1. A computer-implemented process for constructing virtual environments, comprising: using a computer to perform process actions for: generating environmental information by scanning a real-world environment to classify geometry of surfaces and objects within that environment; receiving a master set of virtual building blocks, each virtual building block including a plurality of characteristics and including semantic and geometric constraints relating to the virtual building blocks; procedurally molding a physically constrained virtual environment by performing two or more iterations of a joint optimization of a layout of an automatically selected variable subset of at least two of the virtual building blocks selected for each iteration relative to a scene-specific cost function; each iteration of the physically constrained virtual environment comprising a different trial solution of a joint layout of all the virtual building blocks in the automatically selected variable subset; each iteration being consistent with the characteristics and constraints of the variable subset of virtual building blocks and the environmental information of the real-world environment; the scene-specific cost function being derived for each iteration from the characteristics and constraints of the subset of virtual building blocks in combination with the environmental information; displaying the physically constrained virtual environment via a display device, such that at least a portion of the physically constrained virtual environment is anchored to the real-world environment in a way that at least partially matches tactile truth for one or more surfaces and objects within the real-world environment.