### Using Custom Display Modes

Although the SciTech SNAP Graphics Architecture exports a list of supported display modes, internally there is actually no real concept of a standard display mode. Instead SciTech SNAP Graphics maintains a profile of known display modes, and uses that profile to enumerate to applications what display modes are available. The profile of known display modes also includes supported refresh rates, and that information is used to create the GA_modeInfo information returned by the GetVideoModeInfo function. When the application calls the regular SetVideoMode function, internally the drivers end up calling the SetCustomVideoMode function with the resolution and CRTC timings for the known display mode taken from the mode profile.

Sometimes special applications may require the need to set a custom display mode that is not listed in the regular profile of known display modes. To set a completely custom display mode, you can call the SetCustomVideoMode function directly and pass in your own set of CRTC timings that match the display mode of choice (use GA_computeCRTCTimings to compute the CRTC timings with the GTF formulas). Note however that not all resolutions can be supported by all hardware (for instance some hardware requires the X resolution to be on 8 pixel boundaries, some 16 pixel boundaries). In order to determine if a desired custom resolution is actually supported by the hardware, you should call the GetCustomVideoModeInfo function. This function will properly round up the resolution parameters as necessary to support the mode on the underlying hardware.

Note: You can also add a custom display mode to the default mode profile as an alternative to always calling the SetCustomVideoMode function.

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