1 files changed, 809 insertions, 0 deletions
diff --git a/vcl/source/opengl/OpenGLContext.cxx b/vcl/source/opengl/OpenGLContext.cxx
new file mode 100644
index 000000000..c959dac4d
--- /dev/null
+++ b/vcl/source/opengl/OpenGLContext.cxx
@@ -0,0 +1,809 @@
+/* -*- 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/.
+ */
+
+#include <chrono>
+
+#include <vcl/opengl/OpenGLContext.hxx>
+#include <vcl/opengl/OpenGLHelper.hxx>
+#include <vcl/opengl/OpenGLWrapper.hxx>
+#include <vcl/syschild.hxx>
+#include <vcl/sysdata.hxx>
+
+#include <osl/thread.hxx>
+#include <sal/log.hxx>
+
+#include <svdata.hxx>
+#include <salgdi.hxx>
+#include <salinst.hxx>
+
+#include <opengl/framebuffer.hxx>
+#include <opengl/program.hxx>
+#include <opengl/texture.hxx>
+#include <opengl/zone.hxx>
+
+#include <opengl/RenderState.hxx>
+
+#include <config_features.h>
+
+using namespace com::sun::star;
+
+#define MAX_FRAMEBUFFER_COUNT 30
+
+static sal_Int64 nBufferSwapCounter = 0;
+
+GLWindow::~GLWindow()
+{
+}
+
+bool GLWindow::Synchronize(bool /*bOnoff*/) const
+{
+    return false;
+}
+
+OpenGLContext::OpenGLContext():
+    mpWindow(nullptr),
+    m_pChildWindow(nullptr),
+    mbInitialized(false),
+    mnRefCount(0),
+    mbRequestLegacyContext(false),
+    mbVCLOnly(false),
+    mnFramebufferCount(0),
+    mpCurrentFramebuffer(nullptr),
+    mpFirstFramebuffer(nullptr),
+    mpLastFramebuffer(nullptr),
+    mpCurrentProgram(nullptr),
+    mpRenderState(new RenderState),
+    mpPrevContext(nullptr),
+    mpNextContext(nullptr)
+{
+    VCL_GL_INFO("new context: " << this);
+
+    ImplSVData* pSVData = ImplGetSVData();
+    if( pSVData->maGDIData.mpLastContext )
+    {
+        pSVData->maGDIData.mpLastContext->mpNextContext = this;
+        mpPrevContext = pSVData->maGDIData.mpLastContext;
+    }
+    pSVData->maGDIData.mpLastContext = this;
+
+    // FIXME: better hope we call 'makeCurrent' soon to preserve
+    // the invariant that the last item is the current context.
+}
+
+OpenGLContext::~OpenGLContext()
+{
+    assert (mnRefCount == 0);
+
+    mnRefCount = 1; // guard the shutdown paths.
