UT_Filter.h

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/*
 * PROPRIETARY INFORMATION.  This software is proprietary to
 * Side Effects Software Inc., and is not to be reproduced,
 * transmitted, or disclosed in any way without written permission.
 *
 * NAME:        UT_Filter.h ( UT Library, C++)
 *
 * COMMENTS:    Circular symmetric separable filters.  This class allows you to
 *              perform approximate filter weights given different filter
 *              kernels
 *
 *              The lookup tables are valid for 0-1 and should be called with
 *              the square of the distance...  The getWeight() methods can be
 *              used if given simple cartesian coordinates.
 */

#ifndef __UT_Filter__
#define __UT_Filter__

#include "UT_API.h"
#include "UT_FilterType.h"
#include <SYS/SYS_Math.h>
#include <SYS/SYS_Types.h>
#include <string.h> // for memcpy

class UT_Filter;

// Build a convolution window for a given filter
class UT_API UT_FilterWindow {
public:
     UT_FilterWindow()
         : myWeights(myBuffer)
         , myStart(0)
         , mySize(0)
         , myCapacity(BUFSIZE)
         , myVisible(1)
     {
     }

    ~UT_FilterWindow()
     {
         if (myWeights != myBuffer)
             delete [] myWeights;
     }

    UT_FilterWindow(const UT_FilterWindow &) = delete;
    UT_FilterWindow &operator=(const UT_FilterWindow &) = delete;

    bool        setWeights(const UT_Filter &filter, float center,
                            float radius, int res,
                            UT_FilterWrap mode);

    // This should be called if houdini13 filtering is enabled
    template <UT_FilterWrap>
    bool        setWeights(const UT_Filter &filter, float center,
                            float radius, int res);

    // A more efficient version of setWeights().  However, there seems to be an
    // issue with computing the rounding when filtering.  $RTM/texture seems to
    // have a more "linear" result, but $RT/itools/stdin_stdout has an obvious
    // shift in the image.  So, this isn't quite ready for prime time.
    template <UT_FilterWrap>
    bool        setWeightsFast(const UT_Filter &filter, float center,
                            float radius, int res);


    void         blendWithNextMip(int res, UT_FilterWrap mode, 
                                  float mipinterp);

    // Trim out zero weights.  This is typically not done by default, but if
    // you're reusing these weights a lot, you might consider trimming.
    void        trimWeights()
    {
        if (myWeights[0] == 0 || myWeights[mySize-1] == 0)
            pruneZeroWeights();
    }

    const float *getWeights() const     { return myWeights; }
    int          getStart() const       { return myStart; }
    int          getEnd() const         { return myStart + mySize - 1; }
    int          getSize() const        { return mySize; }
    float        getVisible() const     { return myVisible; }

    void        dump(const char *msg="") const;

private:
    void        pruneZeroWeights();

    // Ensure we have enough space to fill the weights.  Prefer to use the
    // local buffer, since this allows the filter to operate without memory
    // allocation.
    template <bool COPY>
    void        resizeWeights(int prevsize=0)
    {
        if (mySize > myCapacity)
        {
            float *weights = myWeights;
            myWeights = new float[mySize];
            myCapacity = mySize;
            if (COPY)
                memcpy(myWeights, weights, prevsize*sizeof(float));
            if (weights != myBuffer)
                delete [] weights;
        }
    }

private:
    static const int    BUFSIZE = 16;

    float        myBuffer[BUFSIZE];
    float       *myWeights;
    int          myStart, mySize;
    int          myCapacity;
    float        myVisible;
};


class UT_API UT_Filter
{
public:
    // Method to lookup the filter by name.
    static UT_FilterType         lookupFilter(const char *name);
    static const char           *getFilterName(UT_FilterType type);
    static const char           *getFilterLabel(UT_FilterType type);

    // Get a well known filter type
    static UT_Filter            *getFilter(UT_FilterType type);

    // Look up the filter wrap type given a string. If the type is unknown,
    // return def.
    static UT_FilterWrap         lookupWrap(const char *keyword,
                                            UT_FilterWrap def);

    // Get a custom filter kernel
    static UT_Filter            *getFilter(float (*evalfunc)(float, void *),
                                           int size, int support = 2,
                                           void *data = 0);

    static void                  releaseFilter(UT_Filter *filter);
    void                         access()       { myRefCount++; }

    /// Fill an array of weights.  The @c center variable specifies the center
    /// of the filter (in resolution space - not 0-1).
    ///
    /// For example, if you have a filter with a radius of 1.3 centered at
    /// pixel 8.4, you should set:
    ///  - @c center = 8.4
    ///  - @c radius = 1.3
    ///  - @c size = floor(8.4+1.3) - floor(8.4-1.3) + 1 = 9-7+1 = 3
    virtual void        fillWeights(float umin, float radius,
                                float *weights, int size) const;

    // Compute average weight over the span l-r.  The valid range for
    // samples is -0.5F to 0.5F (i.e. a filter width of 1)
    virtual float       getWeight(float l, float r) const = 0;

    // Retrieve the filter area to the left of l
    virtual float       getArea(float l) const = 0;

    // Return the filter type
    UT_FilterType       getType() const         { return myType; }

    // Get the filters desired support radius (i.e. 2 for gaussian)
    float               getSupport() const      { return mySupport; }

public:
    virtual ~UT_Filter();

    UT_Filter(const UT_Filter &) = delete;
    UT_Filter &operator=(const UT_Filter &) = delete;

protected:
     UT_Filter() : myRefCount(0), myType(UT_FILTER_BOX) {}

    int                  myRefCount;
    UT_FilterType        myType;
    float                mySupport;
};

#endif