Add Canvas::set_clip_path — anti-aliased arbitrary-path clipping on both backends

Add `Canvas::set_clip_path(&[PathCmd])`, clipping subsequent draws to an arbitrary vector path with an anti-aliased edge, on both the software and GLES backends. It complements the existing rect clip (`set_clip_rects`) and is what an embedder needs to render a shaped clip — a circular avatar, a rounded card, a `VectorDrawable` mask — rather than a bounding box. Kept general rather than tied to any one consumer.
Software backend: rasterise the path into an anti-aliased tiny-skia coverage `Mask` (Winding fill) and install it as the active clip mask. Every software primitive already threads `clip_mask` through tiny-skia (fills, strokes, lines, paths, images, text, blit), so the path clip applies uniformly with smooth edges. `clip_bounds` reports the path's bounding box while it is active.
GLES backend: a 1-bit stencil would clip exactly but leave a hard, aliased edge, so instead the clipped draws are captured into an offscreen layer and composited back through an anti-aliased coverage mask. `set_clip_path` rasterises the path coverage (tiny-skia, anti-aliased), uploads it as a mask texture, allocates a full-canvas layer FBO on first use, and redirects subsequent draws to it via `activate_target`. Ending the clip (`clear_clip` / `set_clip_rects` / a new `set_clip_path`) composites the layer back onto the canvas FBO with a new two-sampler program (`CLIP_COMPOSITE_FRAG_SRC`) that multiplies the layer colour by the mask coverage and blends it premultiplied-over. The layer attaches to the canvas's own shadow FBO, so it needs no stencil bits in the EGL config; it is freed and reallocated on resize and freed on drop, and shared programs/uniforms are copied to sub-canvases like the rest.
Usage: a path clip is bracketed — `set_clip_path` then, after the clipped draws, `clear_clip` or `set_clip_rects` to flush it (on GLES this is when the layer is composited). Snapshot the prior clip with `clip_bounds` beforehand and restore it with `set_clip_rects` to compose with an outer clip without leaking state.
Add an `examples/clip_path.rs` demo (rounded rect, circle, triangle — same smooth result on both backends) and software-backend unit tests covering the bounding box, the empty-path clear, and a pixel-level check that a triangular clip masks a fill to the path silhouette rather than its bounding box. The GLES layer-composite path needs a live GL context and is exercised by the example.
Also fix three rustdoc intra-doc-link warnings surfaced along the way: a private-item link in `app.rs` (`scroll`) and the new GLES doc (`SoftwareCanvas::set_clip_path`) demoted to code spans, and a redundant explicit link target in `chassis.rs`.

src/gles_render/clip.rs

@@ -1,12 +1,15 @@
 // SPDX-License-Identifier: LGPL-2.1-only
 // Copyright (C) 2026 Liberux Labs, S. L. <info@liberux.net>
 
-//! `glScissor`-based clipping + whole-canvas fill / clear for
-//! [`GlesCanvas`]. When [`GlesCanvas::set_clip_rects`] receives
-//! multiple rects the bounding-box union is used as the scissor —
-//! coarse, but the partial-redraw path normally clusters 1–3 rects
-//! so the union is barely larger than the sum. Disjoint regions
-//! would want a stencil-buffer path; not implemented today.
+//! Clipping + whole-canvas fill / clear for [`GlesCanvas`]. Rect clips
+//! ([`GlesCanvas::set_clip_rects`]) use `glScissor`: when given multiple rects
+//! the bounding-box union is the scissor — coarse, but the partial-redraw path
+//! normally clusters 1–3 rects so the union is barely larger than the sum
+//! (disjoint regions are not clipped tightly). Arbitrary path clips
+//! ([`GlesCanvas::set_clip_path`]) are anti-aliased: the clipped draws are
+//! captured into an offscreen layer FBO, then composited back onto the canvas
+//! multiplied by a CPU-rasterised (tiny-skia) anti-aliased coverage mask, so the
+//! clipped edge is smooth rather than the hard edge a 1-bit stencil would give.
 
 use glow::HasContext;
 