+    VCL_GL_INFO("delete context: " << this);
+
+    reset();
+
+    ImplSVData* pSVData = ImplGetSVData();
+    if( mpPrevContext )
+        mpPrevContext->mpNextContext = mpNextContext;
+    if( mpNextContext )
+        mpNextContext->mpPrevContext = mpPrevContext;
+    else
+        pSVData->maGDIData.mpLastContext = mpPrevContext;
+
+    m_pChildWindow.disposeAndClear();
+    assert (mnRefCount == 1);
+}
+
+// release associated child-window if we have one
+void OpenGLContext::dispose()
+{
+    reset();
+    m_pChildWindow.disposeAndClear();
+}
+
+rtl::Reference<OpenGLContext> OpenGLContext::Create()
+{
+    return rtl::Reference<OpenGLContext>(ImplGetSVData()->mpDefInst->CreateOpenGLContext());
+}
+
+void OpenGLContext::requestLegacyContext()
+{
+    mbRequestLegacyContext = true;
+}
+
+#ifdef DBG_UTIL
+
+namespace {
+
+const char* getSeverityString(GLenum severity)
+{
+    switch(severity)
+    {
+        case GL_DEBUG_SEVERITY_LOW:
+            return "low";
+        case GL_DEBUG_SEVERITY_MEDIUM:
+            return "medium";
+        case GL_DEBUG_SEVERITY_HIGH:
+            return "high";
+        default:
+            ;
+    }
+
+    return "unknown";
+}
+
+const char* getSourceString(GLenum source)
+{
+    switch(source)
+    {
+        case GL_DEBUG_SOURCE_API:
+            return "API";
+        case GL_DEBUG_SOURCE_SHADER_COMPILER:
+            return "shader compiler";
+        case GL_DEBUG_SOURCE_WINDOW_SYSTEM:
+            return "window system";
+        case GL_DEBUG_SOURCE_THIRD_PARTY:
+            return "third party";
+        case GL_DEBUG_SOURCE_APPLICATION:
+            return "Libreoffice";
+        case GL_DEBUG_SOURCE_OTHER:
+            return "unknown";
+        default:
+            ;
+    }
+
+    return "unknown";
+}
+
+const char* getTypeString(GLenum type)
+{
+    switch(type)
+    {
+        case GL_DEBUG_TYPE_DEPRECATED_BEHAVIOR:
+            return "deprecated behavior";
+        case GL_DEBUG_TYPE_UNDEFINED_BEHAVIOR:
+            return "undefined behavior";
+        case GL_DEBUG_TYPE_PERFORMANCE:
+            return "performance";
+        case GL_DEBUG_TYPE_PORTABILITY:
+            return "portability";
+        case GL_DEBUG_TYPE_MARKER:
+            return "marker";
+        case GL_DEBUG_TYPE_PUSH_GROUP:
+            return "push group";
+        case GL_DEBUG_TYPE_POP_GROUP:
+            return "pop group";
+        case GL_DEBUG_TYPE_OTHER:
+            return "other";
+        case GL_DEBUG_TYPE_ERROR:
+            return "error";
+        default:
+            ;
+    }
+
+    return "unknown";
+}
+
+extern "C" void
+#if defined _WIN32
+APIENTRY
+#endif
+debug_callback(GLenum source, GLenum type, GLuint id,
+               GLenum severity, GLsizei , const GLchar* message,
+               const GLvoid*)
+{
+    // ignore Nvidia's 131218: "Program/shader state performance warning: Fragment Shader is going to be recompiled because the shader key based on GL state mismatches."
+    // the GLSL compiler is a bit too aggressive in optimizing the state based on the current OpenGL state
+
+    // ignore 131185: "Buffer detailed info: Buffer object x (bound to GL_ARRAY_BUFFER_ARB,
+    // usage hint is GL_STATIC_DRAW) will use VIDEO memory as the source for buffer object operations."
+    if (id == 131218 || id == 131185)
+        return;
+
+    SAL_WARN("vcl.opengl", "OpenGL debug message: source: " << getSourceString(source) << ", type: "
