Struct DiscardScene 

pub struct DiscardScene;

A PaintScene sink that accepts every paint command and records nothing — the zero-GPU-cost target for a subtree that still needs its paint pass driven for the pass’s side effects (hero-rect reporting through PaintCtx::with_hero_registry, other paint-time widget state) even though its pixels will never be composited. The navigator’s transition machinery is the motivating case: a page whose resolved alpha is 0 still has to paint to report hero rects and advance animating children, but every command it emits is otherwise wasted GPU work.

Guarantee

No paint command reaches any scene: every PaintScene method on DiscardScene is a no-op, whether overridden here directly or inherited from the trait’s own no-op (or no-op-delegating) default. Anything driven through PaintCtx rather than through &mut dyn PaintScene — the hero registry, the frame clock, paced-class bubbling — is unaffected, since none of that machinery routes through the scene it’s handed.

Trait Implementations

impl PaintScene for DiscardScene

fn fill_rect(&mut self, _origin: Point, _size: Size, _color: Color)

Emit a filled axis-aligned rectangle at origin with size, filled with the solid color.

fn draw_text(&mut self, _origin: Point, _text: &str)

Emit a run of unshaped text anchored at origin.

fn fill_rounded_rect( &mut self, _origin: Point, _size: Size, _radius: f64, _color: Color, )

Emit a filled axis-aligned rectangle with uniformly rounded corners.

fn fill_rounded_rect_radii( &mut self, origin: Point, size: Size, radii: CornerRadii, color: Color, )

Emit a filled axis-aligned rectangle with per-corner radii — the shape a uniform PaintScene::fill_rounded_rect cannot express (a bottom-anchored sheet with only its top corners rounded, a segmented control’s end caps).

fn stroke_line(&mut self, _p0: Point, _p1: Point, _width: f64, _color: Color)

Stroke a straight line from p0 to p1 with the given width and solid color.

fn push_clip(&mut self, _origin: Point, _size: Size)

Push a rectangular clip (at origin/size) onto the backend clip stack; subsequent draws are clipped to it until the matching PaintScene::pop_clip.

fn push_clip_rounded(&mut self, _origin: Point, _size: Size, _radius: f64)

Push a clip with uniformly rounded corners (at origin/size, corner radius) onto the backend clip stack; subsequent draws are clipped to the rounded shape until the matching PaintScene::pop_clip — the same pop PaintScene::push_clip uses, since there is one clip stack.

fn push_clip_rounded_radii( &mut self, origin: Point, size: Size, radii: CornerRadii, )

Push a clip with per-corner radii onto the backend clip stack, popped by the same PaintScene::pop_clip as every other push.

fn push_clip_path(&mut self, origin: Point, path: &BezPath)

Push a clip to an arbitrary closed outline onto the backend clip stack; subsequent draws are clipped to path’s interior (nonzero winding) until the matching PaintScene::pop_clip — the same pop every other clip uses.

fn pop_clip(&mut self)

Pop the most recently pushed clip, rectangular, rounded or path. Defaulted to a no-op; see PaintScene::push_clip.

fn draw_glyph_run(&mut self, _run: GlyphRun)

Emit a run of already-shaped glyphs into the scene.

fn draw_image(&mut self, _data: &ImageData, _dest: Rect)

Draw an already-decoded image, scaled from its natural (data.widthxdata.height) size to fill the absolute dest rect.

fn draw_shader(&mut self, _program: &ShaderProgram, _dest: Rect, _time: f32)

Draw a fragment-shader-filled rectangle, scaled to fill dest.

fn draw_scene_texture(&mut self, _id: u64, _dest: Rect)

Composite a bound scene texture (pre-rendered via ExternalPass) into the scene.

fn draw_shadow( &mut self, _origin: Point, _size: Size, _radius: f64, _std_dev: f64, _color: Color, )

Draw a gaussian-blurred rounded-rectangle elevation shadow (an approximation of a CSS box-shadow) at origin/size.

fn fill_rect_brush(&mut self, origin: Point, size: Size, brush: &Brush)

Emit a filled axis-aligned rectangle at origin with size, filled with an arbitrary brush (solid color or gradient).

fn fill_rounded_rect_brush( &mut self, _origin: Point, _size: Size, _radius: f64, _brush: &Brush, )

Emit a filled axis-aligned rectangle with uniformly rounded corners, filled with an arbitrary brush (solid color or gradient).

fn push_layer(&mut self, _origin: Point, _size: Size, _alpha: f32)

Push a translucent layer (at origin/size) onto the backend layer stack; subsequent draws are composited at alpha until the matching PaintScene::pop_layer.

fn pop_layer(&mut self)

Pop the most recently pushed layer. Defaulted to a no-op; see PaintScene::push_layer.

fn clear_rect(&mut self, _origin: Point, _size: Size)

Clear an axis-aligned rectangle (at origin/size) to full transparency (alpha 0), erasing everything already painted below it in this scene — a real destination-clearing composite, not merely skipping paint over the region.

fn fill_path(&mut self, _origin: Point, _path: &BezPath, _brush: &Brush)

Fill an arbitrary vector path (e.g. an arc — see frust_scene::arc_path) at origin, using the nonzero winding rule and brush.

fn stroke_path( &mut self, _origin: Point, _path: &BezPath, _width: f64, _brush: &Brush, )

Stroke an arbitrary vector path (e.g. an arc) at origin with width and round caps/joins, using brush.

fn stroke_path_dashed( &mut self, origin: Point, path: &BezPath, width: f64, _dash: DashPattern, brush: &Brush, )

Stroke an arbitrary vector path at origin as a dashed line: the same stroke PaintScene::stroke_path paints, broken into dash’s on/off runs by the render crate at encode time.

fn push_transform(&mut self, _transform: Affine)

Push an affine transform, composed with the current one, onto the backend transform stack; subsequent draws are transformed until the matching PaintScene::pop_transform.

fn pop_transform(&mut self)

Pop the most recently pushed transform, restoring the previous one. Defaulted to a no-op; see PaintScene::push_transform.

fn push_retained( &mut self, _key: u64, origin: Point, size: Size, alpha: f32, scale: f64, )

Push a retained bracket: the body is rasterizable once and cached by key across frames. The alpha and scale are presentation parameters applied to the whole cached body (alpha blending, uniform scale).

fn pop_retained(&mut self)

Pop the most recently pushed retained bracket. Defaulted to the reverse of PaintScene::push_retained’s default: pop layer, then transform. Recorders that don’t override both may see unbalanced stacks if only one is overridden; the default pair is provided for source compatibility.

fn draw_retained( &mut self, _key: u64, _origin: Point, _size: Size, _alpha: f32, _scale: f64, )

Draw the body retained under key from its cached page (see [Command::DrawRetained]). Only valid when the resident-key ledger said key is resident; the default is a no-op for recorders with no retained-layer concept, which never receive such a call.

fn current_transform(&self) -> Option<Affine>

The transform the next command would be recorded under — every PaintScene::push_transform still open, the shell’s device scale included — or None for a scene that does not track one.

fn backdrop_blur(&mut self, _origin: Point, _size: Size, _radius: f64)

Blur whatever is already painted beneath the rectangle at origin/size — a frosted-glass backdrop — with a Gaussian of standard deviation radius (see frust_scene::Command::BackdropBlur).

fn command_index(&self) -> usize

How many commands this scene has recorded so far in the current frame — the painter-order index the next recorded command will occupy.