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Improve shadow doc in PhysicalShapeLayer #8114

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Mar 11, 2019
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Improve shadow doc in PhysicalShapeLayer #8114

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8b75894
Improve shadow doc in PhysicalShapeLayer
liyuqian Mar 11, 2019
c4213c9
Update variable names for consistency with the doc
liyuqian Mar 11, 2019
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36 changes: 23 additions & 13 deletions flow/layers/physical_shape_layer.cc
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Original file line number Diff line number Diff line change
Expand Up @@ -58,32 +58,42 @@ void PhysicalShapeLayer::Preroll(PrerollContext* context,
// join the child paint bounds.
// The offset is calculated as follows:

// .-- (kLightRadius = 800)
// ----- (light)
// | (kLightHeight = 600)
// .--- (kLightRadius)
// -------/ (light)
// | /
// | /
// |/
// |O
// /| (kLightHeight)
// / |
// / |
// / |
// / |
// ------------- (layer)
// |
// | (elevation)
// |
// /| |
// / | | (elevation)
// A / | |B
// ------------------------------------------------ (canvas)
// ----------- (extent of shadow)
// --- (extent of shadow)
//
// E = lx } x = (r + w/2)/h
// E = lt } t = (r + w/2)/h
// } =>
// r + w/2 = hx } E = (l/h)(r + w/2)
// r + w/2 = ht } E = (l/h)(r + w/2)
//
// 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
// t = tangent of AOB, i.e., multiplier for elevation to extent
SkRect bounds(path_.getBounds());
double ex = (kLightRadius * device_pixel_ratio_ + bounds.width() * 0.5) /
// tangent for x
double tx = (kLightRadius * device_pixel_ratio_ + bounds.width() * 0.5) /
kLightHeight;
double ey = (kLightRadius * device_pixel_ratio_ + bounds.height() * 0.5) /
// tangent for y
double ty = (kLightRadius * device_pixel_ratio_ + bounds.height() * 0.5) /
kLightHeight;
bounds.outset(elevation_ * ex, elevation_ * ey);
bounds.outset(elevation_ * tx, elevation_ * ty);
set_paint_bounds(bounds);
#endif // defined(OS_FUCHSIA)
}
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