kens@JARGON.WHOI.EDU (Ken Stewart) (12/28/90)
Howdy Folks --
I'm writing a simple strip-chart application to display various
real-time data streams under X. I'm developing under XView 2.0 but using
Xlib calls for display functions. I've tried two approaches to "scroll" the
display: 1) copy an area of the drawable then draw one new line to connect
the new data point; 2) xor the old polyline to clear then xor the updated
polyline.
The bitblt approach gives the smoothest scrolling. The xor polyline
approach runs about 4 times faster on a SPARC-GX, but flickers annoyingly;
bracketing the drawing calls with server grab/ungrab doesn't help. Relative
speed would depend on the drawable area, but we need reasonably large
displayed areas for good viewable resolution (say, 1024x256).
I've included skeleton examples below. My questions are: 1) is there
a more efficient approach? 2) does anyone have a similar working application
or can point me to a PD source? 3) are there any comments on efficiency/
portability for other X environments? (our applications run mostly on Suns,
but must support remote displays on PC's, Mac's, and other workstations).
Thanks for any help.
Ken Stewart
Deep Submergence Laboratory voice: (508) 457-2000 x2644
Woods Hole Oceanographic Institution fax: (508) 457-2191
WHOI, Blake 109 internet: kens@jargon.whoi.edu
Woods Hole, MA 02543 omnet: k.stewart
**************************************************************************
1) BITBLT
.
.
/* scroll the display right */
XCopyArea( dpy, xwin, xwin, gc, 0, 0,
canvas_width - horiz_incr, canvas_height, horiz_incr, 0 );
/* clear a small region at left */
XClearArea( dpy, xwin, 0, 0, horiz_incr, canvas_height, False );
new_y = ...
/* connect the new data point */
XDrawLine( dpy, xwin, gc, horiz_incr, last_y, 0, new_y );
last_y = new_y;
.
.
2) XOR POLYLINE
.
.
XGrabServer( dpy );
/* clear last displayed polyline */
XDrawLines( dpy, xwin, xorgc, points, num_points, CoordModeOrigin );
/* code omitted here to shift y values in array of points */
.
.
points[0].y = ...
XDrawLines( dpy, xwin, xorgc, points, num_points, CoordModeOrigin );
XFlush( dpy );
XUngrabServer( dpy );
.
.
**************************************************************************stripes@eng.umd.edu (Joshua Osborne) (12/29/90)
In article <9012281317.AA10469@jargon.whoi.edu>, kens@JARGON.WHOI.EDU (Ken Stewart) writes: [...] You may wel get some more speed from this: > ************************************************************************** > > 1) BITBLT > . > . > /* scroll the display right */ > XCopyArea( dpy, xwin, xwin, gc, 0, min_height, > canvas_width - horiz_incr, canvas_height, horiz_incr, 0 ); [replce w/] canvas_width - horiz_incr, max_height, horiz_incr, 0 ); > > /* clear a small region at left */ > XClearArea( dpy, xwin, 0, 0, horiz_incr, canvas_height, False ); [replace w/] XClearArea( dpy, xwin, 0, min_height, horiz_incr, max_height, False ); > > new_y = ... > > /* connect the new data point */ > XDrawLine( dpy, xwin, gc, horiz_incr, last_y, 0, new_y ); > > last_y = new_y; > . > . Less bits to blt most of the time. Should end up being faster. (but you will have to track the max/min values correctly) -- stripes@eng.umd.edu "Security for Unix is like Josh_Osborne@Real_World,The Multitasking for MS-DOS" "The dyslexic porgramer" - Kevin Lockwood "Don't over-comment" - p151 The Elements of Programming Style 2nd Edition Kernighan and Plauger
mouse@LIGHTNING.MCRCIM.MCGILL.EDU (12/31/90)
> I'm writing a simple strip-chart application to display various > real-time data streams under X. I'm [...] using Xlib calls for > display functions. I've tried two approaches to "scroll" the > display: 1) copy an area of the drawable then draw one new line to > connect the new data point; 2) xor the old polyline to clear then xor > the updated polyline. > The bitblt approach gives the smoothest scrolling. The xor polyline > approach runs about 4 times faster on a SPARC-GX, but flickers > annoyingly [...]. > 2) XOR POLYLINE > XGrabServer( dpy ); > /* clear last displayed polyline */ > XDrawLines( dpy, xwin, xorgc, points, num_points, CoordModeOrigin ); > /* code omitted here to shift y values in array of points */ > XDrawLines( dpy, xwin, xorgc, points, num_points, CoordModeOrigin ); > XFlush( dpy ); > XUngrabServer( dpy ); You might try doing the polylines a bit differently. It would mean a little reworking of your code, but it should produce much less flicker to shift the lines one line at a time instead of erasing the old thing completely before drawing any of the new lines. You would need to use XDrawSegments for this, since the lines would no longer be connected, but I would expect it to reduce the flickering drastically. (I haven't tried it. You didn't provide enough to build a compilable program and I am not up to building a test program for it just now.) der Mouse old: mcgill-vision!mouse new: mouse@larry.mcrcim.mcgill.edu
kens@jargon.whoi.EDU (Ken Stewart) (01/04/91)
> > I'm writing a simple strip-chart application ... > I have helped some of our customers with a similar problem, although they > didn't use X. If you maintain a max and a min, and assuming your > fluctuations aren't too great, you can bitblt only the part of the window > which changes ... Dave -- Thanks for the reply; good suggestion. Unless I misunderstood you, though, it's a bit more complicated to keep track of min/max than a simple increment/decrement. If the current min or max scrolls off the end, you probably have to traverse the list of displayed values to replace it; easy to do, though, and not a big performance penalty compared with blitting. I couldn't get through to the return address on your message, so I'm posting this reply back to the net. -Ken
pete@iris49.UUCP (Pete Ware) (01/05/91)
When I was at SAIC I wrote some fairly nice widgets for displaying waveform data (i.e. stripchart like information). It dealt gracefully with displaying 24 hours (7 Mbytes) down to 1/100 of a second. Horizontal and vertical scales can be changed interactively. Contact jim@esosun.css.gov to see if it might be available. The following is from the README file. ---------------------------------------------------------------------- This is a set of widgets for displaying waveforms under the X Window System Version 11 Release 4. The following widgets implement display of a waveform with an optional scale on the left side and optional detections overlaying the waveform. The display may be scrolled left or right. An arbitrary number of waveform widgets may be created and displayed. The widgets handle color or monochrome screens of any resolution. Flexibility in selecting colors, fonts and other appropriate attributes make it easy to customize waveform display on an application by application and user by user basis. Each widget follows the X Toolkit Intrinsics and is compatible with any other widgets based on the Intrinsics. ---------------------------------------------------------------------- --pete Pete Ware / Biosym / San Diego CA / (619) 546-5532 uucp: scripps.edu!bioc1!pete Internet: bioc1!pete@scripps.edu