Three.js解决同平面Z-fighting：polygonOffsetFactor与关闭depthWrite的透明方案哪个更高效？

Great question! Let's break down how each approach works and which one is more efficient for your use case where multiple rectangles share the same plane.

How Each Approach Solves Z-Fighting #

1. Polygon Offset Factor #

This approach leverages GPU hardware depth offsetting. You'd enable polygonOffset: true on each rectangle's material, then set a gradually decreasing polygonOffsetFactor (e.g., starting at 0 for the first rectangle, -0.1 for the next, down to -rectCount * 0.1 for the last one).

What happens under the hood:

• The GPU adjusts the depth value of each rectangle's pixels slightly, pushing later-drawn rectangles "back" just enough in the depth buffer to avoid overlap with earlier ones.
• Depth write remains enabled, so each rectangle's depth information is still written to the buffer. This lets the GPU use early Z-testing to skip drawing pixels that are already covered by closer (offset) rectangles.

2. Transparent Material with depthWrite: false + renderOrder #

Here, you mark rectangles as transparent (transparent: true), disable depthWrite, and set renderOrder to match your desired layering (higher values draw on top).

What happens under the hood:

• Three.js moves these rectangles to its separate transparent object queue. By default, transparent objects are sorted from back to front, but setting renderOrder overrides this to force your layering order.
• Since depthWrite is off, none of these rectangles write their depth to the buffer. This means the GPU can't use early Z-testing to skip overdrawn pixels—every pixel of every rectangle has to be drawn and blended, even if it's covered by a later rectangle.

Efficiency Comparison #

Performance Winner: Polygon Offset #

The polygon offset approach is almost always more efficient for opaque rectangles (which I assume yours are, since you're only dealing with Z-fighting rather than transparency needs):

• Minimal GPU overhead: Depth offsetting is a hardware-accelerated feature, so it adds barely any cost to each draw call.
• Early Z-testing saves overdraw: With depth write enabled, the GPU can quickly discard pixels that are already covered by closer rectangles, drastically reducing the number of pixel operations needed.
• No render path switching: You stay in the standard opaque rendering pipeline, avoiding the overhead of transparency blending and separate queue sorting.

When Might the Transparent Approach Be Necessary? #

The only time you'd need the transparent/depth-write-off approach is if your rectangles actually need to be semi-transparent. But if you're just solving Z-fighting for opaque objects, this approach introduces unnecessary overhead:

• Blending cost: Transparent rendering requires color blending for every pixel, which is more computationally expensive than opaque pixel replacement.
• Increased overdraw: Without depth write, every rectangle's pixels are drawn even if they're fully covered by later ones, leading to more GPU work.
• Queue sorting overhead: Even with renderOrder, Three.js still has to manage a separate queue for transparent objects, adding minor CPU overhead.

Quick Implementation Tip for Polygon Offset #

To avoid creating a separate material for each rectangle, you can use a shader material with a uniform for the offset factor, or dynamically update the material's polygonOffsetFactor for each rectangle. Just make sure your offset values are small enough to avoid visual artifacts (rectangles looking like they're off-plane) but large enough to eliminate Z-fighting. A starting point is polygonOffsetFactor: -1 and polygonOffsetUnits: 1, scaled by your layer count if needed.

内容的提问来源于stack exchange，提问作者karni