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vello_common: Compute rect edge-row tile alphas once per row #4

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vello_common: Compute rect edge-row tile alphas once per row #4

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30 changes: 19 additions & 11 deletions vello_common/src/rect.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -6,8 +6,10 @@
use crate::kurbo::Rect;
#[cfg(not(feature = "std"))]
use crate::kurbo::common::FloatFuncs as _;
use crate::simd::element_wise_splat;
use crate::strip::Strip;
use crate::tile::Tile;
use crate::util::f32_to_u8;
use alloc::vec::Vec;
use fearless_simd::*;

Expand Down Expand Up @@ -97,12 +99,20 @@ fn render_impl<S: Simd>(s: S, rect: Rect, strip_buf: &mut Vec<Strip>, alpha_buf:
let alpha_start = alpha_buf.len() as u32;

let y_cov = coverage(strip_y, rect_y0, rect_y1);
// Only the left-most and right-most tiles can have partial horizontal coverage,
// all tiles in-between are fully covered horizontally.
let left_alpha = combined_tile_alpha(s, &left_x_cov, &y_cov);
let right_alpha = combined_tile_alpha(s, &right_x_cov, &y_cov);
let interior_alpha = combined_tile_alpha(s, &[1.0; Tile::WIDTH as usize], &y_cov);
let mut col = u32::from(left_tile_x);
while col + u32::from(Tile::WIDTH) <= x_end {
// TODO: We could optimize this so this is only computed for the left-most and right-most
// tile of the edge, all intermediate tiles have full horizontal coverage.
let x_cov = coverage(col as u16, rect_x0, rect_x1);
let combined = combined_tile_alpha(s, &x_cov, &y_cov);
let combined = if col == u32::from(left_tile_x) {
left_alpha
} else if col == u32::from(right_tile_x) {
right_alpha
} else {
interior_alpha
};
alpha_buf.extend_from_slice(combined.as_slice());
col += u32::from(Tile::WIDTH);
}
Expand Down Expand Up @@ -165,14 +175,12 @@ fn combined_tile_alpha<S: Simd>(
x_cov: &[f32; Tile::WIDTH as usize],
y_cov: &[f32; Tile::HEIGHT as usize],
) -> u8x16<S> {
let mut buf = [0_u8; 16];
for (col, xc) in x_cov.iter().copied().enumerate() {
for (row, yc) in y_cov.iter().copied().enumerate() {
buf[col * Tile::HEIGHT as usize + row] = (xc * yc * 255.0 + 0.5) as u8;
}
}
// Tiles are stored in column-major order, so each x coverage is repeated
// for all rows, and the y coverages are repeated for all columns.
let x_cov = element_wise_splat(s, f32x4::from_slice(s, x_cov));
let y_cov = f32x16::block_splat(f32x4::from_slice(s, y_cov));

u8x16::from_slice(s, &buf)
f32_to_u8(x_cov * y_cov * 255.0 + 0.5)
}

#[cfg(test)]
Expand Down
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