Implement custom shader for window-close anim

14 files changed, 361 insertions, 30 deletions

diff --git a/Cargo.lock b/Cargo.lock
index 4e0d3015..4249bfa9 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -186,7 +186,7 @@ dependencies = [
  "async-lock 3.3.0",
  "async-task",
  "concurrent-queue",
- "fastrand 2.0.2",
+ "fastrand 2.1.0",
  "futures-lite 2.3.0",
  "slab",
 ]
@@ -434,7 +434,7 @@ dependencies = [
  "async-channel",
  "async-lock 3.3.0",
  "async-task",
- "fastrand 2.0.2",
+ "fastrand 2.1.0",
  "futures-io",
  "futures-lite 2.3.0",
  "piper",
@@ -1081,9 +1081,9 @@ dependencies = [
 
 [[package]]
 name = "fastrand"
-version = "2.0.2"
+version = "2.1.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "658bd65b1cf4c852a3cc96f18a8ce7b5640f6b703f905c7d74532294c2a63984"
+checksum = "9fc0510504f03c51ada170672ac806f1f105a88aa97a5281117e1ddc3368e51a"
 
 [[package]]
 name = "fdeflate"
@@ -1225,7 +1225,7 @@ version = "2.3.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "52527eb5074e35e9339c6b4e8d12600c7128b68fb25dcb9fa9dec18f7c25f3a5"
 dependencies = [
- "fastrand 2.0.2",
+ "fastrand 2.1.0",
  "futures-core",
  "futures-io",
  "parking",
@@ -2203,6 +2203,7 @@ dependencies = [
  "clap",
  "directories",
  "drm-ffi 0.7.1",
+ "fastrand 2.1.0",
  "futures-util",
  "git-version",
  "glam",
@@ -2583,7 +2584,7 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "668d31b1c4eba19242f2088b2bf3316b82ca31082a8335764db4e083db7485d4"
 dependencies = [
  "atomic-waker",
- "fastrand 2.0.2",
+ "fastrand 2.1.0",
  "futures-io",
 ]
 
@@ -3337,7 +3338,7 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "85b77fafb263dd9d05cbeac119526425676db3784113aa9295c88498cbf8bff1"
 dependencies = [
  "cfg-if",
- "fastrand 2.0.2",
+ "fastrand 2.1.0",
  "rustix 0.38.32",
  "windows-sys 0.52.0",
 ]
diff --git a/Cargo.toml b/Cargo.toml
index dd03a2a5..e2cf2f2f 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -51,6 +51,7 @@ calloop = { version = "0.13.0", features = ["executor", "futures-io"] }
 clap = { workspace = true, features = ["string"] }
 directories = "5.0.1"
 drm-ffi = "0.7.1"
+fastrand = "2.1.0"
 futures-util = { version = "0.3.30", default-features = false, features = ["std", "io"] }
 git-version = "0.3.9"
 glam = "0.27.0"
diff --git a/niri-config/src/lib.rs b/niri-config/src/lib.rs
index 14119dc5..0388268d 100644
--- a/niri-config/src/lib.rs
+++ b/niri-config/src/lib.rs
@@ -552,18 +552,24 @@ impl Default for WindowOpenAnim {
     }
 }
 
-#[derive(Debug, Clone, Copy, PartialEq)]
-pub struct WindowCloseAnim(pub Animation);
+#[derive(Debug, Clone, PartialEq)]
+pub struct WindowCloseAnim {
+    pub anim: Animation,
+    pub custom_shader: Option<String>,
+}
 
 impl Default for WindowCloseAnim {
     fn default() -> Self {
-        Self(Animation {
-            off: false,
-            kind: AnimationKind::Easing(EasingParams {
-                duration_ms: 150,
-                curve: AnimationCurve::EaseOutQuad,
-            }),
-        })
+        Self {
+            anim: Animation {
+                off: false,
+                kind: AnimationKind::Easing(EasingParams {
+                    duration_ms: 150,
+                    curve: AnimationCurve::EaseOutQuad,
+                }),
+            },
+            custom_shader: None,
+        }
     }
 }
 
