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diff --git a/vcl/opengl/scale.cxx b/vcl/opengl/scale.cxx
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+/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
+/*
+ * This file is part of the LibreOffice project.
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/.
+ *
+ * This file incorporates work covered by the following license notice:
+ *
+ *   Licensed to the Apache Software Foundation (ASF) under one or more
+ *   contributor license agreements. See the NOTICE file distributed
+ *   with this work for additional information regarding copyright
+ *   ownership. The ASF licenses this file to you under the Apache
+ *   License, Version 2.0 (the "License"); you may not use this file
+ *   except in compliance with the License. You may obtain a copy of
+ *   the License at http://www.apache.org/licenses/LICENSE-2.0 .
+ */
+
+#include <sal/config.h>
+#include <sal/log.hxx>
+
+#include <cmath>
+
+#include <vcl/opengl/OpenGLHelper.hxx>
+
+#include <vcl/bitmap.hxx>
+
+#include <opengl/zone.hxx>
+#include <opengl/salbmp.hxx>
+#include <opengl/program.hxx>
+#include <opengl/texture.hxx>
+#include <opengl/RenderState.hxx>
+
+#include <ResampleKernel.hxx>
+
+using vcl::Kernel;
+using vcl::Lanczos3Kernel;
+
+bool OpenGLSalBitmap::ImplScaleFilter(
+    const rtl::Reference< OpenGLContext > &xContext,
+    const double& rScaleX,
+    const double& rScaleY,
+    GLenum        nFilter )
+{
+    OpenGLFramebuffer* pFramebuffer;
+    OpenGLProgram* pProgram;
+    GLenum nOldFilter;
+    int nNewWidth( mnWidth * rScaleX );
+    int nNewHeight( mnHeight * rScaleY );
+
+    pProgram = xContext->UseProgram( "textureVertexShader",
+                                     "textureFragmentShader" );
+    if( !pProgram )
+        return false;
+
+    OpenGLTexture aNewTex(nNewWidth, nNewHeight);
+    pFramebuffer = xContext->AcquireFramebuffer( aNewTex );
+
+    pProgram->SetTexture( "sampler", maTexture );
+    nOldFilter = maTexture.GetFilter();
+    maTexture.SetFilter( nFilter );
+    pProgram->ApplyMatrix(mnWidth, mnHeight);
+    pProgram->DrawTexture( maTexture );
+    maTexture.SetFilter( nOldFilter );
+    pProgram->Clean();
+
+    OpenGLContext::ReleaseFramebuffer( pFramebuffer );
+
+    mnWidth = nNewWidth;
+    mnHeight = nNewHeight;
+    maTexture = aNewTex;
+
+    CHECK_GL_ERROR();
+    return true;
+}
+
+void OpenGLSalBitmap::ImplCreateKernel(
+    const double& fScale,
+    const Kernel& rKernel,
+    GLfloat*& pWeights,
+    sal_uInt32& aKernelSize )
+{
+    const double fSamplingRadius(rKernel.GetWidth());
+    const double fScaledRadius((fScale < 1.0) ? fSamplingRadius / fScale : fSamplingRadius);
+    const double fFilterFactor(std::min(fScale, 1.0));
+    int aNumberOfContributions;
+    double aSum( 0 );
+
+    aNumberOfContributions = (static_cast< sal_uInt32 >(fabs(ceil(fScaledRadius))) * 2) + 1 - 6;
+    aKernelSize = aNumberOfContributions / 2 + 1;
+
+    // avoid a crash for now; re-think me.
