Disable mipmaps for GUI textures

For some reason, the mipmap generator seems to be broken on Linux Intel graphics (works on Nvidia). This was breaking the scrollbar arrows, which are minified enough to show using a mipmap.

components/myguiplatform/myguitexture.cpp

@@ -87,6 +87,8 @@ namespace osgMyGUI
             throw std::runtime_error("No texturemanager set");
 
         mTexture = mTextureManager->getTexture2D(fname, osg::Texture2D::CLAMP_TO_EDGE, osg::Texture2D::CLAMP_TO_EDGE);
+        // disable mip-maps
+        mTexture->setFilter(osg::Texture2D::MIN_FILTER, osg::Texture2D::LINEAR);
 
         // FIXME
         mFormat = MyGUI::PixelFormat::R8G8B8;

components/resource/texturemanager.cpp

@@ -64,7 +64,30 @@ namespace Resource
         for (std::map<MapKey, osg::ref_ptr<osg::Texture2D> >::iterator it = mTextures.begin(); it != mTextures.end(); ++it)
         {
             osg::ref_ptr<osg::Texture2D> tex = it->second;
-            tex->setFilter(osg::Texture::MIN_FILTER, mMinFilter);
+
+            // Keep mip-mapping disabled if the texture creator explicitely requested it.
+            osg::Texture::FilterMode oldMin = tex->getFilter(osg::Texture::MIN_FILTER);
+            if (oldMin == osg::Texture::LINEAR || oldMin == osg::Texture::NEAREST)
+            {
+                osg::Texture::FilterMode newMin = osg::Texture::LINEAR;
+                switch (mMinFilter)
+                {
+                case osg::Texture::LINEAR:
+                case osg::Texture::LINEAR_MIPMAP_LINEAR:
+                case osg::Texture::LINEAR_MIPMAP_NEAREST:
+                    newMin = osg::Texture::LINEAR;
+                    break;
+                case osg::Texture::NEAREST:
+                case osg::Texture::NEAREST_MIPMAP_LINEAR:
+                case osg::Texture::NEAREST_MIPMAP_NEAREST:
+                    newMin = osg::Texture::NEAREST;
+                    break;
+                }
+                tex->setFilter(osg::Texture::MIN_FILTER, newMin);
+            }
+            else
+                tex->setFilter(osg::Texture::MIN_FILTER, mMinFilter);
+
             tex->setFilter(osg::Texture::MAG_FILTER, mMagFilter);
             tex->setMaxAnisotropy(static_cast<float>(mMaxAnisotropy));
         }