FSImp limits and measures its own execution time. This determines, per frame, how much of an ADD-ON file is to be interpreted, how much of a bitmap is loaded from file or moved into VRAM as well as other jobs.
Each X-Plane frame starts off on an empty canvas. Before each frame is complete, every polygon has to be rendered. FSImp adds many polygons to every frame. The exact number that it adds depends on the direction of view, the ADD-ON sceneries present and the recent FPS rates. FSImp also loads bitmaps as necessary and monitors FPS rates. It also interprets ADD-ON FS scenery files when loading a tile to generate models.
Other bottlenecks for frame rates can be the graphic card pixel fill rate and how well the graphic card can process bitmaps which contain translucent or transparent pixels (alpha).
Scenery designers often have difficulty with their products as it will run on a wide variety of different machines and settings. FSImp attempts to maintain frame rates on the fly (dynamically). Naturally it cannot do the impossible! It has a number of parameters to help maintain frame rates. Later version may attempt to automate these parameters. These are accessed via this dialog.
There is a closed loop "PID" control system to over-simplify models based on their distance.
This takes the present FPS error as input and this is multiplied by its proportional correction factor Kp. The result is used to determine which models are to be over-simplified. This attempts to maintain the target FPS rate.
When FSImp is maintaining small target rates (teleport, paused) then the X-Plane flight model and the reaction time to inputs will be delayed. In these cases it is not recommended to fly but rather perform preflight checks. If you want, then you may close the message dialog in which case FSImp returns to background processing and maintaining air/ground target FPS.
To estimate the maximum FPS use the debug dialog uncheck Draw and close all dialogs for a while
| Name | Description | Min | Max | Default |
| Calc time sec | FSImp performs some FPS calculations on a regular basis. This specifies the time interval in seconds. Too small consumes time, too large may make FSImp unresponsive. | 0.1 | 1.0 | |
| Teleport FPS | FSImp attempts to maintain this FPS rate after teleporting. Too small makes the sim unresponsive, too large prolongs the tile loading time. | 4 | ||
| Paused FPS | FSImp attempts to maintain this FPS rate when the sim is paused - usually p key. | 6 | ||
| Air FPS | FSImp attempts to maintain this FPS rate when in the air (flying). Too small makes flying unresponsive, too large may not be attainable and sceneries will not be displayed. | 16 | ||
| Ground FPS | FSImp attempts to maintain this FPS rate when on the ground (taxiing etc). | 12 | ||
| Toler FPS | An FPS tolerance to quieten FSImp a little. | 0.2 | ||
| State time min s | After drawing FSImp performs background work - BGL BMP monitoring, model regeneration. For this work to proceed more quickly, it can be given a time slice of every frame. | 0 | 0.01 | |
| Exec time % | Forces FSImp to consume a percentage of the target time for drawing plus background work each frame. | 0 | ||
| Dist delay | Objects distances do not have to be performed continuously. This specifies a time delay factor in seconds per nautical mile. When this is small, the number of objects and polygons displayed will react more quickly to FPS changes. If large then large FPS fluctuations, that change slowly, may occur | 0 | 1.5 | |
| Cull behind m | Objects that are more than this distance, in meters, behind the viewer are not displayed. | 150 | ||
| Cull backface | Polygons that face away from the viewer are not displayed. 0 removes no polygons, 1 removes all polygons | 0 | 1 | 0.25 |
| Cull extra deg | Objects and polygon to the left and right of the visible region plus this extra angle are not displayed. If too small, then as you turn objects will pop into view. If too large then many objects will be displayed unnecessarily and so hitting FPS | 0 | 90 | 10 |
| Small object m | The length, in meters, of a small object. | 2.0 | ||
| Small dist nm | Small objects are only shown when nearer than this distance, in nautical miles. | 0.2 | ||
| Filter airports | The X-Plane file APT.DAT is parsed to extract runway information. This file is large (about 15Mb). You can enter a list of ICAO prefixes separated by commas to quicken up the parsing of this file. eg K,E,LF,0 accepts US European French airports and all small airfields only. Note that 0 (zero) means airfields with a numerical part | |||
| Use cache | Information about models generated for a tile can be saved in a special folder for future visits. This increases the loading time on the first visit but reduces the loading time on further visits substantially. | No | Yes | Yes |
| Regen points/frm | Objects are continuously regenerated depending on distance and FPS rates (dynamic level of detail LOD). This parameter limits the number of points that are regenerated per frame for immediate drawing. If too small then partially drawn models will be visible. | 5000 | ||
| Regen ticks/frm | Limits the number of points that are regenerated per frame for later drawing. If too small then partially drawn models will be visible for longer. | 10000 | ||
| Regen points/frm | A close object has a minimum lifetime, in frames, before being regenerated | 15 | ||
| Object hold s | An object which goes out of view remains in memory for this time in case it is required again soon. | 30 | ||
| Far Kp | The proportional correction from FPS error to distant simplification. If too small then it takes a long time to reach FPS. If too big then the display will become unstable as objects will be alternately shown and hidden. | 1 | ||
| Pixel min | Polygons must have at least this area, in pixels, in order to be displayed | 5.0 | ||
| Pixel max | When FPS is below target, distant polygons must have at least this area, in pixels, in order to be displayed | 200 | ||
| Far dist nm | Beyond this distance, in nautical miles, objects are not displayed. | 10 | ||
| Scenery density | The scenery density can be selected between very sparse and very dense, or auto. Each ADD-ON FS scenery decides for itself which models to show depending on the scenery density. When Auto is selected FSImp dynamically sets the density depending on frame rates. | v.Dense | ||
| GL Display lists | A technique which may accelerate drawing on some graphic systems. | no | ||
| GL Element lists | A technique which may accelerate drawing on some graphic systems. | yes | ||
| GL Quads | Allow 4 sided (quads) or only 3 sided (tris) polygons. May accelerate drawing on some graphic systems. | yes | ||
| AGL gentle ft | When flying below this level (landing/takeoff), FSImp slows BGL interpretation and stops bitmap selecting into VRAM as these may cause stuttering | 100 | ||
| Quarter tile | Instead of 1x1 degree tiles, you may choose a quarter of this size. This can save on system RAM and loading time, but may force tiles to be loaded more often. | yes | ||
| Transparent mode | Models that use bitmaps that are partiall transparent/translucent must be sorted by distance before being displayed
| Model |