openexr_api.cpp

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/*
*
 * ***** BEGIN GPLLICENSE BLOCK *****
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License
 * as published by the Free Software Foundation; either version 2
 * of the License, or (at your option) any later version. 
 *
 * This program 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 General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
 *
 * Copyright by Gernot Ziegler <gz@lysator.liu.se>.
 * All rights reserved.
 *
 * The Original Code is: all of this file.
 *
 * Contributor(s): Austin Benesh, Ton Roosendaal (float, half, speedup, cleanup...).
 *
 * ***** END GPL LICENSE BLOCK *****
 */

#include <stdlib.h>
#include <stdio.h>
#include <stddef.h>
#include <string>


#include <openexr_api.h>

extern "C"
{

// The following prevents a linking error in debug mode for MSVC using the libs in CVS
#if defined(WITH_OPENEXR) && defined(_WIN32) && defined(_DEBUG) && !defined(__MINGW32__) && !defined(__CYGWIN__)
_CRTIMP void __cdecl _invalid_parameter_noinfo(void)
{
}
#endif

#include "MEM_guardedalloc.h"

#include "BLI_blenlib.h"
#include "BLI_math_color.h"

#include "IMB_imbuf_types.h"
#include "IMB_imbuf.h"
#include "IMB_allocimbuf.h"
#include "IMB_metadata.h"

#include "openexr_multi.h"
}

#include <iostream>

#if defined (_WIN32) && !defined(FREE_WINDOWS)
#include <half.h>
#include <IlmImf/ImfVersion.h>
#include <IlmImf/ImfArray.h>
#include <IlmImf/ImfIO.h>
#include <IlmImf/ImfChannelList.h>
#include <IlmImf/ImfPixelType.h>
#include <IlmImf/ImfInputFile.h>
#include <IlmImf/ImfOutputFile.h>
#include <IlmImf/ImfCompression.h>
#include <IlmImf/ImfCompressionAttribute.h>
#include <IlmImf/ImfStringAttribute.h>
#include <Imath/ImathBox.h>
#else
#include <half.h>
#include <ImfVersion.h>
#include <ImathBox.h>
#include <ImfArray.h>
#include <ImfIO.h>
#include <ImfChannelList.h>
#include <ImfPixelType.h>
#include <ImfInputFile.h>
#include <ImfOutputFile.h>
#include <ImfCompression.h>
#include <ImfCompressionAttribute.h>
#include <ImfStringAttribute.h>
#endif

using namespace Imf;
using namespace Imath;

class Mem_IStream: public IStream
{
public:
    
    Mem_IStream (unsigned char *exrbuf, size_t exrsize):
        IStream("dummy"), _exrpos (0), _exrsize(exrsize)  { _exrbuf = exrbuf; }
    
    virtual bool    read (char c[], int n);
    virtual Int64   tellg ();
    virtual void    seekg (Int64 pos);
    virtual void    clear ();
    //virtual ~Mem_IStream() {}; // unused
    
private:

    Int64 _exrpos;
    Int64 _exrsize;
    unsigned char *_exrbuf;
};

bool Mem_IStream::read (char c[], int n)
{
    if (n + _exrpos <= _exrsize)
    {
        memcpy(c, (void *)(&_exrbuf[_exrpos]), n);
        _exrpos += n;
        return true;
    }
    else
        return false;
}

Int64 Mem_IStream::tellg ()
{
    return _exrpos;
}

void Mem_IStream::seekg (Int64 pos)
{
    _exrpos = pos;
}

void Mem_IStream::clear () 
{ 
}

struct _RGBAZ
{
    half r;
    half g;
    half b;
    half a;
    half z;
};

typedef struct _RGBAZ RGBAZ;

extern "C"
{
    
int imb_is_a_openexr(unsigned char *mem)
{
    return Imf::isImfMagic ((const char *)mem);
}

static void openexr_header_compression(Header *header, int compression)
{
    switch(compression)
    {
        case 0:
            header->compression() = NO_COMPRESSION;
            break;
        case 1:
            header->compression() = PXR24_COMPRESSION;
            break;
        case 2:
            header->compression() = ZIP_COMPRESSION;
            break;
        case 3:
            header->compression() = PIZ_COMPRESSION;
            break;
        case 4:
            header->compression() = RLE_COMPRESSION;
            break;
        default:
            header->compression() = ZIP_COMPRESSION;
            break; 
    }
}

static void openexr_header_metadata(Header *header, struct ImBuf *ibuf)
{
    ImMetaData* info;

    for(info= ibuf->metadata; info; info= info->next)
        header->insert(info->key, StringAttribute(info->value));
}

