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Add examples demonstrating how to follow the player with a camera #12658

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alice-i-cecile opened this issue Mar 22, 2024 · 6 comments
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C-Examples An addition or correction to our examples D-Trivial Nice and easy! A great choice to get started with Bevy

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@alice-i-cecile
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What problem does this solve or what need does it fill?

Following a player with the camera is an essential task for a large fraction of games. However, there are several pitfalls for new game devs:

  • the obvious way to write the system to do this will lead to conflicting borrows on the Transform of Player and Camera
  • the camera should move via delta-time, to ensure approximate frame-rate independence
  • the camera should be eased towards the player, rather than simply using direct parenting to avoid jerk
  • the camera movement and player movement systems must be precisely ordered to avoid jitter

What solution would you like?

Add two examples that :

  1. A simple top-down 2D camera controller with WASD player movement and a simple environment.
  2. A first person camera with a simple fly cam player controller.

What alternative(s) have you considered?

We could ship first-party camera controllers. This is not as good of a solution, as these tend to need to be heavily modified by the end user.

It's better to teach the developer how to fish, and possibly link to other resources on designing good camera controllers.

Additional context

Once this is done, we can consider adding other camera controller examples in follow-up PRs: e.g. RTS-style cameras, or a third person over the shoulder camera.

@alice-i-cecile alice-i-cecile added D-Trivial Nice and easy! A great choice to get started with Bevy C-Examples An addition or correction to our examples labels Mar 22, 2024
@theredfish
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theredfish commented Mar 22, 2024

I'm definitely interested by this! I will need some camera logic in my game and I'm currently using Dolly. Would be great to explore alternatives with the Bevy API. We could also add some user documentation/guide maybe ?

Can I be assigned on it?

@alice-i-cecile
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Assigned! Feel free to open up a draft PR early and ask for help :)

@theredfish
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Thanks, I'll do that :)

github-merge-queue bot pushed a commit that referenced this issue Jun 10, 2024
# Objective

This PR addresses the 2D part of #12658. I plan to separate the examples
and make one PR per camera example.

## Solution

Added a new top-down example composed of:

- [x] Player keyboard movements
- [x] UI for keyboard instructions
- [x] Colors and bloom effect to see the movement of the player
- [x] Camera smooth movement towards the player (lerp)

## Testing

```bash
cargo run --features="wayland,bevy/dynamic_linking" --example 2d_top_down_camera
```



https://github.com/bevyengine/bevy/assets/10638479/95db0587-e5e0-4f55-be11-97444b795793
mockersf pushed a commit that referenced this issue Jun 10, 2024
# Objective

This PR addresses the 2D part of #12658. I plan to separate the examples
and make one PR per camera example.

## Solution

Added a new top-down example composed of:

- [x] Player keyboard movements
- [x] UI for keyboard instructions
- [x] Colors and bloom effect to see the movement of the player
- [x] Camera smooth movement towards the player (lerp)

## Testing

```bash
cargo run --features="wayland,bevy/dynamic_linking" --example 2d_top_down_camera
```



https://github.com/bevyengine/bevy/assets/10638479/95db0587-e5e0-4f55-be11-97444b795793
@theredfish
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A first person camera with a simple fly cam player controller.

Hi @alice-i-cecile , regarding this example do we want to just control the camera or create some kind of character with some behaviours and attach the camera to it?

@alice-i-cecile
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I'd like to have a simple character with basic movement. The camera shouldn't be controlled directly by the player, only the character.

github-merge-queue bot pushed a commit that referenced this issue Jun 17, 2024
# Objective

A very common way to organize a first-person view is to split it into
two kinds of models:

 - The *view model* is the model that represents the player's body.
 - The *world model* is everything else.

The reason for this distinction is that these two models should be
rendered with different FOVs.
The view model is typically designed and animated with a very specific
FOV in mind, so it is
generally *fixed* and cannot be changed by a player. The world model, on
the other hand, should
be able to change its FOV to accommodate the player's preferences for
the following reasons:
- *Accessibility*: How prone is the player to motion sickness? A wider
FOV can help.
- *Tactical preference*: Does the player want to see more of the
battlefield?
 Or have a more zoomed-in view for precision aiming?
- *Physical considerations*: How well does the in-game FOV match the
player's real-world FOV?
Are they sitting in front of a monitor or playing on a TV in the living
room? How big is the screen?

## Solution

I've added an example implementing the described setup as follows.

The `Player` is an entity holding two cameras, one for each model. The
view model camera has a fixed
FOV of 70 degrees, while the world model camera has a variable FOV that
can be changed by the player.

 I use different `RenderLayers` to select what to render.

- The world model camera has no explicit `RenderLayers` component, so it
uses the layer 0.
All static objects in the scene are also on layer 0 for the same reason.
- The view model camera has a `RenderLayers` component with layer 1, so
it only renders objects
explicitly assigned to layer 1. The arm of the player is one such
object.
The order of the view model camera is additionally bumped to 1 to ensure
it renders on top of the world model.
- The light source in the scene must illuminate both the view model and
the world model, so it is
 assigned to both layers 0 and 1.

To better see the effect, the player can move the camera by dragging
their mouse and change the world model's FOV with the arrow keys. The
arrow up key maps to "decrease FOV" and the arrow down key maps to
"increase FOV". This sounds backwards on paper, but is more intuitive
when actually changing the FOV in-game since a decrease in FOV looks
like a zoom-in.
I intentionally do not allow changing the view model's FOV even though
it would be illustrative because that would be an anti-pattern and bloat
the code a bit.

The example is called `first_person_view_model` and not just
`first_person` because I want to highlight that this is not a simple
flycam, but actually renders the player.

