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# 3.2 Screen Attributes

In CLX, each display screen is represented by a screen structure. The display-roots function returns the list of screen structures for the display. The following paragraphs discuss the attributes of CLX screen structures.

screen-backing-stores | screen | Function

| screen A screen. Returns a value indicating when the screen supports backing stores, although it may be storage limited in the number of windows it can support at once. The value returned can be one of :always, :never, or :when-mapped . backing-stores-type One of :always, :never, or :when-mapped.

screen-black-pixel | screen | Function

| screen A screen. Returns the black pixel value for the specified screen. black-pixel Type pixel.

screen-default-colormap | screen | Function

| screen A screen. Returns the default-colormap for the specified screen . The default-colormap is initially associated with the root window. Clients with minimal color requirements creating windows of the same depth as the root may want to allocate from this map by default. Most routine allocations of color should be made out of this colormap. default-colormap Type colormap .

screen-depths | screen | Function

| screen A screen. Returns an association list that specifies what drawable depths are supported on the specified screen. Elements of the returned association list have the form (depth visual*), where each visual is a visual-info structure. Pixmaps are supported for each depth listed, and windows of that depth are supported if at least one visual type is listed for the depth. A pixmap depth of one is always supported and listed, but windows of depth one might not be supported. A depth of zero is never listed, but zero-depth :input-only windows are always supported. depths Type alist.

screen-event-mask-at-open | screen | Function

| screen A screen. Returns the initial root event mask for the specified screen . event-mask-at-open Type mask32.

screen-height | screen | Function

| screen A screen. Returns the height of the specified screen in pixel units. height Type card16.

screen-height-in-millimeters | screen | Function

| screen A screen. Returns the height of the specified screen in millimeters. The returned height can be used with the width in millimeters to determine the physical size and the aspect ratio of the screen. height-in-millimeters Type card16.

screen-max-installed-maps | screen | Function

| screen A screen. Returns the maximum number of colormaps that can be installed simultaneously with install-colormap. max-installed-colormaps Type card16.

screen-min-installed-maps | screen | Function

| screen A screen. Returns the minimum number of colormaps that can be guaranteed to be installed simultaneously. min-installed-colormaps Type card16.

screen-p | screen | Function

| Returns non-nil if the screen argument is a screen structure; otherwise, returns nil. screen-p Type boolean.

screen-plist | screen | Function

| screen A screen. Returns and (with setf) sets the property list for the specified screen. This function provides a hook where extensions can add data. plist Type list.

screen-root | screen | Function

| screen A screen. Returns the root-window for the specified screen. This function is useful with functions that take a parent window as an argument. The class of the root window is always :input-output. root-window Type window or null.

screen-root-depth | screen | Function

| screen A screen. Returns the depth of the root window for the specified screen . Other depths can also be supported on this screen. root-window-depth Type image-depth.

screen-root-visual | screen | Function

| screen A screen. Returns the default visual type for the root window for the specified screen. root-window-visual Type card29.

screen-save-unders-p | screen | Function

| screen A screen. If true, the server can support the save-under mode in create-window and in changing window attributes. save-unders-p Type boolean.

screen-white-pixel | screen | Function

| screen A screen. Returns the white pixel value for the specified screen. white-pixel Type pixel.

screen-width | screen | Function

| screen A screen. Returns the width of the specified screen in pixel units. width Type card16.

screen-width-in-millimeters | screen | Function

| screen A screen. Returns the width of the specified screen in millimeters. The returned width can be used with the height in millimeters to determine the physical size and the aspect ratio of the screen. width-in-millimeters Type card16.

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