static int imb_save_openexr_half(struct ImBuf *ibuf, const char *name, int flags)
{
    int channels = ibuf->channels;
    int width = ibuf->x;
    int height = ibuf->y;
    int write_zbuf = (flags & IB_zbuffloat) && ibuf->zbuf_float != NULL;   // summarize
    
    try
    {
        Header header (width, height);
        
        openexr_header_compression(&header, ibuf->ftype & OPENEXR_COMPRESS);
        openexr_header_metadata(&header, ibuf);
        
        header.channels().insert ("R", Channel (HALF));
        header.channels().insert ("G", Channel (HALF));
        header.channels().insert ("B", Channel (HALF));
        if (ibuf->planes==32 && channels >= 4)
            header.channels().insert ("A", Channel (HALF));
        if (write_zbuf)     // z we do as float always
            header.channels().insert ("Z", Channel (FLOAT));
        
        FrameBuffer frameBuffer;            
        OutputFile *file = new OutputFile(name, header);            
        
        /* we store first everything in half array */
        RGBAZ *pixels = new RGBAZ[height * width];
        RGBAZ *to = pixels;
        int xstride= sizeof (RGBAZ);
        int ystride= xstride*width;

        /* indicate used buffers */
        frameBuffer.insert ("R", Slice (HALF,  (char *) &pixels[0].r, xstride, ystride));   
        frameBuffer.insert ("G", Slice (HALF,  (char *) &pixels[0].g, xstride, ystride));
        frameBuffer.insert ("B", Slice (HALF,  (char *) &pixels[0].b, xstride, ystride));
        if (ibuf->planes==32 && channels >= 4)
            frameBuffer.insert ("A", Slice (HALF, (char *) &pixels[0].a, xstride, ystride));
        if (write_zbuf)
            frameBuffer.insert ("Z", Slice (FLOAT, (char *)(ibuf->zbuf_float + (height-1)*width),
                                            sizeof(float), sizeof(float) * -width));
        if(ibuf->rect_float) {
            float *from;

            if(ibuf->profile == IB_PROFILE_LINEAR_RGB) {
                for (int i = ibuf->y-1; i >= 0; i--)
                {
                    from= ibuf->rect_float + channels*i*width;

                    for (int j = ibuf->x; j > 0; j--)
                    {
                        to->r = from[0];
                        to->g = from[1];
                        to->b = from[2];
                        to->a = (channels >= 4)? from[3]: 1.0f;
                        to++; from += 4;
                    }
                }
            }
            else {
                for (int i = ibuf->y-1; i >= 0; i--)
                {
                    from= ibuf->rect_float + channels*i*width;

                    for (int j = ibuf->x; j > 0; j--)
                    {
                        to->r = srgb_to_linearrgb(from[0]);
                        to->g = srgb_to_linearrgb(from[1]);
                        to->b = srgb_to_linearrgb(from[2]);
                        to->a = (channels >= 4)? from[3]: 1.0f;
                        to++; from += 4;
                    }
                }
            }
        }
        else {
            unsigned char *from;

            if(ibuf->profile == IB_PROFILE_LINEAR_RGB) {
                for (int i = ibuf->y-1; i >= 0; i--)
                {
                    from= (unsigned char *)ibuf->rect + channels*i*width;

                    for (int j = ibuf->x; j > 0; j--)
                    {
                        to->r = (float)(from[0])/255.0;
                        to->g = (float)(from[1])/255.0;
                        to->b = (float)(from[2])/255.0;
                        to->a = (float)(channels >= 4) ? from[3]/255.0 : 1.0f;
                        to++; from += 4;
                    }
                }
            }
            else {
                for (int i = ibuf->y-1; i >= 0; i--)
                {
                    from= (unsigned char *)ibuf->rect + channels*i*width;

                    for (int j = ibuf->x; j > 0; j--)
                    {
                        to->r = srgb_to_linearrgb((float)from[0] / 255.0);
                        to->g = srgb_to_linearrgb((float)from[1] / 255.0);
                        to->b = srgb_to_linearrgb((float)from[2] / 255.0);
                        to->a = channels >= 4 ? (float)from[3]/255.0 : 1.0f;
                        to++; from += 4;
                    }
                }
            }
        }
        
