Shrink Wrap

Boxshot supports shrink wrap packaging simulation with multiple adjustable parameters. In order to start the simulation, select the object(s) you want to wrap, then right click it and select Tools → Shrink Wrap… from the context menu.

Shrink wrap simulator in Boxshot

On the left there is a simulation parameters panel, where you can configure the film and other simulation options and start the simulation itself. On the right there is a simulation scene preview with the wrapped object painted white and film painted blue. You can rotate the preview by dragging it with a mouse, pan it by dragging with a right mouse button pressed and zoom using the mouse wheel.

Film Parameters

The film is done as “tube” wrapped around the object along the selected axis. You can configure the dimensions of the tube and its radius to keep the initial position of the film close to the wrapped object. Boxshot automatically adjusts the film parameters to the wrapped object, but you can adjust it further if needed.

From top to bottom, the film parameters are:

The film goes along one of the axes: X, Y or Z. Its length along that axis is configured using the Height parameter and it can be shifted along that axis using the Offset option.

By default Boxshot uses the wrapped object dimensions to compute the initial film size, so you might want to adjust it. For instance the film on the image above should cover just the middle of the bottle, so its height is adjusted to be 12cm and the offset is configured to –2cm to place the film at the middle of the bottle.

Shrink Film Simulation

Once the film is configured, you can start the simulation by clicking the Start button at the bottom of the left panel. Boxshot will run the simulation and you will see the film slowly shrinks and wraps the object:

Shrink wrap simulation running in Boxshot

The simulation speed depends on many parameters and may take a while for some scenes. Give it time and wait until you are happy with the film shape you see in preview. Then click the Stop button to end the simulation. Have another look at the film and click the OK button to add the simulated film to the scene.

Adding shrink film object to the scene in Boxshot

If for some reasons you are not happy with the simulation results, you can stop it, re–configure the simulation parameters and run it again using the Start button. You can do this as many times as you need until you get the results you want. Then you can click OK to add the film to the scene.

Advanced Options

There’s more simulation options for the brave ones. Note that some of them are pretty nerdy and you should use them on your own risk. Boxshot remembers the last simulation options you used for a project, so you might need a new project for checking the default values if something is messed up.

Advances shrink film options in Boxshot

The advanced parameters are:

Some of the parameters, especially the last ones are very low–level and we don’t recommend adjusting them without a good reason. Below are some details on the parameters you might want to change:

Stretch factor

The shrink film is pre–stretched and when it is heated up it tries to shrink down to its normal state. The pre–stretching might depend on the direction, so the film can shrink along its width, but not length. This way you can make the tube shrinking in diameter, but keep its length intact. The Stretch factor parameters configure exactly that. By default the Shrink factor U is set to 30, which means the film wants to shrink down by 30 times when heated. This gives enough shrink to wrap the object tight. On the other hand, the Shrink factor V is set to 1.01, which means that the film will almost not shrink down along its length, keeping the height of the tube intact.

Cell size

Boxshot simulates the film by dividing it to cells of a given size. The film effectively becomes a net of nodes with elastic “springs” between them. That net then shrinks down around the shape, wrapping it up closely. The Cell size parameter configures the distance between the nodes of the net. Obviously, the smaller the cell size is, the more precise is the simulation. The backside is that the smaller the cell size is, the more nodes needs to be simulated and the more time the process takes. This is pretty similar to rendering, where the time may rise significantly when you increase the resolution. The rule of thumb here is to keep the cell size as big as possible, while it doesn’t affect the visual appearance of the film. This is especially important if you wrap a big object, like a pallet with some boxes on top. It is safe to make the cell size of 1–2cm in that case.

Simulation Speed

The time it takes the film to wrap around the object depends on many factors. One of them is described above: the cell size. The smaller is the cell, the more cells is needed, the more CPU power is required to process all the elements of the mesh. Try keeping the number of cells smaller and the cell size bigger, if possible.

The other factor is the time step used during the simulation. For each simulation step, Boxshot needs to shrink the film to some extent and check if it touches the object somewhere. If the step is too big, the film may go too deep into the object, so the artifacts will be visible. In order to avoid that, Boxshot tries smaller steps and this directly affects the simulation time. The smaller the step, the longer it takes to shrink the film down to the object size.

The step size depends on film thickness, density and stiffness. Thickness and density define the film mass. The heavier is the film, the larger steps can be used, and the simulation can run faster. The stiffness works the opposite way. The higher it is, the smaller steps are needed and the slower is the simulation. As we don’t recommend changing stiffness without a good reason, and as the film density is rarely changed, the only parameter which is worth configuring is the film thickness. It is 0.05cm (0.5mm) by default and if you wrap something big, it is worth making the film thicker to speed the things up.

So, the conclusion is: to make the simulation faster, try keeping Cell size and Thickness parameters as large as possible, while it doesn’t affect the simulated film appearance.

Possible Issues

In some (rare) cases you might see simulation artifacts, like the object elements coming through the film or slightly visible through it. That’s acceptable as the film is simulated with the finite number of triangles and cannot perfectly wrap the object of any shape. We try our best to adjust the algorithm to avoid those issues, but they still could happen. Here’s what you can do.

Adjust the wrapped object shape

Check if you can avoid long hard edges in the wrapped object. Try using bevels, soft corners, rounded edges etc. This adds tiny details to the wrapped objects which are better wrapped by the film.

Adjust the film margin and thickness

The margin option lets you effectively push the film out of the object surface. If the film comes too tight to the object, it may create z–fighting artifacts at rendering. Increasing the margin could easily fix most of the issues of this type. Note that increasing the margin too much makes the film flying on top of the object which might look weird. Same for the film thickness. Increasing it might hide some minor object element that come through the film.

Adjusting cell size

Sometimes it helps to make the film a little bit more or less detailed. Changing the film structure might end up with a different simulation results and the problem goes away.

Adjusting the film parameters

You might also want to change the initial film size, radius, angle or other parameters to affect the simulation result.

Finally, if nothing above helps and the result still looks way too bad, please feel free to contact us with your scene and film parameters, so we can have a look.

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