examples/Multimedia/ICL/ICLCodec/PngScanlineDecoder.cpp

/*
Copyright (c) 2007-2010 Nokia Corporation and/or its subsidiary(-ies). All rights reserved.

Redistribution and use in source and binary forms, with or without
modification, are permitted provided that the following conditions are met:

* Redistributions of source code must retain the above copyright notice, this
  list of conditions and the following disclaimer.
* Redistributions in binary form must reproduce the above copyright notice,
  this list of conditions and the following disclaimer in the documentation
  and/or other materials provided with the distribution.
* Neither the name of Nokia Corporation nor the names of its contributors
  may be used to endorse or promote products derived from this software
  without specific prior written permission.

THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

Description:  
*/



#include "PNGCodec.h"

const TInt KPngScanlineFilterTypeLength = 1;

const TInt KColStart[KPngNumInterlacedPasses] = { 0, 4, 0, 2, 0, 1, 0, 0 };
const TInt KRowStart[KPngNumInterlacedPasses] = { 0, 0, 4, 0, 2, 0, 1, 0 };
const TInt KColIncrement[KPngNumInterlacedPasses] = { 8, 8, 4, 4, 2, 2, 1, 0 };
const TInt KRowIncrement[KPngNumInterlacedPasses] = { 8, 8, 8, 4, 4, 2, 2, 0 };
const TInt KBlockWidth[KPngNumInterlacedPasses] = { 8, 4, 4, 2, 2, 1, 1, 0 };
const TInt KBlockHeight[KPngNumInterlacedPasses] = { 8, 8, 4, 4, 2, 2, 1, 0 };

//
// These classes specialise the PNG reader to read
// scanlines with different bitmap depths/colour types
//

class CBitDepth1Decoder : public CPngReadSubCodec
        {
private:
        virtual void DoConstructL();
        virtual TInt ScanlineBufferSize(TInt aPixelLength);
        virtual void DoDecode(TUint8* aDataPtr,const TUint8* aDataPtrLimit);
        };

class CBitDepth2Decoder : public CPngReadSubCodec
        {
private:
        virtual void DoConstructL();
        virtual TInt ScanlineBufferSize(TInt aPixelLength);
        virtual void DoDecode(TUint8* aDataPtr,const TUint8* aDataPtrLimit);
        };

class CBitDepth4Decoder : public CPngReadSubCodec
        {
private:
        virtual void DoConstructL();
        virtual TInt ScanlineBufferSize(TInt aPixelLength);
        virtual void DoDecode(TUint8* aDataPtr,const TUint8* aDataPtrLimit);
        };

class CBitDepth8Decoder : public CPngReadSubCodec
        {
private:
        virtual void DoConstructL();
        virtual TInt ScanlineBufferSize(TInt aPixelLength);
        virtual void DoDecode(TUint8* aDataPtr,const TUint8* aDataPtrLimit);
        };

class CBitDepth8ColorType2Decoder : public CPngReadSubCodec
        {
private:
        virtual void DoConstructL();
        virtual TInt ScanlineBufferSize(TInt aPixelLength);
        virtual void DoDecode(TUint8* aDataPtr,const TUint8* aDataPtrLimit);
        };

class CBitDepth8ColorType4Decoder : public CPngReadSubCodec
        {
private:
        virtual void DoConstructL();
        virtual TInt ScanlineBufferSize(TInt aPixelLength);
        virtual void DoDecode(TUint8* aDataPtr,const TUint8* aDataPtrLimit);
        };

class CBitDepth8ColorType6Decoder : public CPngReadSubCodec
        {
private:
        virtual void DoConstructL();
        virtual TInt ScanlineBufferSize(TInt aPixelLength);
        virtual void DoDecode(TUint8* aDataPtr,const TUint8* aDataPtrLimit);
        };

class CBitDepth16ColorType0Decoder : public CPngReadSubCodec
        {
private:
        virtual void DoConstructL();
        virtual TInt ScanlineBufferSize(TInt aPixelLength);
        virtual void DoDecode(TUint8* aDataPtr,const TUint8* aDataPtrLimit);
        };

class CBitDepth16ColorType2Decoder : public CPngReadSubCodec
        {
private:
        virtual void DoConstructL();
        virtual TInt ScanlineBufferSize(TInt aPixelLength);
        virtual void DoDecode(TUint8* aDataPtr,const TUint8* aDataPtrLimit);
        };

class CBitDepth16ColorType4Decoder : public CPngReadSubCodec
        {
private:
        virtual void DoConstructL();
        virtual TInt ScanlineBufferSize(TInt aPixelLength);
        virtual void DoDecode(TUint8* aDataPtr,const TUint8* aDataPtrLimit);
        };

class CBitDepth16ColorType6Decoder : public CPngReadSubCodec
        {
private:
        virtual void DoConstructL();
        virtual TInt ScanlineBufferSize(TInt aPixelLength);
        virtual void DoDecode(TUint8* aDataPtr,const TUint8* aDataPtrLimit);
        };

