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; * src/xterm.c: Improve commentary.

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Po Lu 2022-04-06 12:42:45 +08:00
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src/xterm.c
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@ -142,14 +142,22 @@ along with GNU Emacs. If not, see <https://www.gnu.org/licenses/>. */
draw text in inverse video, and the cursor graphics context is used
to display the cursor in the most common case.
N.B. that some of the other window systems supported by use an
emulation of graphics contexts to hold the foreground and
background colors used in a glyph string, while the some others
ports compute those colors directly based on the colors of the
string's face and its highlight, but only on X are graphics
contexts a data structure inherent to the window system.
COLOR ALLOCATION
In X, pixel values for colors are not guaranteed to correspond to
their individual components. The rules for converting colors into
pixel values are defined by the visual class of each display opened
by Emacs. When a display is opened, a suitable visual is obtained
from the X server, and a colormap is created based on that visual,
which is then used for each frame created.
In (and only in) X, pixel values for colors are not guaranteed to
correspond to their individual components. The rules for
converting colors into pixel values are defined by the visual class
of each display opened by Emacs. When a display is opened, a
suitable visual is obtained from the X server, and a colormap is
created based on that visual, which is then used for each frame
created.
The colormap is then used by the X server to convert pixel values
from a frame created by Emacs into actual colors which are output
@ -202,6 +210,10 @@ along with GNU Emacs. If not, see <https://www.gnu.org/licenses/>. */
which is used to determine the color values for given pixel
values.
In other window systems supported by Emacs, color allocation is
handled by the window system itself, to whom Emacs simply passes 24
(or 32-bit) RGB values.
OPTIONAL FEATURES
While X servers and client libraries tend to come with many