Implement gradient color interpolation option (#548)

* Added the better color averaging code (tested & functional)

* rustfmt

* Make Color f32 0..1, clarify premul/unpremul

* Fix imports and test name

* Premultiply gradient colors matching CSS

* Fix indentation

* fixup

* Add gradient image

---------

Co-authored-by: K's Thinkpad <K.T.Kraft@protonmail.com>

1 files changed, 53 insertions, 0 deletions

diff --git a/niri-visual-tests/src/cases/gradient_oklch_increasing.rs b/niri-visual-tests/src/cases/gradient_oklch_increasing.rs
new file mode 100644
index 00000000..2a020923
--- /dev/null
+++ b/niri-visual-tests/src/cases/gradient_oklch_increasing.rs
@@ -0,0 +1,53 @@
+use niri::render_helpers::border::BorderRenderElement;
+use niri_config::{
+    Color, CornerRadius, GradientColorSpace, GradientInterpolation, HueInterpolation,
+};
+use smithay::backend::renderer::element::RenderElement;
+use smithay::backend::renderer::gles::GlesRenderer;
+use smithay::utils::{Logical, Physical, Rectangle, Size};
+
+use super::TestCase;
+
+pub struct GradientOklchIncreasing {
+    gradient_format: GradientInterpolation,
+}
+
+impl GradientOklchIncreasing {
+    pub fn new(_size: Size<i32, Logical>) -> Self {
+        Self {
+            gradient_format: GradientInterpolation {
+                color_space: GradientColorSpace::Oklch,
+                hue_interpolation: HueInterpolation::Increasing,
+            },
+        }
+    }
+}
+
+impl TestCase for GradientOklchIncreasing {
+    fn render(
+        &mut self,
+        _renderer: &mut GlesRenderer,
+        size: Size<i32, Physical>,
+    ) -> Vec<Box<dyn RenderElement<GlesRenderer>>> {
+        let (a, b) = (size.w / 6, size.h / 3);
+        let size = (size.w - a * 2, size.h - b * 2);
+        let area = Rectangle::from_loc_and_size((a, b), size).to_f64();
+
+        [BorderRenderElement::new(
+            area.size,
+            Rectangle::from_loc_and_size((0., 0.), area.size),
+            self.gradient_format,
+            Color::new_unpremul(1., 0., 0., 1.),
+            Color::new_unpremul(0., 1., 0., 1.),
+            0.,
+            Rectangle::from_loc_and_size((0., 0.), area.size),
+            0.,
+            CornerRadius::default(),
+            1.,
+        )
+        .with_location(area.loc)]
+        .into_iter()
+        .map(|elem| Box::new(elem) as _)
+        .collect()
+    }
+}