* prevent resizing brushes to zero volume by faces drag, try to stop at minimal configuration

radiant/brush.cpp

@@ -540,3 +540,49 @@ void Brush::vertexModeSnap( const float snap, bool all ){
 			vector3_snap( i.m_vertexTransformed, snap );
 	vertexModeBuildHull( all );
 }
+
+#include "grid.h"
+void BrushInstance::transformComponents( const Matrix4& matrix ){
+	auto transform = [this]( const Matrix4& matrix ){
+		for ( auto& fi : m_faceInstances )
+			fi.transformComponents( matrix );
+	};
+
+	transform( matrix );
+
+	const Vector3 translation = matrix4_get_translation_vec3( matrix );
+	if( translation != g_vector3_identity ){ //has translation
+		Matrix4 ma( matrix );
+		Vector3& tra = vector4_to_vector3( ma.t() );
+		tra = g_vector3_identity;
+		if( g_matrix4_identity == ma ){ //only translation
+			for ( const auto& fi : m_faceInstances ){
+				if( fi.isSelected() ){ //has faces selected
+					if( !m_brush.contributes() ){ //do binary search of worthy transform
+						for( std::size_t axis = 0; axis < 3; ++axis ){
+							const float grid = translation[axis] < 0? -GetGridSize() : GetGridSize();
+							int maxI = static_cast<int>( translation[axis] / grid + .5f );
+							int minI = 0;
+							while( maxI > minI ){
+								const int curI = minI + ( maxI - minI + 1 ) / 2;
+								tra[axis] = curI * grid;
+								m_brush.revertTransform();
+								transform( ma );
+								if( m_brush.contributes() ){
+									minI = curI;
+								}
+								else{
+									maxI = curI - 1;
+								}
+							}
+							tra[axis] = minI * grid;
+						}
+						m_brush.revertTransform();
+						transform( ma );
+					}
+					break;
+				}
+			}
+		}
+	}
+}

radiant/brush.h

@@ -1307,6 +1307,9 @@ const Plane3& plane3() const {
 	m_observer->evaluateTransform();
 	return m_planeTransformed.plane3();
 }
+const Plane3& plane3_() const {
+	return m_planeTransformed.plane3();
+}
 FacePlane& getPlane(){
 	return m_plane;
 }
@@ -2232,6 +2235,74 @@ void copy( const Brush& other ){
 	planeChanged();
 }
 
+/// for the only use to quickly check, if about to be transformed brush makes sense
+bool contributes() const {
+	/* plane_unique() ripoff, calling no evaluation */
+	auto plane_unique_ = [this]( std::size_t index ) -> bool {
+		// duplicate plane
+		for ( std::size_t i = 0; i < m_faces.size(); ++i )
+		{
+			if ( index != i && !plane3_inside( m_faces[index]->plane3_(), m_faces[i]->plane3_(), index < i ) ) {
+				return false;
+			}
+		}
+		return true;
+	};
+
+	/* windingForClipPlane() ripoff, calling no evaluation */
+	auto windingForClipPlane_ = [this, &plane_unique_]( const Plane3& plane ) -> bool {
+		FixedWinding buffer[2];
+		bool swap = false;
+
+		// get a poly that covers an effectively infinite area
+		Winding_createInfinite( buffer[swap], plane, m_maxWorldCoord );
+
+		// chop the poly by all of the other faces
+		for ( std::size_t i = 0; i < m_faces.size(); ++i )
+		{
+			const Face& clip = *m_faces[i];
+
+			if ( plane3_equal( clip.plane3_(), plane )
+				|| !plane3_valid( clip.plane3_() ) || !plane_unique_( i )
+				|| plane3_opposing( plane, clip.plane3_() ) ) {
+				continue;
+			}
+
+			if( buffer[swap].points.empty() ){
+				break;
+			}
+
+			buffer[!swap].clear();
+
+			{
+				// flip the plane, because we want to keep the back side
+				Plane3 clipPlane( vector3_negated( clip.plane3_().normal() ), -clip.plane3_().dist() );
+				Winding_Clip( buffer[swap], plane, clipPlane, i, buffer[!swap] );
+			}
+			swap = !swap;
+		}
+
+		return buffer[swap].size() > 2;
+	};
+
+
+	std::size_t contributing = 0;
+
+	for ( std::size_t i = 0; i < m_faces.size(); ++i )
+	{
+		Face& f = *m_faces[i];
+
+		if ( plane3_valid( f.plane3_() ) && plane_unique_( i ) ) {
+			if( windingForClipPlane_( f.plane3_() ) ){
+				++contributing;
+				if( contributing > 3 )
+					return true;
+			}
+		}
+	}
+	return false;
+}
+
 private:
 void edge_push_back( FaceVertexId faceVertex ){
 	m_select_edges.push_back( SelectableEdge( m_faces, faceVertex ) );
@@ -3782,12 +3853,8 @@ void selectVerticesOnTestedFaces( SelectionTest& test ){
 }
 
 
-void transformComponents( const Matrix4& matrix ){
-	for ( FaceInstances::iterator i = m_faceInstances.begin(); i != m_faceInstances.end(); ++i )
-	{
-		( *i ).transformComponents( matrix );
-	}
-}
+void transformComponents( const Matrix4& matrix );
+
 const AABB& getSelectedComponentsBounds() const {
 	m_aabb_component = AABB();