Advanced Scripting Tips - Revision history

Raffriff42: add link

2016-01-05T01:17:27Z

add link

← Older revision		Revision as of 03:17, 5 January 2016
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	=====Introducting GScript=====		=====Introducting GScript=====

	There is a plugin called [~~http://forum.doom9.org/showthread.php?t=147846~~ GScript] which adds new capabilities to the Avisynth language. This can be an alternative to using recursive functions. Here is an example of the factorial function mentioned under Recursion, but written in GScript:		There is a plugin called [[GScript]] which adds new capabilities to the Avisynth language. This can be an alternative to using recursive functions. Here is an example of the factorial function mentioned under Recursion, but written in GScript:

	messageclip(string(factorial(5)))		messageclip(string(factorial(5)))

Raffriff42: remove ref to Manual

2014-09-21T16:18:38Z

remove ref to Manual

← Older revision		Revision as of 18:18, 21 September 2014
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	The comparison can't recognize that they're different numbers. If you do int(float(n1)), then it gets recognized as 16777476.		The comparison can't recognize that they're different numbers. If you do int(float(n1)), then it gets recognized as 16777476.

	The reason is that floats in Avisynth are 32bit numbers with 24bit mantissa, which means they can hold numbers only up to +-16777216 accurately. If you try to store 16777216+1 as a float, it will be imprecise. The comparison operator returns true even though the numbers are different because, the expression is temporarily converted to float, which is less precise than int, and lower bits of the numbers are truncated. If there is a float in an expression, both sides are converted to float first. This is called promotion~~. The current manual doesn~~'~~t explicitly state the rules for promotion~~, ~~but refers to using~~ C rules. This is explained further at [http://en.wikipedia.org/wiki/Type_conversion wikipedia: Type conversion]		The reason is that floats in Avisynth are 32bit numbers with 24bit mantissa, which means they can hold numbers only up to +-16777216 accurately. If you try to store 16777216+1 as a float, it will be imprecise. The comparison operator returns true even though the numbers are different because, the expression is temporarily converted to float, which is less precise than int, and lower bits of the numbers are truncated. If there is a float in an expression, both sides are converted to float first. This is called ''promotion'', and uses C language rules. This is explained further at [http://en.wikipedia.org/wiki/Type_conversion wikipedia: Type conversion]

	[[Category:Advanced topics]]		[[Category:Advanced topics]]

Raffriff42: cleanup

2014-09-19T03:39:19Z

cleanup

Raffriff42: Category:Advanced topics + formatting

2014-09-19T03:36:32Z

Category:Advanced topics + formatting

← Older revision		Revision as of 05:36, 19 September 2014
Line 1:		Line 1:
	~~[[Category:Advanced topics]]~~		=====An example of using recursion=====

	~~====An example of using recursion====~~		messageclip(string(factorial(5)))
			function factorial(int n) {
			n<2?1:factorial(n-1)*n
			}

	~~messageclip(string(factorial(5)))~~
	~~function factorial(int n) {~~
	~~n<2?1:factorial(n-1)*n~~
	}
	How this works: let's use factorial(2) as an example. First we test		How this works: let's use factorial(2) as an example. First we test
	n<2?		n<2?
Line 16:		Line 15:

	Here is an example recursive function that works with video.		Here is an example recursive function that works with video.
	stackverticaln(colorbars(height=240),2)		stackverticaln(colorbars(height=240),2)
	function stackverticaln(clip v, int n) {		function stackverticaln(clip v, int n) {
	n<2?v:stackvertical(v,stackverticaln(v,n-1))		n<2?v:stackvertical(v,stackverticaln(v,n-1))
	}		}

	In this example we follow the same pattern: we return the argument unchanged if n<2, but perform an operation involving "current" and the n-1 version of our function.		In this example we follow the same pattern: we return the argument unchanged if n<2, but perform an operation involving "current" and the n-1 version of our function.
Line 38:		Line 37:
	There is in fact a way to generalize this:		There is in fact a way to generalize this:
	#Shows how a for-next loop can be emulated with generalrecursion		#Shows how a for-next loop can be emulated with generalrecursion
	demo=0#try also demo 1,2		demo=0 #try also demo 1,2
	select (demo, stackverticaln(colorbars(height=240),2), \		select (demo, stackverticaln(colorbars(height=240),2), \
	messageclip(string(factorial(5))), \		messageclip(string(factorial(5))), \
Line 64:		Line 63:
	}		}