@@ -1420,10 +1426,21 @@ where
         node: &knuffel::ast::SpannedNode<S>,
         ctx: &mut knuffel::decode::Context<S>,
     ) -> Result<Self, DecodeError<S>> {
-        let default = Self::default().0;
-        Ok(Self(Animation::decode_node(node, ctx, default, |_, _| {
-            Ok(false)
-        })?))
+        let default = Self::default().anim;
+        let mut custom_shader = None;
+        let anim = Animation::decode_node(node, ctx, default, |child, ctx| {
+            if &**child.node_name == "custom-shader" {
+                custom_shader = parse_arg_node("custom-shader", child, ctx)?;
+                Ok(true)
+            } else {
+                Ok(false)
+            }
+        })?;
+
+        Ok(Self {
+            anim,
+            custom_shader,
+        })
     }
 }
 
diff --git a/src/backend/tty.rs b/src/backend/tty.rs
index ddf6c54b..d35106eb 100644
--- a/src/backend/tty.rs
+++ b/src/backend/tty.rs
@@ -500,6 +500,9 @@ impl Tty {
             if let Some(src) = config.animations.window_resize.custom_shader.as_deref() {
                 shaders::set_custom_resize_program(gles_renderer, Some(src));
             }
+            if let Some(src) = config.animations.window_close.custom_shader.as_deref() {
+                shaders::set_custom_close_program(gles_renderer, Some(src));
+            }
             drop(config);
 
             niri.layout.update_shaders();
diff --git a/src/backend/winit.rs b/src/backend/winit.rs
index ab71ea2e..047ebb06 100644
--- a/src/backend/winit.rs
+++ b/src/backend/winit.rs
@@ -140,6 +140,9 @@ impl Winit {
         if let Some(src) = config.animations.window_resize.custom_shader.as_deref() {
             shaders::set_custom_resize_program(renderer, Some(src));
         }
+        if let Some(src) = config.animations.window_close.custom_shader.as_deref() {
+            shaders::set_custom_close_program(renderer, Some(src));
+        }
         drop(config);
 
         niri.layout.update_shaders();
diff --git a/src/layout/closing_window.rs b/src/layout/closing_window.rs
index c1f4e599..bdeb73a5 100644
--- a/src/layout/closing_window.rs
+++ b/src/layout/closing_window.rs
@@ -1,6 +1,8 @@
+use std::collections::HashMap;
 use std::time::Duration;
 
 use anyhow::Context as _;
+use glam::{Mat3, Vec2};
 use niri_config::BlockOutFrom;
 use smithay::backend::allocator::Fourcc;
 use smithay::backend::renderer::element::texture::TextureRenderElement;
@@ -8,13 +10,15 @@ use smithay::backend::renderer::element::utils::{
     Relocate, RelocateRenderElement, RescaleRenderElement,
 };
 use smithay::backend::renderer::element::{Id, Kind, RenderElement};
-use smithay::backend::renderer::gles::{GlesRenderer, GlesTexture};
-use smithay::backend::renderer::Renderer as _;
+use smithay::backend::renderer::gles::{GlesRenderer, GlesTexture, Uniform};
+use smithay::backend::renderer::{Renderer as _, Texture};
 use smithay::utils::{Logical, Point, Rectangle, Scale, Size, Transform};
 
 use crate::animation::Animation;
 use crate::niri_render_elements;
 use crate::render_helpers::primary_gpu_texture::PrimaryGpuTextureRenderElement;
+use crate::render_helpers::shader_element::ShaderRenderElement;
+use crate::render_helpers::shaders::{mat3_uniform, ProgramType, Shaders};
 use crate::render_helpers::snapshot::RenderSnapshot;
 use crate::render_helpers::{render_to_encompassing_texture, RenderTarget};
 
@@ -49,11 +53,15 @@ pub struct ClosingWindow {
 
     /// The closing animation.
     anim: Animation,
+
+    /// Random seed for the shader.
+    random_seed: f32,
 }
 
 niri_render_elements! {
     ClosingWindowRenderElement => {
         Texture = RelocateRenderElement<RescaleRenderElement<PrimaryGpuTextureRenderElement>>,
+        Shader = ShaderRenderElement,
     }
 }
 
@@ -100,6 +108,7 @@ impl ClosingWindow {
             texture_offset,
             blocked_out_texture_offset,
             anim,
+            random_seed: fastrand::f32(),
         })
     }
 