//
// CPngReadSubCodec: base class for classes that read scanlines
//

// Factory function
CPngReadSubCodec* CPngReadSubCodec::NewL(CImageProcessor* aImageProc,CImageProcessor* aMaskProc,const TPngImageInformation& aInfo)
        {
        CPngReadSubCodec* self = NULL;

        switch (aInfo.iBitDepth)
                {
        case 1:
                self = new(ELeave) CBitDepth1Decoder;
                break;
        case 2:
                self = new(ELeave) CBitDepth2Decoder;
                break;
        case 4:
                self = new(ELeave) CBitDepth4Decoder;
                break;
        case 8:
                switch (aInfo.iColorType)
                        {
                case TPngImageInformation::EGrayscale:
                case TPngImageInformation::EIndexedColor:
                        self = new(ELeave) CBitDepth8Decoder;
                        break;
                case TPngImageInformation::EDirectColor:
                        self = new(ELeave) CBitDepth8ColorType2Decoder;
                        break;
                case TPngImageInformation::EAlphaGrayscale:
                        self = new(ELeave) CBitDepth8ColorType4Decoder;
                        break;
                case TPngImageInformation::EAlphaDirectColor:
                        self = new(ELeave) CBitDepth8ColorType6Decoder;
                        break;
                default:
                        User::Leave(KErrNotSupported);
                        break;
                        }
                break;
        case 16:
                switch (aInfo.iColorType)
                        {
                case TPngImageInformation::EGrayscale:
                        self = new(ELeave) CBitDepth16ColorType0Decoder;
                        break;
                case TPngImageInformation::EDirectColor:
                        self = new(ELeave) CBitDepth16ColorType2Decoder;
                        break;
                case TPngImageInformation::EAlphaGrayscale:
                        self = new(ELeave) CBitDepth16ColorType4Decoder;
                        break;
                case TPngImageInformation::EAlphaDirectColor:
                        self = new(ELeave) CBitDepth16ColorType6Decoder;
                        break;
                case TPngImageInformation::EIndexedColor:
                default:
                        User::Leave(KErrNotSupported);
                        break;
                        }
                break;
        default:
                User::Leave(KErrNotSupported);
                break;
                }

        CleanupStack::PushL(self);
        self->ConstructL(aImageProc,aMaskProc,aInfo);
        CleanupStack::Pop(); // self
        return self;
        }

CPngReadSubCodec::CPngReadSubCodec():
        iScanlineDes1(NULL,0),
        iScanlineDes2(NULL,0)
        {}

CPngReadSubCodec::~CPngReadSubCodec()
        {
        delete iScanlineBuffer1;
        delete iScanlineBuffer2;
        }

void CPngReadSubCodec::ConstructL(CImageProcessor* aImageProc,CImageProcessor* aMaskProc,const TPngImageInformation& aInfo)
        {
        iImageProc = aImageProc;
        iMaskProc = aMaskProc;
        iInfo = aInfo;
        iScanlineBufferSize = ScanlineBufferSize(iInfo.iSize.iWidth);

        DoConstructL();

        iScanlineBuffer1 = HBufC8::NewMaxL(iScanlineBufferSize);
        iScanlineBuffer2 = HBufC8::NewMaxL(iScanlineBufferSize);

        if (iInfo.iInterlaceMethod == TPngImageInformation::EAdam7Interlace)
                {
                iInterlacedScanlineBufferSize[0] = ScanlineBufferSize((iInfo.iSize.iWidth + 7) >> 3);
                iInterlacedScanlineBufferSize[1] = ScanlineBufferSize((iInfo.iSize.iWidth + 3) >> 3);
                iInterlacedScanlineBufferSize[2] = ScanlineBufferSize((iInfo.iSize.iWidth + 3) >> 2);
                iInterlacedScanlineBufferSize[3] = ScanlineBufferSize((iInfo.iSize.iWidth + 1) >> 2);
                iInterlacedScanlineBufferSize[4] = ScanlineBufferSize((iInfo.iSize.iWidth + 1) >> 1);
                iInterlacedScanlineBufferSize[5] = ScanlineBufferSize(iInfo.iSize.iWidth >> 1);
                iInterlacedScanlineBufferSize[6] = iScanlineBufferSize;
                iInterlacedScanlineBufferSize[7] = 0;
                iPass = 0;

