gui: support radial gradients

config/src/background.rs

@@ -31,6 +31,11 @@ impl Default for BlendMode {
 pub enum GradientOrientation {
     Horizontal,
     Vertical,
+    Radial {
+        radius: Option<f64>,
+        cx: Option<f64>,
+        cy: Option<f64>,
+    },
 }
 
 impl Default for GradientOrientation {

docs/config/appearance.md

@@ -327,6 +327,15 @@ return {
 See [Styling Inactive Panes](#style-inactive-panes) for more information
 on hue, saturation, brigthness transformations.
 
+## Window Background Gradient
+
+*Since: nightly builds only*
+
+<img src="../../../screenshots/radial-gradient.png">
+
+See [window_background_gradient](lua/config/window_background_gradient.md)
+for configuration information on gradients.
+
 ## Window Background Opacity
 
 *since: 20201031-154415-9614e117*

docs/config/lua/config/window_background_gradient.md

@@ -13,7 +13,8 @@ return {
   window_background_gradient = {
     -- Can be "Vertical" or "Horizontal".  Specifies the direction
     -- in which the color gradient varies.  The default is "Horizontal",
-    -- with the gradient going from left-to-right
+    -- with the gradient going from left-to-right.
+    -- Radial gradients are also supported; see the other example below
     orientation = "Vertical",
 
     -- Specifies the set of colors that are interpolated in the gradient.
@@ -56,7 +57,44 @@ return {
 }
 ```
 
+<img src="../../../screenshots/vertical-gradient.png">
+
 Gradients are implemented using the `colorgrad` crate.
 Take a look at <https://github.com/mazznoer/colorgrad-rs#using-web-color-format>
 for some usage examples and additional information about gradients.
 
+## Radial gradient:
+
+Radial gradients are implemented using a notional perfect circle that is
+subsequently stretched to fill the dimensions of the window.
+
+```lua
+return {
+  color_scheme = "Github",
+  window_background_gradient = {
+     colors = {"deeppink", "gold"},
+     orientation = {
+       Radial={
+         -- Specifies the x coordinate of the center of the circle,
+         -- in the range 0.0 through 1.0.  The default is 0.5 which
+         -- is centered in the X dimension.
+         cx = 0.75,
+
+         -- Specifies the y coordinate of the center of the circle,
+         -- in the range 0.0 through 1.0.  The default is 0.5 which
+         -- is centered in the Y dimension.
+         cy = 0.75,
+
+         -- Specifies the radius of the notional circle.
+         -- The default is 0.5, which combined with the default cx
+         -- and cy values places the circle in the center of the
+         -- window, with the edges touching the window edges.
+         -- Values larger than 1 are possible.
+         radius = 1.25,
+       }
+     },
+  }
+}
+```
+
+<img src="../../../screenshots/radial-gradient.png">

wezterm-gui/src/termwindow/mod.rs

@@ -333,11 +333,20 @@ fn load_background_image(config: &ConfigHandle, dimensions: &Dimensions) -> Opti
     match &config.window_background_gradient {
         Some(g) => match g.build() {
             Ok(grad) => {
-                let width = dimensions.pixel_width as u32;
-                let height = dimensions.pixel_height as u32;
+                let mut width = dimensions.pixel_width as u32;
+                let mut height = dimensions.pixel_height as u32;
+
+                if matches!(g.orientation, GradientOrientation::Radial { .. }) {
+                    // To simplify the math, we compute a perfect circle
+                    // for the radial gradient, and let the texture sampler
+                    // perturb it to fill the window
+                    width = width.min(height);
+                    height = height.min(width);
+                }
+
                 let mut imgbuf = image::RgbaImage::new(width, height);
-                let fw = dimensions.pixel_width as f64;
-                let fh = dimensions.pixel_height as f64;
+                let fw = width as f64;
+                let fh = height as f64;
 
                 fn to_pixel(c: colorgrad::Color) -> image::Rgba<u8> {
                     let (r, g, b, a) = c.rgba_u8();
@@ -358,7 +367,14 @@ fn load_background_image(config: &ConfigHandle, dimensions: &Dimensions) -> Opti
                 // visible color banding.  The default 64 was selected
                 // because it it was the smallest value on my mac where
                 // the banding wasn't obvious.
-                let noise_amount = g.noise.unwrap_or(64);
+                let noise_amount = g.noise.unwrap_or_else(|| {
+                    if matches!(g.orientation, GradientOrientation::Radial { .. }) {
+                        16
+                    } else {
+                        64
+                    }
+                });
+
                 fn noise(rng: &fastrand::Rng, noise_amount: usize) -> f64 {
                     if noise_amount == 0 {
                         0.
@@ -390,6 +406,21 @@ fn load_background_image(config: &ConfigHandle, dimensions: &Dimensions) -> Opti
                             )));
                         }
                     }
+                    GradientOrientation::Radial { radius, cx, cy } => {
+                        let radius = fw * radius.unwrap_or(0.5);
+                        let cx = fw * cx.unwrap_or(0.5);
+                        let cy = fh * cy.unwrap_or(0.5);
+
+                        for (x, y, pixel) in imgbuf.enumerate_pixels_mut() {
+                            let nx = noise(&rng, noise_amount);
+                            let ny = noise(&rng, noise_amount);
+
+                            let t = (nx + (x as f64 - cx).powi(2) + (ny + y as f64 - cy).powi(2))
+                                .sqrt()
+                                / radius;
+                            *pixel = to_pixel(grad.at(t));
+                        }
+                    }
                 }
 
                 let data = imgbuf.into_vec();