+            << getTypeString(type) << ", id: " << id << ", severity: " << getSeverityString(severity) << ", with message: " << message);
+}
+
+}
+
+#endif
+
+bool OpenGLContext::init( vcl::Window* pParent )
+{
+    if(mbInitialized)
+        return true;
+
+    OpenGLZone aZone;
+
+    m_xWindow.reset(pParent ? nullptr : VclPtr<vcl::Window>::Create(nullptr, WB_NOBORDER|WB_NODIALOGCONTROL));
+    mpWindow = pParent ? pParent : m_xWindow.get();
+    if(m_xWindow)
+        m_xWindow->setPosSizePixel(0,0,0,0);
+    //tdf#108069 we may be initted twice, so dispose earlier effort
+    m_pChildWindow.disposeAndClear();
+    initWindow();
+    return ImplInit();
+}
+
+bool OpenGLContext::ImplInit()
+{
+    VCL_GL_INFO("OpenGLContext not implemented for this platform");
+    return false;
+}
+
+static OUString getGLString(GLenum eGlEnum)
+{
+    OUString sString;
+    const GLubyte* pString = glGetString(eGlEnum);
+    if (pString)
+    {
+        sString = OUString::createFromAscii(reinterpret_cast<const char*>(pString));
+    }
+
+    CHECK_GL_ERROR();
+    return sString;
+}
+
+bool OpenGLContext::InitGL()
+{
+    VCL_GL_INFO("OpenGLContext::ImplInit----end");
+    VCL_GL_INFO("Vendor: " << getGLString(GL_VENDOR) << " Renderer: " << getGLString(GL_RENDERER) << " GL version: " << OpenGLHelper::getGLVersion());
+    mbInitialized = true;
+
+    // I think we need at least GL 3.0
+    if (epoxy_gl_version() < 30)
+    {
+        SAL_WARN("vcl.opengl", "We don't have at least OpenGL 3.0");
+        return false;
+    }
+
+    // Check that some "optional" APIs that we use unconditionally are present
+    if (!glBindFramebuffer)
+    {
+        SAL_WARN("vcl.opengl", "We don't have glBindFramebuffer");
+        return false;
+    }
+
+    return true;
+}
+
+void OpenGLContext::InitGLDebugging()
+{
+#ifdef DBG_UTIL
+    // only enable debug output in dbgutil build
+    if (epoxy_has_gl_extension("GL_ARB_debug_output"))
+    {
+        OpenGLZone aZone;
+
+        if (glDebugMessageCallbackARB)
+        {
+            glEnable(GL_DEBUG_OUTPUT_SYNCHRONOUS_ARB);
+            glDebugMessageCallbackARB(&debug_callback, nullptr);
+
+#ifdef GL_DEBUG_SEVERITY_NOTIFICATION_ARB
+            // Ignore i965’s shader compiler notification flood.
+            glDebugMessageControlARB(GL_DEBUG_SOURCE_SHADER_COMPILER_ARB, GL_DEBUG_TYPE_OTHER_ARB, GL_DEBUG_SEVERITY_NOTIFICATION_ARB, 0, nullptr, true);
+#endif
+        }
+        else if ( glDebugMessageCallback )
+        {
+            glEnable(GL_DEBUG_OUTPUT);
+            glDebugMessageCallback(&debug_callback, nullptr);
+
+            // Ignore i965’s shader compiler notification flood.
+            glDebugMessageControl(GL_DEBUG_SOURCE_SHADER_COMPILER, GL_DEBUG_TYPE_OTHER, GL_DEBUG_SEVERITY_NOTIFICATION, 0, nullptr, true);
+        }
+    }
+
+    // Test hooks for inserting tracing messages into the stream
+    VCL_GL_INFO("LibreOffice GLContext initialized");
+#endif
+}
+
+void OpenGLContext::restoreDefaultFramebuffer()
+{
+    glBindFramebuffer(GL_FRAMEBUFFER, 0);
+}
+
+void OpenGLContext::setWinPosAndSize(const Point &rPos, const Size& rSize)
+{
+    if (m_xWindow)
+        m_xWindow->SetPosSizePixel(rPos, rSize);
+    if (m_pChildWindow)
+        m_pChildWindow->SetPosSizePixel(rPos, rSize);
+
+    GLWindow& rGLWin = getModifiableOpenGLWindow();
+    rGLWin.Width = rSize.Width();
