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Merge pull request #401 from linebender/tile_relative
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Improve numerical robustness in path tiling
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@raphlinus
raphlinus authored Nov 2, 2023
2 parents 1e7f850 + 5a9ddf4 commit 7a2271d
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Showing 8 changed files with 247 additions and 109 deletions.
5 changes: 3 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 +207,9 @@ pub struct SegmentCount {
#[derive(Clone, Copy, Debug, Zeroable, Pod, Default)]
#[repr(C)]
pub struct PathSegment {
pub origin: [f32; 2],
pub delta: [f32; 2],
// Points are relative to tile origin
pub point0: [f32; 2],
pub point1: [f32; 2],
pub y_edge: f32,
pub _padding: u32,
}
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78 changes: 78 additions & 0 deletions examples/scenes/src/test_scenes.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -44,6 +44,7 @@ pub fn test_scenes() -> SceneSet {
scene!(blend_grid),
scene!(conflation_artifacts),
scene!(labyrinth),
scene!(robust_paths),
scene!(base_color_test: animated),
scene!(clip_test: animated),
scene!(longpathdash(Cap::Butt), "longpathdash (butt caps)", false),
Expand Down Expand Up @@ -1119,6 +1120,83 @@ fn labyrinth(sb: &mut SceneBuilder, _: &mut SceneParams) {
)
}

fn robust_paths(sb: &mut SceneBuilder, _: &mut SceneParams) {
let mut path = BezPath::new();
path.move_to((16.0, 16.0));
path.line_to((32.0, 16.0));
path.line_to((32.0, 32.0));
path.line_to((16.0, 32.0));
path.close_path();
path.move_to((48.0, 18.0));
path.line_to((64.0, 23.0));
path.line_to((64.0, 33.0));
path.line_to((48.0, 38.0));
path.close_path();
path.move_to((80.0, 18.0));
path.line_to((82.0, 16.0));
path.line_to((94.0, 16.0));
path.line_to((96.0, 18.0));
path.line_to((96.0, 30.0));
path.line_to((94.0, 32.0));
path.line_to((82.0, 32.0));
path.line_to((80.0, 30.0));
path.close_path();
path.move_to((112.0, 16.0));
path.line_to((128.0, 16.0));
path.line_to((128.0, 32.0));
path.close_path();
path.move_to((144.0, 16.0));
path.line_to((160.0, 32.0));
path.line_to((144.0, 32.0));
path.close_path();
path.move_to((168.0, 8.0));
path.line_to((184.0, 8.0));
path.line_to((184.0, 24.0));
path.close_path();
path.move_to((200.0, 8.0));
path.line_to((216.0, 24.0));
path.line_to((200.0, 24.0));
path.close_path();
path.move_to((241.0, 17.5));
path.line_to((255.0, 17.5));
path.line_to((255.0, 19.5));
path.line_to((241.0, 19.5));
path.close_path();
path.move_to((241.0, 22.5));
path.line_to((256.0, 22.5));
path.line_to((256.0, 24.5));
path.line_to((241.0, 24.5));
path.close_path();
sb.fill(Fill::NonZero, Affine::IDENTITY, Color::YELLOW, None, &path);
sb.fill(
Fill::EvenOdd,
Affine::translate((300.0, 0.0)),
Color::LIME,
None,
&path,
);

path.move_to((8.0, 4.0));
path.line_to((8.0, 40.0));
path.line_to((260.0, 40.0));
path.line_to((260.0, 4.0));
path.close_path();
sb.fill(
Fill::NonZero,
Affine::translate((0.0, 100.0)),
Color::YELLOW,
None,
&path,
);
sb.fill(
Fill::EvenOdd,
Affine::translate((300.0, 100.0)),
Color::LIME,
None,
&path,
);
}

fn base_color_test(sb: &mut SceneBuilder, params: &mut SceneParams) {
// Cycle through the hue value every 5 seconds (t % 5) * 360/5
let color = Color::hlc((params.time % 5.0) * 72.0, 80.0, 80.0);
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4 changes: 3 additions & 1 deletion examples/with_winit/Cargo.toml
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Original file line number Diff line number Diff line change
Expand Up @@ -46,5 +46,7 @@ android_logger = "0.13.0"
console_error_panic_hook = "0.1.7"
console_log = "1"
wasm-bindgen-futures = "0.4.33"
web-sys = { version = "0.3.60", features = [ "HtmlCollection", "Text" ] }
# Note: pinning the exact dep here because 0.3.65 broke semver. Update this
# when revving wgpu.
web-sys = { version = "=0.3.64", features = [ "HtmlCollection", "Text" ] }
getrandom = { version = "0.2.10", features = ["js"] }
134 changes: 63 additions & 71 deletions shader/fine.wgsl
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Original file line number Diff line number Diff line change
Expand Up @@ -130,16 +130,15 @@ let ROBUST_EPSILON: f32 = 2e-7;
// is invited to study the even-odd case first, as there only one bit is
// needed to represent a winding number parity, thus there is a lot less
// bit shifting, and less shuffling altogether.
