GScript - language extensions for Avisynth

[Gavino]

This is something I started as a 'proof of concept' for my own amusement.
As I think some people will find it useful, I am making it generally available.

GScript is a plugin that extends the Avisynth scripting language to provide additional control-flow constructs:
multi-line conditionals (if-then-else blocks), 'while' loops and 'for' loops.
Rather than trying to simulate these constructs with functions, GScript effectively extends the language syntax, making it easy to use the new constructs in a natural way and in arbitrary combinations.

Here are the constructs in detail:

'if' statement

if ( condition ) {
  statements
}
else {
  statements
}

where condition is any boolean expression.
The statements can be any Avisynth statements, including the GScript extensions themselves, and so the new constructs can be nested.
The else part may be omitted (equivalent to else {}).

GScript also provides the 'else if' construct (optionally repeated to create a chain of conditionals). Thus

if ( condition ) {
  statements
}
else if ( condition ) {
  statements
}
else if (...) { ... }
...
else {
  statements
}

'while' loop

while ( condition ) {
  statements
}

The statements are repeated while the condition is true.

Example:

while (Height() < h) {
  StackVertical(last, c) 
}

'for' loop

for ( variable = init , limit , step ) {
  statements
}

init, limit and step are integer expressions, with step non-zero. step is optional and defaults to 1.

First the variable is set to the value of init.
The statements are repeated until the exit condition is met,
ie variable exceeds limit (if step > 0), or is less then limit (if step < 0).
After each iteration, variable is incremented by step.
If the initial value satisfies the exit condition, the number of iterations will be zero.

Example:

for (i=1, nBlurs) {
  Blur(0.5)
}

Using GScript
Once the plugin is loaded (either via LoadPlugin or by installing GScript.dll in your plugins folder), there are two ways to use the extended language features.
Firstly, a script (or part of a script) containing extensions can be passed as a text string to the GScript function (similar to the way functions like ScriptClip or MT are used). For example,

GScript("""
if (i > 10) {
  x = 1
  y = 2
  z = 3
}
else {
  x = 4
  y = 5
  z = 6
}
""")

The second way is to use the GImport function, which reads the entire contents of a file. This is similar to the standard Import, but supports the use of GScript extensions directly in the file.
The advantage of this is that you don't have to put quotes around the script, or worry about possible problems if the embedded script itself contains both triple and single quotes.
Thus, you can write entire scripts directly in the extended language and just pass to Avisynth a single GImport command to read it.

GImport("MyGScript.avs")

For completeness, there is also a function GEval, analagous to the standard Eval, which evaluates an arbitrary string that is permitted to contain GScript extensions.

Update: Version 1.1 (GScript_11.zip) released 6th Dec 2009

[J_Darnley]

Good god man! This is brilliant.

[leeperry]

nice! so basically this could be used w/ mod2 only scripts? if not mod2 > add padding lines?

[Didée]

Originally Posted by leeperry

nice! so basically this could be used w/ mod2 only scripts? if not mod2 > add padding lines?

Sure, it could. You could also buy a laser beam cutting machine when you need to cut a piece of paper.

For *such* a simple task, Avisynth's standard language (conditional operation through bool ? this : that) is fully sufficient ...

src = last

dest_modulo = 2    #  or 4, 6, 8, 1337, ...
src_modulo  = src.width()%dest_modulo
padding     = dest_modulo - src_modulo

src_modulo==0 ? src : src.addborders(0,0,padding,0)

[Gavino]

Originally Posted by leeperry

nice! so basically this could be used w/ mod2 only scripts? if not mod2 > add padding lines?

Yes, although you could probably do this just as easily with the standard conditional operator (... ? ... : ... ).
EDIT: as Didée has just shown!

Where the extended 'if' becomes really useful is when you need to write more than one statement in one of the conditional 'branches'.
Without GScript, you are limited to the rather messy techniques described here, which can't be easily nested. See also here.

[Archimedes]

If then constructs can also be realized in this way.

isYV12() ? Eval("""
  # do
  # something
""") : Eval("""
  # do
  # something
""")

[tin3tin]

Very nice indeed! This way of coding in a more readable syntax(plus the extra functions) is more that welcome. One could hope that this would eventually be implemented in Avisynth so the quotes around the script would not be needed at all.

[leeperry]

hehe ok thanks fellas, as we say in France "caviar doesn't taste better w/ a big spoon"...ideally I'd love to an automatic script that'd make everything mod2 in ffdshow by simply adding horizontal black bars *only* if required, I'll look into Didée's script

[mikeytown2]

Gavino, thanks for doing this! It makes script development a lot simpler now

[shoopdabloop]

finally, as an actionscript 3 programmer, i can feel a little more comfortable in avisynth.