@@ -108,16 +117,18 @@ impl ClosingWindow {
     }
 
     pub fn are_animations_ongoing(&self) -> bool {
-        !self.anim.is_clamped_done()
+        !self.anim.is_done()
     }
 
     pub fn render(
         &self,
+        renderer: &mut GlesRenderer,
         view_rect: Rectangle<i32, Logical>,
         scale: Scale<f64>,
         target: RenderTarget,
     ) -> ClosingWindowRenderElement {
-        let val = self.anim.clamped_value();
+        let progress = self.anim.value();
+        let clamped_progress = self.anim.clamped_value().clamp(0., 1.);
 
         let (texture, offset) = if target.should_block_out(self.block_out_from) {
             (&self.blocked_out_texture, self.blocked_out_texture_offset)
@@ -125,6 +136,43 @@ impl ClosingWindow {
             (&self.texture, self.texture_offset)
         };
 
+        if Shaders::get(renderer).program(ProgramType::Close).is_some() {
+            let area_loc = Vec2::new(view_rect.loc.x as f32, view_rect.loc.y as f32);
+            let area_size = Vec2::new(view_rect.size.w as f32, view_rect.size.h as f32);
+
+            let geo_loc = Vec2::new(self.pos.x as f32, self.pos.y as f32);
+            let geo_size = Vec2::new(self.geo_size.w as f32, self.geo_size.h as f32);
+
+            let input_to_geo = Mat3::from_scale(area_size / geo_size)
+                * Mat3::from_translation((area_loc - geo_loc) / area_size);
+
+            let tex_scale = Vec2::new(self.texture_scale.x as f32, self.texture_scale.y as f32);
+            let tex_loc = Vec2::new(offset.x as f32, offset.y as f32);
+            let tex_size = Vec2::new(texture.width() as f32, texture.height() as f32) / tex_scale;
+
+            let geo_to_tex =
+                Mat3::from_translation(-tex_loc / tex_size) * Mat3::from_scale(geo_size / tex_size);
+
+            return ShaderRenderElement::new(
+                ProgramType::Close,
+                view_rect.size,
+                None,
+                1.,
+                vec![
+                    mat3_uniform("niri_input_to_geo", input_to_geo),
+                    Uniform::new("niri_geo_size", geo_size.to_array()),
+                    mat3_uniform("niri_geo_to_tex", geo_to_tex),
+                    Uniform::new("niri_progress", progress as f32),
+                    Uniform::new("niri_clamped_progress", clamped_progress as f32),
+                    Uniform::new("niri_random_seed", self.random_seed),
+                ],
+                HashMap::from([(String::from("niri_tex"), texture.clone())]),
+                Kind::Unspecified,
+            )
+            .with_location(Point::from((0, 0)))
+            .into();
+        }
+
         let elem = TextureRenderElement::from_static_texture(
             Id::new(),
             self.texture_renderer_id,
@@ -132,7 +180,7 @@ impl ClosingWindow {
             texture.clone(),
             self.texture_scale.x as i32,
             Transform::Normal,
-            Some(val.clamp(0., 1.) as f32),
+            Some(1. - clamped_progress as f32),
             None,
             None,
             None,
@@ -145,7 +193,7 @@ impl ClosingWindow {
         let elem = RescaleRenderElement::from_element(
             elem,
             (center - offset).to_physical_precise_round(scale),
-            (val / 5. + 0.8).max(0.),
+            ((1. - clamped_progress) / 5. + 0.8).max(0.),
         );
 
         let mut location = self.pos.to_f64() + offset;
diff --git a/src/layout/workspace.rs b/src/layout/workspace.rs
index a2515a76..08f170f8 100644
--- a/src/layout/workspace.rs
+++ b/src/layout/workspace.rs
@@ -1344,7 +1344,7 @@ impl<W: LayoutElement> Workspace<W> {
             tile_pos.x -= offset;
         }
 
-        let anim = Animation::new(1., 0., 0., self.options.animations.window_close.0);
+        let anim = Animation::new(0., 1., 0., self.options.animations.window_close.anim);
 
         let res = ClosingWindow::new(
             renderer,
@@ -2095,7 +2095,7 @@ impl<W: LayoutElement> Workspace<W> {
         // Draw the closing windows on top.
         let view_rect = Rectangle::from_loc_and_size((self.view_pos(), 0), self.view_size);
         for closing in &self.closing_windows {
-            let elem = closing.render(view_rect, output_scale, target);
+            let elem = closing.render(renderer.as_gles_renderer(), view_rect, output_scale, target);
             rv.push(elem.into());
         }
 
diff --git a/src/niri.rs b/src/niri.rs
index 6605cc79..7fc94365 100644
--- a/src/niri.rs
+++ b/src/niri.rs
@@ -941,6 +941,16 @@ impl State {
             shaders_changed = true;
         }
 
