/// <summary>
/// Emits a layer containing a filled box.
/// </summary>
/// <param name="context">The <see cref="View.RenderContext" /> object used to emit
/// layers.</param>
/// <param name="bounds">The bounding box of the box to be rendered.</param>
/// <param name="fillColor">The interior color of the box to be rendered.</param>
public static void EmitBoxFill(View.RenderContext context, Box2 bounds, Rgba fillColor)
{
context.EmitLayer(new SolidColorLayerInfo()
{
Bounds = bounds,
FillColor = fillColor,
});
}
/// <summary>
/// Emits a layer set containing the stroke of a box.
/// </summary>
/// <param name="context">The <see cref="View.RenderContext" /> object used to emit
/// layers.</param>
/// <param name="bounds">The bounding box of the box to be rendered.</param>
/// <param name="strokeColor">The color of the box to be rendered.</param>
/// <param name="width">The width of the stroked line. Must not be negative.</param>
public static void EmitBoxStroke(View.RenderContext context, Box2 bounds, Rgba strokeColor, float width)
{
if (!(width >= 0))
{
throw new ArgumentOutOfRangeException(nameof(width));
}
bounds = bounds.Normalized;
if (width <= 0)
{
// Make sure to always emit the same number of layers
context.EmitLayer(null); context.EmitLayer(null);
context.EmitLayer(null); context.EmitLayer(null);
return;
}
if (bounds.Width < width * 2 || bounds.Height < width * 2)
{
// The bounding rect is narrower than the stroke width
context.EmitLayer(new SolidColorLayerInfo()
{
Bounds = bounds,
FillColor = strokeColor,
});
context.EmitLayer(null); context.EmitLayer(null); context.EmitLayer(null);
return;
}
// Render the stroke of a box using four filled rectangles. This has a T-junction
// issue but should be okay in practice.
context.EmitLayer(new SolidColorLayerInfo()
{
Bounds = new Box2(bounds.Min, new Vector2(bounds.Max.X, bounds.Min.Y + width)),
FillColor = strokeColor,
});
context.EmitLayer(new SolidColorLayerInfo()
{
Bounds = new Box2(new Vector2(bounds.Min.X, bounds.Max.Y - width), bounds.Max),
FillColor = strokeColor,
});
context.EmitLayer(new SolidColorLayerInfo()
{
Bounds = new Box2(
new Vector2(bounds.Min.X, bounds.Min.Y + width),
new Vector2(bounds.Min.X + width, bounds.Max.Y - width)
),
FillColor = strokeColor,
});
context.EmitLayer(new SolidColorLayerInfo()
{
Bounds = new Box2(
new Vector2(bounds.Max.X - width, bounds.Min.Y + width),
new Vector2(bounds.Max.X, bounds.Max.Y - width)
),
FillColor = strokeColor,
});
}
/// <summary>
/// Emits a layer containing a blurred, filled box.
/// </summary>
/// <param name="context">The <see cref="View.RenderContext" /> object used to emit
/// layers.</param>
/// <param name="bounds">The bounding box of the box to be rendered.</param>
/// <param name="opacity">The opacity of the box to be rendered.</param>
/// <param name="radius">The blur radius. Must not be negative.</param>
public static void EmitBoxFillShadow(View.RenderContext context, Box2 bounds, float opacity, float radius)
{
if (!(radius >= 0))
{
throw new ArgumentOutOfRangeException(nameof(radius));
}
// exp(-x^2) is sufficiently small for `x > 2`, so map `[-radius, radius]` to
// `[-2, 2]` in the blur kernel's space.
radius *= 1 / 2f;
bounds = bounds.Normalized;
Vector2 relativeSize = bounds.Size * (0.5f / radius);
if (Math.Max(relativeSize.X, relativeSize.Y) > 1e10)
{
// Guard against extremely large bounds and/or small (or zero) `radius`
context.EmitLayer(new SolidColorLayerInfo()
{
Bounds = bounds,
FillColor = new Rgba(0, 0, 0, opacity),
});
// Make sure to always emit the same number of layers
context.EmitLayer(null); context.EmitLayer(null); context.EmitLayer(null);
return;
}
Vector2 center = (bounds.Min + bounds.Max) * 0.5f;
// Approximate `erf(x+w) - erf(x-w)` for each axis (where `w = relativeSize.{X,Y}`)
// by transforming `erf(x)`. Down below is where the magic happens.
const float a1 = 1.06527f, a2 = 1.13511f, a3 = -3.1682f;
Vector2 erfOffset = default;
Vector2 erfDensity = default;
for (int axis = 0; axis < 2; ++axis)
{
float w = relativeSize.GetElementAt(axis);
erfOffset.ElementAt(axis) = w + a1 - a1 / (1 + a2 * MathF.Exp(a3 * w));
erfDensity.ElementAt(axis) = 2 / (1 + MathF.Exp(w * (-10 / 3f))) - 1;
}
opacity *= erfDensity.X * erfDensity.Y;
// Render pieces of transformed `erf(x) * erf(y)`
var source = BlurredBox.Image;
Vector2 sourceOrigin = new Vector2(BlurredBox.Width * BlurredBox.Resolution);
Vector2 sourceInset = erfOffset * BlurredBox.Resolution;
Vector2 sourceOuterCorner = new Vector2(BlurredBox.Width) * BlurredBox.Resolution;
Box2 sourceBox = new Box2(
sourceOrigin - sourceInset,
sourceOrigin + sourceOuterCorner
);
Vector2 layerSize = (erfOffset + new Vector2(BlurredBox.Width)) * radius;
for (int i = 0; i < 4; ++i)
{
// For each quadrant...
bool ix = (i & 1) != 0, iy = (i & 2) != 0;
float fx = ix ? 1f : -1f, fy = iy ? 1f : -1f;
Vector2 dvec = new Vector2(fx, fy);
context.EmitLayer(new ImageLayerInfo()
{
Bounds = new Box2(center, center + layerSize * dvec),
Image = source,
Source = sourceBox,
Opacity = opacity,
});
}
}