The scene above contains balloons that are flying past a window and filling the room with color. This tutorial will show you how to create this caustic balloon effect using a Gobo light filter connected to a spot_light pointing through the window. We will also cover the shading steps used for the balloons. Thanks to Slava Sych for this tutorial.

Lighting

Create a camera and point it towards the window as per the image above. Create a skydome_light and connect a physical_sky to its color attribute.

Skydome Light

The settings for the Skydome_light used in this example are as follows:

• exposure: 2.
• samples: 3.
• shadow_color (HSV): 4.213 , 0.785, 0.053.
• camera_visibility: 0.
• transmission_visibility: 0.

Physical Sky

The settings for the physical_sky used in this example are as follows:

• turbidity: 8.916.
• elevation: 90.
• azimuth: 247.229.
• intensity: 2.
• sky_tint_color (HSV): 353.299 , 0.588 , 1.000.
• sun_tint: 44.261 , 0.177 , 1.000.

_{skydome_light. The window glass is hidden and shadows are disabled for the balloons.}

Spot Light

• Create a spot_light and place it behind the balloons. Rotate it so that it is pointing through the window.

The settings for the spot_light used in this example are as follows:

• cone_angle: 144.213.
• exposure: 19.
• samples: 3.
• radius: 44 (for softer shadows).
• shadow_color (HSV): 13.230, 0.785, 0.019.
• specular_visibility (Contribution): 0.1.
• SSS_visibility (Contribution): 0.1.

_{spot_light positioned behind the balloon shapes}

Gobo Filter

Connect a gobo filter to the spot_light.

• Set the filter_mode to Mix.
• Increase the density to 0.65.
• Connect a noise shader to the slide_map of the gobo.

Noise Shader

The settings for the noise shader used in this example are as follows:

• octaves: 4.
• distortion: 1.687.
• lacunarity: 2.831.
• scale XYZ: 33 (this value may need to change depending on the size of your scene).
• coord_space: UV.
• mode: vector (for RGB color noise).

To further adjust the effect you could try inserting a color_correct shader before the noise shader. In this case, the saturation was adjusted to 1.6.

_{Final results for the spot_light}

_{Final setup for gobo filter}

Shading

Assign a standard_surface to the balloon objects and rename it to BalloonMat.

Balloon Material

The settings for the Balloon material used in this example are as follows:

• specular_roughness : 0.36.
• subsurface_weight: 0.5.
• subsurface_scale: 10.
• subsurface_type: randomwalk2.

Create a layerRGBA shader and connect it to the base_color, subsurface_color and subsurface_r adius of the BalloonMat.

LayerRGBA->aiBalloonMat

• Create and connect a utility shader to input1 of the layerRGBA.
• Create and connect a colorJitter shader to input2 of the layerRGBA. The color_jitter will be used to further adjust the variation and color of the balloons.
• In layer2 of the layerRGBA , change the operation to multiply and the mix to 0.645.

ColorJitter

The settings for the color_jitter shader used in this example are as follows:

• Change the type to Object .
• gain_max: 4.
• saturation_min: 0.38.
• saturation_max: 1.076.
• seed: 2313.

Utility

The settings for the Utility shader used in this example are as follows:

• Shade Mode: flat.
• Color Mode: object. This will use give us random colors for each of the balloons.

_{Final shading network for Balloons}