How to create 3D optical illusions

01. Start with the illusion

I start by setting up the illusion of an impossible triangle. First, I create an 'isometric camera', which is an Orthographic camera with a rotation of 54.736 degrees, 0, 45 degrees. The isometric projection has the particular property that, if you move +1 unit in the Y axis, then -1 unit in the X axis, and -1 unit in the Z axis, it looks like you go back to the starting point from the camera view.

For projects like this, I created a free add-on for Blender, called Paradox Toolkit, that implements this principle to construct impossible figures, and aligns the end points to create the illusion of continuity.

To render impossible figures, I recommend using a 'rasterisation' engine like Eevee, because ray-tracing engines like Cycles usually reveal the location of the illusion.

02. Block out the main shapes

Next I use the illusion object as a guideline to block the rest of my scene. I place three L-shaped blocks around the original triangle, and add one additional bar to match the illusion. For the snake I block out the body using a 'Path' curve, and I reshape a box to get an idea of the proportions of the head.

03. Refine the triangle

I proceed to refine the triangle blocks. I round the corners using the Bevel tool, and add the Bevel and Subdivision modifiers to give the edges a softer look. Artefacts may appear at the illusion point if the modifications on the front block don't match the ones on the back block, but adding a few support loops generally fixes this issue.

04. Create a generative scale pattern

Making the scales is my favourite part of the process. Since these are made almost entirely with generative techniques, I can experiment with different types of patterns very quickly. For this project I model a leaf-like shape, using the scales of the bush viper as reference, and refine it using the solidify, bevel, and subdivision modifiers.

Then I use three Array modifiers to create the scale pattern: one to make a single row, another to create the second row with an offset, and the last one to repeat the pattern in the vertical direction.

05. Make the scales follow the curve

To arrange the scale pattern around the body I use two Curve modifiers: the first one is to bend them into

a tube using a Bezier Circle, and the second one is to deform them across the body curve.

Here I adjust the curve thickness and twist to make the scale flow look more natural. I also edited the overall shape of the body and added a second set of scales for the belly, using the same techniques.

06. Create the head mesh

The head is the most complicated part of the process for me. I look for reference images of vipers to model a base mesh that follows roughly the same triangular structure. Then I duplicate the original scale object, and I begin placing them one by one... and that is as time consuming as it sounds.

I use the edge loops of the base mesh as guidelines, and I try to keep the scale flow consistent using their local coordinate system while moving them around. I use 'Linked Duplicates' of the original scale, both to save memory, and to speed up the process if I need to make any modifications.

06. Create the head mesh

The head is the most complicated part of the process for me. I look for reference images of vipers to model a base mesh that follows roughly the same triangular structure. Then I duplicate the original scale object, and I begin placing them one by one... and that is as time consuming as it sounds.

I use the edge loops of the base mesh as guidelines, and I try to keep the scale flow consistent using their local coordinate system while moving them around. I use 'Linked Duplicates' of the original scale, both to save memory, and to speed up the process if I need to make any modifications.

07. Adjust the materials and lights

With the snake ready, I proceed to adjust the materials and lighting in Eevee, which is Blender's real-time render engine. I use the Z coordinate to create a mask that slightly darkens the scales towards the base. I also add a soft colour gradient to the individual scales, that will look like an exaggerated ambient occlusion.

I include a rim light to brighten the far side of the scales in the head, and use a combination of Spot and Point lights to add the highlights around the eye.

08. Work on background and composition

For the last step I add a background light to drive the viewers' attention towards the head. In the compositor I fine-tune the Ambient Occlusion, add a soft Vignette effect, and adjust the saturation and values until I'm happy with the result.