Making movies with IDL, part II
, I gave an example of making a movie with IDLffVideoWrite and DG. This week, I’ll use NG to make a similar movie.
The example is again written as a procedure. Start the program by declaring some test data and making a simple visualization:
data = dist(30)
s = surface(data, color='blue', /buffer)
c = contour(data, n_levels=10, zvalue=0.0, /overplot)
t = text(0.5, 0.9, 'IDL Movie Example - NG', alignment=0.5, font_size=16)
Note that the BUFFER property is set on the call to SURFACE. It forces the visualization to be rendered to an offscreen buffer; it’s the analog to the DG Z buffer device.
Next, set up the IDLffVideoWrite object:
video_file = 'ng_movie_ex.mp4'
video = idlffvideowrite(video_file)
framerate = 10
wdims = s.window.dimensions
stream = video.addvideostream(wdims, wdims, framerate)
As in last week’s example, I’ve chosen to output to an MPEG-4 video file. The dimensions of the movie are taken from the dimensions of the buffer (the default, 640 x 512) created in the call to the SURFACE function.
The next step is to make and load frames into the movie file:
nframes = 50
for i=0, nframes-1 do begin
s.rotate, 1.0, /yaxis ; degrees
c.zvalue = i*max(s.zrange)/nframes ; data coordinates
timestamp = video.put(stream, s.copywindow())
On each iteration of the loop:
- The Rotate method rotates the surface by one degree about the global y-axis of the visualization (this is from Object Graphics; +x is right, +y is up, +z is pointed toward you)
- By modifying its ZVALUE property, the contour plot moves up by a fraction of the total height of the surface.
- The CopyWindow method (the analog to the TVRD function in DG) takes a picture of the visualization in the buffer. The picture is a pixel-interleaved RGB image, with dimensions 3 x 640 x 512.
- The Put method of IDLffVideoWrite loads this picture as a frame into the video stream.
End the program by destroying the video object and the buffered graphic:
print, 'File "' + video_file + '" written to current directory.'
Click below to see the resulting video on the VIS YouTube channel
- I have a more complex NG movie example that uses the SetData method introduced in 8.1. You can download it from this [exelisvis.com] page; look for the “What's New in IDL 8.1” webinar files, grab them and look for the program called VIDEO_WRITE1. I may give this example the blog treatment at a later point.