3.6 Images

Besides of text and bitmaps labels can display images. Images differ from bitmaps in that they allow for more than two colors to be displayed.

Images are provided as objects in Oz. These objects are also tickle objects (see Section 3.2), but are different from widget objects.

D ={Property.get 'oz.home'}#'/doc/wp/' 
I ={New Tk.image tkInit(type:photo format:ppm file:D#'truck-left.ppm')}
L1={New Tk.label tkInit(parent:W image:I)}
L2={New Tk.label tkInit(parent:W image:I)}
L3={New Tk.label tkInit(parent:W image:I)}
{Tk.send pack(L1 L2 L3 padx:1#m pady:1#m side:left)}

Figure 3.6: Three labels displaying the same image.

The program in Figure 3.6 creates an image object and displays the image in three labels. Changing the configuration of the image, changes the displayed image in all label widgets. For example, feeding the following expression

{I tk(configure file:D#'truck-right.ppm')}

replaces all three displayed trucks by trucks heading in the inverse direction.

type and format

Images can be of two different types. The value of the type configuration option can be photo (as in our example), or bitmap. If the type is photo, the image can display files in two different formats. The format is specified by the format option. Valid values for the format option are gif and ppm.

bitmap images

In case the value for the type option is bitmap, the value given for the file option must be a valid bitmap file.

referring to images by URLs

In addition to files, images can also be referred to by URLs. For example,

{New Tk.image tkInit(type:photo format:gif

would have loaded a gif file from the given URL. Note that the graphics engine itself is not capable of handling URLs. Instead, the image object handles URLs by localizing a URL to a local file (see also Chapter 15 of ``System Modules''). The local file then is used by the graphics engine.

In Section 8.4 an abstraction is presented that eases the handling of images considerably.

Reference information on images can be found in image.

Christian Schulte
Version 1.4.0 (20080702)