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Try to fix clip optimization #1202

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b7f21a5
Try to fix clip optimization
dfrg Sep 8, 2025
ce709c0
fmt
dfrg Sep 8, 2025
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119 changes: 118 additions & 1 deletion examples/scenes/src/test_scenes.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -56,6 +56,7 @@ macro_rules! scene {
}

export_scenes!(
clipped_blend(clipped_blend),
splash_with_tiger(impls::splash_with_tiger(), "splash_with_tiger", false),
funky_paths(funky_paths),
stroke_styles(impls::stroke_styles(Affine::IDENTITY), "stroke_styles", false),
Expand Down Expand Up @@ -100,14 +101,130 @@ mod impls {
use rand::Rng;
use rand::{SeedableRng, rngs::StdRng};
use vello::kurbo::{
Affine, BezPath, Cap, Circle, Ellipse, Join, PathEl, Point, Rect, Shape, Stroke, Vec2,
Affine, BezPath, Cap, Circle, Ellipse, Join, PathEl, Point, Rect, Shape, Stroke, Triangle,
Vec2,
};
use vello::peniko::color::{AlphaColor, Lch, palette};
use vello::peniko::*;
use vello::*;

const FLOWER_IMAGE: &[u8] = include_bytes!("../../assets/splash-flower.jpg");

pub(super) fn clipped_blend(scene: &mut Scene, params: &mut SceneParams<'_>) {
params.resolution = Some(Vec2::new(1000., 1200.));
let transform = Affine::translate((10., 100.));
params.text.add_run(
&mut *scene,
None,
32.,
Color::WHITE,
transform.then_translate((10., -30.).into()),
None,
&Style::Fill(Fill::EvenOdd),
"No Clip",
);

scene.fill(
Fill::EvenOdd,
transform,
palette::css::BLUE,
None,
&Rect::from_origin_size((0., 0.), (400., 400.)),
);
scene.push_layer(
Mix::Multiply,
1.0,
transform,
&Triangle::from_coords((200., 0.), (0., 400.), (400., 400.)),
);
scene.fill(
Fill::EvenOdd,
transform,
palette::css::AQUAMARINE,
None,
&Rect::from_origin_size((0., 0.), (400., 400.)),
);
scene.pop_layer();

let transform = Affine::translate((0., 600.));
params.text.add_run(
&mut *scene,
None,
32.,
Color::WHITE,
transform.then_translate((10., -30.).into()),
None,
&Style::Fill(Fill::EvenOdd),
"Mix::Normal",
);

scene.fill(
Fill::EvenOdd,
transform,
palette::css::BLUE,
None,
&Rect::from_origin_size((0., 0.), (400., 400.)),
);
let layer_shape = Triangle::from_coords((200., 0.), (0., 400.), (400., 400.));
scene.push_layer(Mix::Normal, 1.0, transform, &layer_shape);
scene.push_layer(Mix::Multiply, 1.0, transform, &layer_shape);
scene.fill(
Fill::EvenOdd,
transform,
palette::css::AQUAMARINE,
None,
&Rect::from_origin_size((0., 0.), (400., 400.)),
);
scene.pop_layer();
scene.pop_layer();

let transform = Affine::translate((500., 600.));
params.text.add_run(
&mut *scene,
None,
32.,
Color::WHITE,
transform.then_translate((10., -30.).into()),
None,
&Style::Fill(Fill::EvenOdd),
"Mix::Clip",
);

scene.fill(
Fill::EvenOdd,
transform,
palette::css::BLUE,
None,
&Rect::from_origin_size((0., 0.), (400., 400.)),
);
let layer_shape = Triangle::from_coords((200., 0.), (0., 400.), (400., 400.));
scene.push_layer(Mix::Clip, 1.0, transform, &layer_shape);
scene.push_layer(
Mix::Clip,
1.0,
transform,
&Rect::from_origin_size((200.0, 200.0), (200.0, 200.0)),
);
scene.push_layer(Mix::Multiply, 1.0, transform, &layer_shape);
scene.fill(
Fill::EvenOdd,
transform,
palette::css::AQUAMARINE,
None,
&Rect::from_origin_size((0., 0.), (400., 400.)),
);
scene.pop_layer();
scene.pop_layer();
scene.fill(
Fill::EvenOdd,
transform,
palette::css::RED,
None,
&Rect::from_origin_size((0.0, 100.0), (400.0, 100.0)),
);
scene.pop_layer();
}

pub(super) fn emoji(scene: &mut Scene, params: &mut SceneParams<'_>) {
let text_size = 120. + 20. * (params.time * 2.).sin() as f32;
let s = "🎉🤠✅";
Expand Down
12 changes: 8 additions & 4 deletions vello_shaders/shader/coarse.wgsl
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Original file line number Diff line number Diff line change
Expand Up @@ -131,9 +131,9 @@ fn write_image(info_offset: u32) {
cmd_offset += 2u;
}

fn write_begin_clip() {
fn write_begin_clip(flags: u32) {
alloc_cmd(1u);
ptcl[cmd_offset] = CMD_BEGIN_CLIP;
ptcl[cmd_offset] = CMD_BEGIN_CLIP | flags;
cmd_offset += 1u;
}

