[GEOT-5713] Add support for lesscss color operation functions

modules/library/main/src/main/java/org/geotools/filter/FunctionImpl.java

@@ -187,6 +187,55 @@ private void validateArguments() throws IllegalArgumentException {
             }
         }
     }
+
+    /**
+     * Evaluates a specific argument against the context, checking for required values and
+     * proper conversion.
+     * 
+     * @param object
+     * @param argumentIndex
+     * @return
+     */
+    protected Object getParameterValue(Object object, int argumentIndex) {
+        Parameter<?> parameter = getFunctionName().getArguments().get(argumentIndex);
+        if (params.size() <= argumentIndex) {
+            if (parameter.getMinOccurs() == 0) {
+                return null;
+            } else {
+                throw new IllegalArgumentException(
+                        String.format("No arguments specified for arg " + "%s, minOccurs = %d",
+                                parameter.getName().toString(), parameter.getMinOccurs()));
+            }
+        }
+
+        final Expression expression = params.get(argumentIndex);
+        Object value = expression.evaluate(object, parameter.getType());
+        if (value == null && expression.evaluate(object) != null) {
+            throw new IllegalArgumentException(String.format(
+                    "Failure converting value for "
+                            + "argument %s. %s could not be converted to %s",
+                    parameter.getName(), expression.toString(), parameter.getType().getName()));
+        }
+        return value;
+    }
+
+    /**
+     * Evaluates a specific argument against the context, checking for required values and
+     * proper conversion. This version accepts a default value
+     * 
+     * @param object
+     * @param argumentIndex
+     * @param defaultValue
+     * @return
+     */
+    protected Object getParameterValue(Object object, int argumentIndex, Object defaultValue) {
+        Object value = getParameterValue(object, argumentIndex);
+        if(value == null) {
+            return defaultValue;
+        } else {
+            return value;
+        }
+    }
 
     /**
      * Gathers up and groups the parameters to the function based on the declared parameters.

modules/library/main/src/main/java/org/geotools/filter/function/color/AbstractHSLFunction.java

@@ -0,0 +1,66 @@
+/*
+ *    GeoTools - The Open Source Java GIS Toolkit
+ *    http://geotools.org
+ * 
+ *    (C) 2017, Open Source Geospatial Foundation (OSGeo)
+ *    
+ *    This library is free software; you can redistribute it and/or
+ *    modify it under the terms of the GNU Lesser General Public
+ *    License as published by the Free Software Foundation;
+ *    version 2.1 of the License.
+ *
+ *    This library is distributed in the hope that it will be useful,
+ *    but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ *    Lesser General Public License for more details.
+ */
+package org.geotools.filter.function.color;
+
+import static org.geotools.filter.capability.FunctionNameImpl.parameter;
+
+import java.awt.Color;
+
+import org.geotools.filter.FunctionImpl;
+import org.geotools.filter.capability.FunctionNameImpl;
+import org.opengis.filter.capability.FunctionName;
+
+/**
+ * Base for lesscss.org HSL color manipulation functions
+ *
+ * @author Andrea Aime - GeoSolutions
+ */
+public abstract class AbstractHSLFunction extends FunctionImpl {
+
+    enum Method {
+        absolute, relative
+    };
+
+    public static FunctionName NAME = new FunctionNameImpl("abstractHSL",
+            parameter("result", Color.class), parameter("color", Color.class),
+            parameter("amount", Float.class), parameter("method", Method.class, 0, 1));
+
+    public AbstractHSLFunction(String name) {
+        this.functionName = new FunctionNameImpl(name, NAME.getReturn(), NAME.getArguments());
+    }
+
+    @Override
+    public Object evaluate(Object object) {
+        Color source = (Color) getParameterValue(object, 0);
+        float amount = (Float) getParameterValue(object, 1);
+        Method method = (Method) getParameterValue(object, 2, Method.absolute);
+
+        HSLColor hsl = new HSLColor(source);
+        if (method == Method.absolute) {
+            adjustAbsolute(amount, hsl);
+        } else {
+            adjstRelative(amount, hsl);
+        }
+
+        return hsl.toRGB();
+    }
+
+    protected abstract void adjstRelative(float amount, HSLColor hsl);
+
+    protected abstract void adjustAbsolute(float amount, HSLColor hsl);
+
+}

modules/library/main/src/main/java/org/geotools/filter/function/color/ConstrastFunction.java

