I'm sending a patch for lisp/pixel-scroll.el.

This patch lets mouse wheel scroll vertically by number of pixels
returned by `frame-char-height' as suggested as below.

  https://lists.gnu.org/archive/html/emacs-devel/2017-09/msg00385.html

Also, by considering response of display engine as suggested as below,
this patch offers stable vertically scrolling even when window is
horizontally scrolled.

  https://lists.gnu.org/archive/html/emacs-devel/2017-10/msg00621.html

ChangeLog entry and patch to NEWS also are attached.


* ChangeLog

2017-10-21 Tak Kunihiro <tkk@misasa.okayama-u.ac.jp>

        Scroll vertically by number of pixels returned by `frame-char-height' with or without horizontally scrolled

        * lisp/pixel-scroll.el (pixel-resolution-fine-flag): When t, scroll pixels returned by `frame-char-height'.
        (pixel-scroll-up): Scroll by `frame-char-height'. Fix algorithm to move cursor to avoid unexpected jump.
        (pixel-scroll-down): Scroll by `frame-char-height'.
        (pixel-bob-at-top-p): Consider number of pixels that is about to scroll.
        (pixel-posn-y-at-point): Consider existence of an overlay string.  Return nil when horizontally scrolled.
        (pixel-point-at-top-p): Consider number of pixels that is about to scroll. Use different algorithm when horizontally scrolled.
        (pixel-point-at-bottom-p): Consider number of pixels that is about to scroll. Return nil when horizontally scrolled.
        (pixel-scroll-pixel-down): Move cursor when horizontally scrolled.
        (pixel--whistlestop-line-up): Change cosmetics and move cursor when horizontally scrolled.
        (pixel-line-height): Call `pixel-visual-line-height' instead of `line-pixel-height'.
        (pixel-visual-line-height): New function to return height in pixels of text line where cursor is with or without horizontally scrolled, considering response of display engine.
        (pixel-visible-pos-in-window): New function to return position of a char shown on text line where cursor is on screen with or without horizontally scrolled.