One or more computer-readable storage media comprising computer-executable instructions, which, when executed by one or more processing units of one or more computing devices, cause the one or more computing devices to: render, as an image onto a two-dimensional surface represented by an inside of a sphere, a three-dimensional environment as perceived by a viewer at a center of the sphere, wherein the rendering comprises generating both texture information and depth information for the image, the depth information being based on a location of a viewer as compared with location of objects in the three-dimensional environment; characterized in that the computer-executable instructions, which, when executed by one or more processing units of one or more computing devices, further cause the one or more computing devices to: apply a stencil buffer to the rendered two-dimensional image, leaving only a first portion of the rendered two-dimensional image; generate, for display through a virtual-reality display device, a simulated three-dimensional thumbnail image that is representative of a three-dimensional environment by parallax shading the first portion of the rendered two-dimensional image based on the depth information and a location of a right eye of a viewer and separately parallax shading the first portion of the rendered two-dimensional image based on the depth information and a location of a left eye of the viewer, wherein parallax shading comprises applying colorimetric variations and/or positional variations to individual pixels to simulate the perception of depth; regenerating, for display through the virtual-reality display device, the simulated three-dimensional thumbnail image by again parallax shading the first portion of the rendered two-dimensional image based on the depth information and a new location of the right eye of the viewer and separately again parallax shading the first portion of the rendered two-dimensional image based on the depth information and a new location of the left eye of the viewer, wherein the new location of the right eye and the new location of the left eye are because the viewer moved their head, the regenerating in response to the viewer moving their head causing the simulated three-dimensional thumbnail image to appear, to the viewer, through the virtual-reality display device, to behave as a three-dimensional object; and presenting to the user the three-dimensional environment represented by the simulated three-dimensional thumbnail in response to detecting a user action directed towards the simulated three-dimensional thumbnail. render, as an image onto a two-dimensional surface represented by an inside of a sphere, a three-dimensional environment as perceived by a viewer at a center of the sphere, wherein the rendering comprises generating both texture information and depth information for the image, the depth information being based on a location of a viewer as compared with location of objects in the three-dimensional environment; characterized in that the computer-executable instructions, which, when executed by one or more processing units of one or more computing devices, further cause the one or more computing devices to: apply a stencil buffer to the rendered two-dimensional image, leaving only a first portion of the rendered two-dimensional image; generate, for display through a virtual-reality display device, a simulated three-dimensional thumbnail image that is representative of a three-dimensional environment by parallax shading the first portion of the rendered two-dimensional image based on the depth information and a location of a right eye of a viewer and separately parallax shading the first portion of the rendered two-dimensional image based on the depth information and a location of a left eye of the viewer, wherein parallax shading comprises applying colorimetric variations and/or positional variations to individual pixels to simulate the perception of depth; regenerating, for display through the virtual-reality display device, the simulated three-dimensional thumbnail image by again parallax shading the first portion of the rendered two-dimensional image based on the depth information and a new location of the right eye of the viewer and separately again parallax shading the first portion of the rendered two-dimensional image based on the depth information and a new location of the left eye of the viewer, wherein the new location of the right eye and the new location of the left eye are because the viewer moved their head, the regenerating in response to the viewer moving their head causing the simulated three-dimensional thumbnail image to appear, to the viewer, through the virtual-reality display device, to behave as a three-dimensional object; and presenting to the user the three-dimensional environment represented by the simulated three-dimensional thumbnail in response to detecting a user action directed towards the simulated three-dimensional thumbnail.