                iScanlineDes1.Set(&(iScanlineBuffer1->Des())[0],iInterlacedScanlineBufferSize[0],iInterlacedScanlineBufferSize[0]);
                iScanlineDes2.Set(&(iScanlineBuffer2->Des())[0],iInterlacedScanlineBufferSize[0],iInterlacedScanlineBufferSize[0]);
                }
        else
                {
                iScanlineDes1.Set(&(iScanlineBuffer1->Des())[0],iScanlineBufferSize,iScanlineBufferSize);
                iScanlineDes2.Set(&(iScanlineBuffer2->Des())[0],iScanlineBufferSize,iScanlineBufferSize);
                }
        }

TDes8& CPngReadSubCodec::FirstBuffer()
        {
        iScanlineDes1.FillZ();
        iCurrentScanlineBuffer = 2;
        return iScanlineDes2;
        }

TDes8& CPngReadSubCodec::DecodeL()
        {
        TUint8* dataPtr = (iCurrentScanlineBuffer == 1) ? &iScanlineDes1[1] : &iScanlineDes2[1];
        const TUint8* dataPtrLimit = dataPtr + iScanlineDes1.Length() - 1;

        FilterScanlineDataL(dataPtr,dataPtrLimit);
        DoDecode(dataPtr,dataPtrLimit);
        UpdatePos();

        if (iCurrentScanlineBuffer == 1)
                {
                iCurrentScanlineBuffer = 2;
                return iScanlineDes2;
                }
        else
                {
                iCurrentScanlineBuffer = 1;
                return iScanlineDes1;
                }
        }

void CPngReadSubCodec::FilterScanlineDataL(TUint8* aDataPtr,const TUint8* aDataPtrLimit)
        {
        TInt filterType = (iCurrentScanlineBuffer == 1) ? iScanlineDes1[0] : iScanlineDes2[0];

        switch (filterType)
                {
        case 0: // None
                break;
        case 1: // Sub
                {
                aDataPtr += iBytesPerPixel;

                while (aDataPtr < aDataPtrLimit)
                        {
                        aDataPtr[0] = TUint8(aDataPtr[0] + aDataPtr[-iBytesPerPixel]);
                        aDataPtr++;
                        }
                }
                break;
        case 2: // Up
                {
                TUint8* altDataPtr = (iCurrentScanlineBuffer == 1) ? &iScanlineDes2[1] : &iScanlineDes1[1];

                while (aDataPtr < aDataPtrLimit)
                        *aDataPtr++ = TUint8(*aDataPtr + *altDataPtr++);
                }
                break;
        case 3: // Average
                {
                const TUint8* tempDataPtrLimit = Min<const TUint8*>(aDataPtr + iBytesPerPixel,aDataPtrLimit);
                TUint8* altDataPtr = (iCurrentScanlineBuffer == 1) ? &iScanlineDes2[1] : &iScanlineDes1[1];

                while (aDataPtr < tempDataPtrLimit)
                        {
                        aDataPtr[0] = TUint8(aDataPtr[0] + (altDataPtr[0] / 2));
                        aDataPtr++;
                        altDataPtr++;
                        }

                while (aDataPtr < aDataPtrLimit)
                        {
                        aDataPtr[0] = TUint8(aDataPtr[0] + ((altDataPtr[0] + aDataPtr[-iBytesPerPixel]) / 2));
                        aDataPtr++;
                        altDataPtr++;
                        }
                }
                break;
        case 4: // Paeth
                {
                const TUint8* tempDataPtrLimit = Min<const TUint8*>(aDataPtr + iBytesPerPixel,aDataPtrLimit);
                TUint8* altDataPtr = (iCurrentScanlineBuffer == 1) ? &iScanlineDes2[1] : &iScanlineDes1[1];

                while (aDataPtr < tempDataPtrLimit)
                        {
                        aDataPtr[0] = TUint8(aDataPtr[0] + altDataPtr[0]);
                        aDataPtr++;
                        altDataPtr++;
                        }

                while (aDataPtr < aDataPtrLimit)
                        {
                        aDataPtr[0] = TUint8(aDataPtr[0] + PaethPredictor(aDataPtr[-iBytesPerPixel],altDataPtr[0],altDataPtr[-iBytesPerPixel]));
                        aDataPtr++;
                        altDataPtr++;
                        }
                }
                break;
        default: // Error
                User::Leave(KErrCorrupt);
                break;
                }
        }

