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Improve elevation bounds for physical shape layers #8044

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dnfield merged 3 commits into from
Mar 6, 2019
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Improve elevation bounds for physical shape layers #8044

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9544191
improve elevation bounds
dnfield Mar 5, 2019
50dae57
update calculation
dnfield Mar 5, 2019
5159ec2
update diagram
dnfield Mar 5, 2019
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4 changes: 2 additions & 2 deletions flow/layers/physical_shape_layer.cc
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Original file line number Diff line number Diff line change
Expand Up @@ -51,11 +51,11 @@ void PhysicalShapeLayer::Preroll(PrerollContext* context,
set_needs_system_composite(true);
#else
// Add some margin to the paint bounds to leave space for the shadow.
// The margin is hardcoded to an arbitrary maximum for now because Skia
// The margin is set to a multiple of elevation_ for now because Skia
// doesn't provide a way to calculate it. We fill this whole region
// and clip children to it so we don't need to join the child paint bounds.
SkRect bounds(path_.getBounds());
bounds.outset(20.0, 20.0);
bounds.outset(elevation_ * 1.5, elevation_ * 1.5);

@liyuqian liyuqian Mar 5, 2019 •
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The following outset might be more accurate according to the physical model used by Flutter and Skia:

ex = (kLightRadius * device_pixel_ratio_ + bounds.width() * 0.5) / kLightHeight;
ey = (kLightRadius * device_pixel_ratio_ + bounds.height() * 0.5) / kLightHeight;
bounds.outset(elevation_ * ex, elevation_ * ey);

See
img_20190305_143908
for the illustration.

@liyuqian liyuqian Mar 5, 2019

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BTW, be careful about device_pixel_ratio_. It seems that all elevation_, kLightRadius, kLightHeight should be multiplied with device_pixel_ratio_. The ratio of elevation_ and kLightHeight cancels out, but you'll still need kLightRadius * device_pixel_ratio_.

@dnfield dnfield Mar 5, 2019

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I've updated it and tried to incorporate your diagram as a comment. Does that look right?

set_paint_bounds(bounds);
#endif // defined(OS_FUCHSIA)
}
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