Expand Down Expand Up @@ -320,7 +320,6 @@ fn main(
let is_clip = (tag & 1u) != 0u;
var is_blend = false;
if is_clip {
let BLEND_CLIP = (128u << 8u) | 3u;
let scene_offset = draw_monoids[drawobj_ix].scene_offset;
let dd = config.drawdata_base + scene_offset;
let blend = scene[dd];
Expand Down Expand Up @@ -413,7 +412,12 @@ fn main(
if tile.segment_count_or_ix == 0u && tile.backdrop == 0 {
clip_zero_depth = clip_depth + 1u;
} else {
write_begin_clip();
let blend = scene[dd];
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@DJMcNab DJMcNab Sep 8, 2025

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Handy that this was available. Seeing what the blend mode was at "write begin clip" time was my greatest worry in implementing this (as in I was worried it would be annoying)

if blend == BLEND_CLIP {
write_begin_clip(NON_ISOLATED_BLENDING_FLAG);
} else {
write_begin_clip(0);
}
render_blend_depth += 1u;
max_blend_depth = max(max_blend_depth, render_blend_depth);
}
Expand Down
16 changes: 11 additions & 5 deletions vello_shaders/shader/fine.wgsl
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Original file line number Diff line number Diff line change
Expand Up @@ -958,10 +958,11 @@ fn main(
// main interpretation loop
while true {
let tag = ptcl[cmd_ix];
if tag == CMD_END {
let cmd = tag & 0xFFu;
if cmd == CMD_END {
break;
}
switch tag {
switch cmd {
case CMD_FILL: {
let fill = read_fill(cmd_ix);
#ifdef msaa
Expand All @@ -987,18 +988,23 @@ fn main(
cmd_ix += 2u;
}
case CMD_BEGIN_CLIP: {
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@DJMcNab DJMcNab Sep 8, 2025

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My vague plan for implementing this was to turn it into a whole new command, as the operations are at least a little different. I presume you didn't want to do that to avoid the code duplication?

let is_non_isolated = (tag & NON_ISOLATED_BLENDING_FLAG) != 0;
var rgba_mul = vec4(0.0);
if is_non_isolated {
rgba_mul = vec4(1.0);
}
if clip_depth < BLEND_STACK_SPLIT {
for (var i = 0u; i < PIXELS_PER_THREAD; i += 1u) {
blend_stack[clip_depth][i] = pack4x8unorm(rgba[i]);
rgba[i] = vec4(0.0);
}
rgba[i] *= rgba_mul;
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@DJMcNab DJMcNab Sep 8, 2025

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You're sure the backdrop isn't now double counted, even if it has alpha? I think that a over a if a is partially transparent isn't equal to a.

}
} else {
let blend_in_scratch = clip_depth - BLEND_STACK_SPLIT;
let local_tile_ix = local_id.x * PIXELS_PER_THREAD + local_id.y * TILE_WIDTH;
let local_blend_start = blend_offset + blend_in_scratch * TILE_WIDTH * TILE_HEIGHT + local_tile_ix;
for (var i = 0u; i < PIXELS_PER_THREAD; i += 1u) {
blend_spill[local_blend_start + i] = pack4x8unorm(rgba[i]);
rgba[i] = vec4(0.0);
rgba[i] *= rgba_mul;
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@DJMcNab DJMcNab Sep 8, 2025

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Obviously this is assuming that doing a floating point multiply is extremely cheap, right?
At least in the non-isolated case, not doing anything at all is of course more ideal. Although that would of course involve hoisting the condition, leading to code duplication.

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I presume that the multiply by one (or indeed by zero) can't cause rendering differences. Given that these are only colours, I can't see that it can.

}
}
clip_depth += 1u;
Expand Down
7 changes: 7 additions & 0 deletions vello_shaders/shader/shared/ptcl.wgsl
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Expand Up @@ -24,6 +24,13 @@ const CMD_END_CLIP = 11u;
const CMD_JUMP = 12u;
const CMD_BLUR_RECT = 13u;

// Full blend state for clip + normal.
const BLEND_CLIP = (128u << 8u) | 3u;

// Flag set on CMD_BEGIN_CLIP to allow blending to punch through
// the layer.
const NON_ISOLATED_BLENDING_FLAG = 0x100u;

// The individual PTCL structs are written here, but read/write is by
// hand in the relevant shaders

Expand Down
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