	====Introducting GScript====		=====Introducting GScript=====

	There is a plugin called ~~GScript~~ [http://forum.doom9.org/showthread.php?t=147846] which adds new capabilities to the Avisynth language. This can be an alternative to using recursive functions. Here is an example of the factorial function mentioned under Recursion, but written in GScript:		There is a plugin called [http://forum.doom9.org/showthread.php?t=147846 GScript] which adds new capabilities to the Avisynth language. This can be an alternative to using recursive functions. Here is an example of the factorial function mentioned under Recursion, but written in GScript:

	messageclip(string(factorial(5)))		messageclip(string(factorial(5)))
Line 79:		Line 78:
	}		}

	====Weave 3 clips and the Pointresize trick (and issues)====		=====Weave 3 clips and the Pointresize trick (and issues)=====

	colorbars(width=640/3)		colorbars(width=640/3)
	r=RGBAdjust(g=0,b=0)		r=RGBAdjust(g=0,b=0)
	g=RGBAdjust(r=0,b=0)		g=RGBAdjust(r=0,b=0)
	b=RGBAdjust(r=0,g=0)		b=RGBAdjust(r=0,g=0)
	weave3(r.turnright,g.turnright,b.turnright).turnleft#Makes a CRT monitor special effect		weave3(r.turnright,g.turnright,b.turnright).turnleft #Makes a CRT monitor special effect
	function weave3(clip a, clip b, clip c) {~~#vertically interleave 3 clips~~
	x=a#what is x? It's the line which will get deleted. It doesn't matter what you set here, it could be any of the inputs		#vertically interleave 3 clips
	a.isrgb?interleave(x,b,a,c):interleave(a,c,b,x)#0 1 2 3->01 23->0213->213 or abc in rgb; 021 or xab in yuv		function weave3(clip a, clip b, clip c)
	#x,b,a,c for rgb; a,c,b,x for yv12		{
	assumefieldbased.assumetff.weave		x=a #what is x? It's the line which will get deleted.
	assumefieldbased.assumetff.weave#We've now weaved 4 times, so delete the 4th line next		#It doesn't matter what you set here, it could be any of the inputs
	pointresize(width,height*3/4)#Deletes every 4th line offset 0 in rgb;		a.isrgb?interleave(x,b,a,c):interleave(a,c,b,x)
	#deletes every 4th line offset 3 in yuv. This is the part that's colorspace dependant.
	}		#0 1 2 3->01 23->0213->213 or abc in rgb; 021 or xab in yuv
			#x,b,a,c for rgb; a,c,b,x for yv12

			assumefieldbased.assumetff.weave
			assumefieldbased.assumetff.weave #We've now weaved 4 times, so delete the 4th line next
			pointresize(width,height*3/4)
			#Deletes every 4th line offset 0 in rgb;
			#deletes every 4th line offset 3 in yuv.
			#This is the part that's colorspace dependant.
			}
	How it works: Weave is normally used to put back together a progressive clip which has been split into even and odd lines by SeparateFields. If you think about what it does in general, it takes every pair of frames and weaves them line by line. You might call this "thinking outside of the box", that is, you have to start thinking of what a function actually does as opposed to how you would normally use it. Anyhow, it should be obvious that we can call weave twice to weave the lines of 4 frames together into one. It seems impossible to weave only 3 times, however. That's true - you can't produce a 3x weave, but you can use a PointResize trick to delete lines in a specific way. Let's look more closely at how PointResize works.		How it works: Weave is normally used to put back together a progressive clip which has been split into even and odd lines by SeparateFields. If you think about what it does in general, it takes every pair of frames and weaves them line by line. You might call this "thinking outside of the box", that is, you have to start thinking of what a function actually does as opposed to how you would normally use it. Anyhow, it should be obvious that we can call weave twice to weave the lines of 4 frames together into one. It seems impossible to weave only 3 times, however. That's true - you can't produce a 3x weave, but you can use a PointResize trick to delete lines in a specific way. Let's look more closely at how PointResize works.

