Fix #4792: Particle stages with "orientation x" had wrong rotation, c…

…ausing textures to be flipped sideways

radiant/particles/RenderableParticleStage.cpp

@@ -110,7 +110,9 @@ void RenderableParticleStage::calculateStageViewRotation(const Matrix4& viewRota
 
 	case IStageDef::ORIENTATION_X:
 		// Rotate the z vector such that it faces the x axis, and use that as transform
-		_viewRotation = Matrix4::getRotation(Vector3(0,0,1), Vector3(1,0,0));
+		// To keep the up/down orientation of the material, rotate it 90 degrees around z 
+		// before applying the z-to-x tilt (issue #4792)
+		_viewRotation = Matrix4::getRotation(Vector3(0,0,1), Vector3(1,0,0)).getMultipliedBy(Matrix4::getRotationAboutZDegrees(-90));
 		break;
 
 	case IStageDef::ORIENTATION_Y: