Sorting each individual polygon in a model would be very slow, so the Sketchfab viewer sorts for transparency by meshes. All visible objects in the scene must be rendered, sorted, and merged into the final image. It is usually defined using a grayscale (Luminance channel) or Alpha texture, or a solid gray value.īlending mode is useful for translucent materials like glass, or materials with varying transparency.īlending is a very slow transparency method. Transparent objects are blended together. The same principle applies to 3D rendering. Users of Photoshop and other image editing software will be familiar with blending modes in image layers. They use different blending modes (or mixing modes) which determine how two layers of an image are blended into each other. There are many methods of rendering transparent objects in real time. Sketchfab makes a compromise between transparency quality and speed by sorting transparent objects and opaque polygons. When achieving real time performance, there is a limitation due to raster algorithms polygons are drawn in batches, and per batch the order in which polygons are drawn can't always be predicted. They can afford to sort each individual triangle before rendering a frame, so blending order is not an issue. Offline renderers like ray tracers and modeling tools favor quality over performance. On the left, the blue square is in front of the orange square, while on the right, the orange square is in front of the blue square. Masking is the fastest transparency method. Masking is useful for materials that require a "cut-out" effect like leaves, text, and logos. Alpha mask requires a texture to be useful. You can use the slider to set an Alpha "threshold", and invert the texture if needed. It is usually defined using a grayscale (Luminance channel) or Alpha texture. Sometimes called an "image mask" or "coverage mask", an alpha mask works by setting visibility in a binary (on / off) way. In addition to a blended opacity channel, an Alpha Mask can be applied to a material. Choosing the appropriate mode will depend on your needs. Among the different blending methods, there are trade-offs between image quality and viewer performance. Transparency is often expensive in terms of processing power and rendering performance. Objects are drawn one by one on top of each other, and depending on the blending mode and the order they are rendered, the result differs. Rendering transparent objects is done by blending colors. Transparency or Opacity describes if something is visible (opaque), invisible (transparent), or partially visible ("partially transparent", "see-through", "translucent", etc.) How does transparency work? This article was adapted from a tutorial on our blog.
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