Affect correct texture units when disabling shadows for stateset

Knowing which are right required making the function non-static, so the shadow manager had to become a singleton as the results of passing it around to where it's needed were hellish.

I'm seeing a bunch of OpenGL errors when actually using this, so I'll investigate whether they're happening on master.
I'm hesitant to look into it too much, though, as I'm affected by https://gitlab.com/OpenMW/openmw/-/issues/7811, and also have the Windows setting enabled that turns driver timeouts into a BSOD so a kernel dump is collected that I can send to AMD.

apps/openmw/mwrender/characterpreview.cpp

@@ -247,7 +247,7 @@ namespace MWRender
         defaultMat->setSpecular(osg::Material::FRONT_AND_BACK, osg::Vec4f(0.f, 0.f, 0.f, 0.f));
         stateset->setAttribute(defaultMat);
 
-        SceneUtil::ShadowManager::disableShadowsForStateSet(Settings::shadows(), *stateset);
+        SceneUtil::ShadowManager::instance().disableShadowsForStateSet(*stateset);
 
         // assign large value to effectively turn off fog
         // shaders don't respect glDisable(GL_FOG)

apps/openmw/mwrender/localmap.cpp

@@ -763,7 +763,7 @@ namespace MWRender
 
         lightSource->setStateSetModes(*stateset, osg::StateAttribute::ON | osg::StateAttribute::OVERRIDE);
 
-        SceneUtil::ShadowManager::disableShadowsForStateSet(Settings::shadows(), *stateset);
+        SceneUtil::ShadowManager::instance().disableShadowsForStateSet(*stateset);
 
         // override sun for local map
         SceneUtil::configureStateSetSunOverride(static_cast<SceneUtil::LightManager*>(mSceneRoot), light, stateset);

apps/openmw/mwrender/sky.cpp

@@ -220,7 +220,7 @@ namespace
             camera->setNodeMask(MWRender::Mask_RenderToTexture);
             camera->setCullMask(MWRender::Mask_Sky);
             camera->addChild(mEarlyRenderBinRoot);
-            SceneUtil::ShadowManager::disableShadowsForStateSet(Settings::shadows(), *camera->getOrCreateStateSet());
+            SceneUtil::ShadowManager::instance().disableShadowsForStateSet(*camera->getOrCreateStateSet());
         }
 
     private:
@@ -274,7 +274,7 @@ namespace MWRender
         if (!mSceneManager->getForceShaders())
             skyroot->getOrCreateStateSet()->setAttributeAndModes(new osg::Program(),
                 osg::StateAttribute::OVERRIDE | osg::StateAttribute::PROTECTED | osg::StateAttribute::ON);
-        SceneUtil::ShadowManager::disableShadowsForStateSet(Settings::shadows(), *skyroot->getOrCreateStateSet());
+        SceneUtil::ShadowManager::instance().disableShadowsForStateSet(*skyroot->getOrCreateStateSet());
         parentNode->addChild(skyroot);
 
         mEarlyRenderBinRoot = new osg::Group;

apps/openmw/mwrender/water.cpp

@@ -276,8 +276,7 @@ namespace MWRender
             camera->setNodeMask(Mask_RenderToTexture);
 
             if (Settings::water().mRefractionScale != 1) // TODO: to be removed with issue #5709
-                SceneUtil::ShadowManager::disableShadowsForStateSet(
-                    Settings::shadows(), *camera->getOrCreateStateSet());
+                SceneUtil::ShadowManager::instance().disableShadowsForStateSet(*camera->getOrCreateStateSet());
         }
 
         void apply(osg::Camera* camera) override
@@ -353,7 +352,7 @@ namespace MWRender
             camera->addChild(mClipCullNode);
             camera->setNodeMask(Mask_RenderToTexture);
 
-            SceneUtil::ShadowManager::disableShadowsForStateSet(Settings::shadows(), *camera->getOrCreateStateSet());
+            SceneUtil::ShadowManager::instance().disableShadowsForStateSet(*camera->getOrCreateStateSet());
         }
 
         void apply(osg::Camera* camera) override

components/sceneutil/shadow.cpp

@@ -13,6 +13,16 @@ namespace SceneUtil
 {
     using namespace osgShadow;
 
+    ShadowManager* ShadowManager::sInstance = nullptr;
+
+    const ShadowManager& ShadowManager::instance()
+    {
+        if (sInstance)
+            return *sInstance;
+        else
+            throw std::logic_error("No ShadowManager exists yet");
+    }
+
     void ShadowManager::setupShadowSettings(
         const Settings::ShadowsCategory& settings, Shader::ShaderManager& shaderManager)
     {
@@ -75,15 +85,11 @@ namespace SceneUtil
             mShadowTechnique->disableDebugHUD();
     }
 
-    void ShadowManager::disableShadowsForStateSet(const Settings::ShadowsCategory& settings, osg::StateSet& stateset)
+    void ShadowManager::disableShadowsForStateSet(osg::StateSet& stateset) const
     {
-        if (!settings.mEnableShadows)
+        if (!mEnableShadows)
             return;
 
