diff --git a/progs/xdemos/glxgears.c b/progs/xdemos/glxgears.c
index 8db717f..52c697f 100644
--- a/progs/xdemos/glxgears.c
+++ b/progs/xdemos/glxgears.c
@@ -100,6 +100,7 @@ static GLfloat angle = 0.0;
 static GLboolean fullscreen = GL_FALSE;	/* Create a single fullscreen window */
 static GLboolean stereo = GL_FALSE;	/* Enable stereo.  */
 static GLboolean animate = GL_TRUE;	/* Animation */
+static GLboolean teartest = GL_FALSE;	/* Run a tear test. */
 static GLfloat eyesep = 5.0;		/* Eye separation. */
 static GLfloat fix_point = 40.0;	/* Fixation point distance.  */
 static GLfloat left, right, asp;	/* Stereo frustum params.  */
@@ -312,7 +313,53 @@ draw_gears(void)
       draw();
    }
 }
-
+void draw_tear_test(int n)
+{
+	GLint params[4];
+	GLint matrixmode;
+	GLboolean depthtest;
+	GLboolean lighting;
+	int bw = 10;
+	int w,h,x0;
+	glGetIntegerv(GL_VIEWPORT, params);
+	glGetIntegerv(GL_MATRIX_MODE, &matrixmode);
+	glGetBooleanv(GL_DEPTH_TEST, &depthtest);
+	glGetBooleanv(GL_LIGHTING, &lighting);
+	if(depthtest)glDisable(GL_DEPTH_TEST);
+	if(lighting)glDisable(GL_LIGHTING);
+	w = params[2];
+	h = params[3];
+	glMatrixMode(GL_PROJECTION);
+	glPushMatrix();
+	glLoadIdentity();
+	glOrtho(0, w, h, 0, 0, 1);
+	glMatrixMode(GL_MODELVIEW);
+	glPushMatrix();
+	glLoadIdentity();
+
+	if (n & 1)glColor3f(1.0,1.0,1.0);
+	else glColor3f(0,0,0);
+
+	glBegin(GL_QUADS);
+	glVertex2i(0, 0);
+	glVertex2i(0, h);
+	glVertex2i(bw, h);
+	glVertex2i(bw, 0);
+
+	x0 = w - bw;
+	glVertex2i(x0, 0);
+	glVertex2i(x0, h);
+	glVertex2i(x0 + w, h);
+	glVertex2i(x0 + w, 0);
+	glEnd();
+
+	glPopMatrix();
+	glMatrixMode(GL_PROJECTION);
+	glPopMatrix();
+	glMatrixMode(matrixmode);
+	if(depthtest)glEnable(GL_DEPTH_TEST);
+	if(lighting)glEnable(GL_LIGHTING);
+}
 
 /** Draw single frame, do SwapBuffers, compute FPS */
 static void
@@ -335,6 +382,7 @@ draw_frame(Display *dpy, Window win)
    }
 
    draw_gears();
+   if(teartest)draw_tear_test(frames);
    glXSwapBuffers(dpy, win);
 
    frames++;
@@ -637,6 +685,7 @@ usage(void)
    printf("  -fullscreen             run in fullscreen mode\n");
    printf("  -info                   display OpenGL renderer info\n");
    printf("  -geometry WxH+X+Y       window geometry\n");
+   printf("  -teartest               Output small alternately colored sidebars.\n");
 }
  
 
@@ -666,6 +715,9 @@ main(int argc, char *argv[])
       else if (strcmp(argv[i], "-fullscreen") == 0) {
          fullscreen = GL_TRUE;
       }
+      else if (strcmp(argv[i], "-teartest") == 0) {
+         teartest = GL_TRUE;
+      }
       else if (i < argc-1 && strcmp(argv[i], "-geometry") == 0) {
          XParseGeometry(argv[i+1], &x, &y, &winWidth, &winHeight);
          i++;