feat: SVG.Grayscale ( Fixes #230 )

Commands/Filters/SVG.Grayscale.ps.ps1

@@ -0,0 +1,82 @@
+[ValidatePattern('SVG\.Grayscale')]
+param()
+
+function SVG.Grayscale
+{
+    <#
+    .SYNOPSIS
+        Grayscale Filter
+    .DESCRIPTION
+        Creates a grayscale filter in SVG.
+
+        This uses a fixed saturation of zero, to remove all colors within the image.
+    .EXAMPLE
+        SVG -ViewBox 200 @(
+            SVG.Circle -R 100 -CX 100 -CY 100 -Fill '#4488ff' -Filter 'url(#grayscale)' |
+                SVG.Grayscale
+        ) -OutputPath .\Grayscale.svg
+    .LINK
+        https://developer.mozilla.org/en-US/docs/Web/SVG/Element/feColorMatrix
+    #>
+    [inherit('SVG.filter', Dynamic, Abstract)]
+    [CmdletBinding()]
+    param(
+
+    )
+
+    begin {
+        $animationElements = 'animate','set','animateTransform','animateMotion'
+        $defaultId = 'grayscale'
+    }
+
+    process {
+        # Create the splat for the filter and filter entry
+        $feSplat = [Ordered]@{type='saturate';Values=0}
+        $filterSplat = [Ordered]@{} + $PSBoundParameters
+
+        # Check if we have any content
+        $content = $filterSplat['Content']
+        if ($content.LocalName) {
+            # If it's not a filter
+            if ($content.LocalName -ne 'filter') {
+                # Set the input to SourceGraphic
+                $feSplat['In'] = 'SourceGraphic'
+                # If it's an animation element, set the content to the animation element
+                if ($content.LocalName -in $animationElements) {
+                    $feSplat['Content'] = $content
+                }                
+            }
+        } else {
+            # If there was no content, set the input to SourceGraphic
+            $feSplat['In'] = 'SourceGraphic'
+        }
+
+        # Create the saturation filter (using [feColorMatrix](https://developer.mozilla.org/en-US/docs/Web/SVG/Element/feColorMatrix))
+        $newFilter = SVG.feColorMatrix @feSplat
+
+        $filterSplat['Content'] =
+            # If the content is a filter, add the filter to the content
+            if ($content.LocalName -eq 'Filter') {
+                @($content.childNodes) + $newFilter
+            } else {
+                $newFilter
+            }
+
+        # If there's no ID, set it to $defaultId
+        if (-not $filterSplat['ID']) {
+            $filterSplat['ID'] = $defaultId
+        }
+
+        if ($content -and 
+            $content.LocalName -ne 'filter' -and 
+            $content.LocalName -notin $animationElements) {
+            SVG.defs @(SVG.filter @filterSplat)
+            if ($content.setAttribute) {
+                $content.setAttribute('style',"filter:url('#$($filterSplat['ID'])')")
+            }
+            $content
+        } else {
+            SVG.filter @filterSplat
+        }        
+    }
+}