-        const int numberOfShadowMapsPerLight = settings.mNumberOfShadowMaps;
-
-        int baseShadowTextureUnit = 8 - numberOfShadowMapsPerLight;
-
         osg::ref_ptr<osg::Image> fakeShadowMapImage = new osg::Image();
         fakeShadowMapImage->allocateImage(1, 1, 1, GL_DEPTH_COMPONENT, GL_FLOAT);
         *(float*)fakeShadowMapImage->data() = std::numeric_limits<float>::infinity();
@@ -92,14 +98,15 @@ namespace SceneUtil
         fakeShadowMapTexture->setWrap(osg::Texture::WRAP_T, osg::Texture::CLAMP_TO_EDGE);
         fakeShadowMapTexture->setShadowComparison(true);
         fakeShadowMapTexture->setShadowCompareFunc(osg::Texture::ShadowCompareFunc::ALWAYS);
-        for (int i = baseShadowTextureUnit; i < baseShadowTextureUnit + numberOfShadowMapsPerLight; ++i)
+        for (int i = mShadowSettings->getBaseShadowTextureUnit();
+             i < mShadowSettings->getBaseShadowTextureUnit() + mShadowSettings->getNumShadowMapsPerLight(); ++i)
         {
             stateset.setTextureAttributeAndModes(i, fakeShadowMapTexture,
                 osg::StateAttribute::ON | osg::StateAttribute::OVERRIDE | osg::StateAttribute::PROTECTED);
-            stateset.addUniform(
-                new osg::Uniform(("shadowTexture" + std::to_string(i - baseShadowTextureUnit)).c_str(), i));
-            stateset.addUniform(
-                new osg::Uniform(("shadowTextureUnit" + std::to_string(i - baseShadowTextureUnit)).c_str(), i));
+            stateset.addUniform(new osg::Uniform(
+                ("shadowTexture" + std::to_string(i - mShadowSettings->getBaseShadowTextureUnit())).c_str(), i));
+            stateset.addUniform(new osg::Uniform(
+                ("shadowTextureUnit" + std::to_string(i - mShadowSettings->getBaseShadowTextureUnit())).c_str(), i));
         }
     }
 
@@ -111,6 +118,9 @@ namespace SceneUtil
         , mOutdoorShadowCastingMask(outdoorShadowCastingMask)
         , mIndoorShadowCastingMask(indoorShadowCastingMask)
     {
+        if (sInstance)
+            throw std::logic_error("A ShadowManager already exists");
+
         mShadowedScene->setShadowTechnique(mShadowTechnique);
 
         if (Stereo::getStereo())
@@ -127,6 +137,8 @@ namespace SceneUtil
         mShadowTechnique->setWorldMask(worldMask);
 
         enableOutdoorMode();
+
+        sInstance = this;
     }
 
     ShadowManager::~ShadowManager()
@@ -135,7 +147,7 @@ namespace SceneUtil
             Stereo::Manager::instance().setShadowTechnique(nullptr);
     }
 
-    Shader::ShaderManager::DefineMap ShadowManager::getShadowDefines(const Settings::ShadowsCategory& settings)
+    Shader::ShaderManager::DefineMap ShadowManager::getShadowDefines(const Settings::ShadowsCategory& settings) const
     {
         if (!mEnableShadows)
             return getShadowsDisabledDefines();

components/sceneutil/shadow.hpp

@@ -26,10 +26,10 @@ namespace SceneUtil
     class ShadowManager
     {
     public:
-        static void disableShadowsForStateSet(const Settings::ShadowsCategory& settings, osg::StateSet& stateset);
-
         static Shader::ShaderManager::DefineMap getShadowsDisabledDefines();
 
+        static const ShadowManager& instance();
+
         explicit ShadowManager(osg::ref_ptr<osg::Group> sceneRoot, osg::ref_ptr<osg::Group> rootNode,
             unsigned int outdoorShadowCastingMask, unsigned int indoorShadowCastingMask, unsigned int worldMask,
             const Settings::ShadowsCategory& settings, Shader::ShaderManager& shaderManager);
@@ -37,13 +37,17 @@ namespace SceneUtil
 
         void setupShadowSettings(const Settings::ShadowsCategory& settings, Shader::ShaderManager& shaderManager);
 
-        Shader::ShaderManager::DefineMap getShadowDefines(const Settings::ShadowsCategory& settings);
+        void disableShadowsForStateSet(osg::StateSet& stateset) const;
+
+        Shader::ShaderManager::DefineMap getShadowDefines(const Settings::ShadowsCategory& settings) const;
 
         void enableIndoorMode(const Settings::ShadowsCategory& settings);
 
         void enableOutdoorMode();
 
     protected:
+        static ShadowManager* sInstance;
+
         bool mEnableShadows;
 
         osg::ref_ptr<osgShadow::ShadowedScene> mShadowedScene;