[Gavino]

Originally Posted by tin3tin

One could hope that this would eventually be implemented in Avisynth so the quotes around the script would not be needed at all.

If the extensions gain sufficient acceptance, it would be fairly trivial to put them into the Avisynth core.

To implement the plugin, I used a modified version of the Avisynth parser code. The changes are relatively self-contained and all clearly marked in my source code. It would take little more than a cut-and-paste job to put those changes into the 'real' parser.

[tin3tin]

(I know that it ain't xmas - but imagine what you could do with those functions combined with two new functions(just idears): one to paint a pixel(x,y,color) and one to read the color of a pixel(x,y) then the more complicated imagemanipulation filters could be prototyped in avisynth.)

Anyway thanks again for the Gscript plugin.

[tin3tin]

A bunch of gradients done with gscript.

Uncomment the various Gradient lines to check them out:

loadplugin("GScript.dll")

function Gradient(int gwidth, int gheight, int ared, int agreen, int ablue, int bred, int bgreen, int bblue, int cred, int cgreen, int cblue)
{
blankclip(1,gwidth,1)
GScript("""
for (i=1, gheight,1){
    r=int(spline(i,0,ared,int(gheight/2),bred,gheight,cred,true)/float(gheight)*255)
    g=int(spline(i,0,agreen,int(gheight/2),bgreen,gheight,cgreen,true)/float(gheight)*255)
    b=int(spline(i,0,ablue,int(gheight/2),bblue,gheight,cblue,true)/float(gheight)*255)
    c=blankclip(1,720,1,color=r*65536 + g*256 + b)
    StackVertical(last, c)
}
""")
crop(0,1,0,0)
}
function GradientNoSpline(int gwidth, int gheight, int ared, int agreen, int ablue, int bred, int bgreen, int bblue, int cred, int cgreen, int cblue)
{
blankclip(1,gwidth,1)
GScript("""
for (i=1, gheight,1){
    r=int(spline(i,0,ared,int(gheight/2),bred,gheight,cred,false)/float(gheight)*255)
    g=int(spline(i,0,agreen,int(gheight/2),bgreen,gheight,cgreen,false)/float(gheight)*255)
    b=int(spline(i,0,ablue,int(gheight/2),bblue,gheight,cblue,false)/float(gheight)*255)
    c=blankclip(1,720,1,color=r*65536 + g*256 + b)
    StackVertical(last, c)
}
""")
crop(0,1,0,0)
}

#Gradient(720, 576,86,107,103,184,164,126,140,36,29)#Vintage America
#Gradient(720, 576,59,61,40,113,117,76,255,113,68)#Dawn
#Gradient(720, 576,160, 88, 50, 209,169, 75, 249,209,140)#fruity
#Gradient(720, 576,225,230,250,171,200,226,24,49,82)#Blue
#Gradient(720, 576,236,224,158,145,134,90,191,62,47)
#Gradient(720, 576, 62,102,51,220,240,242,150,35,9)#GreenBlueRed
#Gradient(720, 576,62,153,96,159,235,74,237,255,116)#Greenish
#Gradient(720, 576,117,0,0,215,215,215,0,100,200)#BleuBancRouge
#Gradient(720, 576,178,255,0,194,194,194,255,96,10)#GreenBlueRed
#Gradient(720, 576,118,192,245,223,236,245,245,105,198)#Baby
#Gradient(720, 576,118,192,245,255,170,85,255,0,0)#Sunset
#Gradient(720, 576, 17,0,28,94,0,30,17,9,28)#RedPurple
#Gradient(720, 576, 6,171,170,5,91,161,0,28,54)#Deep Ocean
#Gradient(720, 576,217,204,143,109,140,42,37,64,25)#Grassy Fields
#Gradient(720, 576,103,57,15,217,139,43,42,23,12)#Brown
#Gradient(720, 576,178,150,82,255,94,53,166,222,161)#OrangeGreen
#Gradient(720, 576,249,209,147,75,83,106,193,90,55)#Blue Evening
GradientNoSpline(720, 576,121,121,59,216,186,72,51,7,6)#Red jungle

[Gavino]

Thanks, tin3tin. A good example of how GScript makes this sort of thing easier to write.

Of course, it can also be done in standard Avisynth by using recursive procedures, but most people would find it more natural to write an iterative construction like this directly as a loop.

Note that the GScript call need not be confined to the 'non-standard' parts of the script. For example, each function (or even both together) could be put inside GScript. This way, the GScript parser is invoked only once, rather than on each call to the function.

For example,

GScript("""
function Gradient( ... ) {
  ...
}

function GradientNoSpline( ... ) {
  ...
}
""")

[tin3tin]

Will that make it faster? As it is this gradient function is properly too slow(thanks to stackvertical?) to be really useful.