+        if config.animations.window_close.custom_shader
+            != old_config.animations.window_close.custom_shader
+        {
+            let src = config.animations.window_close.custom_shader.as_deref();
+            self.backend.with_primary_renderer(|renderer| {
+                shaders::set_custom_close_program(renderer, src);
+            });
+            shaders_changed = true;
+        }
+
         if config.debug != old_config.debug {
             debug_config_changed = true;
         }
diff --git a/src/render_helpers/shaders/close_epilogue.frag b/src/render_helpers/shaders/close_epilogue.frag
new file mode 100644
index 00000000..ed05c110
--- /dev/null
+++ b/src/render_helpers/shaders/close_epilogue.frag
@@ -0,0 +1,16 @@
+
+void main() {
+    vec3 coords_geo = niri_input_to_geo * vec3(niri_v_coords, 1.0);
+    vec3 size_geo = vec3(niri_geo_size, 1.0);
+
+    vec4 color = close_color(coords_geo, size_geo);
+
+    color = color * niri_alpha;
+
+#if defined(DEBUG_FLAGS)
+    if (niri_tint == 1.0)
+        color = vec4(0.0, 0.2, 0.0, 0.2) + color * 0.8;
+#endif
+
+    gl_FragColor = color;
+}
diff --git a/src/render_helpers/shaders/close_prelude.frag b/src/render_helpers/shaders/close_prelude.frag
new file mode 100644
index 00000000..db42190b
--- /dev/null
+++ b/src/render_helpers/shaders/close_prelude.frag
@@ -0,0 +1,21 @@
+precision mediump float;
+
+#if defined(DEBUG_FLAGS)
+uniform float niri_tint;
+#endif
+
+varying vec2 niri_v_coords;
+uniform vec2 niri_size;
+
+uniform mat3 niri_input_to_geo;
+uniform vec2 niri_geo_size;
+
+uniform sampler2D niri_tex;
+uniform mat3 niri_geo_to_tex;
+
+uniform float niri_progress;
+uniform float niri_clamped_progress;
+uniform float niri_random_seed;
+
+uniform float niri_alpha;
+
diff --git a/src/render_helpers/shaders/mod.rs b/src/render_helpers/shaders/mod.rs
index 034d8db1..21287a55 100644
--- a/src/render_helpers/shaders/mod.rs
+++ b/src/render_helpers/shaders/mod.rs
@@ -14,12 +14,14 @@ pub struct Shaders {
     pub clipped_surface: Option<GlesTexProgram>,
     pub resize: Option<ShaderProgram>,
     pub custom_resize: RefCell<Option<ShaderProgram>>,
+    pub custom_close: RefCell<Option<ShaderProgram>>,
 }
 
 #[derive(Debug, Clone, Copy)]
 pub enum ProgramType {
     Border,
     Resize,
+    Close,
 }
 
 impl Shaders {
@@ -72,6 +74,7 @@ impl Shaders {
             clipped_surface,
             resize,
             custom_resize: RefCell::new(None),
+            custom_close: RefCell::new(None),
         }
     }
 
@@ -95,6 +98,13 @@ impl Shaders {
         self.custom_resize.replace(program)
     }
 
+    pub fn replace_custom_close_program(
+        &self,
+        program: Option<ShaderProgram>,
+    ) -> Option<ShaderProgram> {
+        self.custom_close.replace(program)
+    }
+
     pub fn program(&self, program: ProgramType) -> Option<ShaderProgram> {
         match program {
             ProgramType::Border => self.border.clone(),
@@ -103,6 +113,7 @@ impl Shaders {
                 .borrow()
                 .clone()
                 .or_else(|| self.resize.clone()),
+            ProgramType::Close => self.custom_close.borrow().clone(),
         }
     }
 }
@@ -162,6 +173,49 @@ pub fn set_custom_resize_program(renderer: &mut GlesRenderer, src: Option<&str>)
     }
 }
 