@@ -0,0 +1,80 @@
+/*
+ *    GeoTools - The Open Source Java GIS Toolkit
+ *    http://geotools.org
+ * 
+ *    (C) 2017, Open Source Geospatial Foundation (OSGeo)
+ *    
+ *    This library is free software; you can redistribute it and/or
+ *    modify it under the terms of the GNU Lesser General Public
+ *    License as published by the Free Software Foundation;
+ *    version 2.1 of the License.
+ *
+ *    This library is distributed in the hope that it will be useful,
+ *    but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ *    Lesser General Public License for more details.
+ */
+package org.geotools.filter.function.color;
+
+import static org.geotools.filter.capability.FunctionNameImpl.parameter;
+
+import java.awt.Color;
+
+import org.geotools.filter.FunctionImpl;
+import org.geotools.filter.capability.FunctionNameImpl;
+import org.opengis.filter.capability.FunctionName;
+
+/**
+ * Contrast lesscss.org color function. Returns the color with highest contrast with a given reference
+ *
+ * @author Andrea Aime - GeoSolutions
+ */
+public class ConstrastFunction extends FunctionImpl {
+
+    public static FunctionName NAME = new FunctionNameImpl("contrast",
+            parameter("result", Color.class), parameter("reference", Color.class),
+            parameter("color1", Color.class, 0, 1), parameter("color2", Color.class, 0, 1),
+            parameter("threshold", Double.class, 0, 1));
+
+    public ConstrastFunction() {
+        this.functionName = NAME;
+    }
+
+    @Override
+    public Object evaluate(Object object) {
+        Color reference = (Color) getParameterValue(object, 0);
+        Color color1 = (Color) getParameterValue(object, 1, Color.BLACK);
+        Color color2 = (Color) getParameterValue(object, 2, Color.WHITE);
+        double threshold = (Double) getParameterValue(object, 3, 0.43);
+
+        double luma1 = luma(color1);
+        double luma2 = luma(color2);
+        Color light, dark;
+        if (luma1 > luma2) {
+            light = color1;
+            dark = color2;
+        } else {
+            light = color2;
+            dark = color1;
+        }
+
+        if (luma(reference) < threshold) {
+            return light;
+        } else {
+            return dark;
+        }
+    }
+
+    private double luma(Color color) {
+        double r = color.getRed() / 255d;
+        double g = color.getGreen() / 255d;
+        double b = color.getBlue() / 255d;
+
+        r = (r <= 0.03928) ? r / 12.92 : Math.pow(((r + 0.055) / 1.055), 2.4);
+        g = (g <= 0.03928) ? g / 12.92 : Math.pow(((g + 0.055) / 1.055), 2.4);
+        b = (b <= 0.03928) ? b / 12.92 : Math.pow(((b + 0.055) / 1.055), 2.4);
+
+        return 0.2126 * r + 0.7152 * g + 0.0722 * b;
+    }
+
+}

modules/library/main/src/main/java/org/geotools/filter/function/color/DarkenFunction.java