TInt CPngReadSubCodec::PaethPredictor(TInt aLeft,TInt aAbove,TInt aAboveLeft)
        {
        TInt p = aLeft + aAbove - aAboveLeft;
        TInt pa = Abs(p - aLeft);
        TInt pb = Abs(p - aAbove);
        TInt pc = Abs(p - aAboveLeft);

        if (pa <= pb && pa <= pc)
                return aLeft;
        else if (pb <= pc)
                return aAbove;
        else
                return aAboveLeft;
        }

void CPngReadSubCodec::WritePixel(TRgb aPixelColor)
        {
        if (iInfo.iInterlaceMethod == TPngImageInformation::EAdam7Interlace)
                {
                const TInt width = Min(KBlockWidth[iPass],iInfo.iSize.iWidth - iPos.iX);
                const TInt endY = Min(iPos.iY + KBlockHeight[iPass],iInfo.iSize.iHeight);

                TPoint pos(iPos);

                while (pos.iY < endY)
                        {
                        iImageProc->SetPos(pos);

                        for (TInt col = 0; col < width; col++)
                                iImageProc->SetPixel(aPixelColor);

                        pos.iY++;
                        }

                iPos.iX += KColIncrement[iPass];
                }
        else
                iImageProc->SetPixel(aPixelColor);
        }

void CPngReadSubCodec::WritePixel(TRgb aPixelColor,TUint8 aAlphaValue)
        {
        ASSERT(iMaskProc);

        TRgb maskColor(TRgb::Gray256(aAlphaValue));

        if (iInfo.iInterlaceMethod == TPngImageInformation::EAdam7Interlace)
                {
                iImageProc->SetPos(iPos);
                iMaskProc->SetPos(iPos);
                iImageProc->SetPixel(aPixelColor);
                iMaskProc->SetPixel(maskColor);

                iPos.iX += KColIncrement[iPass];
                }
        else
                {
                iImageProc->SetPixel(aPixelColor);
                iMaskProc->SetPixel(maskColor);
                }
        }

void CPngReadSubCodec::UpdatePos()
        {
        if (iInfo.iInterlaceMethod == TPngImageInformation::EAdam7Interlace)
                {
                ASSERT(iPass <= 7);

                iPos.iX = KColStart[iPass];
                iPos.iY += KRowIncrement[iPass];

                while (iPos.iX >= iInfo.iSize.iWidth || iPos.iY >= iInfo.iSize.iHeight)
                        {
                        iPass++;
                        iPos.iX = KColStart[iPass];
                        iPos.iY = KRowStart[iPass];
                        iScanlineDes1.Set(&(iScanlineBuffer1->Des())[0],iInterlacedScanlineBufferSize[iPass],iInterlacedScanlineBufferSize[iPass]);
                        iScanlineDes2.Set(&(iScanlineBuffer2->Des())[0],iInterlacedScanlineBufferSize[iPass],iInterlacedScanlineBufferSize[iPass]);
                        iScanlineDes1.FillZ();
                        iScanlineDes2.FillZ();
                        }
                }
        }

//
// CBitDepth1Decoder: specialised reader for 1bpp scanlines
//
void CBitDepth1Decoder::DoConstructL()
        {
        if (!(iInfo.iColorType & TPngImageInformation::EPaletteUsed))
                { // Set up palette to be grayscale values
                iInfo.iPalette[0] = KRgbBlack;
                iInfo.iPalette[1] = KRgbWhite;


                if (iInfo.iTransparencyPresent)
                        {
                        if (iInfo.iTransparentGray <= 1)
                                iInfo.iTransparencyValue[iInfo.iTransparentGray] = 0;
                        }
                }

