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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
Merged

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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38 changes: 32 additions & 6 deletions flow/layers/physical_shape_layer.cc
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Original file line number Diff line number Diff line change
Expand Up @@ -9,6 +9,9 @@

namespace flow {

const SkScalar kLightHeight = 600;
const SkScalar kLightRadius = 800;

PhysicalShapeLayer::PhysicalShapeLayer(Clip clip_behavior)
: isRect_(false), clip_behavior_(clip_behavior) {}

Expand Down Expand Up @@ -51,11 +54,36 @@ 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
// 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.
// We fill this whole region and clip children to it so we don't need to
// join the child paint bounds.
// The offset is calculated as follows:

// .-- (kLightRadius = 800)
// ----- (light)
// | (kLightHeight = 600)
// ------------- (layer)
// |
// | (elevation)
// |
// ------------------------------------------------ (canvas)
// ----------- (extent of shadow)
//
// E = lx } x = (r + w/2)/h
// } =>
// r + w/2 = hx } E = (l/h)(r + w/2)
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@liyuqian liyuqian Mar 5, 2019

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Looks good! It would be better to add a few legends about what E, x, h, l mean.

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@dnfield dnfield Mar 6, 2019

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Done

//
// Where: E = extent of shadow
// l = elevation of layer
// r = radius of the light source
// w = width of the layer
// h = light height
// x = multiplier for elevation to extent
SkRect bounds(path_.getBounds());
bounds.outset(20.0, 20.0);
double ex = (kLightRadius * device_pixel_ratio_ + bounds.width() * 0.5) /
kLightHeight;
double ey = (kLightRadius * device_pixel_ratio_ + bounds.height() * 0.5) /
kLightHeight;
bounds.outset(elevation_ * ex, elevation_ * ey);
set_paint_bounds(bounds);
#endif // defined(OS_FUCHSIA)
}
Expand Down Expand Up @@ -145,8 +173,6 @@ void PhysicalShapeLayer::DrawShadow(SkCanvas* canvas,
SkScalar dpr) {
const SkScalar kAmbientAlpha = 0.039f;
const SkScalar kSpotAlpha = 0.25f;
const SkScalar kLightHeight = 600;
const SkScalar kLightRadius = 800;

SkShadowFlags flags = transparentOccluder
? SkShadowFlags::kTransparentOccluder_ShadowFlag
Expand Down