avoids two transforms in sky.cpp (#3150)

As we discovered in #3148, `Transform` nodes and their low level equivalence `pushModelViewMatrix` are somewhat costly involving a `Matrix::invert` operation per frame.

With this PR we avoid one `Transform` node for sun flashes and avoid another `pushModelViewMatrix` call in case the sun is fully visible.

apps/openmw/mwrender/sky.cpp

@@ -81,15 +81,15 @@ namespace
         return mat;
     }
 
-    osg::ref_ptr<osg::Geometry> createTexturedQuad(int numUvSets=1)
+    osg::ref_ptr<osg::Geometry> createTexturedQuad(int numUvSets=1, float scale=1.f)
     {
         osg::ref_ptr<osg::Geometry> geom = new osg::Geometry;
 
         osg::ref_ptr<osg::Vec3Array> verts = new osg::Vec3Array;
-        verts->push_back(osg::Vec3f(-0.5, -0.5, 0));
-        verts->push_back(osg::Vec3f(-0.5, 0.5, 0));
-        verts->push_back(osg::Vec3f(0.5, 0.5, 0));
-        verts->push_back(osg::Vec3f(0.5, -0.5, 0));
+        verts->push_back(osg::Vec3f(-0.5*scale, -0.5*scale, 0));
+        verts->push_back(osg::Vec3f(-0.5*scale, 0.5*scale, 0));
+        verts->push_back(osg::Vec3f(0.5*scale, 0.5*scale, 0));
+        verts->push_back(osg::Vec3f(0.5*scale, -0.5*scale, 0));
 
         geom->setVertexArray(verts);
 
@@ -621,14 +621,13 @@ private:
         tex->setWrap(osg::Texture::WRAP_S, osg::Texture::CLAMP_TO_EDGE);
         tex->setWrap(osg::Texture::WRAP_T, osg::Texture::CLAMP_TO_EDGE);
 
-        osg::ref_ptr<osg::PositionAttitudeTransform> transform (new osg::PositionAttitudeTransform);
-        const float scale = 2.6f;
-        transform->setScale(osg::Vec3f(scale,scale,scale));
+        osg::ref_ptr<osg::Group> group (new osg::Group);
 
-        mTransform->addChild(transform);
+        mTransform->addChild(group);
 
-        osg::ref_ptr<osg::Geometry> geom = createTexturedQuad();
-        transform->addChild(geom);
+        const float scale = 2.6f;
+        osg::ref_ptr<osg::Geometry> geom = createTexturedQuad(1, scale);
+        group->addChild(geom);
 
         osg::StateSet* stateset = geom->getOrCreateStateSet();
 
@@ -637,7 +636,7 @@ private:
         stateset->setRenderBinDetails(RenderBin_SunGlare, "RenderBin");
         stateset->setNestRenderBins(false);
 
-        mSunFlashNode = transform;
+        mSunFlashNode = group;
 
         mSunFlashCallback = new SunFlashCallback(mOcclusionQueryVisiblePixels, mOcclusionQueryTotalPixels);
         mSunFlashNode->addCullCallback(mSunFlashCallback);
@@ -785,10 +784,12 @@ private:
                     stateset = new osg::StateSet;
                     stateset->setAttributeAndModes(mat, osg::StateAttribute::ON|osg::StateAttribute::OVERRIDE);
                 }
-
+                else if (visibleRatio < 1.f)
+                {
                     const float threshold = 0.6;
                     visibleRatio = visibleRatio * (1.f - threshold) + threshold;
                 }
+            }
 
             float scale = visibleRatio;
 
@@ -797,11 +798,13 @@ private:
                 // no traverse
                 return;
             }
+            else if (scale == 1.f)
+                traverse(node, cv);
             else
             {
                 osg::Matrix modelView = *cv->getModelViewMatrix();
 
-                modelView.preMultScale(osg::Vec3f(visibleRatio, visibleRatio, visibleRatio));
+                modelView.preMultScale(osg::Vec3f(scale, scale, scale));
 
                 if (stateset)
                     cv->pushStateSet(stateset);