//      printf("OpenEXR-save: Writing OpenEXR file of height %d.\n", height);
        
        file->setFrameBuffer (frameBuffer);               
        file->writePixels (height);                   
        delete file;
        delete [] pixels;
    }
    catch (const std::exception &exc)
    {
        printf("OpenEXR-save: ERROR: %s\n", exc.what());
        if (ibuf) IMB_freeImBuf(ibuf);
        
        return (0);
    }
    
    return (1);
}

static int imb_save_openexr_float(struct ImBuf *ibuf, const char *name, int flags)
{
    int channels = ibuf->channels;
    int width = ibuf->x;
    int height = ibuf->y;
    int write_zbuf = (flags & IB_zbuffloat) && ibuf->zbuf_float != NULL;   // summarize

    try
    {
        Header header (width, height);
        
        openexr_header_compression(&header, ibuf->ftype & OPENEXR_COMPRESS);
        openexr_header_metadata(&header, ibuf);
        
        header.channels().insert ("R", Channel (FLOAT));
        header.channels().insert ("G", Channel (FLOAT));
        header.channels().insert ("B", Channel (FLOAT));
        if (ibuf->planes==32 && channels >= 4)
            header.channels().insert ("A", Channel (FLOAT));
        if (write_zbuf)
            header.channels().insert ("Z", Channel (FLOAT));
        
        FrameBuffer frameBuffer;            
        OutputFile *file = new OutputFile(name, header);            
        int xstride = sizeof(float) * channels;
        int ystride = - xstride*width;
        float *rect[4] = {NULL, NULL, NULL, NULL};

        /* last scanline, stride negative */
        rect[0]= ibuf->rect_float + channels*(height-1)*width;
        rect[1]= rect[0]+1;
        rect[2]= rect[0]+2;
        rect[3]= (channels >= 4)? rect[0]+3:rect[0]; /* red as alpha, is this needed since alpha isnt written? */

        frameBuffer.insert ("R", Slice (FLOAT,  (char *)rect[0], xstride, ystride));
        frameBuffer.insert ("G", Slice (FLOAT,  (char *)rect[1], xstride, ystride));
        frameBuffer.insert ("B", Slice (FLOAT,  (char *)rect[2], xstride, ystride));
        if (ibuf->planes==32 && channels >= 4)
            frameBuffer.insert ("A", Slice (FLOAT,  (char *)rect[3], xstride, ystride));
        if (write_zbuf)
            frameBuffer.insert ("Z", Slice (FLOAT, (char *) (ibuf->zbuf_float + (height-1)*width),
                                            sizeof(float), sizeof(float) * -width));
        file->setFrameBuffer (frameBuffer);               
        file->writePixels (height);                   
        delete file;
    }
    catch (const std::exception &exc)
    {
        printf("OpenEXR-save: ERROR: %s\n", exc.what());
        if (ibuf) IMB_freeImBuf(ibuf);
        
        return (0);
    }
    
    return (1);
    //  printf("OpenEXR-save: Done.\n");
}


int imb_save_openexr(struct ImBuf *ibuf, const char *name, int flags)
{
    if (flags & IB_mem) 
    {
        printf("OpenEXR-save: Create EXR in memory CURRENTLY NOT SUPPORTED !\n");
        imb_addencodedbufferImBuf(ibuf);
        ibuf->encodedsize = 0;    
        return(0);
    } 
    
    if (ibuf->ftype & OPENEXR_HALF) 
        return imb_save_openexr_half(ibuf, name, flags);
    else {
        /* when no float rect, we save as half (16 bits is sufficient) */
        if (ibuf->rect_float==NULL)
            return imb_save_openexr_half(ibuf, name, flags);
        else
            return imb_save_openexr_float(ibuf, name, flags);
    }
}

/* ********************* Nicer API, MultiLayer and with Tile file support ************************************ */

/* naming rules:
   - parse name from right to left
   - last character is channel ID, 1 char like 'A' 'R' 'G' 'B' 'X' 'Y' 'Z' 'W' 'U' 'V'
   - separated with a dot; the Pass name (like "Depth", "Color", "Diffuse" or "Combined")
   - separated with a dot: the Layer name (like "Lamp1" or "Walls" or "Characters")
*/

static ListBase exrhandles= {NULL, NULL};

typedef struct ExrHandle {
    struct ExrHandle *next, *prev;
    
    InputFile *ifile;
    TiledOutputFile *tofile;
    OutputFile *ofile;
    int tilex, tiley;
    int width, height;
    int mipmap;
    
    ListBase channels;  /* flattened out, ExrChannel */
    ListBase layers;    /* hierarchical, pointing in end to ExrChannel */
} ExrHandle;

/* flattened out channel */
typedef struct ExrChannel {
    struct ExrChannel *next, *prev;
    
    char name[EXR_TOT_MAXNAME+1];   /* full name of layer+pass */
    int xstride, ystride;       /* step to next pixel, to next scanline */
    float *rect;                /* first pointer to write in */
    char chan_id;               /* quick lookup of channel char */
} ExrChannel;