        // Replicate values to avoid shifts when decoding
        iInfo.iPalette[2] = iInfo.iPalette[1];
        iInfo.iPalette[4] = iInfo.iPalette[1];
        iInfo.iPalette[8] = iInfo.iPalette[1];
        iInfo.iPalette[16] = iInfo.iPalette[1];
        iInfo.iPalette[32] = iInfo.iPalette[1];
        iInfo.iPalette[64] = iInfo.iPalette[1];
        iInfo.iPalette[128] = iInfo.iPalette[1];

        if (iInfo.iTransparencyPresent && iInfo.iTransparencyValue[1] != 255)
                {
                iInfo.iTransparencyValue[2] = iInfo.iTransparencyValue[1];
                iInfo.iTransparencyValue[4] = iInfo.iTransparencyValue[1];
                iInfo.iTransparencyValue[8] = iInfo.iTransparencyValue[1];
                iInfo.iTransparencyValue[16] = iInfo.iTransparencyValue[1];
                iInfo.iTransparencyValue[32] = iInfo.iTransparencyValue[1];
                iInfo.iTransparencyValue[64] = iInfo.iTransparencyValue[1];
                iInfo.iTransparencyValue[128] = iInfo.iTransparencyValue[1];
                }

        iBytesPerPixel = 1;
        if (iInfo.iInterlaceMethod == TPngImageInformation::ENoInterlace)
                {
                TInt pixelPadding = ((iInfo.iSize.iWidth + 7) & ~7) - iInfo.iSize.iWidth;
                iImageProc->SetPixelPadding(pixelPadding);
                if (iMaskProc)
                        iMaskProc->SetPixelPadding(pixelPadding);
                }
        }

TInt CBitDepth1Decoder::ScanlineBufferSize(TInt aPixelLength)
        {
        return ((aPixelLength + 7) / 8) + KPngScanlineFilterTypeLength;
        }

void CBitDepth1Decoder::DoDecode(TUint8* aDataPtr,const TUint8* aDataPtrLimit)
        {
        if (iMaskProc && iInfo.iTransparencyPresent)
                {
                while (aDataPtr < aDataPtrLimit)
                        {
                        TInt dataValue = *aDataPtr++;

                        for (TUint mask=0x80; mask!=0; mask>>=1) // iterate with 0x80, 0x40 .. 0x01
                                WritePixel(iInfo.iPalette[dataValue & mask],iInfo.iTransparencyValue[dataValue & mask]);
                        }
                }
        else
                {
                while (aDataPtr < aDataPtrLimit)
                        {
                        TInt dataValue = *aDataPtr++;

                        for (TUint mask=0x80; mask!=0; mask>>=1) // iterate with 0x80, 0x40 .. 0x01
                                WritePixel(iInfo.iPalette[dataValue & mask]);
                        }
                }
        }


//
// CBitDepth2Decoder: specialised reader for 2bpp scanlines
//
void CBitDepth2Decoder::DoConstructL()
        {
        if (!(iInfo.iColorType & TPngImageInformation::EPaletteUsed))
                { // Set up palette to be grayscale values
                iInfo.iPalette[0] = KRgbBlack;
                iInfo.iPalette[1] = KRgbDarkGray;
                iInfo.iPalette[2] = KRgbGray;
                iInfo.iPalette[3] = KRgbWhite;

                if (iInfo.iTransparencyPresent)
                        {
                        if (iInfo.iTransparentGray <= 3)
                                iInfo.iTransparencyValue[iInfo.iTransparentGray] = 0;
                        }
                }

        // Replicate values to avoid shifts when decoding
        iInfo.iPalette[4] = iInfo.iPalette[1];
        iInfo.iPalette[8] = iInfo.iPalette[2];
        iInfo.iPalette[12] = iInfo.iPalette[3];

        iInfo.iPalette[16] = iInfo.iPalette[1];
        iInfo.iPalette[32] = iInfo.iPalette[2];
        iInfo.iPalette[48] = iInfo.iPalette[3];

        iInfo.iPalette[64] = iInfo.iPalette[1];
        iInfo.iPalette[128] = iInfo.iPalette[2];
        iInfo.iPalette[192] = iInfo.iPalette[3];

        if (iInfo.iTransparencyPresent)
                {
                iInfo.iTransparencyValue[4] = iInfo.iTransparencyValue[1];
                iInfo.iTransparencyValue[8] = iInfo.iTransparencyValue[2];
                iInfo.iTransparencyValue[12] = iInfo.iTransparencyValue[3];

                iInfo.iTransparencyValue[16] = iInfo.iTransparencyValue[1];
                iInfo.iTransparencyValue[32] = iInfo.iTransparencyValue[2];
                iInfo.iTransparencyValue[48] = iInfo.iTransparencyValue[3];

                iInfo.iTransparencyValue[64] = iInfo.iTransparencyValue[1];
                iInfo.iTransparencyValue[128] = iInfo.iTransparencyValue[2];
                iInfo.iTransparencyValue[192] = iInfo.iTransparencyValue[3];
                }

        iBytesPerPixel = 1;
        if (iInfo.iInterlaceMethod == TPngImageInformation::ENoInterlace)
                {
                TInt pixelPadding = ((iInfo.iSize.iWidth + 3) & ~3) - iInfo.iSize.iWidth;
                iImageProc->SetPixelPadding(pixelPadding);
                if (iMaskProc)
                        iMaskProc->SetPixelPadding(pixelPadding);
                }
        }