Line 130:		Line 138:
	You can perform geometric operations like Weave in multiples of 4 and yet operate on multiples of 3 by simply deleting the extra result		You can perform geometric operations like Weave in multiples of 4 and yet operate on multiples of 3 by simply deleting the extra result

	====Using Runtime Variables at Compile Time====		=====Using Runtime Variables at Compile Time=====

	Please review the section on [[The_script_execution_model]]. Most scripts that you write are executed during "compile time", while runtime scripts can only be executed in a ScriptClip or other runtime function. Sometimes it's useful to access the runtime special variables in your normal script. Note that they can only have a single, unchanging value in this case.		Please review the section on [[The_script_execution_model]]. Most scripts that you write are executed during "compile time", while runtime scripts can only be executed in a ScriptClip or other runtime function. Sometimes it's useful to access the runtime special variables in your normal script. Note that they can only have a single, unchanging value in this case.
Line 141:		Line 149:
	Will result in returning a float value of 64. Note that this '''only''' works for once, but you can find the runtime value for any frame. One potential use for this would be to calibrate recorded colorbars; extract one frame from your recording, then use crop statements to isolate each of the 7 colors bars, and find averageluma for each. The script can then report if you need to increase brightness or contrast during recording. This isn't a supported feature, but will probably remain. Tested in 2.58.		Will result in returning a float value of 64. Note that this '''only''' works for once, but you can find the runtime value for any frame. One potential use for this would be to calibrate recorded colorbars; extract one frame from your recording, then use crop statements to isolate each of the 7 colors bars, and find averageluma for each. The script can then report if you need to increase brightness or contrast during recording. This isn't a supported feature, but will probably remain. Tested in 2.58.

	====Casting/Promotion and Floating Point Traps====		=====Casting/Promotion and Floating Point Traps=====

	The float conversion of large numbers is imprecise. Example:		The float conversion of large numbers is imprecise. Example:
Line 155:		Line 163:

	The reason is that floats in Avisynth are 32bit numbers with 24bit mantissa, which means they can hold numbers only up to +-16777216 accurately. If you try to store 16777216+1 as a float, it will be imprecise. The comparison operator returns true even though the numbers are different because, the expression is temporarily converted to float, which is less precise than int, and lower bits of the numbers are truncated. If there is a float in an expression, both sides are converted to float first. This is called promotion. The current manual doesn't explicitly state the rules for promotion, but refers to using C rules. This is explained further at [http://en.wikipedia.org/wiki/Type_conversion wikipedia: Type conversion]		The reason is that floats in Avisynth are 32bit numbers with 24bit mantissa, which means they can hold numbers only up to +-16777216 accurately. If you try to store 16777216+1 as a float, it will be imprecise. The comparison operator returns true even though the numbers are different because, the expression is temporarily converted to float, which is less precise than int, and lower bits of the numbers are truncated. If there is a float in an expression, both sides are converted to float first. This is called promotion. The current manual doesn't explicitly state the rules for promotion, but refers to using C rules. This is explained further at [http://en.wikipedia.org/wiki/Type_conversion wikipedia: Type conversion]

			[[Category:Advanced topics]]

Raffriff42: Category:Advanced topics, su

2014-09-19T03:21:56Z

Category:Advanced topics, su

← Older revision		Revision as of 05:21, 19 September 2014
Line 1:		Line 1:
	~~'''~~An example of using recursion~~'''~~		[[Category:Advanced topics]]

			====An example of using recursion====

	messageclip(string(factorial(5)))		messageclip(string(factorial(5)))
Line 21:		Line 23:
	In this example we follow the same pattern: we return the argument unchanged if n<2, but perform an operation involving "current" and the n-1 version of our function.		In this example we follow the same pattern: we return the argument unchanged if n<2, but perform an operation involving "current" and the n-1 version of our function.

