Use the StateSetUpdater to modify alpha for Animation objects (bug #5001)

CHANGELOG.md

@@ -83,6 +83,7 @@
     Bug #4989: Object dimension-dependent VFX scaling behavior is inconsistent
     Bug #4990: Dead bodies prevent you from hitting
     Bug #4999: Drop instruction behaves differently from vanilla
+    Bug #5001: Possible data race in the Animation::setAlpha()
     Bug #5004: Werewolves shield their eyes during storm
     Feature #1774: Handle AvoidNode
     Feature #2229: Improve pathfinding AI

apps/openmw/mwrender/animation.cpp

@@ -460,6 +460,46 @@ namespace
 
 namespace MWRender
 {
+    class TransparencyUpdater : public SceneUtil::StateSetUpdater
+    {
+    public:
+        TransparencyUpdater(const float alpha)
+            : mAlpha(alpha)
+        {
+        }
+
+        void setAlpha(const float alpha)
+        {
+            mAlpha = alpha;
+        }
+
+    protected:
+        virtual void setDefaults(osg::StateSet* stateset)
+        {
+            osg::Material* material = static_cast<osg::Material*>(stateset->getAttribute(osg::StateAttribute::MATERIAL));
+
+            osg::BlendFunc* blendfunc (new osg::BlendFunc);
+            stateset->setAttributeAndModes(blendfunc, osg::StateAttribute::ON|osg::StateAttribute::OVERRIDE);
+
+            // FIXME: overriding diffuse/ambient/emissive colors
+            material = new osg::Material;
+            material->setColorMode(osg::Material::OFF);
+            material->setDiffuse(osg::Material::FRONT_AND_BACK, osg::Vec4f(1,1,1,mAlpha));
+            material->setAmbient(osg::Material::FRONT_AND_BACK, osg::Vec4f(1,1,1,1));
+            stateset->setAttributeAndModes(material, osg::StateAttribute::ON|osg::StateAttribute::OVERRIDE);
+            stateset->addUniform(new osg::Uniform("colorMode", 0), osg::StateAttribute::ON|osg::StateAttribute::OVERRIDE);
+        }
+
+        virtual void apply(osg::StateSet* stateset, osg::NodeVisitor* /*nv*/)
+        {
+            osg::Material* material = static_cast<osg::Material*>(stateset->getAttribute(osg::StateAttribute::MATERIAL));
+            material->setAlpha(osg::Material::FRONT_AND_BACK, mAlpha);
+        }
+
+    private:
+        float mAlpha;
+    };
+
     class GlowUpdater : public SceneUtil::StateSetUpdater
     {
     public:
@@ -1772,32 +1812,21 @@ namespace MWRender
             return;
         mAlpha = alpha;
 
+        // TODO: we use it to fade actors away too, but it would be nice to have a dithering shader instead.
         if (alpha != 1.f)
         {
-            // If we have an existing material for alpha transparency, just override alpha level
-            osg::StateSet* stateset = mObjectRoot->getOrCreateStateSet();
-            osg::Material* material = static_cast<osg::Material*>(stateset->getAttribute(osg::StateAttribute::MATERIAL));
-            if (material)
+            if (mTransparencyUpdater == nullptr)
             {
-                material->setAlpha(osg::Material::FRONT_AND_BACK, alpha);
+                mTransparencyUpdater = new TransparencyUpdater(alpha);
+                mObjectRoot->addUpdateCallback(mTransparencyUpdater);
             }
             else
-            {
-                osg::BlendFunc* blendfunc (new osg::BlendFunc);
-                stateset->setAttributeAndModes(blendfunc, osg::StateAttribute::ON|osg::StateAttribute::OVERRIDE);
-
-                // FIXME: overriding diffuse/ambient/emissive colors
-                material = new osg::Material;
-                material->setColorMode(osg::Material::OFF);
-                material->setDiffuse(osg::Material::FRONT_AND_BACK, osg::Vec4f(1,1,1,alpha));
-                material->setAmbient(osg::Material::FRONT_AND_BACK, osg::Vec4f(1,1,1,1));
-                stateset->setAttributeAndModes(material, osg::StateAttribute::ON|osg::StateAttribute::OVERRIDE);
-                stateset->addUniform(new osg::Uniform("colorMode", 0), osg::StateAttribute::ON|osg::StateAttribute::OVERRIDE);
-                mObjectRoot->setStateSet(stateset);
-            }
+                mTransparencyUpdater->setAlpha(alpha);
         }
         else
         {
+            mObjectRoot->removeUpdateCallback(mTransparencyUpdater);
+            mTransparencyUpdater = nullptr;
             mObjectRoot->setStateSet(nullptr);
         }
 

apps/openmw/mwrender/animation.hpp

@@ -35,6 +35,7 @@ namespace MWRender
 class ResetAccumRootCallback;
 class RotateController;
 class GlowUpdater;
+class TransparencyUpdater;
 
 class EffectAnimationTime : public SceneUtil::ControllerSource
 {
@@ -266,6 +267,7 @@ protected:
 
     osg::ref_ptr<SceneUtil::LightSource> mGlowLight;
     osg::ref_ptr<GlowUpdater> mGlowUpdater;
+    osg::ref_ptr<TransparencyUpdater> mTransparencyUpdater;
 
     float mAlpha;