fn fill_path_ms(fill: CmdFill, wg_id: vec2<u32>, local_id: vec2<u32>, result: ptr<function, array<f32, PIXELS_PER_THREAD>>) {
fn fill_path_ms(fill: CmdFill, local_id: vec2<u32>, result: ptr<function, array<f32, PIXELS_PER_THREAD>>) {
let even_odd = (fill.size_and_rule & 1u) != 0u;
// This isn't a divergent branch because the fill parameters are workgroup uniform,
// provably so because the ptcl buffer is bound read-only.
if even_odd {
fill_path_ms_evenodd(fill, wg_id, local_id, result);
fill_path_ms_evenodd(fill, local_id, result);
return;
}
let n_segs = fill.size_and_rule >> 1u;
let tile_origin = vec2(f32(wg_id.x) * f32(TILE_HEIGHT), f32(wg_id.y) * f32(TILE_WIDTH));
let th_ix = local_id.y * (TILE_WIDTH / PIXELS_PER_THREAD) + local_id.x;
// Initialize winding number arrays to a winding number of 0, which is 0x80 in an
// 8 bit biased signed integer encoding.
Expand All @@ -163,31 +162,18 @@ fn fill_path_ms(fill: CmdFill, wg_id: vec2<u32>, local_id: vec2<u32>, result: pt
// TODO: might save a register rewriting this in terms of limit
if th_ix < slice_size {
let segment = segments[seg_off];
// Note: coords relative to tile origin probably a good idea in coarse path,
// especially as f16 would work. But keeping existing scheme for compatibility.
let xy0 = segment.origin - tile_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 @@ -224,8 +210,9 @@ fn fill_path_ms(fill: CmdFill, wg_id: vec2<u32>, local_id: vec2<u32>, result: pt
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 - tile_origin;
let xy1_in = xy0_in + segment.delta;
// Coordinates are relative to tile origin
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 All @@ -237,6 +224,8 @@ fn fill_path_ms(fill: CmdFill, wg_id: vec2<u32>, local_id: vec2<u32>, result: pt
let dy = xy1.y - xy0.y;
let idxdy = 1.0 / (dx + dy);
var a = dx * idxdy;
// is_positive_slope is true for \ and | slopes, false for /. For
// horizontal lines, it follows the original data.
let is_positive_slope = xy1.x >= xy0.x;
let x_sign = select(-1.0, 1.0, is_positive_slope);
let xt0 = floor(xy0.x * x_sign);
Expand All @@ -257,15 +246,29 @@ fn fill_path_ms(fill: CmdFill, wg_id: vec2<u32>, local_id: vec2<u32>, result: pt
let z = floor(zf);
let x = x0i + i32(x_sign * z);
let y = i32(y0i) + i32(sub_ix) - i32(z);
// is_delta captures whether the line crosses the top edge of this
// pixel. If so, then a delta is added to `sh_winding`, followed by
// a prefix sum, so that a winding number delta is applied to all
// pixels to the right of this one.
var is_delta: bool;
// We need to adjust winding number if slope is positive and there
// is a crossing at the left edge of the pixel.
// is_bump captures whether x0 crosses the left edge of this pixel.
var is_bump = false;
let zp = floor(a * f32(sub_ix - 1u) + b);
if sub_ix == 0u {
is_delta = y0i == xy0.y && y0i != xy1.y;
is_bump = xy0.x == 0.0;
// The first (top-most) pixel in the line. It is considered to be
// a line crossing when it touches the top of the pixel.
