Features:
* Scales dash spacing with border width.
* Laying out dashes around rounded corners.
* Varying border widths with rounded corners - now uses an ellipse for the inner edge of the border.
* When there are no rounded corners, each straight border is laid out separately, so that the dashes to meet at the corners.
* All sides of each dash are antialiased.


Release Notes:
- N/A
---------
Co-authored-by: Michael Sloan <michael@zed.dev>
Co-authored-by: Ben <ben@zed.dev>
Release Notes:
- Render unstaged hunks in the project diff editor with a slashed
background
---------
Co-authored-by: maxbrunsfeld <max@zed.dev>
Co-authored-by: Max Brunsfeld <maxbrunsfeld@gmail.com>
TODO:
- [x] BackgroundOrientation
- [x] PatternDash
- [x] `pattern_horizontal_dash` & `pattern_vertical_dash`
- [x] Metal dash shader
- [x] Blade dash shader
- [x] Update ui::Divider to use new pattern
---
This PR introduces proper dashed dividers using the new `PatternDash`
background shader.

Before this we were using 128 elements to create a dashed divider, which
is both expensive, and would not scale beyond a certain size. This
allows us to simplify the divider element as well.
Changes:
- Adds `BackgroundOrientation` to `gpui::color::Background` to allow
specifying a direction for a pattern
- Adds the PatternDash pattern variant
- Updates `ui::Divider`'s dashed variants to be more efficient
Misc:
- Documents the `ui::Divider` component
- Treat `.metal` files as `C` in the Zed project until we get some metal
syntax highlighting.
Release Notes:
- N/A
TODO:
- [x] Add BackgroundTag::PatternSlash
- [x] Support metal slash pattern fills
- [x] Support blade slash pattern fills
---
Adds support for a new background type in gpui, `pattern_slash`.
Usage:
```rust
div().size(px(56.0)).bg(pattern_slash(gpui::red()))
```
This will create a 56px square with a red slash pattern fill.
You can run the pattern example with `cargo run -p gpui --example
pattern`:

---
After talking with @as-cii at length about how we want to support
patterns in gpui, we decided for now we'll simply add a new
BackgroundTag specific to this pattern.
It isn't the best long term plan however – we'll likely want to
introduce the concept of a `Fill` at some point so we can have
`Fill::Solid`, `Fill::Gradient(LinearGradient)`, etc in the future.
The pattern is designed to seamlessly tile vertically for elements of
the same height. For example, for use in editor line backgrounds:

---
Release Notes:
(do we do gpui release notes?)
- Adds support for slash pattern fills in `gpui`.
---------
Co-authored-by: Antonio Scandurra <me@as-cii.com>
Closes#22433
Before/After (macOS):

For some reason the non-blurred one seems much lower quality, so we may
need to tinker with the samples, or something else.

I'm unsure if this is a problem on Linux/in the Blade renderer, but
since no changes were made outside of the medal shaders we can probably
take this macOS-specific win for now.
Release Notes:
- gpui: Fixed an issue where shadows with a `blur_radius` of 0 would not
render.
Release Notes:
- N/A
---
Add this for let GPUI element to support fade in-out animation.
## Platform test
- [x] macOS
- [x] blade `cargo run -p gpui --example opacity --features macos-blade`
## Usage
```rs
div()
.opacity(0.5)
.bg(gpui::black())
.text_color(gpui::black())
.child("Hello world")
```
This will apply the `opacity` it self and all children to use `opacity`
value to render colors.
## Example
```
cargo run -p gpui --example opacity
cargo run -p gpui --example opacity --features macos-blade
```
<img width="612" alt="image"
src="https://github.com/user-attachments/assets/f1da87ed-31f5-4b55-a023-39e8ee1ba349">
Release Notes:
- Fixed a (potential) small error in erf estimation. Technically, the
error is negligible.
I am not sure where the current calculation for erf come from and if it
is intended or a simple mistake. However it looks slightly different
from the official calculation, notably
[this](https://en.wikipedia.org/wiki/Error_function#Approximation_with_elementary_functions)
from Wikipedia.
I will add a comment if it is intended.
Release Notes:
- Added [object-fit
API](https://developer.mozilla.org/en-US/docs/Web/CSS/object-fit) to the
`img` element. This allows the user to decide how the image is scaled
within the element bounds.
- Fixes corner radius not working as expected on overflowing elements.
After implementing it a while ago, our previous interpolation scheme
didn't really make sense to me and was causing borders to be rendered
incorrectly. We don't really draw backgrounds and borders as part of
the same draw call anymore, but it seemed reasonable to have a correct
implementation in the shader anyway.
This commit uses Porter-Duff compositing (i.e., `over`) to produce
a color that is the result of superimposing the border on top of the
background. Then, we linearly interpolate towards the background color
as we slide out of the border and into the background.