38.13.7 Defining Images

The functions create-image, defimage and find-image provide convenient ways to create image descriptors.

Function: create-image file &optional type &rest props

This function creates and returns an image descriptor which uses the data in file.

The optional argument type is a symbol specifying the image type. If type is omitted or nil, create-image tries to determine the image type from the file's first few bytes, or else from the file's name.

The remaining arguments, props, specify additional image properties--for example,

(create-image "foo.xpm" 'xpm :heuristic-mask t)

The function returns nil if images of this type are not supported. Otherwise it returns an image descriptor.

Macro: defimage variable doc &rest specs

This macro defines variable as an image name. The second argument, doc, is an optional documentation string. The remaining arguments, specs, specify alternative ways to display the image.

Each argument in specs has the form of a property list, and each one should specify at least the :type property and the :file property. Here is an example:

(defimage test-image '((:type xpm :file "~/test1.xpm") (:type xbm :file "~/test1.xbm")))

defimage tests each argument, one by one, to see if it is usable--that is, if the type is supported and the file exists. The first usable argument is used to make an image descriptor which is stored in the variable variable.

If none of the alternatives will work, then variable is defined as nil.

Function: find-image specs

This function provides a convenient way to find an image satisfying one of a list of image specifications specs.

Each specification in specs is a property list with contents depending on image type. All specifications must at least contain the properties :type type and either :file file or :data DATA, where type is a symbol specifying the image type, e.g. xbm, file is the file to load the image from, and data is a string containing the actual image data. The first specification in the list whose type is supported, and file exists, is used to construct the image specification to be returned. If no specification is satisfied, nil is returned.

The image is looked for first on load-path and then in data-directory.