+    rGLWin.Height = rSize.Height();
+    adjustToNewSize();
+}
+
+void OpenGLContext::adjustToNewSize()
+{
+    const GLWindow& rGLWin = getOpenGLWindow();
+    glViewport(0, 0, rGLWin.Width, rGLWin.Height);
+}
+
+void OpenGLContext::InitChildWindow(SystemChildWindow *pChildWindow)
+{
+    pChildWindow->SetMouseTransparent(true);
+    pChildWindow->SetParentClipMode(ParentClipMode::Clip);
+    pChildWindow->EnableEraseBackground(false);
+    pChildWindow->SetControlForeground();
+    pChildWindow->SetControlBackground();
+}
+
+void OpenGLContext::initWindow()
+{
+}
+
+void OpenGLContext::destroyCurrentContext()
+{
+    //nothing by default
+}
+
+void OpenGLContext::reset()
+{
+    if( !mbInitialized )
+        return;
+
+    OpenGLZone aZone;
+
+    // reset the clip region
+    maClipRegion.SetEmpty();
+    mpRenderState.reset(new RenderState);
+
+    // destroy all framebuffers
+    if( mpLastFramebuffer )
+    {
+        OpenGLFramebuffer* pFramebuffer = mpLastFramebuffer;
+
+        makeCurrent();
+        while( pFramebuffer )
+        {
+            OpenGLFramebuffer* pPrevFramebuffer = pFramebuffer->mpPrevFramebuffer;
+            delete pFramebuffer;
+            pFramebuffer = pPrevFramebuffer;
+        }
+        mnFramebufferCount = 0;
+        mpFirstFramebuffer = nullptr;
+        mpLastFramebuffer = nullptr;
+    }
+
+    // destroy all programs
+    if( !maPrograms.empty() )
+    {
+        makeCurrent();
+        maPrograms.clear();
+    }
+
+    if( isCurrent() )
+        resetCurrent();
+
+    mbInitialized = false;
+
+    // destroy the context itself
+    destroyCurrentContext();
+}
+
+SystemWindowData OpenGLContext::generateWinData(vcl::Window* /*pParent*/, bool /*bRequestLegacyContext*/)
+{
+    return {};
+}
+
+bool OpenGLContext::isCurrent()
+{
+    (void) this; // loplugin:staticmethods
+    return false;
+}
+
+void OpenGLContext::makeCurrent()
+{
+    if (isCurrent())
+        return;
+
+    OpenGLZone aZone;
+
+    clearCurrent();
+
+    // by default nothing else to do
+
+    registerAsCurrent();
+}
+
+bool OpenGLContext::isAnyCurrent()
+{
+    return false;
+}
+
+bool OpenGLContext::hasCurrent()
+{
+    ImplSVData* pSVData = ImplGetSVData();
+    rtl::Reference<OpenGLContext> pCurrentCtx = pSVData->maGDIData.mpLastContext;
+    return pCurrentCtx.is() && pCurrentCtx->isAnyCurrent();
+}
+
+void OpenGLContext::clearCurrent()
+{
+    ImplSVData* pSVData = ImplGetSVData();
+
+    // release all framebuffers from the old context so we can re-attach the
+    // texture in the new context
+    rtl::Reference<OpenGLContext> pCurrentCtx = pSVData->maGDIData.mpLastContext;
+    if( pCurrentCtx.is() && pCurrentCtx->isCurrent() )
+        pCurrentCtx->ReleaseFramebuffers();
+}
+
+void OpenGLContext::prepareForYield()
+{
+    ImplSVData* pSVData = ImplGetSVData();
+
+    // release all framebuffers from the old context so we can re-attach the
+    // texture in the new context
+    rtl::Reference<OpenGLContext> pCurrentCtx = pSVData->maGDIData.mpLastContext;
+
+    if ( !pCurrentCtx.is() )
+        return;                 // Not using OpenGL
+
+    SAL_INFO("vcl.opengl", "Unbinding contexts in preparation for yield");
+
+    // Find the first context that is current and reset it.
+    // Usually the last context is the current, but not in case a new
+    // OpenGLContext is created already but not yet initialized.
