How can I get the color of a pixel on screen with Node.js or C?-CodePudding

I am trying to get the color of a pixel on my screen using node.js. I want it to be returned in RGB format, e.g. (255, 0, 0). My current solution is to use screenshot-desktop to screenshot my entire screen in JPG format, decode it to get the raw pixel data, and get the color of a given pixel. However, this lags out my entire computer for 1-2 seconds as it is taking the screenshot. This is unusable as I would like to do this multiple times per second. So my question is: How can I get the color of a given pixel on the screen, without taking a full screenshot?

I am using Linux with X11. There is an X11 library for node.js, so I asssume I should use that to get the pixel color, I'm just not sure how. If you could show me how to do it in C then I can easily use node.js to do the same thing.

Thanks!

CodePudding user response：

Oh my gosh I just figured it out after posting this. I was using robotjs for reading the mouse position and I totally forgot it can do screen stuff too! So, the solution would be to do

var robot = require('robotjs');
var color = robot.getPixelColor(x, y);

CodePudding user response：

X11 solution using x11 node library ( I am the author ):

query windows tree with QueryTree starting at the root window
get every child geometry using GetGeometry request
if your point is not inside any child, use current window id and get 1x1 pixmap from the current image: GetImage(format, currentWindow, x, y, 1, 1, planeMask) ( 2 for format and 0xffffffff for plane mask should work ). Make sure you calculate relative x y position as you travers windows tree.
if child window covers your point query children for that window and repeat again. Note that QueryTree returns windows in bottom to top stacking order so make sure you pick last one covering your point

Once you have 1x1 pixmap from the topmost window under your point - the buffer should contain only color bytes for your image, RGB order and bit mask might depend on red_mask, green_mask, blue_mask from display.screen[0].depths[visual].

If you cache "topmost window" between requests and only start from root when no match anymore the above solution might be much more performant then the one using robotjs ( although much more low level and complicated ) Good luck!