@@ -18,6 +21,8 @@ impl GlesCanvas
 {
 	pub fn set_clip_rects( &mut self, rects: &[Rect] )
 	{
+		// A rect clip replaces any active path clip: flush its layer first.
+		self.flush_clip_layer();
 		// Scissor is global GL state; rebind our FBO first so the scissor
 		// applies to this canvas and not whatever target was active before.
 		self.activate_target();
@@ -58,6 +63,114 @@ impl GlesCanvas
 		// to match below.
 		unsafe { self.gl.disable( glow::SCISSOR_TEST ); }
 		self.clip_scissor = None;
+		self.flush_clip_layer();
+	}
+
+	/// Allocate the offscreen clip layer (a full-canvas colour FBO) on first
+	/// use. Freed and re-allocated at the new size by `resize`.
+	fn ensure_clip_layer( &mut self )
+	{
+		if self.clip_layer.is_some() { return; }
+		// SAFETY: GL context current (canvas invariant). Allocates an FBO + colour
+		// texture sized to the canvas and attaches it; the handles are stored so
+		// `Drop`/`resize` manage their lifetime. Restores the canvas FBO binding.
+		unsafe
+		{
+			let fbo = self.gl.create_framebuffer().expect( "clip-layer FBO" );
+			let tex = super::helpers::alloc_fbo_tex( &self.gl, self.version, self.width, self.height );
+			self.gl.bind_framebuffer( glow::FRAMEBUFFER, Some( fbo ) );
+			self.gl.framebuffer_texture_2d( glow::FRAMEBUFFER, glow::COLOR_ATTACHMENT0, glow::TEXTURE_2D, Some( tex ), 0 );
+			self.gl.bind_framebuffer( glow::FRAMEBUFFER, Some( self.fbo ) );
+			self.clip_layer = Some( ( fbo, tex ) );
+		}
+	}
+
+	/// Clip subsequent draws to an arbitrary vector path, with an anti-aliased
+	/// edge. Begins capturing draws into the offscreen clip layer; the path's
+	/// anti-aliased coverage is rasterised (tiny-skia) into `clip_mask_tex` and
+	/// applied when the layer is composited back by `flush_clip_layer` (on the
+	/// next `clear_clip` / `set_clip_rects`). GLES counterpart of the software
+	/// backend's `set_clip_path`.
+	pub fn set_clip_path( &mut self, cmds: &[ crate::types::PathCmd ] )
+	{
+		// A new path clip supersedes any layer still open.
+		self.flush_clip_layer();
+		let Some( path ) = crate::render::helpers::build_ts_path( cmds ) else { self.clear_clip(); return; };
+		let b  = path.bounds();
+		let x0 = b.left().floor().max( 0.0 );
+		let y0 = b.top().floor().max( 0.0 );
+		let x1 = b.right().ceil().min( self.width  as f32 );
+		let y1 = b.bottom().ceil().min( self.height as f32 );
+		let pw = ( x1 - x0 ).max( 0.0 ) as u32;
+		let ph = ( y1 - y0 ).max( 0.0 ) as u32;
+		if pw == 0 || ph == 0 || pw > 8192 || ph > 8192 { self.clear_clip(); return; }
+
+		// Rasterise the path coverage (anti-aliased, opaque inside) into a
+		// bbox-sized pixmap; the composite shader multiplies the layer by it.
+		let Some( mut pixmap ) = tiny_skia::Pixmap::new( pw, ph ) else { return; };
+		let mut paint = tiny_skia::Paint::default();
+		paint.set_color( tiny_skia::Color::WHITE );
+		paint.anti_alias = true;
+		let tf = tiny_skia::Transform::from_translate( -x0, -y0 );
+		pixmap.fill_path( &path, &paint, tiny_skia::FillRule::Winding, tf, None );
+		let rgba = pixmap.data().to_vec();
+
+		let mask = super::helpers::upload_rgba_texture( &self.gl, self.version, &rgba, pw as i32, ph as i32 );
+		self.clip_mask_tex = Some( mask );
+		self.clip_bbox     = Rect { x: x0, y: y0, width: pw as f32, height: ph as f32 };
+
+		self.ensure_clip_layer();
+		// Redirect to the layer and clear it transparent so untouched pixels stay
+		// empty (they contribute nothing to the composite).
+		self.clip_layer_active = true;
+		self.clip_scissor      = None;
+		self.activate_target();
+		// SAFETY: GL context current; `activate_target` bound the layer FBO.
+		unsafe
+		{
+			self.gl.clear_color( 0.0, 0.0, 0.0, 0.0 );
+			self.gl.clear( glow::COLOR_BUFFER_BIT );
+		}
+	}
+
+	/// Composite the clip layer back onto the canvas FBO, multiplied by the
+	/// anti-aliased coverage mask, then end the path clip. No-op when no path
+	/// clip is open.
+	fn flush_clip_layer( &mut self )
+	{
+		if !self.clip_layer_active { return; }
+		self.clip_layer_active = false;
+		let Some( ( _, layer_tex ) ) = self.clip_layer else { return; };
+		let Some( mask_tex ) = self.clip_mask_tex.take() else { return; };
+		let bbox = self.clip_bbox;
+		let mvp  = super::helpers::ortho_rect( self.width, self.height, bbox );
+		// SAFETY: GL context current. Bind the canvas FBO, disable scissor, and
+		// draw a quad over the bbox sampling the layer (unit 0) and coverage mask
+		// (unit 1); the premultiplied result is blended SRC_OVER. All handles are
+		// canvas-owned; the transient mask texture is deleted after the draw.
+		unsafe
+		{
+			self.gl.bind_framebuffer( glow::FRAMEBUFFER, Some( self.fbo ) );
+			self.gl.viewport( 0, 0, self.width as i32, self.height as i32 );
+			self.gl.disable( glow::SCISSOR_TEST );
+			self.gl.use_program( Some( self.clip_composite_program ) );
+			self.gl.uniform_matrix_4_f32_slice( Some( &self.u_clip_mvp ), false, &mvp );
+			self.gl.uniform_2_f32( Some( &self.u_clip_canvas ), self.width as f32, self.height as f32 );
+			self.gl.uniform_4_f32( Some( &self.u_clip_bbox ), bbox.x, bbox.y, bbox.width, bbox.height );
+			self.gl.active_texture( glow::TEXTURE0 );
+			self.gl.bind_texture( glow::TEXTURE_2D, Some( layer_tex ) );
+			self.gl.uniform_1_i32( Some( &self.u_clip_layer ), 0 );
+			self.gl.active_texture( glow::TEXTURE1 );
+			self.gl.bind_texture( glow::TEXTURE_2D, Some( mask_tex ) );
+			self.gl.uniform_1_i32( Some( &self.u_clip_mask ), 1 );
+			self.gl.bind_vertex_array( Some( self.quad_vao ) );
+			self.gl.draw_arrays( glow::TRIANGLES, 0, 6 );
+			self.gl.bind_vertex_array( None );
+			self.gl.bind_texture( glow::TEXTURE_2D, None );
+			self.gl.active_texture( glow::TEXTURE0 );
+			self.gl.bind_texture( glow::TEXTURE_2D, None );
+			self.gl.delete_texture( mask_tex );
+		}
 	}
 
