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# Objective Add depth prepass and support for opaque, alpha mask, and alpha blend modes for the 3D PBR target. ## Solution NOTE: This is based on top of #2861 frustum culling. Just lining it up to keep @cart loaded with the review train. 🚂 There are a lot of important details here. Big thanks to @cwfitzgerald of wgpu, naga, and rend3 fame for explaining how to do it properly! * An `AlphaMode` component is added that defines whether a material should be considered opaque, an alpha mask (with a cutoff value that defaults to 0.5, the same as glTF), or transparent and should be alpha blended * Two depth prepasses are added: * Opaque does a plain vertex stage * Alpha mask does the vertex stage but also a fragment stage that samples the colour for the fragment and discards if its alpha value is below the cutoff value * Both are sorted front to back, not that it matters for these passes. (Maybe there should be a way to skip sorting?) * Three main passes are added: * Opaque and alpha mask passes use a depth comparison function of Equal such that only the geometry that was closest is processed further, due to early-z testing * The transparent pass uses the Greater depth comparison function so that only transparent objects that are closer than anything opaque are rendered * The opaque fragment shading is as before except that alpha is explicitly set to 1.0 * Alpha mask fragment shading sets the alpha value to 1.0 if it is equal to or above the cutoff, as defined by glTF * Opaque and alpha mask are sorted front to back (again not that it matters as we will skip anything that is not equal... maybe sorting is no longer needed here?) * Transparent is sorted back to front. Transparent fragment shading uses the alpha blending over operator Co-authored-by: Carter Anderson <mcanders1@gmail.com> |
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