Render Form

Figure 4.13: The Render form

This form is used to create a file with an image of the currently displayed graphics scene. VMD can write input script files for a number of external rendering packages. These packages are listed in table 6.1. Once VMD creates a scene description in one of the supported formats, the particular package can use this file to create a final output image. See Chapter §  for more information on how rendering is performed.

Rendering

The rendering process works in two stages. The first step writes an input file for the image processing program selected in the Output Formats browser, and the second (optionally) starts the rendering process. The file is given the name entered in the Output Filename field; a default name is given when a new format is selected, so it is best to hold off entering the filename until after the file format is selected. Another way to select the filename is available by pressing the List... button, which opens up a file browser.

Pressing the Go button writes the data file. After that, the Render Command is executed. The default command should start the appropriate rendering program if it is available.

The fastest of the currently supported programs are Raster3D and Tachyon . The rendering command for Raster3D has been set up to call the programs program ipaste or xv when the RGB output file is finished. VMD will wait for the rendering to finish, which causes VMD to freeze, so you may want to run the job in the background. This can be done by enclosing the existing text with ()'s and putting an & at the end. For example, the way to make the Raster3D render command run in the background is:

        (render < %s -sgi %s.rgb; ipaste %s.rgb)&

Caveats

There are some issues to consider when using the rendering commands, which can lead to discrepancies between the scene displayed in the VMD graphics display window and the image generated by external rendering applications. These issues include:

• Geometry may look slightly different; in VMD curved surfaces are polygonalized and drawn using a number of polygonal facets, curved surfaces may be rendered entirely smoothly in the final output (which is generally looked upon as an improvement!)
• The rendered object colors or intensities may be slightly different due to different colormaps, gamma values, or lighting models; This is particularly true with the material properties used for performing complex shading. VMD's real-time rendering of these material properties is often simplistic or limited compared to full-fledged photorealistic renderers, so there can potentially be big differences between implementations of transparency, specular highlights, etc.
• Many of the external renderers do not support true orthographic rendering. This can bed ``faked'' by translating the camera very far away from the molecule, followed by zooming the camera so that the image size is acceptable again. This will significantly decrease the perspective effect, but is not a true orthographic projection.
• The rendering commands do not currently support stereo output, so even if the display is currently in stereo mode, a non-stereo perspective will be used for the rendering program input script; Rendering in stereo is accomplished by setting the display mode to ``left'', then rendering an image, followed by ``right'', and rendering again. This will yield a stereo pair to the best of VMD's ability with the external rendering program.
• The near and far clipping planes are ignored by all external renderers;
• Text is generally not available as a graphics primitive in the renderer scene languages, so label text will not appear, although the lines of bond, angle, etc. labels will be drawn. The only exception is in Postscript output, which supports text output.
• Dotted spheres are not drawn with dots.
• The background color may be black, as not all output formats support a background color other than black;