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Simplify and extend trans-stacking-context subpixel accumulation

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Simplify the situations in which subpixels are accumulated, so that it
is only done for translation or identity transformation matrices. Also,
apply accumulated subpixels to more operations in PaintContext. This
fixes several pre-existing reftests and hopefully will eliminate
off-by-one errors in flaky reftests.

Fixes #10881.
This commit is contained in:
Martin Robinson 2016-08-01 13:50:04 +02:00
parent 5dac1f64c1
commit 4aabbf33d4
5 changed files with 39 additions and 34 deletions
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41
components/gfx/display_list/mod.rs
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@ -18,7 +18,7 @@ use app_units::Au;
use azure::azure::AzFloat;
use azure::azure_hl::Color;
use euclid::approxeq::ApproxEq;
use euclid::num::Zero;
use euclid::num::{One, Zero};
use euclid::rect::TypedRect;
use euclid::side_offsets::SideOffsets2D;
use euclid::{Matrix2D, Matrix4D, Point2D, Rect, Size2D};
@ -457,20 +457,18 @@ impl DisplayList {
let transform = transform.translate(pixel_snapped_origin.x as AzFloat,
pixel_snapped_origin.y as AzFloat,
0.0).mul(&stacking_context.transform);
let inverse_transform = transform.invert();
// Here we are trying to accumulate any subpixel distances across transformed
// stacking contexts. This allows us transform stacking context with a
// pixel-snapped transform, but continue to propagate any subpixels from stacking
// context origins to children.
let subpixel_offset = Point2D::new(origin.x.to_f32_px() - pixel_snapped_origin.x,
origin.y.to_f32_px() - pixel_snapped_origin.y);
let subpixel_offset = inverse_transform.transform_point(&subpixel_offset) -
inverse_transform.transform_point(&Point2D::zero());;
let subpixel_offset = Point2D::new(Au::from_f32_px(subpixel_offset.x),
Au::from_f32_px(subpixel_offset.y));
(transform, subpixel_offset)
if transform.is_identity_or_simple_translation() {
let pixel_snapped_origin = Point2D::new(Au::from_f32_px(pixel_snapped_origin.x),
Au::from_f32_px(pixel_snapped_origin.y));
(transform, origin - pixel_snapped_origin)
} else {
// In the case of a more complicated transformation, don't attempt to
// preserve subpixel offsets. This causes problems with reference tests
// that do scaling and rotation and it's unclear if we even want to be doing
// this.
(transform, Point2D::zero())
}
}
};
@ -1462,3 +1460,18 @@ impl WebRenderImageInfo {
/// The type of the scroll offset list. This is only populated if WebRender is in use.
pub type ScrollOffsetMap = HashMap<StackingContextId, Point2D<f32>>;
pub trait SimpleMatrixDetection {
fn is_identity_or_simple_translation(&self) -> bool;
}
impl SimpleMatrixDetection for Matrix4D<f32> {
#[inline]
fn is_identity_or_simple_translation(&self) -> bool {
let (_0, _1) = (Zero::zero(), One::one());
self.m11 == _1 && self.m12 == _0 && self.m13 == _0 && self.m14 == _0 &&
self.m21 == _0 && self.m22 == _1 && self.m23 == _0 && self.m24 == _0 &&
self.m31 == _0 && self.m32 == _0 && self.m33 == _1 && self.m34 == _0 &&
self.m44 == _1
}
}