Straferunning

Straferunning (SR) combines running forward and moving sideways (strafing) at the same time, which results in moving faster than is possible in either direction alone. One of the advantages is being able to jump farther than is otherwise possible.

There are two straferunning speeds: SR40 and SR50. The 40 and 50 refer to the sideways (strafing) speed. The run-forward speed is 50 in either case. The total is a combination of both. These numbers refer to the magnitude of the input commands ("thrust"); the actual player movement speed is also influenced by friction drag and other factors.

SR40

SR40 combines Run, Forward, and a strafe-movement (Strafe-Left or Strafe-Right). For example, SR40 to the right may be activated by invoking Run, Forward, and Strafe-Right simultaneously. In the default keyboard arrangement: Shift+↑+.. It may also be activated using Run, Forward, Strafe-On, and Turn-Right: Shift+↑+Alt+→.

SR40 results in a speed of √(40² + 50²) = 64 (128% of normal run-forward speed) at an angle of arctan(40/50) = 38.7 degrees (to the right of directly forward). The engine does not perform any special calculations for this: The results are simply due to solving the triangle formed when the player moves forward 50 and sideways 40 in a single time unit.

The maximum jump distance (between platforms at equal height) is 181 units.

The Doom engine nominally caps player movement inputs at 50. However, for purposes of this limit, the engine considers Forward/Backward and Strafing separately. Thus, invoking both inputs at once allows one to exceed the nominal input limit, and thus run faster.

SR50

SR50 combines Run, Forward, strafe-movement, Strafe-On, and turn. For example, SR50 to the right may be activated using Run, Forward, Strafe-Right, Strafe-On, and Turn-Right. With the default keyboard arrangement: Shift+↑+.+Alt+→.

SR50 results in a speed of √(50² + 50²) = 70.7 (141% of normal run-forward speed) at an angle of arctan(50/50) = 45 degrees.

The maximum jump distance (between platforms at equal height) is 196 units.

SR50 is the fastest speed obtainable (except for wallrunning), but it is awkward to activate and it is not possible to turn while in SR50 mode.

SR50 is possible because the Doom engine adds multiple strafe inputs together and limits the resulting value to 50. A single strafe input produces a speed of 40 (assuming the sprint key is held), so two inputs must be used to reach the maximum speed. Mouse-strafing inputs can go all the way up to 50, so SR50 can be achieved with mouse alone.

Other notes

The use of mouse buttons and customized keyboard arrangements can facilitate straferunning: see Controls.

According to John Romero, straferunning did not come about until almost a year after Doom's release, and was unanticipated in the design of the original levels.

Sources

• The Doom Movement Bible by Andrew Stine (Linguica)
• Various other posts on the Doomworld forums

See also

• Glide
• Speedrun
• SR-50 automation
• Straferunning