 	/// Snapshot of the active scissor as a `Vec<Rect>` (empty when no

src/gles_render/framebuffer.rs

@@ -83,22 +83,32 @@ impl GlesCanvas
 	/// disable scissor when the canvas has no clip).
 	pub( super ) fn activate_target( &self )
 	{
-		// SAFETY: rebinds canvas-owned FBO + viewport + scissor. All values
-		// (`self.fbo`, `self.width`, `self.height`, `self.clip_scissor`)
+		// While a path clip is active, draws are redirected to the offscreen clip
+		// layer (unclipped); the anti-aliased mask is applied when the layer is
+		// composited back on clip end. Otherwise draws go to `fbo` with the
+		// active scissor.
+		// SAFETY: rebinds a canvas-owned FBO + viewport + scissor. All values
+		// (`self.fbo`, `self.clip_layer`, `self.width/height`, `self.clip_scissor`)
 		// live as long as `&self`, and the bind is idempotent.
+		let target = match ( self.clip_layer_active, self.clip_layer )
+		{
+			( true, Some( ( fbo, _ ) ) ) => fbo,
+			_                            => self.fbo,
+		};
+		let to_layer = self.clip_layer_active && self.clip_layer.is_some();
 		unsafe
 		{
-			self.gl.bind_framebuffer( glow::FRAMEBUFFER, Some( self.fbo ) );
+			self.gl.bind_framebuffer( glow::FRAMEBUFFER, Some( target ) );
 			self.gl.viewport( 0, 0, self.width as i32, self.height as i32 );
 			match self.clip_scissor
 			{
-				Some( r ) =>
+				Some( r ) if !to_layer =>
 				{
 					let ( x, y, w, h ) = self.scissor_pixels( r );
 					self.gl.enable( glow::SCISSOR_TEST );
 					self.gl.scissor( x, y, w, h );
 				}
-				None =>
+				_ =>
 				{
 					self.gl.disable( glow::SCISSOR_TEST );
 				}

