56.4 Drawing attention

9.3

Racket

56.4 Drawing attention🔗ℹ

Use a temporary effect to draw attention to an object.

procedure
(pulse target
[ #:scale-factor scale-factor
#:opacity-factor opacity-factor
#:cycles cycles
#:about about]) → pulse-request?
  target : (or/c visual? symbol? visual-path?)
  scale-factor : any/c = 6/5
  opacity-factor : (real-in 0 1) = 1
  cycles : exact-positive-integer? = 1
  about : (or/c 'center 'reference vec2?) = 'center

Temporarily changes selected affine/opacity components of a present target through a deterministic squared-sine there-and-back envelope. The envelope is exactly zero at both clip endpoints, and the exact clip-start component values are restored at completion. #:cycles is an exact positive integer.

Only nonidentity components are written: a scale factor of one writes no scale, and an opacity factor of one writes no opacity. A pulse can therefore run with same-target movement when it does not write translation, but it conflicts with any overlapping request that writes one of its selected components. Direct Visual targets are checked immediately; symbol and nested-path targets are checked at the leaf’s exact local start.

procedure
(pulse-request? value) → boolean?
value : any/c

Recognizes a pulse request.

procedure
(confetti origin-or-target
[ #:count count
#:seed seed
#:spread spread
#:height height
#:gravity gravity
#:palette palette
#:id id]) → confetti-request?
  origin-or-target : (or/c vec2? visual? symbol? visual-path?)
  count : exact-positive-integer? = 24
  seed : exact-integer? = 0
  spread : (and/c finite-real? (>=/c 0)) = 2
  height : (and/c finite-real? (>=/c 0)) = 2
  gravity : (and/c finite-real? (>=/c 0)) = 3
   palette : (or/c (listof color-spec?) (vectorof color-spec?))
= default-confetti-palette
  id : (or/c #f symbol?) = #f

Creates a deterministic temporary overlay of simple path pieces. The complete piece plan is generated at construction from seed, without reading or mutating global random state. A vec2 is a fixed launch point; a Visual, symbol, or path target is resolved to its world reference point once at the play clip’s start. Consequently, the target is not rewritten and later target motion does not change an already compiled particle trajectory.

Each piece follows a direct ballistic formula using spread, height, and gravity, so arbitrary-time sampling and forward playback produce the same frame. With an explicit id, helpers use deterministic child identities under that name; otherwise their identities are derived from the composition expansion origin. They appear only at interior samples and are all removed exactly at completion. Reusing an explicit id in a simultaneous play is rejected as a normal component conflict. Inspection records the resolved origin, seed, generated count, and helper IDs.

procedure
(confetti-request? value) → boolean?
value : any/c

Recognizes a request created by confetti.

I	Concepts
II	Cookbook
III	Guide
IV	Complete Example Programs
V	Reference

52	Find a task or a name
53	Modules to require
54	Scenes and sampling
55	Scene states
56	Animation requests
57	Native model details
58	Visuals
59	Geometry
60	Number Lines and Coordinate Decorations
61	Point Markers, Scatter Plots, and Filled Areas
62	Probability and Statistical Diagrams
63	Calculus lessons
64	Colors
65	Slides
66	Slide command-line tools
67	Source Programs and Authored Timelines
68	Interactive Preview and Inspection
69	Preview controls and diagnostics
70	Projects and Final Rendering
71	Project execution and cache details
72	Pict Renderer Protocol
73	3D reference map
74	3D: Objects, groups, and paths
75	3D: Cameras and projection
76	3D: Views inside a Scene
77	3D: Animating 3D objects
78	3D: Animating the 3D camera
79	3D: Cuts, caps, and section measurements
80	3D: Supplementary surface, section, and annotation bindings
81	3D: Cuts, sections, and numerical volume
82	3D: Vectors
83	3D: Linear maps and rotations
84	3D: Affine transforms
85	3D: Bounds, rays, and planes
86	3D: Spatial maps and homotopies
87	3D: Materials and lights
88	3D: Lighting inspection
89	3D: Shadow descriptors and stable bounds
90	3D: Finite-light animation
91	3D: Software finite-light evaluation
92	3D: Colour space and final output
93	3D: Relations and geometric annotations
94	3D: Projected labels
95	3D: Textured billboards
96	3D: Spatial curves and vector diagrams
97	3D: Spatial anchors and label layout
98	3D: Anchors and projected labels
99	3D: Parametric surfaces and calculus
100	3D: Adaptive, trimmed, and implicit surfaces
101	3D: Constructive solids
102	3D: Surface constructors and queries
103	3D: Meshes
104	3D: Triangle topology
105	3D: Polygonal faces
106	3D: Deterministic convex hulls
107	3D: Polyhedral duals
108	3D: Schlegel diagrams and polyhedral nets
109	3D: Conservative mesh correspondence
110	3D: Topology-safe mesh matching
111	3D: Checking and repairing mesh orientation
112	3D: Clipping, sections, and transparency
113	3D: Prepared spatial ODE trajectories and vector fields
114	3D: Seeds and streamline sets
115	3D: Poincare sections and return maps
116	3D: Equilibria and local linearization
117	3D: Flow maps and volume change
118	3D: Drawing and inspecting trajectories
119	3D: Reading prepared trajectories
120	3D: Drawing vector fields and particles
121	3D: Trajectory display
122	3D: Spatial inspection and exact picking
123	3D: Retained renderer backends
124	3D: Compiled geometry and instances
125	3D: Frame requests and results
126	3D: Software rendering and statistics
127	3D: Optional Racket/ Open GL backend
128	Experimental Derived Visuals
129	Source Package Hygiene

56.1	Moving, rotating, and scaling
56.2	Changing color, width, and opacity
56.3	Adding, revealing, and removing objects
56.4	Drawing attention
56.5	Drawing and morphing paths
56.6	Matching compound path outlines
56.7	Replacing and matching shapes
56.8	Writing and transforming text and formulas
56.9	Changing named values
56.10	Moving the camera
56.11	Combining and timing requests
56.12	Choosing a speed curve
56.13	Other animation requests