Intuition Images, Line Drawing and Text

Intuition supports two general approaches to creating images, lines, and text in displays: through Intuition library calls and through graphics library calls.

This article explains the use of Intuition structures and functions for creating display imagery. The Intuition graphical functions provide a high level interface to the graphics library, giving the application quick and easy rendering capabilities. As with any high level calls, some power and flexibility is sacrificed in order to provide a simple interface.

For more flexibility and control over the graphics, the application can directly call functions in the graphics library as discussed in Graphics Primitives. Intuition also has additional features for defining custom graphic objects. See BOOPSI for more information on these objects.

Intuition Graphic Objects

Intuition graphic objects are easy to create and economical to use. There are just three basic types of graphic objects you can use yet these three types cover most rendering needs:

Images are graphic objects that can contain any imagery. They consist of a rectangular bitmap that can be any size and describes each individual pixel to be displayed.

Borders are connected lines of any length and number, drawn between an arbitrary series of points. They consist of a series of two dimensional coordinates that describe the points between which lines will be drawn.

IntuiText strings are text strings of any length drawn in any font. They consist of a text string and font specification that describes the text to be rendered.

Each of these three objects may be chained together with other members of the same type. For instance, many lines of text may be rendered as a single object by linking many instances of IntuiText objects together. Only objects of the same type may be linked.

Any of these types can be rendered into any of the Intuition display elements (window, requester, menu, etc.). In fact, the application can often display the same structure in more than one position or more than one of the elements at the same time.

Displaying Images, Borders and IntuiText

Images, Borders and IntuiText objects may be directly or indirectly rendered into the display by the application. The application can draw these objects directly into windows or screens by using one of the functions DrawImage(), DrawBorder() or PrintIText(). The application supplies the appropriate pointer to a Border, Image or IntuiText structure as an argument to the function, as well as position information and a pointer to the correct RastPort. These rendering functions are discussed in more detail below.

The application can also draw these objects indirectly by attaching them to a menu, gadget or requester. As Intuition places these elements on the display, it also renders the associated graphics. The Requester, Gadget, and MenuItem structures contain one or more fields reserved for rendering information. See the specific articles on these items for information on attaching graphical objects to them.

Positioning Graphic Objects

The position of these objects is specified as the sum of two independent components: an external component which gives the position of a base reference point for the list of objects, and an internal component which gives the relative offset of a specific object to the base reference point.

The external component is used to position the object list within the display element. For objects drawn indirectly by attaching them to a menu, gadget or requester, this is always a point within the menu, gadget or requester (the top left corner).

For objects drawn directly with the DrawImage(), DrawBorder() or PrintIText() functions, specific x and y coordinates are provided as arguments that specify an offset within the screen’s or window’s RastPort at which to display the list of objects.

Each object also has an internal, relative component that is added to the external component described above to determine the final position of the object. This allows the application to reuse a graphical object and have it appear relative to each object to which it is attached. For example, if the application has numerous gadgets of the same size, it can use a single Border structure to draw lines around all the gadgets. When the gadgets are drawn, the base position of the lines will be taken from each specific gadget in turn.

More Information

For more information on each Intuition graphic object see:

Function Reference

The following are brief descriptions of the Intuition functions that relate to the use of graphics under Intuition. See the SDK for details on each function call.

Function	Description
DrawBorder()	Draw a border into a rast port.
DrawImage()	Draw a image into a rast port.
PrintIText()	Draw Intuition text into a rast port.
IntuiTextLength()	Find the length of an IntuiText string.
BeginRefresh()	Begin optimized rendering after a refresh event.
EndRefresh()	End optimized rendering after a refresh event.
GetScreenDrawInfo()	Get screen drawing information.
FreeScreenDrawInfo()	Free screen drawing information.

Intuition Images, Line Drawing and Text

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