+    if (aKernelSize > 16)
+        aKernelSize = 16;
+
+    pWeights = new GLfloat[16];
+    memset( pWeights, 0, 16 * sizeof( GLfloat ) );
+
+    for( sal_uInt32 i(0); i < aKernelSize; i++ )
+    {
+        const GLfloat aWeight( rKernel.Calculate( fFilterFactor * i ) );
+        if( fabs( aWeight ) >= 0.0001 )
+        {
+            pWeights[i] = aWeight;
+            aSum += i > 0 ? aWeight * 2 : aWeight;
+        }
+    }
+
+    for( sal_uInt32 i(0); i < aKernelSize; i++ )
+    {
+        pWeights[i] /= aSum;
+    }
+}
+
+bool OpenGLSalBitmap::ImplScaleConvolution(
+    const rtl::Reference< OpenGLContext > &xContext,
+    const double& rScaleX,
+    const double& rScaleY,
+    const Kernel& aKernel )
+{
+    OpenGLFramebuffer* pFramebuffer;
+    OpenGLProgram* pProgram;
+    GLfloat* pWeights( nullptr );
+    sal_uInt32 nKernelSize;
+    GLfloat aOffsets[32];
+    int nNewWidth( mnWidth * rScaleX );
+    int nNewHeight( mnHeight * rScaleY );
+
+    // TODO Make sure the framebuffer is alright
+
+    pProgram = xContext->UseProgram( "textureVertexShader",
+                                      "convolutionFragmentShader" );
+    if( pProgram == nullptr )
+        return false;
+
+    // horizontal scaling in scratch texture
+    if( mnWidth != nNewWidth )
+    {
+        OpenGLTexture aScratchTex(nNewWidth, nNewHeight);
+
+        pFramebuffer = xContext->AcquireFramebuffer( aScratchTex );
+
+        for( sal_uInt32 i = 0; i < 16; i++ )
+        {
+            aOffsets[i * 2] = i / static_cast<double>(mnWidth);
+            aOffsets[i * 2 + 1] = 0;
+        }
+        ImplCreateKernel( rScaleX, aKernel, pWeights, nKernelSize );
+        pProgram->SetUniform1fv( "kernel", 16, pWeights );
+        pProgram->SetUniform2fv( "offsets", 16, aOffsets );
+        pProgram->SetTexture( "sampler", maTexture );
+        pProgram->DrawTexture( maTexture );
+        pProgram->Clean();
+
+        maTexture = aScratchTex;
+        OpenGLContext::ReleaseFramebuffer( pFramebuffer );
+    }
+
+    // vertical scaling in final texture
+    if( mnHeight != nNewHeight )
+    {
+        OpenGLTexture aScratchTex(nNewWidth, nNewHeight);
+
+        pFramebuffer = xContext->AcquireFramebuffer( aScratchTex );
+
+        for( sal_uInt32 i = 0; i < 16; i++ )
+        {
+            aOffsets[i * 2] = 0;
+            aOffsets[i * 2 + 1] = i / static_cast<double>(mnHeight);
+        }
+        ImplCreateKernel( rScaleY, aKernel, pWeights, nKernelSize );
+        pProgram->SetUniform1fv( "kernel", 16, pWeights );
+        pProgram->SetUniform2fv( "offsets", 16, aOffsets );
+        pProgram->SetTexture( "sampler", maTexture );
+        pProgram->DrawTexture( maTexture );
+        pProgram->Clean();
+
+        maTexture = aScratchTex;
+        OpenGLContext::ReleaseFramebuffer( pFramebuffer );
+    }
+
+    mnWidth = nNewWidth;
+    mnHeight = nNewHeight;
+
+    CHECK_GL_ERROR();
+    return true;
+}
+
+/*
+ "Area" scaling algorithm, which seems to give better results for downscaling
+ than other algorithms. The principle (taken from opencv, see resize.cl)
+ is that each resulting pixel is the average of all the source pixel values
+ it represents. Which is trivial in the case of exact multiples for downscaling,
+ the generic case needs to also consider that some source pixels contribute
+ only partially to their resulting pixels (because of non-integer multiples).
+*/
+bool OpenGLSalBitmap::ImplScaleArea( const rtl::Reference< OpenGLContext > &xContext,
+                                     double rScaleX, double rScaleY )
+{
+    int nNewWidth( mnWidth * rScaleX );
+    int nNewHeight( mnHeight * rScaleY );
+
+    if( nNewWidth == mnWidth && nNewHeight == mnHeight )
+        return true;
+
+    double ixscale = 1 / rScaleX;
+    double iyscale = 1 / rScaleY;
+    bool fast = ( ixscale == std::trunc( ixscale ) && iyscale == std::trunc( iyscale )
+        && int( nNewWidth * ixscale ) == mnWidth && int( nNewHeight * iyscale ) == mnHeight );
+
+    bool bTwoPasses = false;
+
+    // The generic case has arrays only up to 100 ratio downscaling, which is hopefully enough
+    // in practice, but protect against buffer overflows in case such an extreme case happens
+    // (and in such case the precision of the generic algorithm probably doesn't matter anyway).
