R: Light an image using the alpha channel as a bump map.

feSpecularLighting {gridSVG} | R Documentation

## Light an image using the alpha channel as a bump map.

### Description

This filter primitive lights a source graphic using the alpha channel as a bump map. The resulting image is an RGBA image based on the light colour. The lighting calculation follows the standard specular component of the Phong lighting model. The resulting image depends on the light colour, light position and surface geometry of the input bump map. The result of the lighting calculation is added. The filter primitive assumes that the viewer is at infinity in the z direction (i.e., the unit vector in the eye direction is (0,0,1) everywhere).

This filter primitive produces an image which contains the specular reflection part of the lighting calculation. Such a map is intended to be combined with a texture using the add term of the arithmetic method in `feComposite`. Multiple light sources can be simulated by adding several of these light maps before applying it to the texture image.

### Usage

    feSpecularLighting(input = NA,
                       surfaceScale = 1, specularConstant = 1,
                       specularExponent = 1, kernelUnitLength = NA,
                       col = "white", lightSource = NULL, ...)

### Arguments

`input` | Identifies an input for this filter primtive. See `filterInputs`.
`surfaceScale` | Scale applied to the input alpha surface.
`specularConstant` | `kd` in the Phong lighting model. Must be non-negative.
`specularExponent` | Numeric exponent for specular term, larger is more "shiny". Range [1,128].
`kernelUnitLength` | The first number is the `dx` value. The second number is the `dy` value. If the `dy` value is not specified, it defaults to the same value as `dx`. Indicates the intended distance in current filter units (i.e., units as determined by the value of parent filter container's `primitiveUnits`) for `dx` and `dy`, respectively, in the surface normal calculation formulas. By specifying value(s) for `kernelUnitLength`, the kernel becomes defined in a scalable, abstract coordinate system. If `kernelUnitLength` is not specified, the `dx` and `dy` values should represent very small deltas relative to a given (x,y) position, which might be implemented in some cases as one pixel in the intermediate image offscreen bitmap, which is a pixel-based coordinate system, and thus potentially not scalable.
`col` | The colour to apply to the light from `lightSource`.
`lightSource` | A light source object, produced by one of `feDistantLight`, `fePointLight`, or `feSpotLight`.
`...` | Further arguments to be passed onto `fe`.

### Details

For more information about this primitive, consult the reference to the SVG specification.

### Value

An `fe.specular.lighting` object.

### Author(s)

Simon Potter

### References

http://www.w3.org/TR/SVG/filters.html#feSpecularLightingElement

### See Also

`filterEffect` `fe`, `feDistantLight`, `fePointLight`, `feSpotLight`.

[Package gridSVG version 1.6-0 Index]