	How to think about recursion		'''How to think about recursion'''

	In the second example, you can think of what it's doing this way:		In the second example, you can think of what it's doing this way:
Line 62:		Line 64:
	}		}

	~~'''~~Introducting GScript~~'''~~		====Introducting GScript====

	There is a plugin called GScript [http://forum.doom9.org/showthread.php?t=147846] which adds new capabilities to the Avisynth language. This can be an alternative to using recursive functions. Here is an example of the factorial function mentioned under Recursion, but written in GScript:		There is a plugin called GScript [http://forum.doom9.org/showthread.php?t=147846] which adds new capabilities to the Avisynth language. This can be an alternative to using recursive functions. Here is an example of the factorial function mentioned under Recursion, but written in GScript:
Line 77:		Line 79:
	}		}

	~~'''~~Weave 3 clips and the Pointresize trick (and issues)~~'''~~		====Weave 3 clips and the Pointresize trick (and issues)====

	colorbars(width=640/3)		colorbars(width=640/3)
Line 114:		Line 116:
	and if you weave again you get a,c;b,d;e,g;f,h... thus you have to be aware of the order that your frames will get weaved when you weave more than once. How can we rearrange the input to interleave to produce the order x,a,b,c when it will display as a,c,b,d? The first and final lines in the group of 4 don't change, but the middle two do, thus the answer is x,b,a,c.		and if you weave again you get a,c;b,d;e,g;f,h... thus you have to be aware of the order that your frames will get weaved when you weave more than once. How can we rearrange the input to interleave to produce the order x,a,b,c when it will display as a,c,b,d? The first and final lines in the group of 4 don't change, but the middle two do, thus the answer is x,b,a,c.

	Putting it together		'''Putting it together'''

	After understanding how two weaves work, we deduce that our clips must be interleaved in the order x,b,a,c and PointResize'd to 3/4 height. When we write our script it works fine, but we notice that in YUV modes it doesn't work.		After understanding how two weaves work, we deduce that our clips must be interleaved in the order x,b,a,c and PointResize'd to 3/4 height. When we write our script it works fine, but we notice that in YUV modes it doesn't work.

	The PointResize Issue		'''The PointResize Issue'''

	In RGB, PointResize deletes the first of each group of 4 lines. However, in YUV modes, it deletes the '''last''' of each group of 4 lines. For this reason we had to test if the clip is RGB and adjust the interleave order as necessary. This difference exists in 2.58; and is undocumented in the current documentation which comes with the program. PointResize will still produce an image that looks fine and be the proper size, but it's still inconsistent in how it does that in various colorspaces.		In RGB, PointResize deletes the first of each group of 4 lines. However, in YUV modes, it deletes the '''last''' of each group of 4 lines. For this reason we had to test if the clip is RGB and adjust the interleave order as necessary. This difference exists in 2.58; and is undocumented in the current documentation which comes with the program. PointResize will still produce an image that looks fine and be the proper size, but it's still inconsistent in how it does that in various colorspaces.

	In Summary		'''In Summary'''

	You can use PointResize, with care, to delete specific lines in an image		You can use PointResize, with care, to delete specific lines in an image
Line 128:		Line 130:
	You can perform geometric operations like Weave in multiples of 4 and yet operate on multiples of 3 by simply deleting the extra result		You can perform geometric operations like Weave in multiples of 4 and yet operate on multiples of 3 by simply deleting the extra result

	~~'''~~Using Runtime Variables at Compile Time~~'''~~		====Using Runtime Variables at Compile Time====

	Please review the section on [[The_script_execution_model]]. Most scripts that you write are executed during "compile time", while runtime scripts can only be executed in a ScriptClip or other runtime function. Sometimes it's useful to access the runtime special variables in your normal script. Note that they can only have a single, unchanging value in this case.		Please review the section on [[The_script_execution_model]]. Most scripts that you write are executed during "compile time", while runtime scripts can only be executed in a ScriptClip or other runtime function. Sometimes it's useful to access the runtime special variables in your normal script. Note that they can only have a single, unchanging value in this case.
Line 139:		Line 141:
	Will result in returning a float value of 64. Note that this '''only''' works for once, but you can find the runtime value for any frame. One potential use for this would be to calibrate recorded colorbars; extract one frame from your recording, then use crop statements to isolate each of the 7 colors bars, and find averageluma for each. The script can then report if you need to increase brightness or contrast during recording. This isn't a supported feature, but will probably remain. Tested in 2.58.		Will result in returning a float value of 64. Note that this '''only''' works for once, but you can find the runtime value for any frame. One potential use for this would be to calibrate recorded colorbars; extract one frame from your recording, then use crop statements to isolate each of the 7 colors bars, and find averageluma for each. The script can then report if you need to increase brightness or contrast during recording. This isn't a supported feature, but will probably remain. Tested in 2.58.

