Shapecasts weirdly and unpredictably misbehave when met with inclined surfaces

[john0_dev (KV2)]

When using shapecasts and casting them against inclined surfaces, the RaycastResult.Position can be way more off than expected. This behavior can cause unwanted effects in character & vehicle controllers.

In the below videos, I am casting a cylinder downwards against a WedgePart, and then against a regular angled part (i dont know if the difference matters). The direction towards the result from the ray’s origin is drawn with a neon thin line for clarity. I’ve also tried the same thing with a cylinder mesh instead of a regular part cylinder, and the behavior is the same.

WedgePart:

Angled regular part:

The effect can be very severe, as RaycastResult.Position can even be mid-air in a very far position:

It’s worth noting that even when the position is off bounds or mid-air, RaycastResult.Instance is still accurate.

The script used is located inside ShapecastProjection in workspace.

Reproduction file: shapecast inaccuracy bug reproduction.rbxl (58.1 KB)

Expected behavior

Shapecasts should be accurate and deterministic in all conditions

[john0_dev (KV2)]

This is still happening. Any updates? I did some more tests, and it occurs with spherecasts too, but blockcasts seem to be unaffected by this and work normally

[john0_dev (KV2)]

[NOTEKAMI (NOT)]

Hey, I don’t come with good news for you, but I also observe a similar problem, only in my case the values ​​are very broken.

I’ll try to find more similar posts to combine into one.

This issue is seriously affecting stability.

Blockcast returning math.huge or NaN position despite normal args

While testing acoustic audio, I found a bug that completely broke it, I thought that the problem was in the audio (kinda yes and no), BUT the main problem was that :Blockcast() somehow gets a NaN or math.huge RaycastResult.Position, despire all arguments are normal. This issue only (AFAIK) occurs when :Blockcast() hits rotated parts (I haven’t tested it on Sherecast and Shapecast) Expected behavior :Blockcast() will return a usual position, not math.huge or NaN Repo file in private …

[SubtleTrash]

Hi, it’s been a long time coming. We’re currently diving into this internally, and we think we may have a fix. I or another Roblox Staff member will report back with any updates.