Attachment 29196 Details for Bug 22770 – Test program to demonstrate differing zero-width-line algorithms

Test program to demonstrate differing zero-width-line algorithms

short-segments.c (text/plain), 4.35 KB, created by Carl Worth on 2009-09-03 16:52:20 UTC

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Creator: Carl Worth

Created: 2009-09-03 16:52:20 UTC

Size: 4.35 KB

patch

obsolete

>/* gcc -o short-segments `pkg-config --cflags x11` short-segments.c `pkg-config --libs x11` */
>#include <stdio.h>
>#include <stdlib.h>
>
>#include <X11/Xlib.h>
>
>#define ARRAY_LENGTH(arr) (sizeof (arr) / sizeof (arr[0]))
>
>/* This is a test case written to explore the issue dscribed in the
> * following bug report:
> *
> * PolySegment draws one pixel short when x1/y1 > x2/y2
> * http://bugs.freedesktop.org/show_bug.cgi?id=22770
> *
> * In the below comments, the "xf86-video-intel implementation"
> * describes objectionable results from the point of view of the
> * original bug reporter, while the "vesa implementation" describes
> * desired results. So from that point of view, seeing any red pixels
> * in the result would be undesired, and also not seeing the green
> * pixels would be undesired.
> *
> * -Carl Worth <cworth@cworth.org>
> */
>static void
>xlib_draw (Display *dpy, Window window, int width, int height)
>{
>    GC gc;
>    unsigned long gc_mask = 0;
>    XGCValues gc_values;
>    XSegment segments[2] = {
>	/* The original bug report included segments drawn from right
>	 * to left and from bottom to top like this: */
>	{ 2, 2, 1, 2 }, { 2, 2, 2, 1 }
>
>	/* If instead, the segments are drawn from left to right and
>	 * from top to bottom like this, then the vesa driver starts
>	 * behaving like the xf86-video-intel driver.
>	{ 1, 2, 2, 2 }, { 2, 1, 2, 2 }
>	*/
>    };
>
>    gc_mask = 0;
>    gc_mask |= GCForeground;	gc_values.foreground = 0x00ff0000;
>
>    /* The original bug report draws segments with line_width at the
>     * default value of 0. This triggers device-specific line drawing
>     * for which either the undesired or desired result is
>     * allowed. Instead, if the segments are drawn with line_width of
>     * 1 like so:
>
>    gc_mask |= GCLineWidth;	gc_values.line_width = 1;
>
>    * then an algorithm carefully specified in the X protocol will be
>    * used consistently by either "vesa" or "xf86-video-intel". This
>    * algorithm happens to yield the undesired behavior. But since
>    * this is the only method of obtaining consistent results across
>    * different implementations, I recommend line_width of 1 be used
>    * and the coordinates be adjusted to obtain the desired results.
>    */
>
>    gc = XCreateGC (dpy, window, gc_mask, &gc_values);
>
>    /* A red pixel. The vesa implementation (with line_width 0) will
>     * cover this with black. The xf86-video-intel implementation
>     * (again with line_width 0) will leave this red pixel showing. */
>    XFillRectangle (dpy, window, gc, 2, 2, 1, 1);
>
>    gc_mask = 0;
>    gc_mask |= GCForeground;	gc_values.foreground = 0x0000ff00;
>    XChangeGC (dpy, gc, gc_mask, &gc_values);
>
>    /* Two green pixels. The xf86-video-intel implementation will
>     * convert these with black. The vesa implementation will leave these
>     * green pixels showing. */
>    XFillRectangle (dpy, window, gc, 1, 2, 1, 1);
>    XFillRectangle (dpy, window, gc, 2, 1, 1, 1);
>
>    gc_mask = 0;
>    gc_mask |= GCForeground;	gc_values.foreground = 0;
>    gc_mask |= GCCapStyle;	gc_values.cap_style = CapNotLast;
>    XChangeGC (dpy, gc, gc_mask, &gc_values);
>
>    /* Finally, draw the two segments of interest. */
>    XDrawSegments (dpy, window, gc, segments, 2);
>
>    XFreeGC (dpy, gc);
>}
>
>static void
>handle_events(Display *dpy, Window window, int width, int height)
>{
>    XEvent xev;
>    KeyCode quit_code = XKeysymToKeycode (dpy, XStringToKeysym("Q"));
>
>    XNextEvent (dpy, &xev);
>
>    while (1) {
>	XNextEvent (dpy, &xev);
>	switch (xev.type) {
>	case KeyPress:
>	    if (xev.xkey.keycode == quit_code)
>		return;
>	break;
>	case ConfigureNotify:
>	    width = xev.xconfigure.width;
>	    height = xev.xconfigure.height;
>	break;
>	case Expose:
>	    if (xev.xexpose.count == 0)
>		xlib_draw (dpy, window, width, height);
>	break;
>	}
>    }
>}
>
>int
>main (int argc, char *argv[])
>{
>    Display *dpy;
>    Window root, window;
>    int width = 4, height = 4;
>
>    dpy = XOpenDisplay (NULL);
>
>    if (dpy == NULL) {
>	fprintf(stderr, "Failed to open display %s\n", XDisplayName(NULL));
>	return 1;
>    }
>
>    window = XCreateSimpleWindow(dpy, DefaultRootWindow (dpy),
>				 0, 0, width, height, 0,
>				 WhitePixel(dpy, DefaultScreen (dpy)),
>				 WhitePixel(dpy, DefaultScreen (dpy)));
>
>    XSelectInput(dpy, window,
>		 KeyPressMask | StructureNotifyMask | ExposureMask);
>
>    XMapWindow (dpy, window);
>
>    handle_events (dpy, window, width, height);
>
>    XDestroyWindow (dpy, window);
>    XCloseDisplay (dpy);
>
>    return 0;
>}

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Attachments on bug 22770: 27691 | 27692 | 27693 | 27694 | 28240 | 28241 | 29156 | 29196

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