 {
if p1.x == 0.0 {
p0.x = EPSILON;
if p0.y == 0.0 {
// Entire tile
p1.x = EPSILON;
p1.y = f32(TILE_HEIGHT);
} else {
// Make segment disappear
p1.x = 2.0 * EPSILON;
p1.y = p0.y;
}
} else if p0.y == 0.0 {
p0.x = EPSILON;
} else {
y_edge = p0.y;
}
} else if p1.x == 0.0 {
if p1.y == 0.0 {
p1.x = EPSILON;
} else {
y_edge = p1.y;
}
}
if !is_down {
let tmp = xy0;
xy0 = xy1;
xy1 = tmp;
let tmp = p0;
p0 = p1;
p1 = tmp;
}
let segment = Segment(xy0 - tile_xy, xy1 - xy0, y_edge - tile_xy.y);
let segment = Segment(p0, p1, y_edge);
segments[seg_start + seg_within_slice] = segment;
}
}
5 changes: 3 additions & 2 deletions shader/shared/segment.wgsl
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Original file line number Diff line number Diff line change
Expand Up @@ -2,8 +2,9 @@

// Segments laid out for contiguous storage
struct Segment {
origin: vec2<f32>,
delta: vec2<f32>,
// Points are relative to tile origin
point0: vec2<f32>,
point1: vec2<f32>,
y_edge: f32,
}

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20 changes: 12 additions & 8 deletions src/cpu_shader/fine.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -58,20 +58,24 @@ fn fill_path(area: &mut [f32], segments: &[PathSegment], fill: &CmdFill, x_tile:
*a = backdrop_f;
}
for segment in &segments[fill.seg_data as usize..][..n_segs as usize] {
let delta = [
segment.point1[0] - segment.point0[0],
segment.point1[1] - segment.point0[1],
];
for yi in 0..TILE_HEIGHT {
let y = segment.origin[1] - (y_tile + yi as f32);
let y = segment.point0[1] - (y_tile + yi as f32);
let y0 = y.clamp(0.0, 1.0);
let y1 = (y + segment.delta[1]).clamp(0.0, 1.0);
let y1 = (y + delta[1]).clamp(0.0, 1.0);
let dy = y0 - y1;
let y_edge = segment.delta[0].signum()
* (y_tile + yi as f32 - segment.y_edge + 1.0).clamp(0.0, 1.0);
let y_edge =
delta[0].signum() * (y_tile + yi as f32 - segment.y_edge + 1.0).clamp(0.0, 1.0);
if dy != 0.0 {
let vec_y_recip = segment.delta[1].recip();
let vec_y_recip = delta[1].recip();
let t0 = (y0 - y) * vec_y_recip;
let t1 = (y1 - y) * vec_y_recip;
let startx = segment.origin[0] - x_tile;
let x0 = startx + t0 * segment.delta[0];
let x1 = startx + t1 * segment.delta[0];
let startx = segment.point0[0] - x_tile;
let x0 = startx + t0 * delta[0];
let x1 = startx + t1 * delta[0];
let xmin0 = x0.min(x1);
let xmax0 = x0.max(x1);
for i in 0..TILE_WIDTH {
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54 changes: 37 additions & 17 deletions src/cpu_shader/path_tiling.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -115,28 +115,48 @@ fn path_tiling_main(
xy1 = Vec2::new(x_clip, yt);
}
}
let mut y_edge = 1e9;
// Apply numerical robustness logic
let mut p0 = xy0 - tile_xy;
let mut p1 = xy1 - tile_xy;
const EPSILON: f32 = 1e-6;
if p0.x == 0.0 {
if p1.x == 0.0 {
p0.x = EPSILON;
if p0.y == 0.0 {
// Entire tile
p1.x = EPSILON;
p1.y = TILE_HEIGHT as f32;
} else {
// Make segment disappear
p1.x = 2.0 * EPSILON;
p1.y = p0.y;
}
} else if p0.y == 0.0 {
p0.x = EPSILON;
} else {
y_edge = p0.y;
}
} else if p1.x == 0.0 {
if p1.y == 0.0 {
p1.x = EPSILON;
} else {
y_edge = p1.y;
}
}
if !is_down {
(xy0, xy1) = (xy1, xy0);
(p0, p1) = (p1, p0);
}
// TODO (part of move to 8 byte encoding for segments): don't store y_edge at all,
// resolve this in fine.
let y_edge = if xy0.x == tile_xy.x && xy1.x != tile_xy.x && xy0.y != tile_xy.y {
xy0.y
} else if xy1.x == tile_xy.x && xy1.y != tile_xy.y {
xy1.y
} else {
1e9
};
let segment = PathSegment {
origin: (xy0 - tile_xy).to_array(),
delta: (xy1 - xy0).to_array(),
y_edge: y_edge - tile_xy.y,
point0: p0.to_array(),
point1: p1.to_array(),
y_edge,
_padding: Default::default(),
};
assert!(xy0.x >= tile_xy.x && xy0.x <= tile_xy1.x);
assert!(xy0.y >= tile_xy.y && xy0.y <= tile_xy1.y);
assert!(xy1.x >= tile_xy.x && xy1.x <= tile_xy1.x);
assert!(xy1.y >= tile_xy.y && xy1.y <= tile_xy1.y);
assert!(p0.x >= 0.0 && p0.x <= TILE_WIDTH as f32);
assert!(p0.y >= 0.0 && p0.y <= TILE_HEIGHT as f32);
assert!(p1.x >= 0.0 && p1.x <= TILE_WIDTH as f32);
assert!(p1.y >= 0.0 && p1.y <= TILE_HEIGHT as f32);
segments[(seg_start + seg_within_slice) as usize] = segment;
}
}
Expand Down

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