@@ -0,0 +1,38 @@
+/*
+ *    GeoTools - The Open Source Java GIS Toolkit
+ *    http://geotools.org
+ * 
+ *    (C) 2017, Open Source Geospatial Foundation (OSGeo)
+ *    
+ *    This library is free software; you can redistribute it and/or
+ *    modify it under the terms of the GNU Lesser General Public
+ *    License as published by the Free Software Foundation;
+ *    version 2.1 of the License.
+ *
+ *    This library is distributed in the hope that it will be useful,
+ *    but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ *    Lesser General Public License for more details.
+ */
+package org.geotools.filter.function.color;
+
+/**
+ * Implements the lesscss.org darken function
+ *
+ * @author Andrea Aime - GeoSolutions
+ */
+public class DarkenFunction extends AbstractHSLFunction {
+
+    public DarkenFunction() {
+        super("darken");
+    }
+
+    protected void adjstRelative(float amount, HSLColor hsl) {
+        hsl.setLightness(hsl.getLightness() * (1 - amount));
+    }
+
+    protected void adjustAbsolute(float amount, HSLColor hsl) {
+        hsl.setLightness(hsl.getLightness() - amount);
+    }
+
+}

modules/library/main/src/main/java/org/geotools/filter/function/color/DesaturateFunction.java

@@ -0,0 +1,38 @@
+/*
+ *    GeoTools - The Open Source Java GIS Toolkit
+ *    http://geotools.org
+ * 
+ *    (C) 2017, Open Source Geospatial Foundation (OSGeo)
+ *    
+ *    This library is free software; you can redistribute it and/or
+ *    modify it under the terms of the GNU Lesser General Public
+ *    License as published by the Free Software Foundation;
+ *    version 2.1 of the License.
+ *
+ *    This library is distributed in the hope that it will be useful,
+ *    but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ *    Lesser General Public License for more details.
+ */
+package org.geotools.filter.function.color;
+
+/**
+ * Implements the lesscss.org desaturate function
+ *
+ * @author Andrea Aime - GeoSolutions
+ */
+public class DesaturateFunction extends AbstractHSLFunction {
+
+    public DesaturateFunction() {
+        super("desaturate");
+    }
+
+    protected void adjstRelative(float amount, HSLColor hsl) {
+        hsl.setSaturation(hsl.getSaturation() * (1 - amount));
+    }
+
+    protected void adjustAbsolute(float amount, HSLColor hsl) {
+        hsl.setSaturation(hsl.getSaturation() - amount);
+    }
+
+}

modules/library/main/src/main/java/org/geotools/filter/function/color/GrayscaleFunction.java

@@ -0,0 +1,50 @@
+/*
+ *    GeoTools - The Open Source Java GIS Toolkit
+ *    http://geotools.org
+ * 
+ *    (C) 2017, Open Source Geospatial Foundation (OSGeo)
+ *    
+ *    This library is free software; you can redistribute it and/or
+ *    modify it under the terms of the GNU Lesser General Public
+ *    License as published by the Free Software Foundation;
+ *    version 2.1 of the License.
+ *
+ *    This library is distributed in the hope that it will be useful,
+ *    but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ *    Lesser General Public License for more details.
+ */
+package org.geotools.filter.function.color;
+
+import static org.geotools.filter.capability.FunctionNameImpl.parameter;
+
+import java.awt.Color;
+
+import org.geotools.filter.FunctionImpl;
+import org.geotools.filter.capability.FunctionNameImpl;
+import org.opengis.filter.capability.FunctionName;
+
+/**
+ * Tint lesscss.org color function. Takes one colors and mixes it with white based on a weight (and their eventual alpha)
+ *
+ * @author Andrea Aime - GeoSolutions
+ */
+public class GrayscaleFunction extends FunctionImpl {
+
+    public static FunctionName NAME = new FunctionNameImpl("grayscale",
+            parameter("result", Color.class), parameter("color", Color.class));
+
+    public GrayscaleFunction() {
+        this.functionName = NAME;
+    }
+
+    @Override
+    public Object evaluate(Object object) {
+        Color color = (Color) getParameterValue(object, 0);
+
+        HSLColor hsl = new HSLColor(color);
+        hsl.setSaturation(0);
+        return hsl.toRGB();
+    }
+
+}