/* hierarchical; layers -> passes -> channels[] */
typedef struct ExrPass {
    struct ExrPass *next, *prev;
    char name[EXR_PASS_MAXNAME];
    int totchan;
    float *rect;
    struct ExrChannel *chan[EXR_PASS_MAXCHAN];
    char chan_id[EXR_PASS_MAXCHAN];
} ExrPass;

typedef struct ExrLayer {
    struct ExrLayer *next, *prev;
    char name[EXR_LAY_MAXNAME+1];
    ListBase passes;
} ExrLayer;

/* ********************** */

void *IMB_exr_get_handle(void)
{
    ExrHandle *data= (ExrHandle *)MEM_callocN(sizeof(ExrHandle), "exr handle");
    BLI_addtail(&exrhandles, data);
    return data;
}

/* adds flattened ExrChannels */
/* xstride, ystride and rect can be done in set_channel too, for tile writing */
void IMB_exr_add_channel(void *handle, const char *layname, const char *passname, int xstride, int ystride, float *rect)
{
    ExrHandle *data= (ExrHandle *)handle;
    ExrChannel *echan;
    
    echan= (ExrChannel *)MEM_callocN(sizeof(ExrChannel), "exr tile channel");
    
    if(layname) {
        char lay[EXR_LAY_MAXNAME+1], pass[EXR_PASS_MAXNAME+1];
        BLI_strncpy(lay, layname, EXR_LAY_MAXNAME);
        BLI_strncpy(pass, passname, EXR_PASS_MAXNAME);

        sprintf(echan->name, "%s.%s", lay, pass);
    }
    else
        BLI_strncpy(echan->name, passname, EXR_TOT_MAXNAME-1);
    
    echan->xstride= xstride;
    echan->ystride= ystride;
    echan->rect= rect;
    
    // printf("added channel %s\n", echan->name);
    BLI_addtail(&data->channels, echan);
}

/* only used for writing temp. render results (not image files) */
int IMB_exr_begin_write(void *handle, const char *filename, int width, int height, int compress)
{
    ExrHandle *data= (ExrHandle *)handle;
    Header header (width, height);
    ExrChannel *echan;
    
    data->width= width;
    data->height= height;
    
    for(echan= (ExrChannel *)data->channels.first; echan; echan= echan->next)
        header.channels().insert (echan->name, Channel (FLOAT));
    
    openexr_header_compression(&header, compress);
    // openexr_header_metadata(&header, ibuf); // no imbuf. cant write
    /* header.lineOrder() = DECREASING_Y; this crashes in windows for file read! */
    
    header.insert ("BlenderMultiChannel", StringAttribute ("Blender V2.55.1 and newer"));

    /* avoid crash/abort when we dont have permission to write here */
    try {
        data->ofile = new OutputFile(filename, header);
    }
    catch (const std::exception &exc) {
        std::cerr << "IMB_exr_begin_write: ERROR: " << exc.what() << std::endl;
        data->ofile = NULL;
    }

    return (data->ofile != NULL);
}

void IMB_exrtile_begin_write(void *handle, const char *filename, int mipmap, int width, int height, int tilex, int tiley)
{
    ExrHandle *data= (ExrHandle *)handle;
    Header header (width, height);
    ExrChannel *echan;
    
    data->tilex= tilex;
    data->tiley= tiley;
    data->width= width;
    data->height= height;
    data->mipmap= mipmap;
    
    for(echan= (ExrChannel *)data->channels.first; echan; echan= echan->next)
        header.channels().insert (echan->name, Channel (FLOAT));
    
    header.setTileDescription (TileDescription (tilex, tiley, (mipmap)? MIPMAP_LEVELS: ONE_LEVEL));
    header.lineOrder() = RANDOM_Y;
    header.compression() = RLE_COMPRESSION;
    
    header.insert ("BlenderMultiChannel", StringAttribute ("Blender V2.43"));
    
    data->tofile = new TiledOutputFile(filename, header);
}

/* read from file */
int IMB_exr_begin_read(void *handle, const char *filename, int *width, int *height)
{
    ExrHandle *data= (ExrHandle *)handle;
    
    if(BLI_exists(filename) && BLI_file_size(filename)>32) {    /* 32 is arbitrary, but zero length files crashes exr */
        data->ifile = new InputFile(filename);
        if(data->ifile) {
            Box2i dw = data->ifile->header().dataWindow();
            data->width= *width  = dw.max.x - dw.min.x + 1;
            data->height= *height = dw.max.y - dw.min.y + 1;
            
            const ChannelList &channels = data->ifile->header().channels();
            
            for (ChannelList::ConstIterator i = channels.begin(); i != channels.end(); ++i)
                IMB_exr_add_channel(data, NULL, i.name(), 0, 0, NULL);
            
