In computer graphics programming, hit-testing (hit detection, picking, or pick correlation
) is the process of determining whether a user-controlled cursor (such as a mouse cursor or touch-point on a touch-screen interface) intersects a given graphical object (such as a shape, line, or curve) drawn on the screen. Hit-testing may be performed on the movement or activation of a mouse or other pointing device.
Hit-testing is used by
GUI
The GUI ( "UI" by itself is still usually pronounced . or ), graphical user interface, is a form of user interface that allows users to interact with electronic devices through graphical icons and audio indicator such as primary notation, inste ...
environments to respond to user actions, such as selecting a menu item or a target in a game based on its visual location. In Web programming languages such as
HTML
The HyperText Markup Language or HTML is the standard markup language for documents designed to be displayed in a web browser. It can be assisted by technologies such as Cascading Style Sheets (CSS) and scripting languages such as JavaScri ...
,
SVG, and
CSS
Cascading Style Sheets (CSS) is a style sheet language used for describing the presentation of a document written in a markup language such as HTML or XML (including XML dialects such as SVG, MathML or XHTML). CSS is a cornerstone techno ...
, this is associated with the concept of pointer-events (e.g. user-initiated cursor movement or object selection).
Collision detection
Collision detection is the computational problem of detecting the intersection (Euclidean geometry), intersection of two or more objects. Collision detection is a classic issue of computational geometry and has applications in various computing ...
is a related concept for detecting intersections of two or more different graphical objects, rather than intersection of a cursor with one or more graphical objects.
Algorithm
There are many different algorithms that may be used to perform hit-testing, with different performance or accuracy outcomes. One common hit-test algorithm is presented in the pseudo-code below:
function HitTest(Rectangle r1, Rectangle r2) returns boolean
{
return ((r1.X + r1.Width >= r2.X) and (r1.X <= r2.X + r2.Width) and (r1.Y + r1.Height >= r2.Y) and (r1.Y <= r2.Y + r2.Height));
}
See also
*
Point in polygon
In computational geometry, the point-in-polygon (PIP) problem asks whether a given point in the plane lies inside, outside, or on the boundary of a polygon. It is a special case of point location problems and finds applications in areas that dea ...
*
Computational geometry
Computational geometry is a branch of computer science devoted to the study of algorithms which can be stated in terms of geometry. Some purely geometrical problems arise out of the study of computational geometric algorithms, and such problems ar ...
*
Collision detection
Collision detection is the computational problem of detecting the intersection (Euclidean geometry), intersection of two or more objects. Collision detection is a classic issue of computational geometry and has applications in various computing ...
*
User interface
In the industrial design field of human–computer interaction, a user interface (UI) is the space where interactions between humans and machines occur. The goal of this interaction is to allow effective operation and control of the machine f ...
References
[ Computer Graphics: Principles and Practice 2nd Edition in C, Foley et al, ]Addison-Wesley
Addison-Wesley is an American publisher of textbooks and computer literature. It is an imprint of Pearson PLC, a global publishing and education company. In addition to publishing books, Addison-Wesley also distributes its technical titles through ...
, 1997.
External links
MSDN: Hit Testing in the Visual LayerMSDN: Hit Testing Lines and Curves
Computer graphics
User interfaces
Video game development