[Merged by Bors] - Add RegularPolygon and Circle meshes #3730

rparrett · 2022-01-20T15:35:58Z

Objective

Bevy users often want to create circles and other simple shapes.

All the machinery is in place to accomplish this, and there are external crates that help. But when writing code for e.g. a new bevy example, it's not really possible to draw a circle without bringing in a new asset, writing a bunch of scary looking mesh code, or adding a dependency.

In particular, this PR was inspired by this interaction in another PR: #3721 (comment)

Solution

This PR adds shape::RegularPolygon and shape::Circle (which is just a RegularPolygon that defaults to a large number of sides)

Discussion

There's a lot of ongoing discussion about shapes in bevyengine/rfcs#12 and at least one other lingering shape PR (although it seems incomplete).

That RFC currently includes RegularPolygon and Circle shapes, so I don't think that having working mesh generation code in the engine for those shapes would add much burden to an author of an implementation.

But if we'd prefer not to add additional shapes until after that's sorted out, I'm happy to close this for now.

Alternatives for users

For any users stumbling on this issue, here are some plugins that will help if you need more shapes.

https://github.com/Nilirad/bevy_prototype_lyon
https://github.com/johanhelsing/bevy_smud
https://github.com/Weasy666/bevy_svg
https://github.com/redpandamonium/bevy_more_shapes
https://github.com/ForesightMiningSoftwareCorporation/bevy_polyline

rparrett · 2022-01-20T16:56:48Z

Another thing to note is that this is generating meshes like the pentagon on the right side: (edit: fixed this)

Doing it like what is shown on the left would result in fewer triangles, but I'm not sure if there are any graphical implications with "tiny thin triangles" when using this to draw circles or with UVs or how much we should be concerned about that otherwise.

rparrett · 2022-01-20T20:56:58Z

Now generating the "optimized" mesh like the left side in the diagram above.

alice-i-cecile

Some small nits, but otherwise this looks great. I'd missed this one!

crates/bevy_render/src/mesh/shape/regular_polygon.rs

examples/README.md

TheRawMeatball · 2022-02-04T19:04:50Z

Personally I'd prefer if the choice of which triangulation method to wasn't hard coded, but could be selected at runtime

alice-i-cecile · 2022-02-04T19:07:53Z

@bevyengine/rendering-team; do y'all have opinions on the triangulation strategy?

StarArawn · 2022-02-04T19:11:36Z

@bevyengine/rendering-team; do y'all have opinions on the triangulation strategy?

I personally prefer using something like SDF's for circles as they can scale much better and you don't have to be concerned with sides, but otherwise this seems fine to me.

StarArawn · 2022-02-04T19:12:40Z

Personally I'd prefer if the choice of which triangulation method to wasn't hard coded, but could be selected at runtime

I think if someone wants a different triangulation method they can just build their own mesh?

alice-i-cecile · 2022-02-04T19:15:30Z

I personally prefer using something like SDF's for circles as they can scale much better and you don't have to be concerned with sides, but otherwise this seems fine to me.

Agreed, but this is a solid stop-gap.

HackerFoo · 2022-02-04T20:58:05Z

I use recursive triangulation, like this:

It can produce narrow triangles, but they'll be at the edges anyway. It's a pretty simple algorithm, recursively splitting the list of vertices into thirds. It's only valid for convex polygons, though. I can submit a PR if desired.

rparrett · 2022-02-04T22:03:53Z

@HackerFoo

I only had a vague notion of "long triangle thin triangle bad" to go on, and I couldn't really dig up any concrete information and the (limited) testing I did wasn't revealing. So I just went with fewest triangles / fastest mesh generation.

I'm assuming you had a pretty good reason to implement that recursive strategy in your own app? Seems worthwhile to me if it actually solves some sort of problem.

alice-i-cecile · 2022-02-04T23:52:38Z

I'm assuming you had a pretty good reason to implement that recursive strategy in your own app? Seems worthwhile to me if it actually solves some sort of problem.

The recursive algorithm is much easier to extend to arbitrary polygons. That's probably a minor bit of useful future-proofing here, but not essential. I'm unsure if there are other benefits though.

