context reinit support

core/glbuffer.cpp

@@ -48,6 +48,12 @@ void Buffer::destroy(QOpenGLExtraFunctions * f) {
 }
 
 
+void Buffer::reinit() {
+	buffer_ = 0;
+	prev_size = 0;
+}
+
+
 void Buffer::bind(QOpenGLExtraFunctions * f) {
 	//qDebug() << "bind" << target_ << buffer_;
 	f->glBindBuffer(target_, buffer_);