TInt CBitDepth2Decoder::ScanlineBufferSize(TInt aPixelLength)
        {
        return ((aPixelLength + 3) / 4) + KPngScanlineFilterTypeLength;
        }

void CBitDepth2Decoder::DoDecode(TUint8* aDataPtr,const TUint8* aDataPtrLimit)
        {
        if (iMaskProc && iInfo.iTransparencyPresent)
                {
                while (aDataPtr < aDataPtrLimit)
                        {
                        TInt dataValue = *aDataPtr++;

                        for (TInt mask=0xc0; mask!=0; mask>>=2) // iterate through 0xc0, 0x30, 0x0c and 0x03
                                WritePixel(iInfo.iPalette[dataValue & mask],iInfo.iTransparencyValue[dataValue & mask]);
                        }
                }
        else
                {
                while (aDataPtr < aDataPtrLimit)
                        {
                        TInt dataValue = *aDataPtr++;

                        for (TInt mask=0xc0; mask!=0; mask>>=2) // iterate through 0xc0, 0x30, 0x0c and 0x03
                                WritePixel(iInfo.iPalette[dataValue & mask]);
                        }
                }
        }


//
// CBitDepth4Decoder: specialised reader for 4bpp scanlines
//

void CBitDepth4Decoder::DoConstructL()
        {
        if (!(iInfo.iColorType & TPngImageInformation::EPaletteUsed))
                { // Set up palette to be grayscale values
                for (TInt index = 0; index < 16; index++)
                        iInfo.iPalette[index] = TRgb::Gray16(index);

                if (iInfo.iTransparencyPresent)
                        {
                        if (iInfo.iTransparentGray <= 15)
                                iInfo.iTransparencyValue[iInfo.iTransparentGray] = 0;
                        }
                }

        iBytesPerPixel = 1;
        if (iInfo.iInterlaceMethod == TPngImageInformation::ENoInterlace)
                {
                TInt pixelPadding = ((iInfo.iSize.iWidth + 1) & ~1) - iInfo.iSize.iWidth;
                iImageProc->SetPixelPadding(pixelPadding);
                if (iMaskProc)
                        iMaskProc->SetPixelPadding(pixelPadding);
                }
        }

TInt CBitDepth4Decoder::ScanlineBufferSize(TInt aPixelLength)
        {
        return ((aPixelLength + 1) / 2) + KPngScanlineFilterTypeLength;
        }

void CBitDepth4Decoder::DoDecode(TUint8* aDataPtr,const TUint8* aDataPtrLimit)
        {
        if (iMaskProc && iInfo.iTransparencyPresent)
                {
                while (aDataPtr < aDataPtrLimit)
                        {
                        TInt dataValue = *aDataPtr++;

                        WritePixel(iInfo.iPalette[dataValue >> 4],iInfo.iTransparencyValue[dataValue >> 4]);
                        WritePixel(iInfo.iPalette[dataValue & 0x0f],iInfo.iTransparencyValue[dataValue & 0x0f]);
                        }
                }
        else
                {
                while (aDataPtr < aDataPtrLimit)
                        {
                        TInt dataValue = *aDataPtr++;

                        WritePixel(iInfo.iPalette[dataValue >> 4]);
                        WritePixel(iInfo.iPalette[dataValue & 0x0f]);
                        }
                }
        }


//
// CBitDepth8Decoder: specialised reader for 8bpp scanlines
//

void CBitDepth8Decoder::DoConstructL()
        {
        if (!(iInfo.iColorType & TPngImageInformation::EPaletteUsed))
                { // Set up palette to be grayscale values
                for (TInt index = 0; index < 256; index++)
                        iInfo.iPalette[index] = TRgb::Gray256(index);

                if (iInfo.iTransparencyPresent)
                        {
                        if (iInfo.iTransparentGray <= 255)
                                iInfo.iTransparencyValue[iInfo.iTransparentGray] = 0;
                        }
                }

        iBytesPerPixel = 1;
        }

TInt CBitDepth8Decoder::ScanlineBufferSize(TInt aPixelLength)
        {
        return aPixelLength + KPngScanlineFilterTypeLength;
        }

void CBitDepth8Decoder::DoDecode(TUint8* aDataPtr,const TUint8* aDataPtrLimit)
        {
        if (iMaskProc && iInfo.iTransparencyPresent)
                {
                while (aDataPtr < aDataPtrLimit)
                        {
                        WritePixel(iInfo.iPalette[aDataPtr[0]],iInfo.iTransparencyValue[aDataPtr[0]]);
                        aDataPtr++;
                        }
                }
        else
                {
                while (aDataPtr < aDataPtrLimit)
                        WritePixel(iInfo.iPalette[*aDataPtr++]);
                }
        }