src/gles_render/mod.rs

@@ -9,12 +9,14 @@
 //! [`crate::egl_context`] — this module is just the renderer that runs
 //! once a context is current.
 //!
-//! Clipping is implemented with `glScissor`. When
+//! Rect clipping is implemented with `glScissor`. When
 //! [`GlesCanvas::set_clip_rects`] receives multiple rects the
 //! bounding-box union is used as the scissor — coarse, but the
 //! partial-redraw path normally clusters the dirty rects of 1–3
-//! widgets so the union is barely larger than the sum. Disjoint
-//! regions would want a stencil-buffer path; not implemented today.
+//! widgets so the union is barely larger than the sum. Arbitrary
+//! path clipping ([`GlesCanvas::set_clip_path`]) captures the clipped
+//! draws into an offscreen layer and composites it back through an
+//! anti-aliased coverage mask, for a smooth clipped edge.
 //!
 //! # Submodule layout
 //!
@@ -354,6 +356,23 @@ pub struct GlesCanvas
 	/// (GL_SCISSOR_TEST is enabled), `None` when cleared.
 	clip_scissor:  Option<Rect>,
 
+	/// Anti-aliased path clip (`set_clip_path`). While `clip_layer_active`,
+	/// `activate_target` redirects draws to `clip_layer` (a full-canvas
+	/// offscreen FBO); ending the clip composites that layer back onto `fbo`
+	/// multiplied by `clip_mask_tex` (an anti-aliased coverage texture covering
+	/// `clip_bbox`). The layer FBO is allocated lazily on the first path clip.
+	clip_layer:        Option<( glow::Framebuffer, glow::Texture )>,
+	clip_layer_active: bool,
+	clip_mask_tex:     Option<glow::Texture>,
+	clip_bbox:         Rect,
+	/// Composite program (layer × coverage mask). Shared with sub-canvases.
+	clip_composite_program: glow::Program,
+	u_clip_mvp:        glow::UniformLocation,
+	u_clip_layer:      glow::UniformLocation,
+	u_clip_mask:       glow::UniformLocation,
+	u_clip_canvas:     glow::UniformLocation,
+	u_clip_bbox:       glow::UniformLocation,
+
 	/// Persistent shadow framebuffer. All draw methods bind this;
 	/// [`Self::present`](framebuffer) is the only call that switches
 	/// to the default framebuffer.
@@ -398,6 +417,15 @@ impl Drop for GlesCanvas
 		{
 			self.gl.delete_framebuffer( self.fbo );
 			self.gl.delete_texture( self.fbo_tex );
+			if let Some( ( fbo, tex ) ) = self.clip_layer.take()
+			{
+				self.gl.delete_framebuffer( fbo );
+				self.gl.delete_texture( tex );
+			}
+			if let Some( tex ) = self.clip_mask_tex.take()
+			{
+				self.gl.delete_texture( tex );
+			}
 			if let Some( ( fbo, tex ) ) = self.aux_a.take()
 			{
 				self.gl.delete_framebuffer( fbo );

src/gles_render/setup.rs

@@ -28,6 +28,7 @@ use super::shaders::
 	GLYPH_FRAG_SRC, GLYPH_BATCH_VERT_SRC, GLYPH_BATCH_FRAG_SRC,
 	LINEAR_GRADIENT_FRAG_SRC, RADIAL_GRADIENT_FRAG_SRC,
 	RECT_FRAG_SRC,
+	CLIP_COMPOSITE_FRAG_SRC,
 	SHADOW_INSET_FRAG_SRC, SHADOW_INSET_OVERLAY_FRAG_SRC, SHADOW_OUTER_FRAG_SRC,
 	SUB_BLIT_FRAG_SRC,
 	TEX_FRAG_SRC, VERT_SRC,
@@ -211,6 +212,16 @@ impl GlesCanvas
 			gl.get_uniform_location( glyph_batch_program, "u_sampler" ).unwrap(),
 		)};
 
