Previewing with OpenGL

Any viewport that displays a Composite operator can be switched to OpenGL. The Particles operator automatically switches to an OpenGL view. Other operators cannot take advantage of OpenGL, so this preview option is not available.

Note: If you do not have a graphics card that includes OpenGL hardware, the software simulates the OpenGL results. Obviously, this is slower because there is no hardware acceleration.

When you switch a viewport to use OpenGL, the graphics in the viewport are generated by your OpenGL hardware. combustion sends OpenGL instructions to the graphics card, so the software-based renderer is not used.

The OpenGL preview can display most of the composite features in combustion. Refer to the chart that follows.

These Cards:	Support These Features:
All Cards	Layers and their transformations, transparency, surface properties, lights, shading, shadows, Normal and Add transfer modes.
Some Cards	Subtract transfer mode, reflections, Normal and Add reflection modes.
No Cards	All other transfer modes not already listed above, all other reflection modes not listed above, 3D Depth, 3D Shading, stencil layers.

Note: Surface properties include luminosity, diffuse level, specular level, and glossiness.

You can also set the display quality. For example, you can set the viewports to Best to use anti-aliasing and supersampling.

Features that are unsupported are automatically disabled or unavailable in the controls for the Composite operator. (For example, an unsupported transfer mode appears in lighter gray in the list.) This is also true if the required hardware is not present for a feature that is only supported on some cards.

In other words, if the required OpenGL extensions are not available for a feature, you cannot display it. If the composite uses such a feature when you show the OpenGL preview, the warning icon   appears in the status bar; double-click it to show a list of the error messages. A sample message is "Transfer mode 'Screen' is not supported in OpenGL. 'Normal' was used instead."

To use OpenGL in a viewport:

1. Show a composite in the viewport.

One way to do this is to double-click the Composite operator in the Workspace panel.

2. Do one of the following:
• Choose Window | Use OpenGL.
• Right-click (Windows) or Ctrl-click (Macintosh) the viewport and enable Use OpenGL.

When enabled, a checkmark appears next to the menu option. In the upper left corner of the viewport, the information includes "OpenGL." While playing the clip, the display rate in frames per second (fps) also appears.

When you use the OpenGL preview in a viewport, you lose some functionality. For example, the Window menu (or context menu in the viewport) no longer includes these options:

• View LUT
• View Mode
• Field Mode
• Show Safe Zones
• Show Wireframe Icons
• Use Aspect Ratio
• Onion Skin (and Onion Skin Settings)
• Show Marquee

However, Use Grid is added to the menu so you can show and hide the grid. To use this menu option, the Display Grid option must be enabled in the OpenGL preferences.

Note: The warning icon   on the status bar indicates when something is not displayed in the OpenGL preview; double-click it to show the error message.

OpenGL Diagnostics

From the Help menu, you can choose About OpenGL to display various OpenGL diagnostic information. For example, you can find which version of OpenGL driver is installed or what the maximum texture size is.

The About OpenGL dialog also shows the extensions for your card. If a feature does not work as expected, check if your OpenGL card supports the following extensions that combustion uses:

• GL_EXT_blend_color
• GL_EXT_blend_subtract
• GL_ARB_multitexture
• GL_ARB_texture_env_add
• GL_ARB_texture_env_combine
• GL_ARB_multisample
• WGL_ARB_pbuffer
• WGL_ARB_pixel_format

On NVIDIA video cards on the Windows platform, these extensions are also used:

• GL_NV_texture_rectangle
• GL_NV_register_combiners
• GL_NV_texture_shader