I rendering the portal separately into two parts, the main object and shadow.

Portal

Shadow layer

I encountered several problems in rendering. The first is the voxel size of the portal. I found that when I adjust the voxel size to a smaller value, it will bring better and clearer results, but at the same time, the simulation cache and rendering time will be longer.

The second problem is that when I perform multi-pass rendering, there will be a problem as shown in the figure. In the rendering process, there is no white edge in this circle, but it will suddenly appear when the rendering is completed. It still exists when I composite it in Nuke. In the end, I found that the problem is the alpha channel.

Combination

Here is the process of combination.

I clean up the material first, remove the signs and pipes on the wall. Then extract the projection through the shuffle node and merge it with the portal and the original material.

Then add another scene video to the screen. This expresses the meaning of Gherardo being transferred from another scene.

Then add the portal and shadow.

The last step is to Roto out Gherardo and use another roto node as a mask to make Gherardo through out of the portal. In fact, this is more difficult. Because this camera is in the front. Many problems cannot be concealed by covering up. And due to our early considerations, Gherardo’s actions are not very match with the portal animation. Through discussions with adlo, his suggestion to me is to adjust Roto to make the shot looks real.