HackerFoo · 2022-02-05T01:50:44Z

I did this while I was working on UV mapping. I can't remember if I saw artifacts, but I was using the fan method (on the left of the diagram above) and circles were ugly when looking at them in Blender, so I fixed it. I like the recursive approach because I love recursion, but also because if you draw the triangles from largest to smallest with this method, you get an increasingly accurate approximation of the polygon. So the lowest quality triangles contribute the least to the shape.

It's probably best to stick with the simple fan until it's at least an annoyance, though.

HackerFoo · 2022-03-04T07:42:27Z

crates/bevy_render/src/mesh/shape/regular_polygon.rs

+            sides: 6,
+        }
+    }
+}


Why is a hexagon the default? Does it make sense to provide a default?

HackerFoo · 2022-03-04T07:45:02Z

crates/bevy_render/src/mesh/shape/regular_polygon.rs

+            uvs.push([0.5 * (c + 1.0), 1.0 - 0.5 * (s + 1.0)]);
+        }
+
+        let mut indices = Vec::with_capacity((sides - 1) * 3);


I think this will crash for 0 sides.

What do you think is the most appropriate way to handle that situation?

if sides < 3 { panic!(/* ... */) }

Or clamping the value?

This is now protected by a debug_assert. Still a panic, but it doesn't really make any sense to try to build a polygon with fewer than 3 sides, and now there's a friendly error message.

crates/bevy_render/src/mesh/shape/regular_polygon.rs

adsick · 2022-03-27T11:46:45Z

"Bevy users often want to create circles and other simple shapes." who would have thought?))) I mean the engine is like 1.5 years old and still doesn't have a beginner-approachable drawing API. I love Bevy but can't use it because of that...

Nilirad · 2022-04-12T10:33:45Z

@adsick You can use bevy_prototype_lyon until Bevy gets a proper drawing API.

adsick · 2022-04-13T16:38:13Z

@adsick You can use bevy_prototype_lyon until Bevy gets a proper drawing API.

I know that, looked at the examples, but it seems to me that immediate mode API is more intuitive.

superdump · 2022-05-05T00:03:30Z

bors r+

# Objective Bevy users often want to create circles and other simple shapes. All the machinery is in place to accomplish this, and there are external crates that help. But when writing code for e.g. a new bevy example, it's not really possible to draw a circle without bringing in a new asset, writing a bunch of scary looking mesh code, or adding a dependency. In particular, this PR was inspired by this interaction in another PR: #3721 (comment) ## Solution This PR adds `shape::RegularPolygon` and `shape::Circle` (which is just a `RegularPolygon` that defaults to a large number of sides) ## Discussion There's a lot of ongoing discussion about shapes in <bevyengine/rfcs#12> and at least one other lingering shape PR (although it seems incomplete). That RFC currently includes `RegularPolygon` and `Circle` shapes, so I don't think that having working mesh generation code in the engine for those shapes would add much burden to an author of an implementation. But if we'd prefer not to add additional shapes until after that's sorted out, I'm happy to close this for now. ## Alternatives for users For any users stumbling on this issue, here are some plugins that will help if you need more shapes. https://github.com/Nilirad/bevy_prototype_lyon https://github.com/johanhelsing/bevy_smud https://github.com/Weasy666/bevy_svg https://github.com/redpandamonium/bevy_more_shapes https://github.com/ForesightMiningSoftwareCorporation/bevy_polyline

bors · 2022-05-05T00:22:16Z

Pull request successfully merged into main.

