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 ULTRIX

xclearwindow

XClearArea(3X11)						     MIT X11R4							  XClearArea(3X11)

Name
       XClearArea, XClearWindow - clear area or window

Syntax
       XClearArea(display, w, x, y, width, height, exposures)
	  Display *display;
	  Window w;
	  int x, y;
	  unsigned int width, height;
	  Bool exposures;

       XClearWindow(display, w)
	  Display *display;
	  Window w;

Arguments
       display	 Specifies the connection to the X server.

       exposures Specifies a Boolean value that indicates if events are to be generated.

       w	 Specifies the window.

       width
       height	 Specify the width and height, which are the dimensions of the rectangle.

       x
       y	 Specify the x and y coordinates, which are relative to the origin of the window and specify the upper-left corner of the rectan-
		 gle.

Description
       The function paints a rectangular area in the specified window according to the specified dimensions with the window's background pixel or
       pixmap.	The subwindow-mode effectively is If width is zero, it is replaced with the current width of the window minus x.  If height is
       zero, it is replaced with the current height of the window minus y.  If the window has a defined background tile, the rectangle clipped by
       any children is filled with this tile.  If the window has background the contents of the window are not changed.  In either case, if expo-
       sures is one or more events are generated for regions of the rectangle that are either visible or are being retained in a backing store.
       If you specify a window whose class is a error results.

       can generate and errors.

       The function clears the entire area in the specified window and is equivalent to (display, w, 0, 0, 0, 0, If the window has a defined back-
       ground tile, the rectangle is tiled with a plane-mask of all ones and function.	If the window has background the contents of the window
       are not changed.  If you specify a window whose class is a error results.

       can generate and errors.

Diagnostics
       An	 window is used as a Drawable.

       Some numeric value falls outside the range of values accepted by the request.
		 Unless a specific range is specified for an argument, the full range defined by the argument's type is accepted. Any argument
		 defined as a set of alternatives can generate this error.

       A value for a Window argument does not name a defined Window.

See Also
       XCopyArea(3X11)
       X Window System: The Complete Reference, Second Edition, Robert W. Scheifler and James Gettys

																  XClearArea(3X11)