+    while (pCurrentCtx.is())
+    {
+        if (pCurrentCtx->isCurrent())
+        {
+            pCurrentCtx->resetCurrent();
+            break;
+        }
+
+        pCurrentCtx = pCurrentCtx->mpPrevContext;
+    }
+
+    assert (!hasCurrent());
+}
+
+rtl::Reference<OpenGLContext> OpenGLContext::getVCLContext(bool bMakeIfNecessary)
+{
+    ImplSVData* pSVData = ImplGetSVData();
+    OpenGLContext *pContext = pSVData->maGDIData.mpLastContext;
+    while( pContext )
+    {
+        // check if this context is usable
+        if( pContext->isInitialized() && pContext->isVCLOnly() )
+            break;
+        pContext = pContext->mpPrevContext;
+    }
+    rtl::Reference<OpenGLContext> xContext;
+    vcl::Window* pDefWindow = !pContext && bMakeIfNecessary ? ImplGetDefaultWindow() : nullptr;
+    if (pDefWindow)
+    {
+        // create our magic fallback window context.
+#if HAVE_FEATURE_OPENGL
+        xContext = pDefWindow->GetGraphics()->GetOpenGLContext();
+        assert(xContext.is());
+#endif
+    }
+    else
+        xContext = pContext;
+
+    if( xContext.is() )
+        xContext->makeCurrent();
+
+    return xContext;
+}
+
+/*
+ * We don't care what context we have, but we want one that is live,
+ * ie. not reset underneath us, and is setup for VCL usage - ideally
+ * not swapping context at all.
+ */
+void OpenGLContext::makeVCLCurrent()
+{
+    getVCLContext();
+}
+
+void OpenGLContext::registerAsCurrent()
+{
+    ImplSVData* pSVData = ImplGetSVData();
+
+    // move the context to the end of the contexts list
+    static int nSwitch = 0;
+    VCL_GL_INFO("******* CONTEXT SWITCH " << ++nSwitch << " *********");
+    if( mpNextContext )
+    {
+        if( mpPrevContext )
+            mpPrevContext->mpNextContext = mpNextContext;
+        mpNextContext->mpPrevContext = mpPrevContext;
+
+        mpPrevContext = pSVData->maGDIData.mpLastContext;
+        mpNextContext = nullptr;
+        pSVData->maGDIData.mpLastContext->mpNextContext = this;
+        pSVData->maGDIData.mpLastContext = this;
+    }
+
+    // sync the render state with the current context
+    mpRenderState->sync();
+}
+
+void OpenGLContext::resetCurrent()
+{
+    clearCurrent();
+    // by default nothing else to do
+}
+
+void OpenGLContext::swapBuffers()
+{
+    // by default nothing else to do
+    BuffersSwapped();
+}
+
+void OpenGLContext::BuffersSwapped()
+{
+    nBufferSwapCounter++;
+
+    static bool bSleep = getenv("SAL_GL_SLEEP_ON_SWAP");
+    if (bSleep)
+    {
+        // half a second.
+        osl::Thread::wait( std::chrono::milliseconds(500) );
+    }
+}
+
+
+sal_Int64 OpenGLWrapper::getBufferSwapCounter()
+{
+    return nBufferSwapCounter;
+}
+
+void OpenGLContext::sync()
+{
+    // default is nothing
+    (void) this; // loplugin:staticmethods
+}
+
+void OpenGLContext::show()
+{
+    if (m_pChildWindow)
+        m_pChildWindow->Show();
+    else if (m_xWindow)
+        m_xWindow->Show();
+}
+
+SystemChildWindow* OpenGLContext::getChildWindow()
+{
+    return m_pChildWindow;
+}
+
+const SystemChildWindow* OpenGLContext::getChildWindow() const
+{
+    return m_pChildWindow;
+}
+
+void OpenGLContext::BindFramebuffer( OpenGLFramebuffer* pFramebuffer )
+{
+    OpenGLZone aZone;
+
+    if( pFramebuffer != mpCurrentFramebuffer )
+    {
+        if( pFramebuffer )
+            pFramebuffer->Bind();
+        else
+            OpenGLFramebuffer::Unbind();
+        mpCurrentFramebuffer = pFramebuffer;
+    }
+}
+
+void OpenGLContext::AcquireDefaultFramebuffer()
+{
+    BindFramebuffer( nullptr );
+}
+
+OpenGLFramebuffer* OpenGLContext::AcquireFramebuffer( const OpenGLTexture& rTexture )
