xlib blues (XFree86 - Linux) Post: 91321

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Top Forums Programming xlib blues (XFree86 - Linux) Post 91321 by Alux on Thursday 1st of December 2005 03:40:49 AM

12-01-2005

Registered User

xlib blues (XFree86 - Linux)

My goal is to open a window in the X-server and plot a series of pixels. However, I find many examples I have tried to draw to a window fail and the window remains blank. Therefore, I am here requesting information. I do not know c, and am a beginner. Currently, I am using a mix-match of code, running against the gcc compiler finding errors and fixing them as I go along. I have experienced segmentation faults, but the following code produces a minimal amount of error.

Code:

/* window.c --This program opens a window on the display
* Use "gcc -o window window.c -L/usr/X11R6/lib -lX11
* to compile this code.
*/


#include <X11/X.h>
#include <X11/Xlib.h>
#include<stdio.h>
#define width	320
#define height	200

int main(void)
{
Display *display;
Window window, rootwindow;
int screen;
GC gc;
XImage *img=NULL;
int x;
int y;

display = XOpenDisplay(NULL);
screen = DefaultScreen(display);
gc = DefaultGC(display, screen);
rootwindow = RootWindow(display,screen);
window = XCreateSimpleWindow(display, rootwindow,
                0, 0, width, height, 1, 0, 0);
XMapWindow(display, window);
XImage *xi;
unsigned long pixelvalue1;


xi = XCreateImage(display, 0, 8, ZPixmap,
                   0, malloc(width*height), width, height, 
		   8, 0);

pixelvalue1 = 65535;
for (x = 0; x < width/2; x++)
	{
		for(y = 0; y < height/2; y++)
			{
				XPutPixel(xi, x, y, pixelvalue1);
			}
	}
printf("putting image\n");

XPutImage(display, window, gc, xi, 0, 0, 0, 0, width, height);
sleep (5);
return (0);
}

The result of this code, is to open a window (which it does) for 5 seconds/cycles, and also plot a series of pixels half the length of the width and height specified.

However, what actually happens is it opens a window with a black background, plots nothing, and I am left frustrated with little resources. I suspect the problem may lie in either XCreateImage, or XPutPixel commands. I suspect I have not got the right values for either command.

Can anyone here offer a simple solution to my problem of wanting to plot pixels to a window?

Finally - I would like to elabroate on my plans...

I intend to further the pixel plotting using double buffering, for a simple animation routine I written in PHP graphics. As animation is not available in PHP, this is the reason for myself attempting c coding without any prior knowledge of the c language. However, I do have a basic grasp of BASIC (if, for, while etc), and constant/variable declaration (int, long, double etc).

Please can someone enlighten me with a code snippet as to how I can accomplish my goal of plotting individual pixels to the screen.

Much thanks,

Alux.

Alux

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LEARN ABOUT SUSE

xev

XEV(1)							      General Commands Manual							    XEV(1)

NAME

       xev - print contents of X events

SYNOPSIS

       xev [-display displayname] [-geometry geom] [-bw pixels] [-bs {NotUseful,WhenMapped,Always}] [-id windowid] [-s] [-name string] [-rv]

DESCRIPTION

       Xev creates a window and then asks the X server to send it events whenever anything happens to the window (such as it being moved, resized,
       typed in, clicked in, etc.).  You can also attach it to an existing window.  It is useful for seeing what causes events	to  occur  and	to
       display the information that they contain; it is essentially a debugging and development tool, and should not be needed in normal usage.

OPTIONS

       -display display
	       This option specifies the X server to contact.

       -geometry geom
	       This option specifies the size and/or location of the window, if a window is to be created.

       -bw pixels
	       This option specifies the border width for the window.

       -bs {NotUseful,WhenMapped,Always}
	       This  option  specifies	what  kind of backing store to give the window.  The default is NotUseful. Backing store refers to the the
	       pixels saved off-screen when the X server maintains the contents of a window; NotUseful means that the xev process will redraw  its
	       contents itself, as necessary.

       -id windowid
	       This option specifies that the window with the given id should be monitored, instead of creating a new window.

       -s      This  option  specifies	that save-unders should be enabled on the window. Save unders are similar to backing store, but they refer
	       rather to the saving of pixels off-screen when the current window obscures other windows. Save unders are only  advisory,  and  are
	       normally set for popup dialogs and other transient windows.

       -name string
	       This option specifies the name to assign to the created window.

       -rv     This option specifies that the window should be in reverse video.

SEE ALSO

       X(7), xwininfo(1), xdpyinfo(1), Xlib Programmers Manual, X Protocol Specification
       See X(7) for a full statement of rights and permissions.

AUTHOR

       Jim Fulton, MIT X Consortium

X Version 11							     xev 1.0.4								    XEV(1)

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