Below is a script that demonstrates the ~1 per second glitch I am observing on 2400SK (Firmware: 077.00E09593A) with a simple 60FPS animation:-
' ----------------------------------------------------------------------------
' Vertical Synchronisation Glitch Demo
'
' On some platforms there is now (7.00 firmware) an intermittent
' (~1 per second) failure to SwapBuffers at 60FPS, even for animation times
' less than 4mSecs.
'
' This can be observed as tearing and/or juddering of the vertical bars
' and is reflected in the displayed frame times. The average should
' settle to 16,666 uSecs, the instantaneous value should dither between
' 16 and 17 mSecs.
'
' - left/right buttons adjust simulated animation time +/-1 ms
' ----------------------------------------------------------------------------
Library "v30/bslCore.brs"
' ----------------------------------------------------------------------------
' ----------------------------------------------------------------------------
sub main ()
' Log system info so we know when we are comparing chalk and cheese
'
log_system_info()
' Handy Facts
'
VIDEO_FIELD_MS = 1000.0 / 60.0
' Initialise various resources
'
ecodes = bslUniversalControlEventCodes()
clk = CreateObject("roTimespan")
port = CreateObject("roMessagePort")
screen = CreateObject("roScreen", TRUE)
screen.SetMessagePort(port)
' Prepare font to display statistics on screen
'
font = CreateObject("roFontRegistry").GetDefaultFont()
txt_height = font.getOneLineHeight()
txt_color = &h60ff60ff
txt_margin = 100
' Create some animated stripes to illustrate tearing and judders.
'
num_stripes = 10
stripes = []
for x = 0 to screen.getWidth()-1 step screen.getWidth()/num_stripes
stripes.push(VerticalStripe(screen.getWidth(), screen.getHeight(), x))
end for
' Simulated frame animation time (target & moving average)
'
animation_target_ms = 4
animation_avg_filter = jcEWMAFilter(0.995, animation_target_ms * 1000)
last_animation_overrun_ms = animation_target_ms
' Frame timing stats.
'
last_frame_start = INVALID
frame_avg_filter = jcEWMAFilter(0.995, VIDEO_FIELD_MS * 1000)
last_frame_overrun_ms = 17
' Do initial buffer swap before we start timing loop
'
screen.clear(0)
screen.SwapBuffers()
screen.clear(0)
' Spin around SwappingBuffers and monitoring how long field/frame takes.
'
while TRUE
screen.SwapBuffers()
this_frame_start = clk.TotalMilliseconds()
' Handle any events
' - left/right buttons adjust simulated animation time +/-1 ms
'
msg = port.GetMessage()
if type(msg)="roUniversalControlEvent" then
ecode = msg.GetInt()
if ecode = ecodes.BUTTON_RIGHT_PRESSED then
animation_target_ms = animation_target_ms + 1
else if ecode = ecodes.BUTTON_LEFT_PRESSED then
animation_target_ms = animation_target_ms - 1
else if ecode = ecodes.BUTTON_UP_PRESSED then
stop ' debug
end if
end if
screen.clear(0)
' Animate & render the vertical stripes
'
for each stripe in stripes
stripe.animate(screen)
end for
' Calculate & render statistics.
'
if last_frame_start <> INVALID then
' Calc
last_frame_ms = this_frame_start - last_frame_start
frame_avg_us = int(frame_avg_filter.update(last_frame_ms * 1000))
animation_avg_us = int(animation_avg_filter.update(last_animation_ms * 1000))
if last_frame_ms > 17 then
last_frame_overrun_ms = last_frame_ms
end if
if last_animation_ms > animation_target_ms then
last_animation_overrun_ms = last_animation_ms
end if
' Render
x = txt_margin
y = txt_margin
screen.drawText("Vertical Synchronisation Glitch Demo", x, y, txt_color, font)
y = y + 2 * txt_height
screen.drawText("Animation target: " + animation_target_ms.toStr() + " ms (L = -1, R = +1)", x, y, txt_color, font)
y = y + txt_height
screen.drawText("Animation actual: " + last_animation_ms.toStr() + " ms (Avg: " + animation_avg_us.toStr() + " us, Last overrun: " + last_animation_overrun_ms.toStr() + " ms)", x, y, txt_color, font)
y = y + txt_height
screen.drawText("Frame actual: " + last_frame_ms.toStr() + "ms (Avg: " + frame_avg_us.toStr() + " us, Last overrun: " + last_frame_overrun_ms.toStr() + " ms)", x, y, txt_color, font)
endif
' Spin until the simulated animation time has elapsed.
'
this_animation_ms = clk.TotalMilliseconds() - this_frame_start
while this_animation_ms < animation_target_ms
this_animation_ms = clk.TotalMilliseconds() - this_frame_start
end while
' Go round again
'
last_frame_start = this_frame_start
last_animation_ms = this_animation_ms
end while
end sub
' ----------------------------------------------------------------------------
' Animated Vertical White Stripe
' ----------------------------------------------------------------------------
function VerticalStripe (cw as Integer, ch as Integer, x0 as Integer) as Object
this = {}
this.cw = cw
this.x = x0
this.w = 50
this.h = ch
this.dx = 4
this.clr = &h808080ff
' Animate and render this stripe to canvas.
'
this.animate = function (canvas as Object) as Void
this = m
this.x = this.x + this.dx
if this.x > this.cw then
this.x = this.x - (this.cw + this.w)
end if
canvas.drawRect(this.x, 0, this.w, this.h, this.clr)
end function
return this
end function
' ----------------------------------------------------------------------------
' Exponentially Weighted Moving Average (EWMA) filter
'
' Yt = Xt + α ( Yt-1 - Xt)
' ----------------------------------------------------------------------------
function jcEWMAFilter(alpha as Float, avg0 as Float) as Object
this = {}
this.alpha = alpha
this.avg = avg0
' Insert new sample, returns updated average.
'
this.update = function (x as Float) as Float
this = m
this.avg = x + (this.alpha * (this.avg - x))
return this.avg
end function
return this
end function
' ----------------------------------------------------------------------------
' Log basic system info
' ----------------------------------------------------------------------------
sub log_system_info()
di = CreateObject("roDeviceInfo")
print " Device: "; di.GetDeviceUniqueId()
print " Model: "; di.GetModel(); " ("; di.GetModelDisplayName(); ")"
print "Firmware Version: "; di.GetVersion()
md = di.GetModelDetails()
print " Vendor Name: "; md.VendorName
print " Model Number: "; md.ModelNumber
ai = CreateObject("roAppInfo")
print " App: "; ai.GetTitle(); " ("; ai.GetVersion(); ")"
print " DevID: "; ai.GetDevID()
end sub
