Summary

Have several questions about color blending in gpui.

Description

1. Put transparent rectagles together, and the blended color is strange.

impl Render for Test {
    fn render(&mut self, _window: &mut Window, _cx: &mut Context<Self>) -> impl IntoElement {
        div()
            .h_full()
            .w_full()
            .bg(rgba(0xE0E0E0FF))
            .flex()
            .child(
                div()
                    .bg(gpui::red().alpha(0.5))
                    .h(px(100.0))
                    .w(px(100.0))
                    .flex()
                    .child(
                        div()
                            .bg(gpui::blue().alpha(0.5))
                            .h(px(50.0))
                            .w(px(50.0))
                            .m(px(25.0))
                    )
            )
    }
}

2. Rgba::blend seems neither an simple alpha blend nor an premultiplied simple alpha blend. I think at least alpha of the both colors will contribute to the composited alpha channel.

   zed/crates/gpui/src/color.rs

   Lines 61 to 74 in 61abfd5

   	pub fn blend(&self, other: Rgba) -> Self {
   	if other.a >= 1.0 {
   	other
   	} else if other.a <= 0.0 {
   	return *self;
   	} else {
   	return Rgba {
   	r: (self.r * (1.0 - other.a)) + (other.r * other.a),
   	g: (self.g * (1.0 - other.a)) + (other.g * other.a),
   	b: (self.b * (1.0 - other.a)) + (other.b * other.a),
   	a: self.a,
   	};
   	}
   	}

Expected Behavior:
Blend in figma, the same as examples from w3c compositing and blending

Actual Behavior:
The color of the red and purple part are both different from the examples

Zed Version and System Specs

gpui latest from git