	~~'''~~Casting/Promotion and Floating Point Traps~~'''~~		====Casting/Promotion and Floating Point Traps====

	The float conversion of large numbers is imprecise. Example:		The float conversion of large numbers is imprecise. Example:
Line 152:		Line 154:
	The comparison can't recognize that they're different numbers. If you do int(float(n1)), then it gets recognized as 16777476.		The comparison can't recognize that they're different numbers. If you do int(float(n1)), then it gets recognized as 16777476.

	The reason is that floats in Avisynth are 32bit numbers with 24bit mantissa, which means they can hold numbers only up to +-16777216 accurately. If you try to store 16777216+1 as a float, it will be imprecise. The comparison operator returns true even though the numbers are different because, the expression is temporarily converted to float, which is less precise than int, and lower bits of the numbers are truncated. If there is a float in an expression, both sides are converted to float first. This is called promotion. The current manual doesn't explicitly state the rules for promotion, but refers to using C rules. This is explained further at http://en.wikipedia.org/wiki/Type_conversion		The reason is that floats in Avisynth are 32bit numbers with 24bit mantissa, which means they can hold numbers only up to +-16777216 accurately. If you try to store 16777216+1 as a float, it will be imprecise. The comparison operator returns true even though the numbers are different because, the expression is temporarily converted to float, which is less precise than int, and lower bits of the numbers are truncated. If there is a float in an expression, both sides are converted to float first. This is called promotion. The current manual doesn't explicitly state the rules for promotion, but refers to using C rules. This is explained further at [http://en.wikipedia.org/wiki/Type_conversion wikipedia: Type conversion]

Admin: 1 revision

2013-05-10T12:05:56Z

1 revision

← Older revision	Revision as of 14:05, 10 May 2013
(No difference)

24.222.192.232 at 22:34, 9 November 2011

2011-11-09T22:34:56Z

New page

'''An example of using recursion'''

messageclip(string(factorial(5)))
function factorial(int n) {
n<2?1:factorial(n-1)*n
}
How this works: let's use factorial(2) as an example. First we test
n<2?
and in this case, it's not, so we go on to the next part:
factorial(n-1)*n
in which case we call factorial again, but with n-1. In this case, our "current" n is 2, so we call factorial(1). We do the test again:
n<2?1
and therefore return 1 as our answer. Now, go back to our "current" discussion, we get factorial(n-1)=1. So we find factorial(n-1)*2 or 1*2 and return the answer.

Here is an example recursive function that works with video.
stackverticaln(colorbars(height=240),2)
function stackverticaln(clip v, int n) {
n<2?v:stackvertical(v,stackverticaln(v,n-1))
}

In this example we follow the same pattern: we return the argument unchanged if n<2, but perform an operation involving "current" and the n-1 version of our function.

How to think about recursion

In the second example, you can think of what it's doing this way:
#n=1
v
#n=2
stackvertical(last,v)
#n=3
stackvertical(last,v)
You can also think of it this way:
#n=3
stackvertical(v,stackvertical(v,v))

There is in fact a way to generalize this:
#Shows how a for-next loop can be emulated with generalrecursion
demo=0#try also demo 1,2
select (demo, stackverticaln(colorbars(height=240),2), \
messageclip(string(factorial(5))), \
messageclip(string(sumofn(5))) \
)
function generalrecursion(val start, val current, int n, string func) {
s="n<2?start:"+func+"("+current+",generalrecursion(start,current,n-1,func))"
#return messageclip(s)
eval(s)
}
function mult(int x, int y) {
x*y
}
function add(int x, int y) {
x+y
}
function factorial(n) {
generalrecursion(1,"n",n,"mult")
}
function sumofn(n) {
generalrecursion(1,"n",n,"add")
}
function stackverticaln(clip v, int n) {
generalrecursion(v,"start",n,"stackvertical")
}

