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# MNormalMapConverter.cpp

    //-
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    // rights reserved.
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    // The coded instructions, statements, computer programs, and/or related
    // material (collectively the "Data") in these files contain unpublished
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    // licensors, which is protected by U.S. and Canadian federal copyright
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    // to use, modify, and incorporate this Data into other products for
    // purposes authorized by the Autodesk software license agreement,
    // without fee.
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    // including the above license grant, this restriction and the
    // following disclaimer, must be included in all copies of the
    // Software, in whole or in part, and all derivative works of
    // the Software, unless such copies or derivative works are solely
    // in the form of machine-executable object code generated by a
    // source language processor.
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    //+

    // DESCRIPTION:
    //  Some utilities to do file format conversions and others ...
    //

    #include <maya/MStatus.h>
    #include <math.h>
    #include "MNormalMapConverter.h"

    // Convert the heightfield texture to its corresponding normal map texture
    //
    bool MNormalMapConverter::convertToNormalMap(
            unsigned char* inImagePtr,
            unsigned int width,
            unsigned int height,
            OutFormatType outputPixelFormat,
            float bumpScale,
            unsigned char* outImagePtr )
    {
        bool    isOK = true;

        // Firewall: The input image should not be a NULL pointer,
        //
        if( NULL == inImagePtr )    return false;

        // No output file specified: convert in place
        //
        if( NULL == outImagePtr )
        {
            convertToNormalMap_InPlace( inImagePtr, width, height, outputPixelFormat, bumpScale );
        }
        else
        {
            if( outputPixelFormat == RGBA ) {
                //
                // Not implemented yet
                //
                // similar to the convertToNormalMap_InPlace but we store
                // the resulting texture in the outImagePtr and not
                // in the inImagePtr texture
                //
            }
            else if( outputPixelFormat == HILO ) {
                // Not implemented yet
            }
            else {
                isOK = false;
            }
        }

        return isOK;
    }

    // The heightfield texture inImage will be replaced from grey levels in RGBA
    // to the normal map values as specified by the pixel format
    //
    bool MNormalMapConverter::convertToNormalMap_InPlace(
            unsigned char* inImagePtr,
            unsigned int width,
            unsigned int height,
            OutFormatType outputPixelFormat,
            float bumpScale )
    {
        bool    isOK = true;

        if( outputPixelFormat == RGBA ) {

            bumpScale /= 255.0f;    // will be used on unsignedChar

            unsigned int widthMinus1  =  width - 1;
            unsigned int heightMinus1 = height - 1;
            unsigned int offset = (4 * width);  // = sizeof(rgba) * width

            // ==================
            // Process the texels
            // ==================

            // Get the current pointer to the starting texel at (0,0)
            //
            unsigned char* imagePtr = inImagePtr;

            // For each rows (except the last one)
            //
            unsigned int m, n;
            for( m=0; m<heightMinus1; m++ )
            {
                // Process the texel in each column of this row
                //
                for( n=0; n<widthMinus1; n++ )
                {
                    float deltaU = bumpScale * (float)(imagePtr[0] - imagePtr[4]);
                    float deltaV = bumpScale * (float)(imagePtr[0] - imagePtr[offset]);

                    // Normalize (deltaU, deltaV, 1.)
                    float sqlen = deltaU*deltaU + deltaV*deltaV + 1.0f;
                    float rclen = 1.0f / sqrtf( sqlen );

                    float nx = deltaU * rclen;
                    float ny = deltaV * rclen;
                    float nz = rclen;

                    // Store the vector in red, green, blue
                    *(imagePtr++) = (unsigned char) ((nx + 1.0f) * 127.5f);
                    *(imagePtr++) = (unsigned char) ((ny + 1.0f) * 127.5f);
                    *(imagePtr++) = (unsigned char) ((nz + 1.0f) * 127.5f);

                    // reset the alpha
                    *(imagePtr++) = 255;
                }

                // At the end of the row, just copy the last value. One
                // could implement wraping instead.
                *(imagePtr++) = imagePtr[-4];
                *(imagePtr++) = imagePtr[-4];
                *(imagePtr++) = imagePtr[-4];
                *(imagePtr++) = 255;
            }

            // Fill in the last row (copy from the (last-1) row)
            // memcpy is the faster loop when memory is aligned.
            memcpy(imagePtr, imagePtr-offset, width*4);
        }
        else if( outputPixelFormat == HILO ) {
            // Not implemented yet
        }
        else {
            isOK = false;
        }

        return isOK;
    }

    bool MNormalMapConverter::convertToHeightMap(
        unsigned char* inImagePtr,
        unsigned int width,
        unsigned int height,
        OutFormatType outputPixelFormat,
        float heightScale,
        unsigned char* outImagePtr)
    {
        // Not implemented yet
        //
        return false;
    }