Add OPENMW_DECOMPRESS_TEXTURES environment variable to decompress textures in software if not supported by graphics hardware

Disabled by default due to requiring new functionality that was just added to OSG 3.6 or OpenMW/OSG.

components/resource/imagemanager.cpp

@@ -69,7 +69,6 @@ namespace Resource
                         // This one works too. Should it be included in isTextureCompressionS3TCSupported()? Submitted as a patch to OSG.
                         && !osg::isGLExtensionSupported(0, "GL_S3_s3tc"))
                 {
-                    std::cerr << "Error loading " << filename << ": no S3TC texture compression support installed" << std::endl;
                     return false;
                 }
                 break;
@@ -123,13 +122,32 @@ namespace Resource
                 return mWarningImage;
             }
 
-            osg::Image* image = result.getImage();
+            osg::ref_ptr<osg::Image> image = result.getImage();
+
             image->setFileName(normalized);
             if (!checkSupported(image, filename))
             {
+                static bool uncompress = (getenv("OPENMW_DECOMPRESS_TEXTURES") != 0);
+                if (!uncompress)
+                {
+                    std::cerr << "Error loading " << filename << ": no S3TC texture compression support installed" << std::endl;
                     mCache->addEntryToObjectCache(normalized, mWarningImage);
                     return mWarningImage;
                 }
+                else
+                {
+                    // decompress texture in software if not supported by GPU
+                    // requires update to getColor() to be released with OSG 3.6
+                    osg::ref_ptr<osg::Image> newImage = new osg::Image;
+                    newImage->setFileName(image->getFileName());
+                    newImage->allocateImage(image->s(), image->t(), image->r(), image->isImageTranslucent() ? GL_RGBA : GL_RGB, GL_UNSIGNED_BYTE);
+                    for (int s=0; s<image->s(); ++s)
+                        for (int t=0; t<image->t(); ++t)
+                            for (int r=0; r<image->r(); ++r)
+                                newImage->setColor(image->getColor(s,t,r), s,t,r);
+                    image = newImage;
+                }
+            }
 
             mCache->addEntryToObjectCache(normalized, image);
             return image;