ProgrammingThis forum is for all programming questions.
The question does not have to be directly related to Linux and any language is fair game.
Welcome to LinuxQuestions.org, a friendly and active Linux Community.
You are currently viewing LQ as a guest. By joining our community you will have the ability to post topics, receive our newsletter, use the advanced search, subscribe to threads and access many other special features. Registration is quick, simple and absolutely free. Join our community today!
Note that registered members see fewer ads, and ContentLink is completely disabled once you log in.
If you have any problems with the registration process or your account login, please contact us. If you need to reset your password, click here.
Having a problem logging in? Please visit this page to clear all LQ-related cookies.
Introduction to Linux - A Hands on Guide
This guide was created as an overview of the Linux Operating System, geared toward new users as an exploration tour and getting started guide, with exercises at the end of each chapter.
For more advanced trainees it can be a desktop reference, and a collection of the base knowledge needed to proceed with system and network administration. This book contains many real life examples derived from the author's experience as a Linux system and network administrator, trainer and consultant. They hope these examples will help you to get a better understanding of the Linux system and that you feel encouraged to try out things on your own.
Click Here to receive this Complete Guide absolutely free.
What's the best (meaning easiest way, and the fastest way) to read a pixel when running an x server? Under windows, I was able to drive a gui, watch the screen to react to events (much like the game botters do) using pixelchecksums and getpixelcolors. In my case, I have to watch and automate a java app, that I don't have the source to as part of my job. It's a crippled third party vendor app, and we're forced to use it -- you know the rest of the story with those :-). At any rate, under windows "reading" the screen was easy, but under X11, I don't find the same thing. I considered using everything from python to java. My windows code was actually C++, and later autohotkey. I've looked at xmacro, andriod, expect, etc, but none really give you that low level access I'm after (they use the XTEST extension which states it's not to be used to automate guis). After alot of searching this led to using Xlib directly. Is this the best way? And are there other wrappers for Xlib besides the orginal C? I know of python-xlib wrapper as well, but that's it.
I believe Xlib will do the job, yes. You need to be careful of the window coordinates though. If you literally want a pixel from the screen (an absolute position relative to the (say) 1024x768 background) you will be looking at the "root" window; if you want a pixel from an application window, and you know which window!, then you may want to give window-relative coordinates, which have the 0,0 origin inside the Window Manager's title bar.
If you're grabbing large areas of the screen, don't do it a pixel at a time (too much comms with the server). Xlib has functions to grab an area I think.
All the common C/C++ GUI toolkits wrap Xlib, AFAIK - eg. Qt, GTK. The KDE toolkit builds on Qt.
Back when I was doing such hacks, I found the frame buffer very easy to use. One call (IIRC, fb_open under Solaris), and you get a struct with a pointer to the video memory, and other useful info.
No messing with X and toolkits here -- but you may need to do that if you care where a particular window lies on your screen.
A completely different approach: Provide an instrumented environment (Drawable etc.) to your java app. I'm not sure how easy it will be to architect, but if you can intercept, e.g., calls to draw and have them do what you need (instead of painting pixels), that might be more efficient than polling pixels off the screen.
Thanks! Can you enlighten me a little more with the framebuffer approach? And could someone provide a link with an up to date API that can do it with XLIB? I too looked for it in GTK and came up short. Yes, I am looking to grab a small chunk of pixels in a few locations. I'll let everyone know if I find anything - glad I'm on the right track with using XLib
I think the frame buffer approach and Xlib are quite different. I don't know much about using a frame buffer, but as I understand it, this accesses the hardware "directly" on the machine, whereas the X protocol is designed to operate a display (or many displays) that may be physically remote from where the program is. That makes X slower, but potentially more flexible. Though this isn't likely to be a big issue - most Linux X programs assume run on the same machine as the display.
thanks - that's along the lines of what i was looking for. A toolkit for this would be nice, but as such it's a nice reference. I also found this - which may or may not work out. It's a X virtual frame buffer. FUN FUN! http://www.xfree86.org/4.0.1/Xvfb.1.html