            return 1;
        }
    }
    return 0;
}

/* still clumsy name handling, layers/channels can be ordered as list in list later */
void IMB_exr_set_channel(void *handle, const char *layname, const char *passname, int xstride, int ystride, float *rect)
{
    ExrHandle *data= (ExrHandle *)handle;
    ExrChannel *echan;
    char name[EXR_TOT_MAXNAME + 1];
    
    if(layname) {
        char lay[EXR_LAY_MAXNAME+1], pass[EXR_PASS_MAXNAME+1];
        BLI_strncpy(lay, layname, EXR_LAY_MAXNAME);
        BLI_strncpy(pass, passname, EXR_PASS_MAXNAME);
        
        sprintf(name, "%s.%s", lay, pass);
    }
    else
        BLI_strncpy(name, passname, EXR_TOT_MAXNAME-1);

    echan= (ExrChannel *)BLI_findstring(&data->channels, name, offsetof(ExrChannel, name));

    if(echan) {
        echan->xstride= xstride;
        echan->ystride= ystride;
        echan->rect= rect;
    }
    else
        printf("IMB_exrtile_set_channel error %s\n", name);
}

void IMB_exrtile_clear_channels(void *handle)
{
    ExrHandle *data= (ExrHandle *)handle;
    BLI_freelistN(&data->channels);
}

void IMB_exrtile_write_channels(void *handle, int partx, int party, int level)
{
    ExrHandle *data= (ExrHandle *)handle;
    FrameBuffer frameBuffer;
    ExrChannel *echan;
    
    for(echan= (ExrChannel *)data->channels.first; echan; echan= echan->next) {
        float *rect= echan->rect - echan->xstride*partx - echan->ystride*party;

        frameBuffer.insert (echan->name, Slice (FLOAT,  (char *)rect, 
                            echan->xstride*sizeof(float), echan->ystride*sizeof(float)));
    }
    
    data->tofile->setFrameBuffer (frameBuffer);

    try {
        // printf("write tile %d %d\n", partx/data->tilex, party/data->tiley);
        data->tofile->writeTile (partx/data->tilex, party/data->tiley, level);
    }
    catch (const std::exception &exc) {
        std::cerr << "OpenEXR-writeTile: ERROR: " << exc.what() << std::endl;
    }
}

void IMB_exr_write_channels(void *handle)
{
    ExrHandle *data= (ExrHandle *)handle;
    FrameBuffer frameBuffer;
    ExrChannel *echan;
    
    if(data->channels.first) {
        for(echan= (ExrChannel *)data->channels.first; echan; echan= echan->next) {
            /* last scanline, stride negative */
            float *rect = echan->rect + echan->xstride*(data->height-1)*data->width;
            
            frameBuffer.insert (echan->name, Slice (FLOAT,  (char *)rect, 
                                                    echan->xstride*sizeof(float), -echan->ystride*sizeof(float)));
        }
        
        data->ofile->setFrameBuffer (frameBuffer);
        try {
            data->ofile->writePixels (data->height);    
        }
        catch (const std::exception &exc) {
            std::cerr << "OpenEXR-writePixels: ERROR: " << exc.what() << std::endl;
        }
    }
    else {
        printf("Error: attempt to save MultiLayer without layers.\n");
    }
}

void IMB_exr_read_channels(void *handle)
{
    ExrHandle *data= (ExrHandle *)handle;
    FrameBuffer frameBuffer;
    ExrChannel *echan;
    
    /* check if exr was saved with previous versions of blender which flipped images */
    const StringAttribute *ta = data->ifile->header().findTypedAttribute <StringAttribute> ("BlenderMultiChannel");
    short flip = (ta && strncmp(ta->value().c_str(), "Blender V2.43", 13)==0); /* 'previous multilayer attribute, flipped */
    
    for(echan= (ExrChannel *)data->channels.first; echan; echan= echan->next) {
        
        if(echan->rect) {
            if(flip)
                frameBuffer.insert (echan->name, Slice (FLOAT,  (char *)echan->rect, 
                                            echan->xstride*sizeof(float), echan->ystride*sizeof(float)));
            else
                frameBuffer.insert (echan->name, Slice (FLOAT,  (char *)(echan->rect + echan->xstride*(data->height-1)*data->width), 
                                            echan->xstride*sizeof(float), -echan->ystride*sizeof(float)));
        }
        else 
            printf("warning, channel with no rect set %s\n", echan->name);
    }
    
    data->ifile->setFrameBuffer (frameBuffer);

