如何评价Epic Games今日公布的虚幻引擎5？

“If the performance is there to have the two at the same resolution a new trick becomes available. Vertex density will match pixel density so all pixel work can be pushed to the vertex shader. This gets around the quad problem with tiny triangles. If you aren't familiar with this, all pixel processing on modern GPU's gets grouped into 2x2 quads. Unused pixels in the quad get processed anyways and thrown out. This means if you have many pixel size triangles your pixel performance will approach 1/4 the speed. If the processing is done in the vertex shader instead this problem goes away. At this point the pipeline is looking similar to Reyes.”

"The vast majority of triangles are software rasterised using hyper-optimised compute shaders specifically designed for the advantages we can exploit," explains Brian Karis. "As a result, we've been able to leave hardware rasterisers in the dust at this specific task. Software rasterisation is a core component of Nanite that allows it to achieve what it does. We can't beat hardware rasterisers in all cases though so we'll use hardware when we've determined it's the faster path. On PlayStation 5 we use primitive shaders for that path which is considerably faster than using the old pipeline we had before with vertex shaders."

"Really, the core method here, and the reason there is such a jump in shadow fidelity, is virtual shadow maps. This is basically virtual textures but for shadow maps. Nanite enables a number of things we simply couldn't do before, such as rendering into virtualised shadow maps very efficiently. We pick the resolution of the virtual shadow map for each pixel such that the texels are pixel-sized, so roughly one texel per pixel, and thus razor sharp shadows. This effectively gives us 16K shadow maps for every light in the demo where previously we'd use maybe 2K at most. High resolution is great, but we want physically plausible soft shadows, so we extended some of our previous work on denoising ray-traced shadows to filter shadow map shadows and give us those nice penumbras."

"Lumen uses ray tracing to solve indirect lighting, but not triangle ray tracing," explains Daniel Wright, technical director of graphics at Epic. "Lumen traces rays against a scene representation consisting of signed distance fields, voxels and height fields. As a result, it requires no special ray tracing hardware." To achieve fully dynamic real-time GI, Lumen has a specific hierarchy. "Lumen uses a combination of different techniques to efficiently trace rays," continues Wright. "Screen-space traces handle tiny details, mesh signed distance field traces handle medium-scale light transfer and voxel traces handle large scale light transfer." Lumen uses a combination of techniques then: to cover bounce lighting from larger objects and surfaces, it does not trace triangles, but uses voxels instead, which are boxy representations of the scene's geometry. For medium-sized objects Lumen then traces against signed distance fields which are best described as another slightly simplified version of the scene geometry. And finally, the smallest details in the scene are traced in screen-space, much like the screen-space global illumination we saw demoed in Gears of War 5 on Xbox Series X. By utilising varying levels of detail for object size and utilising screen-space information for the most complex smaller detail, Lumen saves on GPU time when compared to hardware triangle ray tracing."