EmacsLisp : Can the pixel width of text in a proportional font be measured?

Question

Given a face using a proportional font, can an accurate pixel width of a single row of text be measured in Emacs?

_{Note: not monospaced text.}

Answer 1

In the Emacs 24.4+ Manual Section 37.10 Size of Displayed Text

The following function returns the size in pixels of text as if it were displayed in a given window.

Function: window-text-pixel-size &optional window from to x-limit y-limit mode-and-header-line

This function returns the size of the text of window’s buffer in pixels. window must be a live window and defaults to the selected one. The return value is a cons of the maximum pixel-width of any text line and the maximum pixel-height of all text lines.

The optional argument from, if non-nil, specifies the first text position to consider and defaults to the minimum accessible position of the buffer. If from is t, it uses the minimum accessible position that is not a newline character. The optional argument to, if non-nil, specifies the last text position to consider and defaults to the maximum accessible position of the buffer. If to is t, it uses the maximum accessible position that is not a newline character.

See the documentation for full details on the other parameters.

Please Note: window-text-pixel-size is a function introduced in emacs 24.4