'''Introducting GScript'''

There is a plugin called GScript [http://forum.doom9.org/showthread.php?t=147846] which adds new capabilities to the Avisynth language. This can be an alternative to using recursive functions. Here is an example of the factorial function mentioned under Recursion, but written in GScript:

messageclip(string(factorial(5)))
function factorial(n) {
GScript("""
f=1
for (i=1,n) {
f=f*i
}
""")
f
}

'''Weave 3 clips and the Pointresize trick (and issues)'''

colorbars(width=640/3)
r=RGBAdjust(g=0,b=0)
g=RGBAdjust(r=0,b=0)
b=RGBAdjust(r=0,g=0)
weave3(r.turnright,g.turnright,b.turnright).turnleft#Makes a CRT monitor special effect
function weave3(clip a, clip b, clip c) {#vertically interleave 3 clips
x=a#what is x? It's the line which will get deleted. It doesn't matter what you set here, it could be any of the inputs
a.isrgb?interleave(x,b,a,c):interleave(a,c,b,x)#0 1 2 3->01 23->0213->213 or abc in rgb; 021 or xab in yuv
#x,b,a,c for rgb; a,c,b,x for yv12
assumefieldbased.assumetff.weave
assumefieldbased.assumetff.weave#We've now weaved 4 times, so delete the 4th line next
pointresize(width,height*3/4)#Deletes every 4th line offset 0 in rgb;
#deletes every 4th line offset 3 in yuv. This is the part that's colorspace dependant.
}
How it works: Weave is normally used to put back together a progressive clip which has been split into even and odd lines by SeparateFields. If you think about what it does in general, it takes every pair of frames and weaves them line by line. You might call this "thinking outside of the box", that is, you have to start thinking of what a function actually does as opposed to how you would normally use it. Anyhow, it should be obvious that we can call weave twice to weave the lines of 4 frames together into one. It seems impossible to weave only 3 times, however. That's true - you can't produce a 3x weave, but you can use a PointResize trick to delete lines in a specific way. Let's look more closely at how PointResize works.

If you have lines numbered 0,1,2,3,4,5,6,7... and you PointResize(Width,Height/2), you will be selecting every second line, thus 0,2,4,... If you PointResize(Width,Height*3/4) you will select 3 of every 4 lines, thus 1,2,3, 5,6,7,... It is this last case we are interested in, because we can in effect "delete" 1 of every 4 lines, thus eliminating one of our weaves. We now know we want a final weave in this order: x,a,b,c, where x will get deleted and can be set to anything.

We also have to look more closely at how weave works. Let's say our frames are a,b,c,d,e,f,g,h... then weave will do put our lines together as a,b;c,d;e,f;g,h...:

Before Weave
frame a frame b frame c frame d
a0 b0 c0 d0
a1 b1 c1 d1
a2 b2 c2 d2

After Weave
weaved 0 weaved 1
a0 c0
b0 d0
a1 c1
b1 d1

and if you weave again you get a,c;b,d;e,g;f,h... thus you have to be aware of the order that your frames will get weaved when you weave more than once. How can we rearrange the input to interleave to produce the order x,a,b,c when it will display as a,c,b,d? The first and final lines in the group of 4 don't change, but the middle two do, thus the answer is x,b,a,c.

Putting it together

After understanding how two weaves work, we deduce that our clips must be interleaved in the order x,b,a,c and PointResize'd to 3/4 height. When we write our script it works fine, but we notice that in YUV modes it doesn't work.

The PointResize Issue

In RGB, PointResize deletes the first of each group of 4 lines. However, in YUV modes, it deletes the '''last''' of each group of 4 lines. For this reason we had to test if the clip is RGB and adjust the interleave order as necessary. This difference exists in 2.58; and is undocumented in the current documentation which comes with the program. PointResize will still produce an image that looks fine and be the proper size, but it's still inconsistent in how it does that in various colorspaces.