    try {
        data->ifile->readPixels (0, data->height-1);    
    }
    catch (const std::exception &exc) {
        std::cerr << "OpenEXR-readPixels: ERROR: " << exc.what() << std::endl;
    }
}

void IMB_exr_multilayer_convert(void *handle, void *base,  
                                void * (*addlayer)(void *base, char *str), 
                                void (*addpass)(void *base, void *lay, char *str, 
                                                float *rect, int totchan, char *chan_id))
{
    ExrHandle *data= (ExrHandle *)handle;
    ExrLayer *lay;
    ExrPass *pass;

    if(data->layers.first==NULL) {
        printf("cannot convert multilayer, no layers in handle\n");
        return;
    }

    for(lay= (ExrLayer *)data->layers.first; lay; lay= lay->next) {
        void *laybase= addlayer(base, lay->name);
        if(laybase) {
            for(pass= (ExrPass *)lay->passes.first; pass; pass= pass->next) {
                addpass(base, laybase, pass->name, pass->rect, pass->totchan, pass->chan_id);
                pass->rect= NULL;
            }
        }
    }
}


void IMB_exr_close(void *handle)
{
    ExrHandle *data= (ExrHandle *)handle;
    ExrLayer *lay;
    ExrPass *pass;
    
    if(data->ifile)
        delete data->ifile;
    else if(data->ofile)
        delete data->ofile;
    else if(data->tofile)
        delete data->tofile;
    
    data->ifile= NULL;
    data->ofile= NULL;
    data->tofile= NULL;
    
    BLI_freelistN(&data->channels);
    
    for(lay= (ExrLayer *)data->layers.first; lay; lay= lay->next) {
        for(pass= (ExrPass *)lay->passes.first; pass; pass= pass->next)
            if(pass->rect)
                MEM_freeN(pass->rect);
        BLI_freelistN(&lay->passes);
    }
    BLI_freelistN(&data->layers);
    
    BLI_remlink(&exrhandles, data);
    MEM_freeN(data);
}

/* ********* */

static int imb_exr_split_channel_name(ExrChannel *echan, char *layname, char *passname)
{
    int plen, len= strlen(echan->name);
    
    if(len < 4) {
        printf("multilayer read: name too short: %s\n", echan->name);
        return 0;
    }
    if(echan->name[len-2]!='.') {
        printf("multilayer read: name has no Channel: %s\n", echan->name);
        return 0;
    }
    echan->chan_id= echan->name[len-1];
    
    len-= 3;
    while(len>=0) {
        if(echan->name[len]=='.')
            break;
        len--;
    }
    BLI_strncpy(passname, echan->name+len+1, EXR_PASS_MAXNAME);
    plen= strlen(passname);
    if(plen < 3) {
        printf("multilayer read: should not happen: %s\n", echan->name);
        return 0;
    }
    passname[plen-2]= 0;
    
    if(len<1)
        layname[0]= 0;
    else {
        BLI_strncpy(layname, echan->name, EXR_LAY_MAXNAME);
        layname[len]= 0;
    }
    // printf("found lay %s pass %s chan %c\n", layname, passname, echan->chan_id);
    return 1;
}

static ExrLayer *imb_exr_get_layer(ListBase *lb, char *layname)
{
    ExrLayer *lay= (ExrLayer *)BLI_findstring(lb, layname, offsetof(ExrLayer, name));

    if(lay==NULL) {
        lay= (ExrLayer *)MEM_callocN(sizeof(ExrLayer), "exr layer");
        BLI_addtail(lb, lay);
        BLI_strncpy(lay->name, layname, EXR_LAY_MAXNAME);
    }

    return lay;
}

static ExrPass *imb_exr_get_pass(ListBase *lb, char *passname)
{
    ExrPass *pass= (ExrPass *)BLI_findstring(lb, passname, offsetof(ExrPass, name));
    
    if(pass==NULL) {
        pass= (ExrPass *)MEM_callocN(sizeof(ExrPass), "exr pass");

        if(strcmp(passname, "Combined")==0)
            BLI_addhead(lb, pass);
        else
            BLI_addtail(lb, pass);
    }

    BLI_strncpy(pass->name, passname, EXR_LAY_MAXNAME);
    
    return pass;
}

/* creates channels, makes a hierarchy and assigns memory to channels */
static ExrHandle *imb_exr_begin_read_mem(InputFile *file, int width, int height)
{
    ExrLayer *lay;
    ExrPass *pass;
    ExrChannel *echan;
    ExrHandle *data= (ExrHandle *)IMB_exr_get_handle();
    int a;
    char layname[EXR_TOT_MAXNAME], passname[EXR_TOT_MAXNAME];
    
    data->ifile= file;
    data->width= width;
    data->height= height;
    
    const ChannelList &channels = data->ifile->header().channels();

    for (ChannelList::ConstIterator i = channels.begin(); i != channels.end(); ++i)
        IMB_exr_add_channel(data, NULL, i.name(), 0, 0, NULL);
    
