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# contrastShader.cpp

    //-
    // ==========================================================================
    // Copyright 1995,2006,2008 Autodesk, Inc. All rights reserved.
    //
    // Use of this software is subject to the terms of the Autodesk
    // license agreement provided at the time of installation or download,
    // or which otherwise accompanies this software in either electronic
    // or hard copy form.
    // ==========================================================================
    //+

    //
    //    Description    :    Contrast shader plugin
    //
    //    Notes        :     The contrast operation consists in
    //                redistributing the energy around the middle
    //                point. In other words: every intensity below
    //                0.5 is pushed towards black, and every
    //                intensity above is pushed towards white.
    //                The trick is to do that in a "smooth" way.
    //
    //        The way to do that is:
    //            On interval [0,0.5] apply a gamma to intensity
    //            On interval [0.5,1] apply an "inverted" gamma to intensity
    //
    //        That is:
    //            When I<0.5,    newI=0.5*(2*I)^contrast
    //            When I>=0.5,    newI=1-0.5*(2*(1-I))^contrast
    //
    //        This function is C1 on [0,1], and if contrast==1, it is the
    //        identity.
    //
    //        The bias value stems from: why 0.5 and not something else ?
    //        So, we use a function f to remap the [0,1] interval on itself
    //        with the constraint:
    //            f(0)=0
    //            f(bias)=0.5
    //            f(1)=1
    //        and we compose with the above function.
    //
    //        Of course, when bias=0.5, f *has* to be the identity, and of
    //        course, f *has* to be smooth.
    //        A good candidate is f(x)=x^alpha, with alpha=log(0.5)/log(bias)
    //

    #include <math.h>

    #include <maya/MPxNode.h>
    #include <maya/MIOStream.h>
    #include <maya/MString.h>
    #include <maya/MTypeId.h>
    #include <maya/MPlug.h>
    #include <maya/MDataBlock.h>
    #include <maya/MDataHandle.h>
    #include <maya/MFnNumericAttribute.h>
    #include <maya/MFloatVector.h>
    #include <maya/MFnPlugin.h>

    //
    // DESCRIPTION:
    class Contrast:public MPxNode
    {
        public:
                        Contrast();
        virtual         ~Contrast();

        virtual MStatus compute( const MPlug&, MDataBlock& );
        virtual void    postConstructor();

        static void    *creator();
        static MStatus initialize();

        //  Id tag for use with binary file format
        static MTypeId id;

        private:

        // Input attributes
        static MObject aColor;
        static MObject aContrast;
        static MObject aBias;

        // Output attributes
        static MObject aOutColor;
    };

    // static data
    MTypeId Contrast::id( 0x81008 );

    // Attributes
    MObject Contrast::aColor;
    MObject Contrast::aContrast;
    MObject Contrast::aBias;

    MObject Contrast::aOutColor;

    #define MAKE_INPUT(attr)                        \
        CHECK_MSTATUS(attr.setKeyable(true));       \
        CHECK_MSTATUS(attr.setStorable(true));      \
        CHECK_MSTATUS(attr.setReadable(true));      \
        CHECK_MSTATUS(attr.setWritable(true));

    #define MAKE_OUTPUT(attr)                       \
        CHECK_MSTATUS(attr.setKeyable(false));      \
        CHECK_MSTATUS(attr.setStorable(false));     \
        CHECK_MSTATUS(attr.setReadable(true));      \
        CHECK_MSTATUS(attr.setWritable(false));

    //
    // DESCRIPTION:
    void Contrast::postConstructor( )
    {
        setMPSafe(true);
    }

    //
    // DESCRIPTION:
    Contrast::Contrast()
    {
    }

    //
    // DESCRIPTION:
    Contrast::~Contrast()
    {
    }

    //
    // DESCRIPTION:
    void *Contrast::creator()
    {
        return new Contrast();
    }

    //
    // DESCRIPTION:
    MStatus Contrast::initialize()
    {
        MFnNumericAttribute    nAttr;

        // Create input attributes

        aColor = nAttr.createColor("inputColor", "ic");
        MAKE_INPUT(nAttr);

        aContrast = nAttr.createColor("contrast", "c");
        MAKE_INPUT(nAttr);
        CHECK_MSTATUS(nAttr.setDefault(1.f, 1.f, 1.f));

        aBias = nAttr.createColor("bias", "b");
        MAKE_INPUT(nAttr);
        CHECK_MSTATUS(nAttr.setDefault(.5f, .5f, .5f));

        // Create output attributes
        aOutColor = nAttr.createColor("outColor", "oc");
        MAKE_OUTPUT(nAttr);

        /* Plug inputs and outputs
        ---------------------------*/
        CHECK_MSTATUS(addAttribute(aColor));
        CHECK_MSTATUS(addAttribute(aContrast));
        CHECK_MSTATUS(addAttribute(aBias));
        CHECK_MSTATUS(addAttribute(aOutColor));

        /* Build dependancies
        ----------------------*/
        CHECK_MSTATUS(attributeAffects(aColor,    aOutColor));
        CHECK_MSTATUS(attributeAffects(aContrast, aOutColor));
        CHECK_MSTATUS(attributeAffects(aBias,     aOutColor));

        return MS::kSuccess;
    }

    //
    // DESCRIPTION:
    MStatus Contrast::compute(const MPlug& plug, MDataBlock& block)
    {
        // outColor or individial R, G, B channel
        if((plug != aOutColor) && (plug.parent() != aOutColor))
            return MS::kUnknownParameter;

        MFloatVector resultColor;
        MFloatVector & col = block.inputValue(aColor).asFloatVector();
        MFloatVector & cont = block.inputValue(aContrast).asFloatVector();
        MFloatVector & bias = block.inputValue(aBias).asFloatVector();

        float xp;
        float logp5= logf(0.5F);

        xp = powf(col[0], logp5/logf(bias[0]));
        resultColor[0] = xp<0.5F ?
            0.5F*powf(2.0F*xp, cont[0]) :
            1.0F-0.5F*powf(2.0F*(1.0F-xp), cont[0]);

        xp = powf(col[1], logp5/logf(bias[1]));
        resultColor[1] = xp<0.5F ?
            0.5F*powf(2.0F*xp, cont[1]) :
            1.0F-0.5F*powf(2.0F*(1.0F-xp), cont[1]);

        xp = powf(col[2], logp5/logf(bias[2]));
        resultColor[2] = xp<0.5F ?
            0.5F*powf(2.0F*xp, cont[2]) :
            1.0F-0.5F*powf(2.0F*(1.0F-xp), cont[2]);

        // set ouput color attribute
        MDataHandle outColorHandle = block.outputValue( aOutColor );
        MFloatVector& outColor = outColorHandle.asFloatVector();
        outColor = resultColor;
        outColorHandle.setClean();

        return MS::kSuccess;
    }

    //
    // DESCRIPTION:
    MStatus initializePlugin( MObject obj )
    {
        const MString UserClassify( "utility/color" );

        MFnPlugin plugin( obj, PLUGIN_COMPANY, "4.5", "Any");
        CHECK_MSTATUS( plugin.registerNode("contrastNode", Contrast::id,
                            Contrast::creator, Contrast::initialize,
                            MPxNode::kDependNode, &UserClassify ) );

        return MS::kSuccess;
    }

    //
    // DESCRIPTION:
    MStatus uninitializePlugin( MObject obj )
    {
        MFnPlugin plugin( obj );
        CHECK_MSTATUS( plugin.deregisterNode( Contrast::id ) );

        return MS::kSuccess;
    }