+{
+    OpenGLZone aZone;
+
+    OpenGLFramebuffer* pFramebuffer = nullptr;
+    OpenGLFramebuffer* pFreeFbo = nullptr;
+    OpenGLFramebuffer* pSameSizeFbo = nullptr;
+
+    // check if there is already a framebuffer attached to that texture
+    pFramebuffer = mpLastFramebuffer;
+    while( pFramebuffer )
+    {
+        if( pFramebuffer->IsAttached( rTexture ) )
+            break;
+        if( !pFreeFbo && pFramebuffer->IsFree() )
+            pFreeFbo = pFramebuffer;
+        if( !pSameSizeFbo &&
+            pFramebuffer->GetWidth() == rTexture.GetWidth() &&
+            pFramebuffer->GetHeight() == rTexture.GetHeight() )
+            pSameSizeFbo = pFramebuffer;
+        pFramebuffer = pFramebuffer->mpPrevFramebuffer;
+    }
+
+    // else use any framebuffer having the same size
+    if( !pFramebuffer && pSameSizeFbo )
+        pFramebuffer = pSameSizeFbo;
+
+    // else use the first free framebuffer
+    if( !pFramebuffer && pFreeFbo )
+        pFramebuffer = pFreeFbo;
+
+    // if there isn't any free one, create a new one if the limit isn't reached
+    if( !pFramebuffer && mnFramebufferCount < MAX_FRAMEBUFFER_COUNT )
+    {
+        mnFramebufferCount++;
+        pFramebuffer = new OpenGLFramebuffer();
+        if( mpLastFramebuffer )
+        {
+            pFramebuffer->mpPrevFramebuffer = mpLastFramebuffer;
+            mpLastFramebuffer = pFramebuffer;
+        }
+        else
+        {
+            mpFirstFramebuffer = pFramebuffer;
+            mpLastFramebuffer = pFramebuffer;
+        }
+    }
+
+    // last try, use any framebuffer
+    // TODO order the list of framebuffers as a LRU
+    if( !pFramebuffer )
+        pFramebuffer = mpFirstFramebuffer;
+
+    assert( pFramebuffer );
+    BindFramebuffer( pFramebuffer );
+    pFramebuffer->AttachTexture( rTexture );
+
+    state().viewport(tools::Rectangle(Point(), Size(rTexture.GetWidth(), rTexture.GetHeight())));
+
+    return pFramebuffer;
+}
+
+// FIXME: this method is rather grim from a perf. perspective.
+// We should instead (eventually) use pointers to associate the
+// framebuffer and texture cleanly.
+void OpenGLContext::UnbindTextureFromFramebuffers( GLuint nTexture )
+{
+    OpenGLFramebuffer* pFramebuffer;
+
+    // see if there is a framebuffer attached to that texture
+    pFramebuffer = mpLastFramebuffer;
+    while( pFramebuffer )
+    {
+        if (pFramebuffer->IsAttached(nTexture))
+        {
+            BindFramebuffer(pFramebuffer);
+            pFramebuffer->DetachTexture();
+        }
+        pFramebuffer = pFramebuffer->mpPrevFramebuffer;
+    }
+
+    // Lets just check that no other context has a framebuffer
+    // with this texture - that would be bad ...
+    assert( !IsTextureAttachedAnywhere( nTexture ) );
+}
+
+/// Method for debugging; check texture is not already attached.
+bool OpenGLContext::IsTextureAttachedAnywhere( GLuint nTexture )
+{
+    ImplSVData* pSVData = ImplGetSVData();
+    for( auto *pCheck = pSVData->maGDIData.mpLastContext; pCheck;
+               pCheck = pCheck->mpPrevContext )
+    {
+        for( auto pBuffer = pCheck->mpLastFramebuffer; pBuffer;
+                  pBuffer = pBuffer->mpPrevFramebuffer )
+        {
+            if( pBuffer->IsAttached( nTexture ) )
+                return true;
+        }
+    }
+    return false;
+}
+
+void OpenGLContext::ReleaseFramebuffer( OpenGLFramebuffer* pFramebuffer )
+{
+    if( pFramebuffer )
+        pFramebuffer->DetachTexture();
+}
+
+void OpenGLContext::ReleaseFramebuffer( const OpenGLTexture& rTexture )
+{
+    OpenGLZone aZone;
+
+    if (!rTexture) // no texture to release.