    /* now try to sort out how to assign memory to the channels */
    /* first build hierarchical layer list */
    for(echan= (ExrChannel *)data->channels.first; echan; echan= echan->next) {
        if( imb_exr_split_channel_name(echan, layname, passname) ) {
            ExrLayer *lay= imb_exr_get_layer(&data->layers, layname);
            ExrPass *pass= imb_exr_get_pass(&lay->passes, passname);
            
            pass->chan[pass->totchan]= echan;
            pass->totchan++;
            if(pass->totchan>=EXR_PASS_MAXCHAN)
                break;
        }
    }
    if(echan) {
        printf("error, too many channels in one pass: %s\n", echan->name);
        IMB_exr_close(data);
        return NULL;
    }
    
    /* with some heuristics, try to merge the channels in buffers */
    for(lay= (ExrLayer *)data->layers.first; lay; lay= lay->next) {
        for(pass= (ExrPass *)lay->passes.first; pass; pass= pass->next) {
            if(pass->totchan) {
                pass->rect= (float *)MEM_mapallocN(width*height*pass->totchan*sizeof(float), "pass rect");
                if(pass->totchan==1) {
                    echan= pass->chan[0];
                    echan->rect= pass->rect;
                    echan->xstride= 1;
                    echan->ystride= width;
                    pass->chan_id[0]= echan->chan_id;
                }
                else {
                    char lookup[256];
                    
                    memset(lookup, 0, sizeof(lookup));
                           
                    /* we can have RGB(A), XYZ(W), UVA */
                    if(pass->totchan==3 || pass->totchan==4) {
                        if(pass->chan[0]->chan_id=='B' || pass->chan[1]->chan_id=='B' ||  pass->chan[2]->chan_id=='B') {
                            lookup[(unsigned int)'R']= 0;
                            lookup[(unsigned int)'G']= 1;
                            lookup[(unsigned int)'B']= 2;
                            lookup[(unsigned int)'A']= 3;
                        }
                        else if(pass->chan[0]->chan_id=='Y' || pass->chan[1]->chan_id=='Y' ||  pass->chan[2]->chan_id=='Y') {
                            lookup[(unsigned int)'X']= 0;
                            lookup[(unsigned int)'Y']= 1;
                            lookup[(unsigned int)'Z']= 2;
                            lookup[(unsigned int)'W']= 3;
                        }
                        else {
                            lookup[(unsigned int)'U']= 0;
                            lookup[(unsigned int)'V']= 1;
                            lookup[(unsigned int)'A']= 2;
                        }
                        for(a=0; a<pass->totchan; a++) {
                            echan= pass->chan[a];
                            echan->rect= pass->rect + lookup[(unsigned int)echan->chan_id];
                            echan->xstride= pass->totchan;
                            echan->ystride= width*pass->totchan;
                            pass->chan_id[ (unsigned int)lookup[(unsigned int)echan->chan_id] ]= echan->chan_id;
                        }
                    }
                    else { /* unknown */
                        for(a=0; a<pass->totchan; a++) {
                            echan= pass->chan[a];
                            echan->rect= pass->rect + a;
                            echan->xstride= pass->totchan;
                            echan->ystride= width*pass->totchan;
                            pass->chan_id[a]= echan->chan_id;
                        }
                    }
                }
            }
        }
    }
    
    return data;
}


/* ********************************************************* */

typedef struct RGBA
{
    float r;
    float g;
    float b;
    float a;
} RGBA;


/* debug only */
static void exr_print_filecontents(InputFile *file)
{
    const ChannelList &channels = file->header().channels();
    
    for (ChannelList::ConstIterator i = channels.begin(); i != channels.end(); ++i)
    {
        const Channel &channel = i.channel();
        printf("OpenEXR-load: Found channel %s of type %d\n", i.name(), channel.type);
    }
}