In Summary

You can use PointResize, with care, to delete specific lines in an image

You can perform geometric operations like Weave in multiples of 4 and yet operate on multiples of 3 by simply deleting the extra result

'''Using Runtime Variables at Compile Time'''

Please review the section on [[The_script_execution_model]]. Most scripts that you write are executed during "compile time", while runtime scripts can only be executed in a ScriptClip or other runtime function. Sometimes it's useful to access the runtime special variables in your normal script. Note that they can only have a single, unchanging value in this case.

current_frame=0
blankclip(pixel_type="YV12",color_yuv=$408080)
avgluma=AverageLuma
messageclip(string(avgluma))

Will result in returning a float value of 64. Note that this '''only''' works for once, but you can find the runtime value for any frame. One potential use for this would be to calibrate recorded colorbars; extract one frame from your recording, then use crop statements to isolate each of the 7 colors bars, and find averageluma for each. The script can then report if you need to increase brightness or contrast during recording. This isn't a supported feature, but will probably remain. Tested in 2.58.

'''Casting/Promotion and Floating Point Traps'''

The float conversion of large numbers is imprecise. Example:

n1=16777475
n2=float(n1)
errmsg=n1<>n2?"Error: n1<>n2":"n1=n2"
messageclip(string(n1)+" "+string(n2)+" "+errmsg)

Results in "16777475 16777476.000000 n1=n2"

The comparison can't recognize that they're different numbers. If you do int(float(n1)), then it gets recognized as 16777476.

The reason is that floats in Avisynth are 32bit numbers with 24bit mantissa, which means they can hold numbers only up to +-16777216 accurately. If you try to store 16777216+1 as a float, it will be imprecise. The comparison operator returns true even though the numbers are different because, the expression is temporarily converted to float, which is less precise than int, and lower bits of the numbers are truncated. If there is a float in an expression, both sides are converted to float first. This is called promotion. The current manual doesn't explicitly state the rules for promotion, but refers to using C rules. This is explained further at http://en.wikipedia.org/wiki/Type_conversion

← Older revision		Revision as of 05:39, 19 September 2014
Line 36:		Line 36:

	There is in fact a way to generalize this:		There is in fact a way to generalize this:
	#Shows how a for-next loop can be emulated with generalrecursion		#Shows how a for-next loop can be emulated with generalrecursion
	demo=0 #try also demo 1,2		demo=0 #try also demo 1,2
	select (demo, stackverticaln(colorbars(height=240),2), \		select (demo, stackverticaln(colorbars(height=240),2), \
	messageclip(string(factorial(5))), \		messageclip(string(factorial(5))), \
	messageclip(string(sumofn(5))) \		messageclip(string(sumofn(5))) \
	)		)
	function generalrecursion(val start, val current, int n, string func) {		function generalrecursion(val start, val current, int n, string func) {
	s="n<2?start:"+func+"("+current+",generalrecursion(start,current,n-1,func))"		s="n<2?start:"+func+"("+current+",generalrecursion(start,current,n-1,func))"
	#return messageclip(s)		#return messageclip(s)
	eval(s)		eval(s)
	}		}
	function mult(int x, int y) {		function mult(int x, int y) {
	x*y		x*y
	}		}
	function add(int x, int y) {		function add(int x, int y) {
	x+y		x+y
	}		}
	function factorial(n) {		function factorial(n) {
	generalrecursion(1,"n",n,"mult")		generalrecursion(1,"n",n,"mult")
	}		}
	function sumofn(n) {		function sumofn(n) {
	generalrecursion(1,"n",n,"add")		generalrecursion(1,"n",n,"add")
	}		}
	function stackverticaln(clip v, int n) {		function stackverticaln(clip v, int n) {
	generalrecursion(v,"start",n,"stackvertical")		generalrecursion(v,"start",n,"stackvertical")
	}		}

	=====Introducting GScript=====		=====Introducting GScript=====
Line 90:		Line 90:
	{		{
	x=a #what is x? It's the line which will get deleted.		x=a #what is x? It's the line which will get deleted.
	#It doesn't matter what you set here, it could be any of the inputs		#It doesn't matter what you set here, it could be any of the inputs
	a.isrgb?interleave(x,b,a,c):interleave(a,c,b,x)		a.isrgb?interleave(x,b,a,c):interleave(a,c,b,x)