//
// Note: horizontal lines aligned to the pixel grid have already
// been discarded.
is_delta = y0i == xy0.y;
// The pixel is counted as a left edge crossing only at the left
// edge of the tile (and when it is not the top left corner,
// using logic analogous to tiling).
is_bump = xy0.x == 0.0 && y0i != xy0.y;
} else {
// Pixels other than the first are a crossing at the top or on
// the side, based on the conservative line rasterization. When
// positive slope, the crossing is on the left.
is_delta = z == zp;
is_bump = is_positive_slope && !is_delta;
}
Expand Down Expand Up @@ -465,7 +468,7 @@ fn fill_path_ms(fill: CmdFill, wg_id: vec2<u32>, local_id: vec2<u32>, result: pt
// bits 4 * k + 2 and 4 * k + 3 contain 4-reductions
let xored01_4 = xored01 | (xored01 * 4u);
let xored2 = (expected_zero * 0x1010101u) ^ samples2;
let xored2_2 = xored0 | (xored0 * 2u);
let xored2_2 = xored2 | (xored2 * 2u);
let xored3 = (expected_zero * 0x1010101u) ^ samples3;
let xored3_2 = xored3 | (xored3 >> 1u);
// xored23 contains 2-reductions from words 2 and 3, interleaved
Expand All @@ -492,9 +495,8 @@ fn fill_path_ms(fill: CmdFill, wg_id: vec2<u32>, local_id: vec2<u32>, result: pt
// as both have the same effect on winding number.
//
// TODO: factor some logic out to reduce code duplication.
fn fill_path_ms_evenodd(fill: CmdFill, wg_id: vec2<u32>, local_id: vec2<u32>, result: ptr<function, array<f32, PIXELS_PER_THREAD>>) {
fn fill_path_ms_evenodd(fill: CmdFill, local_id: vec2<u32>, result: ptr<function, array<f32, PIXELS_PER_THREAD>>) {
let n_segs = fill.size_and_rule >> 1u;
let tile_origin = vec2(f32(wg_id.x) * f32(TILE_HEIGHT), f32(wg_id.y) * f32(TILE_WIDTH));
let th_ix = local_id.y * (TILE_WIDTH / PIXELS_PER_THREAD) + local_id.x;
if th_ix < TILE_HEIGHT {
if th_ix == 0u {
Expand All @@ -516,29 +518,18 @@ fn fill_path_ms_evenodd(fill: CmdFill, wg_id: vec2<u32>, local_id: vec2<u32>, re
// TODO: might save a register rewriting this in terms of limit
if th_ix < slice_size {
let segment = segments[seg_off];
// Note: coords relative to tile origin probably a good idea in coarse path,
// especially as f16 would work. But keeping existing scheme for compatibility.
let xy0 = segment.origin - tile_origin;
let xy1 = xy0 + segment.delta;
// Coordinates are relative to tile origin
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 @@ -575,8 +566,8 @@ fn fill_path_ms_evenodd(fill: CmdFill, wg_id: vec2<u32>, local_id: vec2<u32>, re
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 - tile_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 @@ -609,12 +600,11 @@ fn fill_path_ms_evenodd(fill: CmdFill, wg_id: vec2<u32>, local_id: vec2<u32>, re
let x = x0i + i32(x_sign * z);
let y = i32(y0i) + i32(sub_ix) - i32(z);
var is_delta: bool;
// We need to adjust winding number if slope is positive and there
// is a crossing at the left edge of the pixel.
// See comments in nonzero case.
var is_bump = false;
let zp = floor(a * f32(sub_ix - 1u) + b);
if sub_ix == 0u {
is_delta = y0i == xy0.y && y0i != xy1.y;
is_delta = y0i == xy0.y;
is_bump = xy0.x == 0.0;
} else {
is_delta = z == zp;
Expand Down Expand Up @@ -811,17 +801,18 @@ 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 @@ -835,7 +826,7 @@ 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;
}
Expand Down Expand Up @@ -864,6 +855,7 @@ fn main(
) {
let tile_ix = wg_id.y * config.width_in_tiles + wg_id.x;
let xy = vec2(f32(global_id.x * PIXELS_PER_THREAD), f32(global_id.y));
let local_xy = vec2(f32(local_id.x * PIXELS_PER_THREAD), f32(local_id.y));
#ifdef full
var rgba: array<vec4<f32>, PIXELS_PER_THREAD>;
for (var i = 0u; i < PIXELS_PER_THREAD; i += 1u) {
Expand All @@ -886,9 +878,9 @@ fn main(
case 1u: {
let fill = read_fill(cmd_ix);
#ifdef msaa
fill_path_ms(fill, wg_id.xy, local_id.xy, &area);
fill_path_ms(fill, local_id.xy, &area);
#else
fill_path(fill, xy, &area);
fill_path(fill, local_xy, &area);
#endif
cmd_ix += 4u;
}
Expand Down
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