//
// CBitDepth8ColorType2Decoder: specialised reader for 8bpp scanlines, direct colour
//

void CBitDepth8ColorType2Decoder::DoConstructL()
        {
        iBytesPerPixel = 3;
        }

TInt CBitDepth8ColorType2Decoder::ScanlineBufferSize(TInt aPixelLength)
        {
        return (aPixelLength * 3) + KPngScanlineFilterTypeLength;
        }

void CBitDepth8ColorType2Decoder::DoDecode(TUint8* aDataPtr,const TUint8* aDataPtrLimit)
        {
        if (iMaskProc && iInfo.iTransparencyPresent)
                {
                while (aDataPtr < aDataPtrLimit)
                        {
                        TInt red = aDataPtr[0];
                        TInt green = aDataPtr[1];
                        TInt blue = aDataPtr[2];
                        TRgb pixelColor(red,green,blue);
                        if (red == iInfo.iTransparentRed && green == iInfo.iTransparentGreen && blue == iInfo.iTransparentBlue)
                                WritePixel(pixelColor,0);
                        else
                                WritePixel(pixelColor,255);
                        aDataPtr += 3;
                        }
                }
        else
                {
                while (aDataPtr < aDataPtrLimit)
                        {
                        WritePixel(TRgb(aDataPtr[0],aDataPtr[1],aDataPtr[2]));
                        aDataPtr += 3;
                        }
                }
        }


//
// CBitDepth8ColorType4Decoder: specialised reader for 8bpp scanlines, alpha greyscale
//

void CBitDepth8ColorType4Decoder::DoConstructL()
        {
        iBytesPerPixel = 2;
        }

TInt CBitDepth8ColorType4Decoder::ScanlineBufferSize(TInt aPixelLength)
        {
        return (aPixelLength * 2) + KPngScanlineFilterTypeLength;
        }

void CBitDepth8ColorType4Decoder::DoDecode(TUint8* aDataPtr,const TUint8* aDataPtrLimit)
        {
        if (iMaskProc)
                {
                while (aDataPtr < aDataPtrLimit)
                        {
                        WritePixel(TRgb::Gray256(aDataPtr[0]),aDataPtr[1]);
                        aDataPtr += 2;
                        }
                }
        else
                {
                while (aDataPtr < aDataPtrLimit)
                        {
                        WritePixel(TRgb::Gray256(aDataPtr[0]));
                        aDataPtr += 2;
                        }
                }
        }


//
// CBitDepth8ColorType4Decoder: specialised reader for 8bpp scanlines, alpha colour
//

void CBitDepth8ColorType6Decoder::DoConstructL()
        {
        iBytesPerPixel = 4;
        }

TInt CBitDepth8ColorType6Decoder::ScanlineBufferSize(TInt aPixelLength)
        {
        return (aPixelLength * 4) + KPngScanlineFilterTypeLength;
        }

void CBitDepth8ColorType6Decoder::DoDecode(TUint8* aDataPtr,const TUint8* aDataPtrLimit)
        {
        if (iMaskProc)
                {
                while (aDataPtr < aDataPtrLimit)
                        {
                        WritePixel(TRgb(aDataPtr[0],aDataPtr[1],aDataPtr[2]),aDataPtr[3]);
                        aDataPtr += 4;
                        }
                }
        else
                {
                while (aDataPtr < aDataPtrLimit)
                        {
                        WritePixel(TRgb(aDataPtr[0],aDataPtr[1],aDataPtr[2]));
                        aDataPtr += 4;
                        }
                }
        }


//
// CBitDepth16ColorType0Decoder: specialised reader for 16bpp scanlines, greyscale
//

void CBitDepth16ColorType0Decoder::DoConstructL()
        {
        iBytesPerPixel = 2;
        }

