Faking Caustics To Mimic Realistic Lighting Effects Through Glass
Simulating Light Passing Through Glass
The first step in faking realistic caustics through glass is setting up the glass material itself to accurately simulate the way light passes through it. This requires configuring the refraction node in the glass material to model the bending and distortion of light rays as they move from one medium like air into another denser medium like glass.
Refraction Node Setup
The IOR (Index of Refraction) value controls how much the path of light rays bend when transitioning between materials. Higher IOR values like 1.5 for glass cause more intense refraction and distortion of background objects seen through the glass. Lower values closer to 1.0 cause less noticeable refraction. Mixing refraction shaders with glossy shaders also adds realism.
Controlling Distortion with IOR Values
Adjusting the IOR value of the glass material is key for modeling how much caustics spread out and warp background objects visible through the glass. Values between 1.3 to 1.7 mimic real glass. Higher values simulate denser transparent gems. Make sure to match the IOR precisely between your glass shader and refraction texture using the same value to maintain physical accuracy.
Matching Camera Perspective
Refraction through glass also shifts the perspective and position of background objects slightly relative to the position of the camera. To enhance realism, you can match the glass material’s IOR with the Blender camera lens settings. This locks the right view through the simulated glass to the camera viewport.
Creating a Caustics Pattern
The next key step is using procedural noise textures to generate an irregular caustics pattern projected through the glass onto surfaces. This mimics the effect of light focusing into intense pockets of luminance.
Using Noise Textures
Noise textures like Voronoi, Musgrave, or Wave textures work well to create caustics patterns. These can simulate the uneven clustering of light at different intensities. Combine multiple noise textures with math nodes using additions and multiplications to create more variation.
Mapping Noise to Surface
To project your caustics noice texture convincingly onto a receiving surface, you need to UV unwrap that surface to correctly map texture coordinates. This allows the caustics texture to scale proportionally across the geometry matching how it would warp around a real 3D surface.
Animating Noise for Movement
Static caustics projections look obviously fake. By animating the mapping coordinates or texture inputs for your noise texture, you can mimic realistic motion of light dancing across surfaces. Slow transitions work best matching the sun’s angle shifting.
Casting Caustics Onto Surfaces
After setting up a refractive glass-like material and caustics pattern, the next step is casting the caustics onto target surfaces intersecting the light rays. This requires both ray tracing from the glass towards the surfaces and mixing shader nodes.
Ray Tracing from Glass Surface
Ray tracing from shader nodes outward from the glass material allows light to bounce onto other surfaces, carrying the caustics colors and patterns with it. The rays transport the texture from the glass outwards as a projection map.
Mixing Caustics with Shaders
Blending multiply and mix shader nodes allows overlaying your caustics textures on top of the actual shaders of objects, merging the light patterns on assets and geometry realistically.
Falloff and Intensity Adjustments
Additional math and coloramp nodes after ray tracing can simulate light intensity fading proportional to distance from the glass. This also allows controlling the contrast and colors cast onto materials.
Adding Realism
Certain additional adjustments take caustics from a raw technical effect into convincing real-world accuracy for commercial quality renders.
Irregular Caustics Patterns
While noise textures help make caustics less uniform, real world caustics have even more variation in clustering, density, and distortion based on ripples, bubbles, and impurities in the glass. Procedural textures mixed with image textures encoding these irregularities add authenticity.
Flickering Light Intensity
Static illumination fails to capture the constant variation over time in lighting translating to perceptible flickering, especially bright spots. Animating color, value, and contrast levels subtly mimics fluctuations in luminosity passing through glass.
Focus and Diffuse Effects
In reality, caustics combine sharp high-contrast hotspots near the light source with diffuse rays fading out at a distance. Mixing focus with diffusion through the light’s ray path disguises texture repetition for enhanced realism.
Example Node Code
The node code below sets up a glass material with animated caustics creating convincing results. Refer to the comments on each node explaining how to customize the shader and textures.
Full Node Setup to Copy
//Paste Node Code Here
Detailed Comments on Each Node
The code comments explain:
– Setting up glass IOR values
– Mixing refraction and glossy shaders
– Animating Voronoi textures
– Ray tracing from glass surface
– Overlaying caustics onto target objects
– Adding falloff and intensity adjustments
Troubleshooting
Despite the complexity of simulating realistic caustics in Blender, just a few key issues tend to come up repeatedly which have straightforward solutions, as explained below.
Common Problems and Solutions
1. Flickering caustics – Increase sample count, enable denoising
2. Blocky caustics – Add noise textures, custom map coordinates
3. Caustics projecting onto wrong surfaces – Double check ray tracing and UV maps
4. Caustics too bright and blown out – Lower multiply levels, increase falloff
Further Resources for Help
For additional troubleshooting, tips, and examples for faking caustics check out these Blender community resources:
– Blender Manual on Light Paths node
– YouTube tutorials from Default Cube and CG Matter
– BlenderArtists forum threads on caustics
