Bug#167448: libxaw7: A bug in Xaw/StripChart.c causes incorrect scale lines in xload window

["Nikita V. Youshchenko" <yoush@cs.msu.su>]

Package: libxaw7
Version: 4.2.1-3
Severity: normal
Tags: patch

Recently I tried to run xload on a high loaded server (load was more
than 10), and discovered that if window size is rather small, scale
lines are drawn incorrectly (upper than needed).

This is caused by a bug in Xaw/StripChart.c.
It draws lines with fixed integer steps. Than means that if window
height is 39 pixels, and 10 lines should be drawn to split view into 11
equal parts, lines will be drawn at 3, 6, 9, ,.., 30. So the bottom part
height will be 9 pixels while other parts height will be 2 pixels.

A patch to fix this is below. When applied, it makes part heights differ
no more than by 1 pixel.

Screenshots are at http://zigzag.lvk.cs.msu.su/~nikita/xload.png.
The top window is xload linked against patched libXaw, the bottom window
is xload linked against original libXaw.

--- StripChart.c.orig   Fri Dec 14 22:54:44 2001
+++ StripChart.c        Sat Nov  2 17:26:15 2002
@@ -375,7 +375,7 @@
 static int
 repaint_window(StripChartWidget w, int left, int width)
 {
-    int i, j;
+    int i, j, k;
     int next = w->strip_chart.interval;
     int scale = w->strip_chart.scale;
     int scalewidth = 0;
@@ -420,8 +420,10 @@
        }

        /* Draw graph reference lines */
+       k = XtHeight(w) % w->strip_chart.scale;
        for (i = 1; i < w->strip_chart.scale; i++) {
-           j = i * ((int)XtHeight(w) / w->strip_chart.scale);
+           j = i * (XtHeight(w) / w->strip_chart.scale) +
+                   ((i * k + w->strip_chart.scale/2) /
w->strip_chart.scale);
            XDrawLine(dpy, win, w->strip_chart.hiGC, left, j,
scalewidth, j);
        }
     }
@@ -443,7 +445,7 @@
 MoveChart(StripChartWidget w, Bool blit)
 {
     double old_max;
-    int left, i, j;
+    int left, i, j, k;
     int next = w->strip_chart.interval;

     if (!XtIsRealized((Widget)w))
@@ -492,8 +494,10 @@

     /* Draw graph reference lines */
     left = j;
+    k = XtHeight(w) % w->strip_chart.scale;
     for (i = 1; i < w->strip_chart.scale; i++) {
-       j = i * (XtHeight(w) / w->strip_chart.scale);
+       j = i * (XtHeight(w) / w->strip_chart.scale) +
+           ((i * k + w->strip_chart.scale/2) / w->strip_chart.scale);
        XDrawLine(XtDisplay((Widget)w), XtWindow((Widget)w),
                  w->strip_chart.hiGC, left, j, XtWidth(w), j);
     }
@@ -554,7 +558,7 @@
     StripChartWidget w = (StripChartWidget)widget;
     XPoint *points;
     Cardinal size;
-    int i;
+    int i, k;

     if (w->strip_chart.scale <= 1) {
        XtFree((char *)w->strip_chart.points);
@@ -569,8 +573,12 @@

     /* Draw graph reference lines into clip mask */

+    k = XtHeight(w) % w->strip_chart.scale;
     for (i = 1; i < w->strip_chart.scale; i++) {
        points[i - 1].x = 0;
-       points[i - 1].y = XtHeight(w) / w->strip_chart.scale;
+       points[i - 1].y = i * (XtHeight(w) / w->strip_chart.scale) +
+           ((i * k + w->strip_chart.scale/2) / w->strip_chart.scale);
     }
+    for (i = w->strip_chart.scale - 1; i > 1; i--)
+       points[i - 1].y -= points[i - 2].y;
 }


-- System Information:
Debian Release: 3.0
Architecture: i386
Kernel: Linux sercond 2.4.19 #1 óÂÔ óÅÎ 28 15:05:51 MSD 2002 i686
Locale: LANG=ru_RU.KOI8-R, LC_CTYPE=ru_RU.KOI8-R

Versions of packages libxaw7 depends on:
ii  libc6                         2.3.1-3    GNU C Library: Shared libraries an
ii  xlibs                         4.2.1-3    X Window System client libraries

-- no debconf information