TInt CBitDepth16ColorType0Decoder::ScanlineBufferSize(TInt aPixelLength)
        {
        return (aPixelLength * 2) + KPngScanlineFilterTypeLength;
        }

void CBitDepth16ColorType0Decoder::DoDecode(TUint8* aDataPtr,const TUint8* aDataPtrLimit)
        {
        if (iMaskProc && iInfo.iTransparencyPresent)
                {
                while (aDataPtr < aDataPtrLimit)
                        {
                        TInt gray = (aDataPtr[0] << 8) | aDataPtr[1];
                        TRgb pixelColor(TRgb::Gray256(aDataPtr[0]));
                        if (gray == iInfo.iTransparentGray)
                                WritePixel(pixelColor,0);
                        else
                                WritePixel(pixelColor,255);
                        aDataPtr += 2;
                        }
                }
        else
                {
                while (aDataPtr < aDataPtrLimit)
                        {
                        WritePixel(TRgb::Gray256(aDataPtr[0]));
                        aDataPtr += 2;
                        }
                }
        }


//
// CBitDepth16ColorType2Decoder: specialised reader for 16bpp scanlines, RGB colour
//

void CBitDepth16ColorType2Decoder::DoConstructL()
        {
        iBytesPerPixel = 6;
        }

TInt CBitDepth16ColorType2Decoder::ScanlineBufferSize(TInt aPixelLength)
        {
        return (aPixelLength * 6) + KPngScanlineFilterTypeLength;
        }

void CBitDepth16ColorType2Decoder::DoDecode(TUint8* aDataPtr,const TUint8* aDataPtrLimit)
        {
        if (iMaskProc && iInfo.iTransparencyPresent)
                {
                while (aDataPtr < aDataPtrLimit)
                        {
                        TInt red = (aDataPtr[0] << 8) | aDataPtr[1];
                        TInt green = (aDataPtr[2] << 8) | aDataPtr[3];
                        TInt blue = (aDataPtr[4] << 8) | aDataPtr[5];
                        TRgb pixelColor(aDataPtr[0],aDataPtr[2],aDataPtr[4]);
                        if (red == iInfo.iTransparentRed && green == iInfo.iTransparentGreen && blue == iInfo.iTransparentBlue)
                                WritePixel(pixelColor,0);
                        else
                                WritePixel(pixelColor,255);
                        aDataPtr += 6;
                        }
                }
        else
                {
                while (aDataPtr < aDataPtrLimit)
                        {
                        WritePixel(TRgb(aDataPtr[0],aDataPtr[2],aDataPtr[4]));
                        aDataPtr += 6;
                        }
                }
        }


//
// CBitDepth16ColorType4Decoder: specialised reader for 16bpp scanlines, alpha greyscale
//

void CBitDepth16ColorType4Decoder::DoConstructL()
        {
        iBytesPerPixel = 4;
        }

TInt CBitDepth16ColorType4Decoder::ScanlineBufferSize(TInt aPixelLength)
        {
        return (aPixelLength * 4) + KPngScanlineFilterTypeLength;
        }

void CBitDepth16ColorType4Decoder::DoDecode(TUint8* aDataPtr,const TUint8* aDataPtrLimit)
        {
        if (iMaskProc)
                {
                while (aDataPtr < aDataPtrLimit)
                        {
                        WritePixel(TRgb::Gray256(aDataPtr[0]),aDataPtr[2]);
                        aDataPtr += 4;
                        }
                }
        else
                {
                while (aDataPtr < aDataPtrLimit)
                        {
                        WritePixel(TRgb::Gray256(aDataPtr[0]));
                        aDataPtr += 4;
                        }
                }
        }


//
// CBitDepth16ColorType6Decoder: specialised reader for 16bpp scanlines, alpha colour
//

void CBitDepth16ColorType6Decoder::DoConstructL()
        {
        iBytesPerPixel = 8;
        }

TInt CBitDepth16ColorType6Decoder::ScanlineBufferSize(TInt aPixelLength)
        {
        return (aPixelLength * 8) + KPngScanlineFilterTypeLength;
        }

void CBitDepth16ColorType6Decoder::DoDecode(TUint8* aDataPtr,const TUint8* aDataPtrLimit)
        {
        if (iMaskProc)
                {
                while (aDataPtr < aDataPtrLimit)
                        {
                        WritePixel(TRgb(aDataPtr[0],aDataPtr[2],aDataPtr[4]),aDataPtr[6]);
                        aDataPtr += 8;
                        }
                }
        else
                {
                while (aDataPtr < aDataPtrLimit)
                        {
                        WritePixel(TRgb(aDataPtr[0],aDataPtr[2],aDataPtr[4]));
                        aDataPtr += 8;
                        }
                }
        }

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