37.17.8 Defining Images

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

Function: create-image file-or-data &optional type data-p &rest props

This function creates and returns an image descriptor which uses the data in file-or-data. file-or-data can be a file name or a string containing the image data; data-p should be nil for the former case, non-nil for the latter case.

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 nil :heuristic-mask t)

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

Macro: defimage symbol specs &optional doc

This macro defines symbol as an image name. The arguments specs is a list which specifies how to display the image. The third argument, doc, is an optional documentation string.

Each argument in specs has the form of a property list, and each one should specify at least the :type property and either the :file or the :data property. The value of :type should be a symbol specifying the image type, the value of :file is the file to load the image from, and the value of :data is a string containing the actual image data. 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 symbol.

If none of the alternatives will work, then symbol 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 in image-load-path.

Variable: image-load-path

This variable’s value is a list of locations in which to search for image files. If an element is a string or a variable symbol whose value is a string, the string is taken to be the name of a directory to search. If an element is a variable symbol whose value is a list, that is taken to be a list of directory names to search.

The default is to search in the images subdirectory of the directory specified by data-directory, then the directory specified by data-directory, and finally in the directories in load-path. Subdirectories are not automatically included in the search, so if you put an image file in a subdirectory, you have to supply the subdirectory name explicitly. For example, to find the image images/foo/bar.xpm within data-directory, you should specify the image as follows:

(defimage foo-image '((:type xpm :file "foo/bar.xpm")))

Function: image-load-path-for-library library image &optional path no-error

This function returns a suitable search path for images used by the Lisp package library.

The function searches for image first using image-load-path, excluding data-directory/images, and then in load-path, followed by a path suitable for library, which includes ../../etc/images and ../etc/images relative to the library file itself, and finally in data-directory/images.

Then this function returns a list of directories which contains first the directory in which image was found, followed by the value of load-path. If path is given, it is used instead of load-path.

If no-error is non-nil and a suitable path can’t be found, don’t signal an error. Instead, return a list of directories as before, except that nil appears in place of the image directory.

Here is an example of using image-load-path-for-library:

(defvar image-load-path) ; shush compiler
(let* ((load-path (image-load-path-for-library
                    "mh-e" "mh-logo.xpm"))
       (image-load-path (cons (car load-path)
                              image-load-path)))
  (mh-tool-bar-folder-buttons-init))