+        return;
+
+    OpenGLFramebuffer* pFramebuffer = mpLastFramebuffer;
+
+    while( pFramebuffer )
+    {
+        if( pFramebuffer->IsAttached( rTexture ) )
+        {
+            BindFramebuffer( pFramebuffer );
+            pFramebuffer->DetachTexture();
+            if (mpCurrentFramebuffer == pFramebuffer)
+                BindFramebuffer( nullptr );
+        }
+        pFramebuffer = pFramebuffer->mpPrevFramebuffer;
+    }
+}
+
+void OpenGLContext::ReleaseFramebuffers()
+{
+    OpenGLZone aZone;
+
+    OpenGLFramebuffer* pFramebuffer = mpLastFramebuffer;
+    while( pFramebuffer )
+    {
+        if (!pFramebuffer->IsFree())
+        {
+            BindFramebuffer( pFramebuffer );
+            pFramebuffer->DetachTexture();
+        }
+        pFramebuffer = pFramebuffer->mpPrevFramebuffer;
+    }
+    BindFramebuffer( nullptr );
+}
+
+OpenGLProgram* OpenGLContext::GetProgram( const OUString& rVertexShader, const OUString& rFragmentShader, const OString& preamble )
+{
+    OpenGLZone aZone;
+
+    // We cache the shader programs in a per-process run-time cache
+    // based on only the names and the preamble. We don't expect
+    // shader source files to change during the lifetime of a
+    // LibreOffice process.
+    OString aNameBasedKey = OUStringToOString(rVertexShader + "+" + rFragmentShader, RTL_TEXTENCODING_UTF8) + "+" + preamble;
+    if( !aNameBasedKey.isEmpty() )
+    {
+        ProgramCollection::iterator it = maPrograms.find( aNameBasedKey );
+        if( it != maPrograms.end() )
+            return it->second.get();
+    }
+
+    // Binary shader programs are cached persistently (between
+    // LibreOffice process instances) based on a hash of their source
+    // code, as the source code can and will change between
+    // LibreOffice versions even if the shader names don't change.
+    OString aPersistentKey = OpenGLHelper::GetDigest( rVertexShader, rFragmentShader, preamble );
+    std::shared_ptr<OpenGLProgram> pProgram = std::make_shared<OpenGLProgram>();
+    if( !pProgram->Load( rVertexShader, rFragmentShader, preamble, aPersistentKey ) )
+        return nullptr;
+
+    maPrograms.insert(std::make_pair(aNameBasedKey, pProgram));
+    return pProgram.get();
+}
+
+OpenGLProgram* OpenGLContext::UseProgram( const OUString& rVertexShader, const OUString& rFragmentShader, const OString& preamble )
+{
+    OpenGLZone aZone;
+
+    OpenGLProgram* pProgram = GetProgram( rVertexShader, rFragmentShader, preamble );
+
+    if (pProgram && pProgram == mpCurrentProgram)
+    {
+        VCL_GL_INFO("Context::UseProgram: Reusing existing program " << pProgram->Id());
+        pProgram->Reuse();
+        return pProgram;
+    }
+
+    mpCurrentProgram = pProgram;
+
+    if (!mpCurrentProgram)
+    {
+        SAL_WARN("vcl.opengl", "OpenGLContext::UseProgram: mpCurrentProgram is 0");
+        return nullptr;
+    }
+
+    mpCurrentProgram->Use();
+
+    return mpCurrentProgram;
+}
+
+/* vim:set shiftwidth=4 softtabstop=4 expandtab: */