+fn compile_close_program(
+    renderer: &mut GlesRenderer,
+    src: &str,
+) -> Result<ShaderProgram, GlesError> {
+    let mut program = include_str!("close_prelude.frag").to_string();
+    program.push_str(src);
+    program.push_str(include_str!("close_epilogue.frag"));
+
+    ShaderProgram::compile(
+        renderer,
+        &program,
+        &[
+            UniformName::new("niri_input_to_geo", UniformType::Matrix3x3),
+            UniformName::new("niri_geo_size", UniformType::_2f),
+            UniformName::new("niri_geo_to_tex", UniformType::Matrix3x3),
+            UniformName::new("niri_progress", UniformType::_1f),
+            UniformName::new("niri_clamped_progress", UniformType::_1f),
+            UniformName::new("niri_random_seed", UniformType::_1f),
+        ],
+        &["niri_tex"],
+    )
+}
+
+pub fn set_custom_close_program(renderer: &mut GlesRenderer, src: Option<&str>) {
+    let program = if let Some(src) = src {
+        match compile_close_program(renderer, src) {
+            Ok(program) => Some(program),
+            Err(err) => {
+                warn!("error compiling custom close shader: {err:?}");
+                return;
+            }
+        }
+    } else {
+        None
+    };
+
+    if let Some(prev) = Shaders::get(renderer).replace_custom_close_program(program) {
+        if let Err(err) = prev.destroy(renderer) {
+            warn!("error destroying previous custom close shader: {err:?}");
+        }
+    }
+}
+
 pub fn mat3_uniform(name: &str, mat: Mat3) -> Uniform {
     Uniform::new(
         name,
diff --git a/wiki/Configuration:-Animations.md b/wiki/Configuration:-Animations.md
index f228a5a8..9bc184eb 100644
--- a/wiki/Configuration:-Animations.md
+++ b/wiki/Configuration:-Animations.md
@@ -169,6 +169,47 @@ animations {
 }
 ```
 
+##### `custom-shader`
+
+<sup>Since: 0.1.6, experimental</sup>
+
+You can write a custom shader for drawing the window during a close animation.
+
+See [this example shader](./examples/close-custom-shader.frag) for a full documentation with several animations to experiment with.
+
+If a custom shader fails to compile, niri will print a warning and fall back to the default, or previous successfully compiled shader.
+
+> [!WARNING]
+> 
+> Custom shaders do not have a backwards compatibility guarantee.
+> I may need to change their interface as I'm developing new features.
+
+Example: close will fill the current geometry with a solid gradient that gradually fades away.
+
+```
+animations {
+    window-resize {
+        spring damping-ratio=1.0 stiffness=800 epsilon=0.0001
+
+        custom-shader r"
+            vec4 close_color(vec3 coords_geo, vec3 size_geo) {
+                vec4 color = vec4(0.0);
+
+                if (0.0 <= coords_geo.x && coords_geo.x <= 1.0
+                        && 0.0 <= coords_geo.y && coords_geo.y <= 1.0)
+                {
+                    vec4 from = vec4(1.0, 0.0, 0.0, 1.0);
+                    vec4 to = vec4(0.0, 1.0, 0.0, 1.0);
+                    color = mix(from, to, coords_geo.y);
+                }
+
+                return color * (1.0 - niri_clamped_progress);
+            }
+        "
+    }
+}
+```
+
 #### `horizontal-view-movement`
 
 All horizontal camera view movement animations, such as:
diff --git a/wiki/examples/close_custom_shader.frag b/wiki/examples/close_custom_shader.frag
new file mode 100644
index 00000000..8a777b99
--- /dev/null
+++ b/wiki/examples/close_custom_shader.frag
@@ -0,0 +1,113 @@
+// Your shader must contain one function (see the bottom of this file).
+//
+// It should not contain any uniform definitions or anything else, as niri
+// provides them for you.
+//
+// All symbols defined by niri will have a niri_ prefix, so don't use it for
+// your own variables and functions.
+
+// The function that you must define looks like this:
+vec4 close_color(vec3 coords_geo, vec3 size_geo) {
+    vec4 color = /* ...compute the color... */;
+    return color;
+}
+
+// It takes as input:
+//
+// * coords_geo: coordinates of the current pixel relative to the window
+//   geometry.
+//
+// These are homogeneous (the Z component is equal to 1) and scaled in such a
+// way that the 0 to 1 coordinates lie within the window geometry. Pixels
