Merge branch 'ivecometomakeanannouncement' into 'master'

Fix moon blending (#6439)

Closes #6439

See merge request OpenMW/openmw!5211

Author: jvoisin

apps/openmw/mwrender/skyutil.cpp

@@ -318,45 +318,32 @@ namespace MWRender
 
     struct MoonUpdater : SceneUtil::StateSetUpdater
     {
-        Resource::ImageManager& mImageManager;
-        osg::ref_ptr<osg::Texture2D> mPhaseTex;
-        osg::ref_ptr<osg::Texture2D> mCircleTex;
-        float mTransparency;
-        float mShadowBlend;
-        osg::Vec4f mAtmosphereColor;
-        osg::Vec4f mMoonColor;
+        float mTransparency{ 1.f };
+        float mShadowBlend{ 1.f };
+        osg::Vec4f mAtmosphereColor{ 1.f, 1.f, 1.f, 1.f };
+        osg::Vec4f mMoonColor{ 1.f, 1.f, 1.f, 1.f };
 
         MoonUpdater(Resource::ImageManager& imageManager)
             : mImageManager(imageManager)
-            , mPhaseTex()
-            , mCircleTex()
-            , mTransparency(1.0f)
-            , mShadowBlend(1.0f)
-            , mAtmosphereColor(1.0f, 1.0f, 1.0f, 1.0f)
-            , mMoonColor(1.0f, 1.0f, 1.0f, 1.0f)
         {
         }
 
         void setDefaults(osg::StateSet* stateset) override
         {
             stateset->addUniform(new osg::Uniform("pass", static_cast<int>(Pass::Moon)));
-            stateset->setTextureAttributeAndModes(0, mPhaseTex);
-            stateset->setTextureAttributeAndModes(1, mCircleTex);
-            stateset->setTextureMode(0, GL_TEXTURE_2D, osg::StateAttribute::ON | osg::StateAttribute::OVERRIDE);
-            stateset->setTextureMode(1, GL_TEXTURE_2D, osg::StateAttribute::ON | osg::StateAttribute::OVERRIDE);
+            stateset->setTextureAttribute(0, mPhaseTex);
+            stateset->setTextureAttribute(1, mCircleTex);
             stateset->addUniform(new osg::Uniform("moonBlend", osg::Vec4f{}));
             stateset->addUniform(new osg::Uniform("atmosphereFade", osg::Vec4f{}));
             stateset->addUniform(new osg::Uniform("diffuseMap", 0));
             stateset->addUniform(new osg::Uniform("maskMap", 1));
             stateset->setAttributeAndModes(
-                createUnlitMaterial(), osg::StateAttribute::ON | osg::StateAttribute::OVERRIDE);
+                new osg::BlendFunc(osg::BlendFunc::ONE, osg::BlendFunc::ONE_MINUS_SRC_ALPHA), osg::StateAttribute::ON);
+            stateset->setAttributeAndModes(createUnlitMaterial(), osg::StateAttribute::ON);
         }
 
         void apply(osg::StateSet* stateset, osg::NodeVisitor*) override
         {
-            stateset->setTextureAttribute(0, mPhaseTex, osg::StateAttribute::ON | osg::StateAttribute::OVERRIDE);
-            stateset->setTextureAttribute(1, mCircleTex, osg::StateAttribute::ON | osg::StateAttribute::OVERRIDE);
-
             if (auto* uMoonBlend = stateset->getUniform("moonBlend"))
                 uMoonBlend->set(mMoonColor * mShadowBlend);
             if (auto* uAtmosphereFade = stateset->getUniform("atmosphereFade"))
@@ -375,6 +362,11 @@ namespace MWRender
 
             reset();
         }
+
+    private:
+        Resource::ImageManager& mImageManager;
+        osg::ref_ptr<osg::Texture2D> mPhaseTex;
+        osg::ref_ptr<osg::Texture2D> mCircleTex;
     };
 
     class CameraRelativeTransformCullCallback

files/shaders/compatibility/sky.frag

@@ -39,8 +39,25 @@ void paintMoon(inout vec4 color)
     vec4 phase = texture2D(diffuseMap, diffuseMapUV);
     vec4 mask = texture2D(maskMap, diffuseMapUV);
 
-    vec4 blendedLayer = phase * moonBlend;
-    color = vec4(blendedLayer.xyz + atmosphereFade.xyz, atmosphereFade.a * mask.a);
+    // Morrowind does this in two passes
+
+    // First pass: moon shadow, normal blending (src alpha, 1 - src alpha)
+    // dst.rgb = mask.rgb * mask.a + dst.rgb * (1 - mask.a)
+    // Second pass: moon phase, additive blending (src alpha, 1)
+    // dst.rgb += phase.rgb * phase.a
+
+    // The same is doable in a single pass through premultiplied alpha blending
+    // color.rgb = mask.rgb * mask.a + phase.rgb * phase.a
+    // color.a = mask.a
+    // dst.rgb = color.rgb + dst.rgb * (1 - color.a)
+
+    vec3 maskTinted = mask.rgb * atmosphereFade.rgb;
+    float maskAlpha = mask.a * atmosphereFade.a;
+    vec3 phaseTinted = phase.rgb * moonBlend.rgb;
+    float phaseAlpha = phase.a * atmosphereFade.a;
+
+    color.rgb = maskTinted * maskAlpha + phaseTinted * phaseAlpha;
+    color.a = maskAlpha;
 }
 
 void paintSun(inout vec4 color)