## Testing

Default FOV:
<img width="1392" alt="image"
src="https://github.com/bevyengine/bevy/assets/9047632/8c2e804f-fac2-48c7-8a22-d85af999dfb2">

Decreased FOV:
<img width="1392" alt="image"
src="https://github.com/bevyengine/bevy/assets/9047632/1733b3e5-f583-4214-a454-3554e3cbd066">

Increased FOV:
<img width="1392" alt="image"
src="https://github.com/bevyengine/bevy/assets/9047632/0b0640e6-5743-46f6-a79a-7181ba9678e8">

Note that the white bar on the right represents the player's arm, which
is more obvious in-game because you can move the camera around.
The box on top is there to make sure that the view model is receiving
shadows.

I tested only on macOS.

---

## Changelog

I don't think new examples go in here, do they?

## Caveat

The solution used here was implemented with help by @robtfm on
[Discord](https://discord.com/channels/691052431525675048/866787577687310356/1241019224491561000):
> shadow maps are specific to lights, not to layers
> if you want shadows from some meshes that are not visible, you could
have light on layer 1+2, meshes on layer 2, camera on layer 1 (for
example)
> but this might change in future, it's not exactly an intended feature

In other words, the example code as-is is not guaranteed to work in the
future. I want to bring this up because the use-case presented here is
extremely common in first-person games and important for accessibility.
It would be good to have a blessed and easy way of how to achieve it.

I'm also not happy about how I get the `perspective` variable in
`change_fov`. Very open to suggestions :)

## Related issues

- Addresses parts of #12658
- Addresses parts of #12588

---------

Co-authored-by: Pascal Hertleif <killercup@gmail.com>
@theredfish
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I think the previous example is enough to cover the needs of a first person camera - that's pretty much what I had in mind to attach the camera to the player. If it's ok we can close this issue as resolved. But if you need something else let me know 👍

mockersf pushed a commit that referenced this issue Jun 19, 2024
# Objective

A very common way to organize a first-person view is to split it into
two kinds of models:

 - The *view model* is the model that represents the player's body.
 - The *world model* is everything else.

The reason for this distinction is that these two models should be
rendered with different FOVs.
The view model is typically designed and animated with a very specific
FOV in mind, so it is
generally *fixed* and cannot be changed by a player. The world model, on
the other hand, should
be able to change its FOV to accommodate the player's preferences for
the following reasons:
- *Accessibility*: How prone is the player to motion sickness? A wider
FOV can help.
- *Tactical preference*: Does the player want to see more of the
battlefield?
 Or have a more zoomed-in view for precision aiming?
- *Physical considerations*: How well does the in-game FOV match the
player's real-world FOV?
Are they sitting in front of a monitor or playing on a TV in the living
room? How big is the screen?

## Solution

I've added an example implementing the described setup as follows.

The `Player` is an entity holding two cameras, one for each model. The
view model camera has a fixed
FOV of 70 degrees, while the world model camera has a variable FOV that
can be changed by the player.

 I use different `RenderLayers` to select what to render.

- The world model camera has no explicit `RenderLayers` component, so it
uses the layer 0.
All static objects in the scene are also on layer 0 for the same reason.
- The view model camera has a `RenderLayers` component with layer 1, so
it only renders objects
explicitly assigned to layer 1. The arm of the player is one such
object.
The order of the view model camera is additionally bumped to 1 to ensure
it renders on top of the world model.
- The light source in the scene must illuminate both the view model and
the world model, so it is
 assigned to both layers 0 and 1.

To better see the effect, the player can move the camera by dragging
their mouse and change the world model's FOV with the arrow keys. The
arrow up key maps to "decrease FOV" and the arrow down key maps to
"increase FOV". This sounds backwards on paper, but is more intuitive
when actually changing the FOV in-game since a decrease in FOV looks
like a zoom-in.
I intentionally do not allow changing the view model's FOV even though
it would be illustrative because that would be an anti-pattern and bloat
the code a bit.

The example is called `first_person_view_model` and not just
`first_person` because I want to highlight that this is not a simple
flycam, but actually renders the player.

## Testing

Default FOV:
<img width="1392" alt="image"
src="https://github.com/bevyengine/bevy/assets/9047632/8c2e804f-fac2-48c7-8a22-d85af999dfb2">

Decreased FOV:
<img width="1392" alt="image"
src="https://github.com/bevyengine/bevy/assets/9047632/1733b3e5-f583-4214-a454-3554e3cbd066">

Increased FOV:
<img width="1392" alt="image"
src="https://github.com/bevyengine/bevy/assets/9047632/0b0640e6-5743-46f6-a79a-7181ba9678e8">

Note that the white bar on the right represents the player's arm, which
is more obvious in-game because you can move the camera around.
The box on top is there to make sure that the view model is receiving
shadows.

I tested only on macOS.

---

## Changelog

I don't think new examples go in here, do they?

## Caveat

The solution used here was implemented with help by @robtfm on
[Discord](https://discord.com/channels/691052431525675048/866787577687310356/1241019224491561000):
> shadow maps are specific to lights, not to layers
> if you want shadows from some meshes that are not visible, you could
have light on layer 1+2, meshes on layer 2, camera on layer 1 (for
example)
> but this might change in future, it's not exactly an intended feature

In other words, the example code as-is is not guaranteed to work in the
future. I want to bring this up because the use-case presented here is
extremely common in first-person games and important for accessibility.
It would be good to have a blessed and easy way of how to achieve it.

I'm also not happy about how I get the `perspective` variable in
`change_fov`. Very open to suggestions :)

## Related issues

- Addresses parts of #12658
- Addresses parts of #12588

---------

Co-authored-by: Pascal Hertleif <killercup@gmail.com>
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