Build succeeded:

# Objective Bevy users often want to create circles and other simple shapes. All the machinery is in place to accomplish this, and there are external crates that help. But when writing code for e.g. a new bevy example, it's not really possible to draw a circle without bringing in a new asset, writing a bunch of scary looking mesh code, or adding a dependency. In particular, this PR was inspired by this interaction in another PR: bevyengine#3721 (comment) ## Solution This PR adds `shape::RegularPolygon` and `shape::Circle` (which is just a `RegularPolygon` that defaults to a large number of sides) ## Discussion There's a lot of ongoing discussion about shapes in <bevyengine/rfcs#12> and at least one other lingering shape PR (although it seems incomplete). That RFC currently includes `RegularPolygon` and `Circle` shapes, so I don't think that having working mesh generation code in the engine for those shapes would add much burden to an author of an implementation. But if we'd prefer not to add additional shapes until after that's sorted out, I'm happy to close this for now. ## Alternatives for users For any users stumbling on this issue, here are some plugins that will help if you need more shapes. https://github.com/Nilirad/bevy_prototype_lyon https://github.com/johanhelsing/bevy_smud https://github.com/Weasy666/bevy_svg https://github.com/redpandamonium/bevy_more_shapes https://github.com/ForesightMiningSoftwareCorporation/bevy_polyline

github-actions bot added the S-Needs-Triage This issue needs to be labelled label Jan 20, 2022

alice-i-cecile added A-Math Fundamental domain-agnostic mathematical operations C-Enhancement A new feature and removed S-Needs-Triage This issue needs to be labelled labels Jan 20, 2022

alice-i-cecile requested changes Feb 4, 2022

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crates/bevy_render/src/mesh/shape/regular_polygon.rs Show resolved Hide resolved

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alice-i-cecile approved these changes Feb 4, 2022

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rparrett force-pushed the regular-polygons branch from 0373e67 to 610185c Compare February 24, 2022 02:10

rparrett added 7 commits March 1, 2022 14:41

Add RegularPolygon and Circle

1e2f715

Add example to readme

fb6f09f

Use usize for sides for consistency

2c137d7

Preallocate vecs

03c7cc7

Minor cleanup

08e366e

Generate mesh with fewer triangles

63fa48c

Add missing doc string

c6e7923

rparrett force-pushed the regular-polygons branch from 610185c to ffe364b Compare March 1, 2022 21:52

rparrett added 3 commits March 1, 2022 15:01

Consolidate examples

10b3f0f

Use new mesh attribute api

630d9c5

Use new default shorthand

8dc3c72

rparrett force-pushed the regular-polygons branch from ffe364b to 8dc3c72 Compare March 1, 2022 22:01

rparrett added 2 commits March 2, 2022 14:08

Add constructors for RegularPolygon and Circle

4b68753

Fix unnecessary return

689c074

rparrett force-pushed the regular-polygons branch from 18e68b6 to 689c074 Compare March 2, 2022 22:03

rparrett added 2 commits March 2, 2022 16:30

Remove accidental newline

994c252

Fix doc comment

880d4a2

superdump approved these changes Mar 4, 2022

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superdump added the S-Ready-For-Final-Review This PR has been approved by the community. It's ready for a maintainer to consider merging it label Mar 4, 2022

HackerFoo suggested changes Mar 4, 2022

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rparrett added 6 commits March 4, 2022 06:36

Vertices terminology seems more correct than subdivisions

d774e70

Fix extra garbage triangle

40b925e

Minor optimization

b02089e

Friendlier panic when sides <= 2

1e1ba1f

Slightly less ambiguous variable names

0a76d2a

Fix larger allocation for indices than necessary

e0b04a6

alice-i-cecile mentioned this pull request Mar 24, 2022

Use a circle for the ball in Breakout #4324

Closed

alice-i-cecile requested a review from superdump April 25, 2022 18:25

superdump approved these changes May 5, 2022

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bors bot changed the title ~~Add RegularPolygon and Circle meshes~~ [Merged by Bors] - Add RegularPolygon and Circle meshes May 5, 2022

bors bot closed this May 5, 2022

alice-i-cecile mentioned this pull request May 5, 2022

Add gamepad_stick_input example #3721

Closed

shaderduck mentioned this pull request May 6, 2022

Use a circle for the ball in Breakout #4682

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[Merged by Bors] - Add RegularPolygon and Circle meshes #3730

[Merged by Bors] - Add RegularPolygon and Circle meshes #3730

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[Merged by Bors] - Add RegularPolygon and Circle meshes #3730

[Merged by Bors] - Add RegularPolygon and Circle meshes #3730

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Objective

Solution

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Alternatives for users

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