+// outside the window geometry will have coordinates below 0 or above 1.
+//
+// The window geometry is its "visible bounds" from the user's perspective.
+//
+// The shader runs over the full screen area, so you must expect and handle
+// coordinates outside the [0, 1] range. If the window is scrolled off-screen,
+// all of the coordinates to the shader can fall outside the [0, 1] range.
+//
+// * size_geo: size of the window geometry in logical pixels.
+//
+// It is homogeneous (the Z component is equal to 1).
+//
+// The function must return the color of the pixel (with premultiplied alpha).
+// The pixel color will be further processed by niri (for example, to apply the
+// final opacity from window rules).
+
+// Now let's go over the uniforms that niri defines.
+//
+// You should only rely on the uniforms documented here. Any other uniforms can
+// change or be removed without notice.
+
+// The window texture.
+uniform sampler2D niri_tex;
+
+// Matrix that converts geometry coordinates into the window texture
+// coordinates.
+//
+// The window texture can and will go outside the geometry (for client-side
+// decoration shadows for example), which is why this matrix is necessary.
+uniform mat3 niri_geo_to_tex;
+
+
+// Unclamped progress of the animation.
+//
+// Goes from 0 to 1 but may overshoot and oscillate.
+uniform float niri_progress;
+
+// Clamped progress of the animation.
+//
+// Goes from 0 to 1, but will stop at 1 as soon as it first reaches 1. Will not
+// overshoot or oscillate.
+uniform float niri_clamped_progress;
+
+// Random float in [0; 1), consistent for the duration of the animation.
+uniform float niri_random_seed;
+
+// Now let's look at some examples. You can copy everything below this line
+// into your custom-shader to experiment.
+
+// Example: fill the current geometry with a solid vertical gradient and
+// gradually make transparent.
+vec4 solid_gradient(vec3 coords_geo, vec3 size_geo) {
+    vec4 color = vec4(0.0);
+
+    // Paint only the area inside the current geometry.
+    if (0.0 <= coords_geo.x && coords_geo.x <= 1.0
+            && 0.0 <= coords_geo.y && coords_geo.y <= 1.0)
+    {
+        vec4 from = vec4(1.0, 0.0, 0.0, 1.0);
+        vec4 to = vec4(0.0, 1.0, 0.0, 1.0);
+        color = mix(from, to, coords_geo.y);
+    }
+
+    // Make it transparent.
+    color *= (1.0 - niri_clamped_progress);
+
+    return color;
+}
+
+// Example: gradually scale down and make transparent, equivalent to the
+// default closing animation.
+vec4 default_close(vec3 coords_geo, vec3 size_geo) {
+    // Scale down the window.
+    float scale = max(0.0, ((1.0 - niri_clamped_progress) / 5.0 + 0.8));
+    coords_geo = vec3((coords_geo.xy - vec2(0.5)) / scale + vec2(0.5), 1.0);
+
+    // Get color from the window texture.
+    vec3 coords_tex = niri_geo_to_tex * coords_geo;
+    vec4 color = texture2D(niri_tex, coords_tex.st);
+
+    // Make the window transparent.
+    color *= (1.0 - niri_clamped_progress);
+
+    return color;
+}
+
+// This is the function that you must define.
+vec4 close_color(vec3 coords_geo, vec3 size_geo) {
+    // You can pick one of the example functions or write your own.
+    return solid_gradient(coords_geo, size_geo);
+}
+
diff --git a/wiki/examples/resize_custom_shader.frag b/wiki/examples/resize_custom_shader.frag
index 71710a9f..a95e678f 100644
--- a/wiki/examples/resize_custom_shader.frag
+++ b/wiki/examples/resize_custom_shader.frag
@@ -37,6 +37,9 @@ vec4 resize_color(vec3 coords_curr_geo, vec3 size_curr_geo) {
 // final opacity from window rules).
 
 // Now let's go over the uniforms that niri defines.
+//
+// You should only rely on the uniforms documented here. Any other uniforms can
+// change or be removed without notice.
 
 // Previous (before resize) window texture.
 uniform sampler2D niri_tex_prev;
@@ -65,12 +68,12 @@ uniform mat3 niri_curr_geo_to_prev_geo;
 uniform mat3 niri_curr_geo_to_next_geo;
 
 
-// Unclamped progress of the resize.
+// Unclamped progress of the animation.
 //
 // Goes from 0 to 1 but may overshoot and oscillate.
 uniform float niri_progress;
 
-// Clamped progress of the resize.
+// Clamped progress of the animation.
 //
 // Goes from 0 to 1, but will stop at 1 as soon as it first reaches 1. Will not
 // overshoot or oscillate.