+    if( ixscale > 100 || iyscale > 100 )
+    {
+        fast = true;
+    }
+    else
+    {
+        if (ixscale > 16 || iyscale > 16)
+        {
+            ixscale = std::floor(std::sqrt(ixscale));
+            iyscale = std::floor(std::sqrt(iyscale));
+            nNewWidth = int(mnWidth / ixscale);
+            rScaleX *= ixscale; // second pass x-scale factor
+            nNewHeight = int(mnHeight / iyscale);
+            rScaleY *= iyscale; // second pass y-scale factor
+            bTwoPasses = true;
+        }
+    }
+
+    // TODO Make sure the framebuffer is alright
+
+    OString sUseReducedRegisterVariantDefine;
+    if (xContext->getOpenGLCapabilitySwitch().mbLimitedShaderRegisters)
+        sUseReducedRegisterVariantDefine = OString("#define USE_REDUCED_REGISTER_VARIANT\n");
+
+    OpenGLProgram* pProgram = xContext->UseProgram( "textureVertexShader",
+        fast ? OUString( "areaScaleFastFragmentShader" ) : OUString( "areaScaleFragmentShader" ),
+        sUseReducedRegisterVariantDefine);
+
+    if( pProgram == nullptr )
+        return false;
+
+    OpenGLTexture aScratchTex(nNewWidth, nNewHeight);
+
+    OpenGLFramebuffer* pFramebuffer = xContext->AcquireFramebuffer( aScratchTex );
+
+    // NOTE: This setup is also done in OpenGLSalGraphicsImpl::DrawTransformedTexture().
+    if( fast )
+    {
+        pProgram->SetUniform1i( "xscale", ixscale );
+        pProgram->SetUniform1i( "yscale", iyscale );
+        // The shader operates on pixels in the surrounding area, so it's necessary
+        // to know the step in texture coordinates to get to the next pixel.
+        // With a texture atlas the "texture" is just a subtexture of a larger texture,
+        // so while with a normal texture we'd map between <0.0,1.0> and <0,mnWidth>,
+        // with a subtexture the texture coordinates range is smaller.
+        GLfloat srcCoords[ 8 ];
+        maTexture.GetWholeCoord( srcCoords );
+        pProgram->SetUniform1f( "xstep", ( srcCoords[ 4 ] - srcCoords[ 0 ] ) / mnWidth );
+        pProgram->SetUniform1f( "ystep", ( srcCoords[ 5 ] - srcCoords[ 1 ] ) / mnHeight );
+        pProgram->SetUniform1f( "ratio", 1.0 / ( ixscale * iyscale ));
+    }
+    else
+    {
+        pProgram->SetUniform1f( "xscale", ixscale );
+        pProgram->SetUniform1f( "yscale", iyscale );
+        pProgram->SetUniform1i( "swidth", mnWidth );
+        pProgram->SetUniform1i( "sheight", mnHeight );
+        // The shader internally actually operates on pixel coordinates,
+        // so it needs to know how to convert to those from the texture coordinates.
+        // With a simple texture that would mean converting e.g. between
+        // <0,mnWidth-1> and <0.0,1.0> coordinates.
+        // However with a texture atlas the "texture" is just a subtexture
+        // of a larger texture, so the texture coordinates need offset and ratio
+        // conversion too.
+        GLfloat srcCoords[ 8 ];
+        maTexture.GetWholeCoord( srcCoords );
+        pProgram->SetUniform1f( "xoffset", srcCoords[ 0 ] );
+        pProgram->SetUniform1f( "yoffset", srcCoords[ 1 ] );
+        pProgram->SetUniform1f( "xtopixelratio", nNewWidth / ( srcCoords[ 4 ] - srcCoords[ 0 ] ));
+        pProgram->SetUniform1f( "ytopixelratio", nNewHeight / ( srcCoords[ 5 ] - srcCoords[ 1 ] ));
+        pProgram->SetUniform1f( "xfrompixelratio", ( srcCoords[ 4 ] - srcCoords[ 0 ] ) / mnWidth );
+        pProgram->SetUniform1f( "yfrompixelratio", ( srcCoords[ 5 ] - srcCoords[ 1 ] ) / mnHeight );
+    }
+
+    pProgram->SetTexture( "sampler", maTexture );
+    pProgram->DrawTexture( maTexture );
+    pProgram->Clean();
+
+    OpenGLContext::ReleaseFramebuffer(pFramebuffer);
+
+    CHECK_GL_ERROR();
+
+    if (bTwoPasses)
+    {
+        mnWidth = nNewWidth;
+        mnHeight = nNewHeight;
+
+        nNewWidth = round(mnWidth * rScaleX);
+        nNewHeight = round(mnHeight * rScaleY);
+
