Gauge Overview - Types of Gauges
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The original type of Gauge used by FS98. It consists of a .gau file, which defines exactly one Gauge. Internally, .gau files are actually Windows .dll files, which are themselves almost the same as normal Windows executable programs. FS attaches a copy of each .gau file to itself when loading a panel.
The bitmaps which determine the look of the Gauge are stored as Resources in the file.
This works well, but is very Windows resource intensive. Each .gau takes up limited resources which results in a relatively low limit on the total number of Gauges which could exist on a panel. Also, Windows does not allow two instances of the same .dll file to be attached to FS98 at the same time. So if you needed two otherwise identical RPM Gauges (on a twin engine plane for example) you would need to have two separately named Gauges.
CFS introduced the concept of "Cluster Gauges". Each .gau file, although still in actuality a renamed .dll file, contains multiple Gauges internally. This reduced the load on Windows and improved Flight Sim performance. The upper limit on number of Gauges on a Panel was increased.
Also new was a scheme to include two versions of each bitmap in a Gauge, one "low resolution", and one "high resolution". CFS would determine, based on the display size when running, which version of the Gauge bitmap to display. (This also applied to background bitmaps).
FS2000 continued the use of Cluster Gauges, but added a parameter field in the panel.cfg file. This allowed some run-time specialization of the Gauge, for example the Gauge could be told to display the RPM of engine 1 or 2 based on the param.
FS2002 introduced a new Gauge type, based on the industry standard XML format. Each Gauge file still contains multiple Gauges, as before, but internally the new format is much different. Gauges are now distributed in compressed Windows CAB files, and internally they have a specific directory structure. Each Gauge's behaviour is described in an XML file. The associated bitmaps are found (usually) in two bitmap directories in the CAB archive named 640 and 1024, for the low and high resolution versions of the bitmaps.
XML Gauges can also exist in a subfolder of the main Flight Simulator Gauges directory. The structure is identical to the internal contents of the CAB file, but the files are extracted onto the disk. This speeds loading of FS2002.
Although slow to load, XML CAB file Gauges are easy to edit and manipulate -- you no longed need the programming tools required to create Windows .dll files. FS Panel Studio allows you to easily access and edit XML Gauges, as well as the bitmaps of any Gauge type.
FS2004 Gauges are functionally the same as FS2002 Gauges. However, Microsoft now allows Gauge files to be located in the Aircraft's Panel folder. For example, the Vickers Vimy has a CAB based set of XML Gauges named Vickers_Vimy.cab located in the Panel folder. NOTE: If you wish to use these Gauges in other Aircraft, first copy them to the common Gauges folder.