/* for non-multilayer, map  R G B A channel names to something that's in this file */
static const char *exr_rgba_channelname(InputFile *file, const char *chan)
{
    const ChannelList &channels = file->header().channels();
    
    for (ChannelList::ConstIterator i = channels.begin(); i != channels.end(); ++i)
    {
        /* const Channel &channel = i.channel(); */ /* Not used yet */
        const char *str= i.name();
        int len= strlen(str);
        if(len) {
            if(BLI_strcasecmp(chan, str+len-1)==0) {
                return str;
            }
        }
    }
    return chan;
}



static int exr_has_zbuffer(InputFile *file)
{
    return !(file->header().channels().findChannel("Z") == NULL);
}

static int exr_is_renderresult(InputFile *file)
{
    const StringAttribute *comments= file->header().findTypedAttribute<StringAttribute>("BlenderMultiChannel");
    if(comments)
//      if(comments->value() == "Blender MultiChannel")
            return 1;
    return 0;
}

struct ImBuf *imb_load_openexr(unsigned char *mem, size_t size, int flags)
{
    struct ImBuf *ibuf = NULL;
    InputFile *file = NULL;
    
    if (imb_is_a_openexr(mem) == 0) return(NULL);
    
    try
    {
        Mem_IStream *membuf = new Mem_IStream(mem, size); 
        int is_multi;
        file = new InputFile(*membuf);
        
        Box2i dw = file->header().dataWindow();
        int width  = dw.max.x - dw.min.x + 1;
        int height = dw.max.y - dw.min.y + 1;
        
        //printf("OpenEXR-load: image data window %d %d %d %d\n", 
        //     dw.min.x, dw.min.y, dw.max.x, dw.max.y);

        if(0) // debug
            exr_print_filecontents(file);
        
        is_multi= exr_is_renderresult(file);
        
        /* do not make an ibuf when */
        if(is_multi && !(flags & IB_test) && !(flags & IB_multilayer)) 
        {
            printf("Error: can't process EXR multilayer file\n");
        }
        else {
        
            ibuf = IMB_allocImBuf(width, height, 32, 0);
            ibuf->ftype = OPENEXR;

            /* openEXR is linear as per EXR spec */
            ibuf->profile = IB_PROFILE_LINEAR_RGB;
            
            if (!(flags & IB_test))
            {
                if(is_multi) /* only enters with IB_multilayer flag set */
                {
                    /* constructs channels for reading, allocates memory in channels */
                    ExrHandle *handle= imb_exr_begin_read_mem(file, width, height);
                    if(handle) {
                        IMB_exr_read_channels(handle);
                        ibuf->userdata= handle;         /* potential danger, the caller has to check for this! */
                        return ibuf;
                    }
                }
                else {
                    FrameBuffer frameBuffer;
                    float *first;
                    int xstride = sizeof(float) * 4;
                    int ystride = - xstride*width;
                    
                    imb_addrectfloatImBuf(ibuf);
                    
                    /* inverse correct first pixel for datawindow coordinates (- dw.min.y because of y flip) */
                    first= ibuf->rect_float - 4*(dw.min.x - dw.min.y*width);
                    /* but, since we read y-flipped (negative y stride) we move to last scanline */
                    first+= 4*(height-1)*width;
                    
                    frameBuffer.insert ( exr_rgba_channelname(file, "R"), 
                                        Slice (FLOAT,  (char *) first, xstride, ystride));
                    frameBuffer.insert ( exr_rgba_channelname(file, "G"), 
                                        Slice (FLOAT,  (char *) (first+1), xstride, ystride));
                    frameBuffer.insert ( exr_rgba_channelname(file, "B"), 
                                        Slice (FLOAT,  (char *) (first+2), xstride, ystride));
                                                                            
                    frameBuffer.insert ( exr_rgba_channelname(file, "A"), 
                                        Slice (FLOAT,  (char *) (first+3), xstride, ystride, 1, 1, 1.0f)); /* 1.0 is fill value */

                    if(exr_has_zbuffer(file)) 
                    {
                        float *firstz;
                        
                        addzbuffloatImBuf(ibuf);
                        firstz= ibuf->zbuf_float - (dw.min.x - dw.min.y*width);
                        firstz+= (height-1)*width;
                        frameBuffer.insert ("Z", Slice (FLOAT,  (char *)firstz , sizeof(float), -width*sizeof(float)));
                    }
                    
                    file->setFrameBuffer (frameBuffer);
                    file->readPixels (dw.min.y, dw.max.y);

                    // XXX, ImBuf has no nice way to deal with this.
                    // ideally IM_rect would be used when the caller wants a rect BUT
                    // at the moment all functions use IM_rect.
                    // Disabling this is ok because all functions should check if a rect exists and create one on demand.
                    //
                    // Disabling this because the sequencer frees immediate.
                    //
                    // if(flag & IM_rect)
                    //     IMB_rect_from_float(ibuf);
                }
            }
            
        }
        delete file;
        return(ibuf);
    }
    catch (const std::exception &exc)
    {
        std::cerr << exc.what() << std::endl;
        if (ibuf) IMB_freeImBuf(ibuf);
        delete file;
        
        return (0);
    }
    
}


} // export "C"