+        ixscale = 1 / rScaleX;
+        iyscale = 1 / rScaleY;
+
+        pProgram = xContext->UseProgram("textureVertexShader", "areaScaleFragmentShader", sUseReducedRegisterVariantDefine);
+        if (pProgram == nullptr)
+            return false;
+
+        OpenGLTexture aScratchTex2(nNewWidth, nNewHeight);
+
+        pFramebuffer = xContext->AcquireFramebuffer(aScratchTex2);
+
+        pProgram->SetUniform1f("xscale", ixscale);
+        pProgram->SetUniform1f("yscale", iyscale);
+        pProgram->SetUniform1i("swidth", mnWidth);
+        pProgram->SetUniform1i("sheight", mnHeight);
+
+        GLfloat srcCoords[ 8 ];
+        aScratchTex.GetWholeCoord( srcCoords );
+        pProgram->SetUniform1f( "xoffset", srcCoords[ 0 ] );
+        pProgram->SetUniform1f( "yoffset", srcCoords[ 1 ] );
+        pProgram->SetUniform1f( "xtopixelratio", nNewWidth / ( srcCoords[ 4 ] - srcCoords[ 0 ] ));
+        pProgram->SetUniform1f( "ytopixelratio", nNewHeight / ( srcCoords[ 5 ] - srcCoords[ 1 ] ));
+        pProgram->SetUniform1f( "xfrompixelratio", ( srcCoords[ 4 ] - srcCoords[ 0 ] ) / mnWidth );
+        pProgram->SetUniform1f( "yfrompixelratio", ( srcCoords[ 5 ] - srcCoords[ 1 ] ) / mnHeight );
+
+        pProgram->SetTexture("sampler", aScratchTex);
+        pProgram->DrawTexture(aScratchTex);
+        pProgram->Clean();
+
+        OpenGLContext::ReleaseFramebuffer(pFramebuffer);
+
+        CHECK_GL_ERROR();
+
+        maTexture = aScratchTex2;
+        mnWidth = nNewWidth;
+        mnHeight = nNewHeight;
+    }
+    else
+    {
+        maTexture = aScratchTex;
+        mnWidth = nNewWidth;
+        mnHeight = nNewHeight;
+    }
+
+    return true;
+}
+
+void OpenGLSalBitmap::ImplScale( const double& rScaleX, const double& rScaleY, BmpScaleFlag nScaleFlag )
+{
+    VCL_GL_INFO( "::ImplScale" );
+
+    mpUserBuffer.reset();
+    OpenGLVCLContextZone aContextZone;
+    rtl::Reference<OpenGLContext> xContext = OpenGLContext::getVCLContext();
+    xContext->state().scissor().disable();
+    xContext->state().stencil().disable();
+
+    if (rScaleX <= 1 && rScaleY <= 1)
+    {
+        nScaleFlag = BmpScaleFlag::BestQuality;
+    }
+
+    if( nScaleFlag == BmpScaleFlag::Fast )
+    {
+        ImplScaleFilter( xContext, rScaleX, rScaleY, GL_NEAREST );
+    }
+    else if( nScaleFlag == BmpScaleFlag::BiLinear )
+    {
+        ImplScaleFilter( xContext, rScaleX, rScaleY, GL_LINEAR );
+    }
+    else if( nScaleFlag == BmpScaleFlag::Default )
+    {
+        const Lanczos3Kernel aKernel;
+
+        ImplScaleConvolution( xContext, rScaleX, rScaleY, aKernel );
+    }
+    else if( nScaleFlag == BmpScaleFlag::BestQuality && rScaleX <= 1 && rScaleY <= 1 )
+    { // Use area scaling for best quality, but only if downscaling.
+        ImplScaleArea( xContext, rScaleX, rScaleY );
+    }
+    else if( nScaleFlag == BmpScaleFlag::Lanczos || nScaleFlag == BmpScaleFlag::BestQuality  )
+    {
+        const Lanczos3Kernel aKernel;
+
+        ImplScaleConvolution( xContext, rScaleX, rScaleY, aKernel );
+    }
+    else
+        SAL_WARN( "vcl.opengl", "Invalid flag for scaling operation" );
+}
+
+bool OpenGLSalBitmap::ScalingSupported() const
+{
+    return true;
+}
+
+bool OpenGLSalBitmap::Scale( const double& rScaleX, const double& rScaleY, BmpScaleFlag nScaleFlag )
+{
+    OpenGLVCLContextZone aContextZone;
+
+    VCL_GL_INFO("::Scale " << int(nScaleFlag)
+             << " from " << mnWidth << "x" << mnHeight
+             << " to " << (mnWidth * rScaleX) << "x" << (mnHeight * rScaleY) );
+
+    if( nScaleFlag == BmpScaleFlag::Fast ||
+        nScaleFlag == BmpScaleFlag::BiLinear ||
+        nScaleFlag == BmpScaleFlag::Lanczos ||
+        nScaleFlag == BmpScaleFlag::Default ||
+        nScaleFlag == BmpScaleFlag::BestQuality )
+    {
+        ImplScale( rScaleX, rScaleY, nScaleFlag );
+        return true;
+    }
+
+    return false;
+}
+
+/* vim:set shiftwidth=4 softtabstop=4 expandtab: */