## Changing OpenGL Options

CAD and Graphic Setup dialog box - OpenGL tab

The Edit | Graphics Display Window | OpenGL menu option displays the OpenGL tab of the CAD and Graphic Setup dialog box. This allows you to change the OpenGL options that affect the display of the model in solid view mode. To change the part to solid view, see "Setting Up the Screen View" in the "Editing the CAD Display" chapter.

Dialog Box Item | Description
Desktop Settings area | There can be different OpenGL options for each desktop display setting. The Desktop Settings area shows what the current desktop settings are. Resolution Ratios of Different Monitor Sizes Wide screen monitors need a 1.6 ratio instead of a 1.3333 ratio used by normal monitors. For example, a resolution of 1200x1600 has a 1.3333 ratio (1600/1200) and works well for a normal size monitor, while a resolution of 1680x1050 has a 1.6 ratio, good for a wide screen monitor. If you use a wide screen monitor and your screen appears stretched (perhaps your circle features appear as ellipses in the Graphics Display window), use a 1.6 resolution ratio to resolve this problem.
Options area | The Options area controls the display characteristics of the model in solid view mode. Some combinations of these options may not be available because of limitations of your graphics card. Also, depending on how your graphics card supports hardware acceleration, some combinations of options may result in lowered graphics performance. If the current option settings will result in lowered performance, a warning message will appear at the bottom of the dialog box.

Double Buffering - When you select the Double Buffering check box, there are actually two display buffers: a front and a back buffer. The front buffer is what you see on the screen. When the screen has to be redrawn, such as when the model is rotated, the image has to be erased from the screen and the image redrawn in its new state. The erasing and drawing is done on the back buffer. You cannot see the actual erasing and drawing of the graphics. Once the graphics are drawn to the back buffer, the back buffer is swapped with the front buffer. This happens quickly so that any transition between the two buffers is virtually undetectable.

A display buffer is graphics memory used to store the image seen on your computer screen.

When the Double Buffering check box is cleared, or in other words, when there is only one display buffer, you can actually see the screen being erased and redrawn (albeit very quickly). The erasing and redrawing of the screen causes a flickering.

In summary, double buffering produces a more visually pleasing graphical display than single buffering.

Z-Buffer Depth - The Z-Buffer Depth list controls how much graphics memory is used for the z-buffer. The z-buffer determines which parts of a 3D model lie in front of other parts of the model. If you use insufficient bits for the z-buffer, visual artifacts may appear on the model in solid view mode. These artifacts are areas on the model that are drawn in front of other parts of the model when they should actually be hidden. These artifacts do not affect the accuracy of PC-DMIS but are simply inaccuracies in the visual display of the model.

Color Depth - The Color Depth list controls how much graphics memory your system uses for the color information of each pixel. This number is usually dependent on the color depth of the Desktop Settings.

Antialiasing - The Antialiasing combo box allows the level of antialiasing by specifying the number of multisamples. 2x antialiasing will sample each pixel twice. 4x antialiasing will sample each pixel four times and so on. When antialiasing is enabled, each pixel is sampled multiple times at slightly different locations within the pixel. An average color is computed from these samples to determine the final pixel color. This effectively reduces the model's jagged edges in the graphics window. Higher antialiasing settings will produce better visual results at the expense of slower system performance.

The Antialiasing options are determined by the capabilities of the graphics accelerator. Some graphics accelerators may support 64x antialiasing while others may only support up to 16x or may not support it at all. If antialiasing is supported, the default is 8x - if not supported, the default is Off.

Tessellation area | The Tessellation area controls the drawn image by setting a tessellation multiplier in the Multiplier Value box. PC-DMIS multiplies the Multiplier Value by the tessellation value for the given CAD system. These values are then used in the generation of the shaded image.

The tessellation value is the default value used to break up surfaces into patches for shading.

The tesselation multiplier updates the Graphics Display window immediately once you click outside of the Multiplier Value box or press TAB to move to a different item on the dialog box.

Important: Modifying this tessellation value will affect perimeter scans because PC-DMIS computes the distance around a curved surface edge by adding the segment lengths of a polyline that represents that edge. The tessellation multiplier changes the length of each polyline segment (lower tolerances result in smaller segments). While the actual perimeter points will lie exactly on the edge curve, different tessellation tolerances will result in small differences in where each point is located along the edge curve.

Pointcloud | The Pointcloud section provides the user with the ability to show the pointcloud when the Always visible check box is checked even if CAD hides it. The pointcloud will be hidden if the Pointcloud Always visible check box is unchecked, such as if the CAD hides it or if the cop label is set to Hide Feature.

Point size - Specifies the size, in pixels, for the points in the pointcloud.