When a KinematicBody is stuck, set the unsafe proportion to the minimum instead of zero.

[madmiraal]

When a KinematicBody is stuck, setting the unsafe proportion to the minimum instead of zero, ensures that collision information is extracted even if the penetration causing the body to be stuck is less than the test_motion_min_contact_depth. More importantly, this ensures that a collision is reported and doesn't allow the body to tunnel. Furthermore, it also ensures that the collision information is extracted from the CollisionShape in the direction of motion not the CollisionShape that happens to be closest or first.

Note: The minimum is 1/2^8 because there are (an arbitrary) eight steps in the binary search.

Fixes #37798.

PS See my comment in #37798 for a more in depth analysis.

[Calinou]

There should probably be a comment above this line to explain why this is done exactly. (Feel free to use GH-38529 as a reference to this pull request.)

[madmiraal]

How about:

// Set unsafe to the minimum after eight steps = 1/2^8.

[Calinou]

I think code comments like these should be more about the why than the how. If I read that comment, I have no idea why it's being done this way 😉

[madmiraal]

Are you talking about why the unsafe is being set to the minimum, why the minimum is 1/2^8 or why 1/(1<<8) = 1/2^8?

[Calinou]

Maybe something like this?

// When a KinematicBody is stuck, setting the unsafe proportion to the
// minimum instead of zero ensures that collision information is extracted
// even if the penetration causing the body to be stuck is less than the
// `test_motion_min_contact_depth`. See GH-38529 for details.

[madmiraal]

Mmm. I think that is excessive. Code shouldn't document why a change was made. It makes it look like setting the value to 1/2^8 is unusual, which it isn't. It is simply the value that unsafe would have been set to if this loop had been allowed to run:

godot/servers/physics_2d/space_2d_sw.cpp

Line 948 in e253451

for (int k = 0; k < 8; k++) { //steps should be customizable..

[Calinou]

Same as above.

[raphaklaus]

Hi guys, just want to know if this one is going to be merged.

[capnm]

Just a few pointers for good git commit messages, that's a good place for an extended 'why'
that also get directly inline displayed in 'smart' editors.
E.g.: https://www.theserverside.com/video/Follow-these-git-commit-message-guidelines

• Limit the subject line to 50 characters.
• Put a blank line between the subject line and the body.
• Wrap the body at 72 characters.
  (The PR comment is I think a good body candidate.)

[akien-mga]

Superseded by #52953.