+		let clip_composite_program = compile_program( &gl, VERT_SRC, CLIP_COMPOSITE_FRAG_SRC );
+		let ( u_clip_mvp, u_clip_layer, u_clip_mask, u_clip_canvas, u_clip_bbox ) = unsafe
+		{(
+			gl.get_uniform_location( clip_composite_program, "u_mvp"    ).unwrap(),
+			gl.get_uniform_location( clip_composite_program, "u_layer"  ).unwrap(),
+			gl.get_uniform_location( clip_composite_program, "u_mask"   ).unwrap(),
+			gl.get_uniform_location( clip_composite_program, "u_canvas" ).unwrap(),
+			gl.get_uniform_location( clip_composite_program, "u_bbox"   ).unwrap(),
+		)};
+
 		let ( glyph_batch_vao, glyph_batch_vbo ) = unsafe
 		{
 			let vao = gl.create_vertex_array().unwrap();
@@ -464,6 +475,16 @@ impl GlesCanvas
 			image_cache:         HashMap::new(),
 			gradient_lut_cache:  HashMap::new(),
 			clip_scissor:   None,
+			clip_layer:        None,
+			clip_layer_active: false,
+			clip_mask_tex:     None,
+			clip_bbox:         crate::types::Rect::default(),
+			clip_composite_program,
+			u_clip_mvp,
+			u_clip_layer,
+			u_clip_mask,
+			u_clip_canvas,
+			u_clip_bbox,
 			fbo,
 			fbo_tex,
 			aux_a:          None,
@@ -665,6 +686,16 @@ impl GlesCanvas
 			image_cache:        HashMap::new(),
 			gradient_lut_cache: HashMap::new(),
 			clip_scissor:       None,
+			clip_layer:             None,
+			clip_layer_active:      false,
+			clip_mask_tex:          None,
+			clip_bbox:              crate::types::Rect::default(),
+			clip_composite_program: self.clip_composite_program,
+			u_clip_mvp:             self.u_clip_mvp,
+			u_clip_layer:           self.u_clip_layer,
+			u_clip_mask:            self.u_clip_mask,
+			u_clip_canvas:          self.u_clip_canvas,
+			u_clip_bbox:            self.u_clip_bbox,
 			fbo,
 			fbo_tex,
 			aux_a:              None,
@@ -768,10 +799,22 @@ impl GlesCanvas
 				glow::FRAMEBUFFER, glow::COLOR_ATTACHMENT0,
 				glow::TEXTURE_2D, Some( self.fbo_tex ), 0,
 			);
+			// The clip layer was sized for the old dimensions — free it so the next
+			// path clip re-allocates at the new size; any in-flight clip is dropped.
+			if let Some( ( fbo, tex ) ) = self.clip_layer.take()
+			{
+				self.gl.delete_framebuffer( fbo );
+				self.gl.delete_texture( tex );
+			}
+			if let Some( tex ) = self.clip_mask_tex.take()
+			{
+				self.gl.delete_texture( tex );
+			}
 			self.gl.viewport( 0, 0, width as i32, height as i32 );
 			self.gl.clear_color( 0.0, 0.0, 0.0, 0.0 );
 			self.gl.clear( glow::COLOR_BUFFER_BIT );
 		}
+		self.clip_layer_active = false;
 		// Auxiliary textures were sized for the old dimensions — drop them so
 		// the next effect that needs them re-allocates at the new size.
 		self.invalidate_aux();

src/gles_render/shaders.rs

@@ -147,6 +147,30 @@ void main()
 }
 "##;
 
+// Clip-layer composite shader for `set_clip_path`. Path-clipped content is
+// drawn to an offscreen layer; this composites that layer onto the canvas
+// multiplied by an anti-aliased coverage mask, giving a smooth clipped edge.
+// `u_layer` is the full-canvas layer texture (premultiplied), `u_mask` the
+// path coverage rasterised over `u_bbox` (x, y, w, h in canvas pixels). The
+// quad is drawn over the bbox; `v_uv` runs 0..1 across it. Both FBO-backed
+// textures are sampled y-flipped (GL's lower-left origin).
+pub( super ) const CLIP_COMPOSITE_FRAG_SRC: &str = r##"
+precision mediump float;
+varying vec2 v_uv;
+uniform sampler2D u_layer;
+uniform sampler2D u_mask;
+uniform vec2 u_canvas;
+uniform vec4 u_bbox;
+void main()
+{
+	vec2 sp  = u_bbox.xy + v_uv * u_bbox.zw;
+	vec2 luv = vec2( sp.x / u_canvas.x, 1.0 - sp.y / u_canvas.y );
+	vec4 col = texture2D( u_layer, luv );
+	float cov = texture2D( u_mask, vec2( v_uv.x, 1.0 - v_uv.y ) ).a;
+	gl_FragColor = col * cov;
+}
+"##;
+
 // Fragment shader for single-channel glyph textures with color tint.
 //
 // Glyphs live in a shared GL_LUMINANCE atlas. `u_uv_scale` and `u_uv_offset`