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Framerate

FrameRate (Statement)​

Format​

framerate numeric_expression
framerate ( numeric_expression )

Description​

Holds the loop it is written in to a steady number of frames a second.

framerate waits until the next frame is due, not for a fixed length of time. Whatever the loop has already spent drawing comes out of the wait instead of being added to it, so the rate you ask for is the rate you get however heavy the scene is and however fast the computer is. A program written on a fast machine keeps its speed on a slow one, and runs slower only when a single frame genuinely takes longer than its share of a second.

Write it once in the loop, usually next to Refresh:

fastgraphics
while true
   clg
   gosub draw
   refresh
   framerate 60
end while

The first framerate of a run does not wait -- it starts the clock. Every one after it waits for its turn.

If a frame overruns, which is to say it took longer than one over the rate, framerate does not try to win the time back by running a burst of short frames afterwards. It starts counting afresh from the moment the slow frame ended, so one heavy frame costs one heavy frame and nothing more.

framerate 0 takes the cap off and forgets the timing, so a later framerate n begins again from that point. A rate of zero or less always means no cap.

The rate need not be a whole number and may be changed while the program runs. A rate higher than the loop can manage simply has no effect: framerate sets a maximum, it cannot make a slow loop fast.

Like Pause, the wait ends at once if you press the Stop button.

framerate is not limited to drawing. Any loop that should run at a steady rate -- reading a port, stepping a simulation, printing a display -- can use it.

FrameRate or Pause?​

Pause waits for a length of time. framerate waits until a moment. In a loop that is the whole difference:

pause 1/60          # one frame's drawing PLUS a sixtieth of a second
framerate 60        # a sixtieth of a second COUNTING the drawing

So a loop ended with pause 1/60 always runs slower than sixty a second, and slower still as the drawing grows. Use Pause when you want to wait a set time, and framerate when you want a loop to run at a set rate.

Example​

# sixty frames at thirty a second should take two seconds,
# even though every frame has work in it
framerate 30
start = msec
for frame = 1 to 60
   pause 0.005                  # stand in for the drawing
   framerate 30
next frame
print "60 frames took " + ((msec - start) / 1000) + " seconds"

start = msec
for frame = 1 to 60
   pause 0.005
   pause 1 / 30                 # the same loop paced with pause
next frame
print "with pause 1/30 instead: " + ((msec - start) / 1000) + " seconds"

will print something close to

60 frames took 2.0 seconds
with pause 1/30 instead: 2.384 seconds

The five milliseconds of work in each frame come out of the wait in the first loop and are added to it in the second.

See Also​

Clg, FastGraphics, Graphsize, Msec, Pause, Refresh

History​

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