How do you manage transparency in your rendering?

1 What is transparency?

Transparency is the property of an object that allows some light to pass through it, while reflecting or refracting the rest. Depending on the amount and wavelength of light that is transmitted, an object can appear more or less transparent. For example, a clear glass window is highly transparent, while a colored glass bottle is partially transparent. Transparency can also vary across an object, creating smooth or sharp transitions between opaque and transparent regions.

2 How to model transparency?

To model transparency, you need to specify how much light is absorbed, reflected, and refracted by an object. This can be done using different parameters, such as opacity, alpha, transparency, or transmittance. Opacity is the inverse of transparency, and measures how much light is blocked by an object. Alpha is a value between 0 and 1 that represents the opacity of a pixel or a fragment. Transparency is a color that indicates how much light of each wavelength is transmitted by an object. Transmittance is a function that calculates the amount of light that reaches the other side of an object.

3 How to render transparency?

To render transparency, you need to consider how transparent objects affect the final color of a pixel. This depends on the rendering algorithm and the blending mode you use. Rendering algorithms are methods to determine the visible surfaces and the illumination of a scene. Some common rendering algorithms are ray tracing, rasterization, and ray marching. Blending modes are rules to combine the colors of overlapping pixels or fragments. Some common blending modes are alpha blending, additive blending, and subtractive blending.

4 What are the challenges of transparency?

Transparency poses some challenges for rendering, such as sorting, aliasing, and depth testing. Sorting is the process of arranging transparent objects in a specific order, usually from back to front, before rendering them. This is necessary to ensure the correct blending of colors and avoid artifacts. However, sorting can be difficult or impossible for complex or intersecting objects, such as hair, fur, or foliage. Aliasing is the distortion of edges or patterns caused by the limited resolution of the screen or the sampling rate. This can create jagged or noisy effects on transparent objects, especially when they are thin or moving. Depth testing is the technique of discarding pixels or fragments that are occluded by closer objects. This can improve the performance and accuracy of rendering, but it can also cause problems for transparent objects, as they may be wrongly discarded or occluded.

5 What are some solutions for transparency?

Transparency can be improved by employing various solutions, such as pre-sorting, post-processing, depth peeling, and stochastic transparency. Pre-sorting can reduce sorting cost and artifacts, but may not work for dynamic or overlapping objects. Post-processing can enhance the appearance and smoothness of transparent objects, but can also increase computational cost and latency. Depth peeling can avoid sorting and depth testing issues, but is expensive and memory-intensive. Stochastic transparency can create a natural and smooth effect, but can also introduce noise and variance that require more samples to reduce them.

6 How to choose the best technique for transparency?

When selecting the best technique for transparency, you need to consider several factors, such as the type and complexity of the transparent objects, the lighting and shading model, the performance and quality trade-off, and the target platform and audience. For instance, you may need to decide between direct or indirect lighting, diffuse or specular reflection, refraction or dispersion. Additionally, you may need to evaluate how much time and memory you have to render the transparent objects and how important the accuracy and realism of the transparency effect is for your users. By evaluating these factors, you can select the most suitable technique for transparency or combine different techniques to achieve the best result.

7 Here’s what else to consider

This is a space to share examples, stories, or insights that don’t fit into any of the previous sections. What else would you like to add?