Caustics Rendering: Cycles Vs. Blender Internal Capabilities And Limitations
Caustics in 3D rendering refer to the patterns of light focused and reflected or refracted by curved surfaces. In the real world, caustics can be seen as shimmering patterns often at the bottom of a swimming pool from the sunlight shining down and reflecting off the water. In 3D software, accurate caustics simulation plays an important role in creating realistic renders.
The Cycles rendering engine in Blender is designed to offer physically-based path tracing capable of realistically simulating caustics. Meanwhile, Blender’s Internal renderer uses rasterization and approximations that limit its ability to render true caustics.
Simulating Realistic Caustics with Cycles
As a path tracing renderer, Cycles works by tracing the path of light rays from the camera into the scene and simulating the way the rays interact with different surfaces. This unbiased approach allows Cycles to capture true caustic patterns from light focussing through curved surfaces.
For example, Cycles can realistically simulate the complex way light passes through a glass, water, or other transparent objects, becomes focused, and projects caustics onto other surfaces. The results are realistic caustics with accurate physic-based properties of light.
Caustics from Water Simulation
Cycles is capable of rendering realistic caustics by using mesh-based water simulations that model the way light is focused and projected as it passes through moving water surfaces. This allows effects like caustics shining and rippling at the bottom of a pool, or reflected caustics shimmering on objects under moving water.
Caustics Through Glass
Glass and transparent materials can focus light into caustic patterns. In Cycles, transparent shader nodes like Glass and Refraction properly focus transmitted light rays and project physically-accurate caustic effects onto surfaces beyond transparent objects based on their curvature and shape.
Metallic Caustics
In addition to transparent materials, glossy and metal surfaces are also capable of producing caustics from sharply reflected light. Cycles can render realistic metallic caustics using physically-based princiles to simulate microfacet reflections off surfaces like metal and glossy paint.
Limitations of Caustics in Blender Internal
Unlike Cycles path tracing, Blender Internal uses a scanline approach to render images rather than simulator light realistically. This means effects like caustics rely on rasterization tricks and approximations rather than physically-accurate light behaviour.
While useful for faster preview renders during modeling, Blender Internal’s caustics effects have a variety of accuracy and quality limitations compared to Cycles:
Caustics Approximation
Instead of accurate light pathways, Internal generates caustics effects using luminance approximations between light, transparent surface, and receiver objects. This leads to artifacts and estimation errors absent from Cycles path tracing.
Resolution Dependance
The rasterization techniques behind Internal’s caustics rely on the render resolution to function. This means caustics quality in internal degrades heavily at lower resolutions while Cycles maintains accuracy.
Limited Transparency Support
Blender Internal only simulates caustics from fully transparent surfaces like glass or water. Cycles can generate caustics through materials with partial transparency like translucent plastics by physically tracing light pathways.
Setting Up a Basic Caustics Material in Cycles
Realistic caustics relies first on proper material setup. Here is an overview for how to configure caustic-capable materials in Cycles:
Glass Material
The Glass shader node is essential for transparent caustics. Connect a Glass Node into the Material Output surface socket to enable light ray focussing and caustics from transmission through transparent surfaces
Water Material
Cycles offers a dedicated Glass Node preconfigured with IOR settings matching realistic water. Attach a Glass Node set to Water to transparent mesh objects to simulate underwater caustics effects from light interacting with rippling water.
Reflection Caustics
In addition to refraction through transparency, caustics appear from sharp relfections off glossy and metallic materials. Enable reflective caustics using the Glossy BSDF shader mixed with shaders like Metal and Glass.
Optimizing Caustics Renders in Cycles
While powerful, caustics effects require extra computation time to render in Cycles. These tips can help optimize cycles caustics performance:
Increase Light Samples
Tracing caustics light paths requires more samples to resolve noise patterns. Increase both the general Render Samples value and specific Light Samples value to improve caustics quality and reduce noise.
Use Multiple Importance
The Multiple Importance feature in Cycles places additional samples selectively in challenging areas like caustics. Enabling Multiple Importance sampling focused on caustics will converge noise faster.
Limit Ray Depth
Caustics involves many transparent surface interactions that increase ray depth counts and render times. Lowering the Max Transparency Ray Depth can cut computation when caustics accuracy isn’t essential.
Bake Indirect Lighting
Baking lighting as voxel data using Cycles Indirect Light Baking feature calculates caustics solutions into a reusable cache for faster rendering without recalculating caustics each frame.
Example Scene Showcasing Cycles Caustics
Examining example scenes provides helpful context for understanding caustics rendering in practice. Here is an example showcase scene built to display various Cycles-rendered caustics types:
Mesh-Based Water Body
The underwater swimming pool chamber features a mesh-deforming water simulation displaying rippling caustics patterns along the tile floor from sunlight shining down through the water’s surface.
Glass Caustics Lighting
Within an adjacent glass-walled greenhouse room, Glass shader nodes enable sunlight to refract through transparent walls and roof planes to project shimmering caustics patterns influenced by the curvature of the glass panels casting interior shadows.
Metallic Caustics
Glossy shader nodes mixed with Metal shaders reflect and focus sharp spotlight beams within both rooms onto floors and walls generating artificial metallic style caustics blending with the natural caustics effects.
Rendering the Example Scene
With the caustics showcase scene assembled, we can configure final render properties and perform a test render evaluating Cycles performance displaying a range of caustics types together:
Sampling Settings
To resolve noise in the combined glass, water, and metallic caustics, 3000 render samples are set along with bounces increased to 8 to allow multi-bounce caustics through the complex water and glass interactions.
Light Path Settings
Transparent Max Bounces boosts ray depth to 10 allowing rays to pass repeatedly through glass panels and water volume to reach floor and wall surfaces, enabling multi-bounce caustics across the scene.
Material Settings
Glass, Water, and Glossy nodes are set enabling caustics bouncing between transparent, metallic and diffuse surfaces. IOR values physicalize optical glass properties and influence caustic focusing realistically.
With Cycles configured for the scene, pressing F12 renders photographic caustics combining water, glass, metal, and natural light sources interacting and focusing into colorful patterns emerging across floors, walls, and objects through the sunny glass-enclosed water chamber architectural space as intended.
Common Problems with Caustics and Solutions
Despite Cycles physically-based accuracy, users can still encounter issues with caustics results. Here are common caustic rendering problems and potential solutions:
Flickering Caustics
Caustics animation sometimes displays temporal flicker between frames due to noise variation. Increase light path sample counts to reduce noise banding and stabilize caustic flickering.
Blocky Caustics
Low resolution can transform smooth caustics into blocky disjointed patterns. Up sample counts combined with render resolution to smooth banding artifacts for cohesive caustics appearance.
Incomplete Caustics
If caustics seem cut-off or fail to display fully, increase ray depth limits allowing rays to pass repeatedly through multiple transparent surfaces enabling multi-surface caustic bouncing to reach target geometry.
Debugging these common caustic artifacts allows you to leverage Cycles for reliable, fast and stable photorealistic caustics rendering.
Further Resources for Learning About Caustics
For artists looking to dive deeper into advanced caustics rendering techniques, these resources offer useful detailed references:
– Blender Manual Caustics Rendering Guide
– Blender Cloud Caustics with Cycles Training Course
– An Introduction to Caustics in Lightwave 3D
– Caustics Physics and Simulation Breakdown by Andrew Price
With an understanding now of caustic theory and workflow in Cycles compared to Internal, the creative possibilities open for integrating realistic caustics into architectural, product design, and artistic 3D visualizations in Blender are virtually unlimited with the power of unbiased path tracing.
