Example for random sampling

[mweatherley]

Objective

We introduced a bunch of neat random sampling stuff in this release; we should do a good job of showing people how to use it, and writing examples is part of this.

Solution

A new Math example, random_sampling, shows off the ShapeSample API functionality. For the moment, it renders a cube and allows the user to sample points from its interior or boundary in sets of either 1 or 100:

On the level of code, these are reflected by two ways of using ShapeSample:

// Get a single random Vec3:
let sample: Vec3 = match *mode {
    Mode::Interior => shape.0.sample_interior(rng),
    Mode::Boundary => shape.0.sample_boundary(rng),
};

// Get 100 random Vec3s:
let samples: Vec<Vec3> = match *mode {
    Mode::Interior => {
        let dist = shape.0.interior_dist();
        dist.sample_iter(&mut rng).take(100).collect()
    }
    Mode::Boundary => {
        let dist = shape.0.boundary_dist();
        dist.sample_iter(&mut rng).take(100).collect()
    }
};

Testing

Run the example!

Discussion

Maybe in the future it would be nice to show off all of the different shapes that we have implemented ShapeSample for, but I wanted to start just by demonstrating the functionality. Here, I chose a cube because it's simple and because it looks good rendered transparently with backface culling disabled.

[lynn-lumen]

Looks good to me :)

[IQuick143]

I don't have much to say about the code itself, but I will note the following:

• Camera motion felt too fast, I think it would be good if you first converted mouse delta to a screen-space percentage and then scaled that by some sensitivity factor, rather than choosing an arbitrary pixel -> radian value.
• The code should explain more that the sampling does NOT take into account the transform of the mesh, the fact they agree is due to how the scene is constructed. (Maybe show the user how to use the cube entity's global transform to transform the sample to world-space?)
• Would be nice if: You could tilt camera up/down.
• Would be nice if: (as you said) You could look at various other shapes
• Would be nice if: Some sort of batching for the point spheres to let me to look at more of them!
• Would be nice if: Some sort of free-running mode where points spawn (and despawn) by themselves).

We can tackle the would be's in another example to improve the readability of this one or just not at all.

[mweatherley]

* Camera motion felt too fast, I think it would be good if you first converted mouse delta to a screen-space percentage and then scaled that by some sensitivity factor, rather than choosing an arbitrary pixel -> radian value.

Hmm, I do use pretty low mouse sensitivity! I actually just copied what I did in the align example. To me the most important thing is that you can see the thing from different angles to get a sense of depth, so I'd be more inclined to just tweak the magic number than doing any kind of more complex logic, but I can definitely tweak it.

* The code should explain more that the sampling does NOT take into account the transform of the mesh, the fact they agree is due to how the scene is constructed. (Maybe show the user how to use the cube entity's global transform to transform the sample to world-space?)

Yeah, I should have addressed that more explicitly. Maybe I'll add the transformation to the sampling code even if it doesn't do anything, just to give the right idea.

[IQuick143]

My rationale for the suggestion of using window units is that:
A) imo it's fairly intuitive when I "grab" the screen, move it by some amount, and it rotates proportionally.
B) it deals pretty much automatically with resolution differences.
C) the magic constant is in more tangible units imo

But it's definitely not a blocker, just some polish I felt would be good.

[alice-i-cecile]

I'll merge this Monday: feel free to tweak it until then :)

[BD103]

Clean and fun to use! Looks good :)