xlib blues (XFree86 - Linux)


 
Thread Tools Search this Thread
Top Forums Programming xlib blues (XFree86 - Linux)
# 1  
Old 12-01-2005
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.
# 2  
Old 12-01-2005
Well...I'm Smilie almost there...

For some reason I cannot access any other color than blue. I would also like to apologise for posting a Linux question in the Unix forum. :/

However, my code has advanced and I would like to share the program I wanted to write.

Code:
/*--------------------------------------------------*
*Open a window on the XFree86 system and draw to it.*
*Created by Robbie Dave after learning about Xlib.h *
*---------------------------------------------------*
Compile with: gcc -o dave dave.c -L/usr/X11R6/lib -lX11
*/

// Include the Xlib.h file so as to use X functions.
#include <X11/Xlib.h>
#define NIL (0)       // A name for the void pointer
//This is the 'main' function in c programs.
int main(void) { 

// Initialise the variables.
Window win;
int win_width = 640;
int win_height = 480;
int win_x;
int win_y;
int screen_num;
GC gc;
XImage *xi=NULL; 
XColor system_color_1; 
XColor exact_color;
Colormap davescol;
int x; 
int y; 
int c;

// Get a pointer (*display) to the X display.
Display *display = XOpenDisplay(NIL);

/*
Obtain the screen number using our *display pointer.
The display pointer does not need the asterisk (*).
*/
screen_num = DefaultScreen(display);

/*
Now we have the screen number and display pointer,
we get the GC (graphics context) of the X system.
*/
gc = DefaultGC(display, screen_num); 

// I assume these are the window offsets set to 0.
win_x = win_y = 0;

// Create the window
win = XCreateSimpleWindow(display, RootWindow(display, screen_num), win_x, win_y, win_width, win_height, 0, BlackPixel(display, screen_num), BlackPixel(display, screen_num));

//Make the screen appear and flush events.
XMapWindow(display, win); 
XFlush(display); 

// Capture the screen for drawing.
xi = XGetImage(display, win, 0,0, win_width, win_height, AllPlanes, ZPixmap); 

//Obtain a colormap to get colors.
davescol = DefaultColormap(display, screen_num); 

// Enter a color into the colormap to use later.
Status rc = XAllocNamedColor(display, davescol, "red", &system_color_1, &exact_color);

	//These two x, y for loops used to plot pixels to window.
	for (x = 0; x < win_width; x++) 
		{ 
		for(y = 0; y < win_height; y++) 
			{
			//Plot a pixel. 
			XPutPixel(xi, x, y, exact_color.pixel);
			/*Experiement with the x, y formula
			for different animations.
			*/
			exact_color.pixel = ((x*x)+(y*y))*0.05;

			if (exact_color.pixel > 65535) 
			{exact_color.pixel=65535;}
			}
	
	}

//This for loop is used for animation.
for(c = 8; c < 64; c++) 
	{ 
	//Animate the colors
	XAddPixel(xi, c);
	//Try to control the animation.
	XFlush(display);
	XSync(display, 1);

	/*
	After plotting to every pixel in the window,
	actually display what you've drawn.
	*/
XPutImage(display, win, gc, xi, 0, 0, 0, 0, win_width, win_height); 
	}

//Clean up the memory a bit, but not much.
XDestroyImage(xi);
XCloseDisplay(display); 
return (0);
}

This program is a simple animatiion that compiles without error with gcc. I am really proud of my work, I just wish I had access to more than one color. For some reason, I can only use blue.

EDIT: After reading yet another Xlib tutorial I discovered how to allocate colors. I still do not understand how to utilize these colors for above animation, but I am getting there...

Ah vell...

Last edited by Alux; 12-03-2005 at 04:41 AM..
Login or Register to Ask a Question

Previous Thread | Next Thread

8 More Discussions You Might Find Interesting

1. Programming

Linux (Xlib) Application hangs on GetGeometry()

Hello, I was just wondering why XGetGeometry() would cause a hang in an application. In the xlib book it says any of there "Get" functions don't necessarily return immediately. Is there a way to make a it return immediately or other functions that will give me the same results. I... (1 Reply)
Discussion started by: TMurray77
1 Replies

2. UNIX for Dummies Questions & Answers

New account blues !

hi .. I tried to create a new account with useradd leghorn (being in root) Also I gave a password for the same using passwd leghorn. So when I go su legorn, it doesnt prompt for the password. Kindly drop in your valuable comments ~cheers (9 Replies)
Discussion started by: leghorn
9 Replies

3. UNIX Desktop Questions & Answers

kde blues

So I'm pretty much a n00b when it comes to Unix but I've decided to give it a shot. I managed to install FreeBSD 6.2 on one partition of my hard drive on my laptop. During the installation I choose to install KDE, not wanting to deal with a non GUI operating system right away! However, whenever I... (1 Reply)
Discussion started by: rinquisitor
1 Replies

4. What is on Your Mind?

Career blues!!!

Hi all, Just writing to know how to approach the situation. I am currently with 2+ exp in a support environment in Unix..mostly on the application side..have not done any Sysadmin work.. My interest is to move towards Unix admin or towards Storage/Networking side..But the problem is that my... (1 Reply)
Discussion started by: ranj@chn
1 Replies

5. BSD

again XFree86

hi everybody i installed FreeBSD 5.x on a box with a video card Diamond SpeedStar A90 and a Fujitsu Siemens Monitor B772-1 when i do "startx" it gives me something like this: fatal error: no devices detected no screen detected i'm lost...i don't know what to... (3 Replies)
Discussion started by: hmaiida
3 Replies

6. UNIX Desktop Questions & Answers

ATI && XFree86 (Linux)

Anyone who have any ideas how-to make X faster. I have a ATI Rage Mobility P/M AGP 2x card and I wanto get it fast, mostly for movie playback and so. Is there OpenGL and GLX support? regards Esaia (1 Reply)
Discussion started by: Esaia
1 Replies

7. Filesystems, Disks and Memory

D'oh! Apple Pro Keyboard Blues

My new Pro Keyboard works great, but the power switch on the computer won't turn the computer on! It's an older model, a Revision D iMac (333), but I know I've used the computer-mounted power switch to power the machine down before. Am I missing something? (1 Reply)
Discussion started by: chenly
1 Replies

8. UNIX for Dummies Questions & Answers

NFS Blues

I have a situation where there are two SCO R5 Open Server Unix boxes in a remote location. The two boxes are inter-related via NFS mounts. My problem occurs when one of the boxes goes down, the NFS relationship stops the remaining machine from carrying on, even though it would be able to do so if... (2 Replies)
Discussion started by: pcs7088
2 Replies
Login or Register to Ask a Question

Featured Tech Videos