[Gavino]

In principle, moving the GScript to outside the function declaration will speed up compilation of the function calls (and hence script loading), but the difference is unlikely to be noticeable. It doesn't affect the 'run-time' - GScript acts purely at 'compile-time'.

I'm not sure if the slowness here comes from the StackVertical or the Spline function - I will look into it and see if it can be made faster in some way.

In your code

r=int(spline(i,0,ared,int(gheight/2),bred,gheight,cred,true)/float(gheight)*255)
... etc ...

why do you effectively multiply by 255/gheight?
I get better results with just r=int(spline(...))

[tin3tin]

why do you effectively multiply by 255/gheight?
I get better results with just r=int(spline(...))

You're right, that's just a leftover from previous attempt I forgot to clean out.

[Gavino]

tin3tin - Looking at this more closely, I think the overhead is due to the repeated use of StackVertical. For an image height of 576, you have 576 instances of StackVertical, each copying an average of 288 lines, so that's over 150000 lines being copied!

A faster way would be to directly use a resizer as the interpolator instead of the Spline function. Try these alternative versions which should produce similar results to yours (I believe identical in the non-spline case).

function Gradient2(int gwidth, int gheight, int ared, int agreen, int ablue,
\          int bred, int bgreen, int bblue, int cred, int cgreen, int cblue)
{
  c1 = BlankClip(1, gwidth, 3, color=ared*65536 + agreen*256 + ablue)
  c2 = BlankClip(1, gwidth, 1, color=bred*65536 + bgreen*256 + bblue)
  c3 = BlankClip(1, gwidth, 3, color=cred*65536 + cgreen*256 + cblue)
  StackVertical(c1, c2, c3)
  Spline16Resize(gwidth, gheight, 0, 2.5, 0, -2.5)
}

function GradientNoSpline2(int gwidth, int gheight, int ared, int agreen, int ablue,
\          int bred, int bgreen, int bblue, int cred, int cgreen, int cblue)
{
  c1 = BlankClip(1, gwidth, 2, color=ared*65536 + agreen*256 + ablue)
  c2 = BlankClip(1, gwidth, 1, color=bred*65536 + bgreen*256 + bblue)
  c3 = BlankClip(1, gwidth, 2, color=cred*65536 + cgreen*256 + cblue)
  StackVertical(c1, c2, c3)
  BilinearResize(gwidth, gheight, 0, 1.5, 0, -1.5)
}

Here, GScript is no longer required, but I think it is fair to say that the problem lay not with GScript itself but with the method you used.

(BTW there was another bug in your original code, where 720 was used in place of gwidth in the BlankClips.)

[tin3tin]

Wow, that's clever - and fast!

Before it was impossible(too slow) to make a gradient lib like this(using 3 out of 5 colors from Kuler):

Gradient(720, 576,86,107,103,184,164,126,140,36,29).Subtitle("Vintage America", align=2,text_color=$FFFFFF)#Vintage America
last+Gradient(720, 576,59,61,40,113,117,76,255,113,68).Subtitle("Dawn", align=2,text_color=$FFFFFF)#Dawn
last+Gradient(720, 576,160, 88, 50, 209,169, 75, 249,209,140).Subtitle("Red Yellow Pink", align=2,text_color=$FFFFFF)#Red Yellow Pink
last+Gradient(720, 576,225,230,250,171,200,226,24,49,82).Subtitle("Blue", align=2,text_color=$FFFFFF)#Blue
last+Gradient(720, 576,236,224,158,145,134,90,191,62,47).Subtitle("White Green Red", align=2,text_color=$FFFFFF)#White Green Red
last+Gradient(720, 576, 62,102,51,220,240,242,150,35,9).Subtitle("Green White Red", align=2,text_color=$FFFFFF)#GreenWhiteRed
last+Gradient(720, 576,62,153,96,159,235,74,237,255,116).Subtitle("Greenish", align=2,text_color=$FFFFFF)#Greenish
last+Gradient(720, 576,117,0,0,215,215,215,0,100,200).Subtitle("Bleu Banc Rouge", align=2,text_color=$FFFFFF)#BleuBancRouge
last+Gradient(720, 576,178,255,0,194,194,194,255,96,10).Subtitle("Green Blue Red", align=2,text_color=$FFFFFF)#GreenBlueRed
last+Gradient(720, 576,118,192,245,223,236,245,245,105,198).Subtitle("Baby", align=2,text_color=$FFFFFF)#Baby
last+Gradient(720, 576,118,192,245,255,170,85,255,0,0).Subtitle("Sunset", align=2,text_color=$FFFFFF)#Sunset
last+Gradient(720, 576, 17,0,28,94,0,30,17,9,28).Subtitle("Red Purple", align=2,text_color=$FFFFFF)#RedPurple
last+Gradient(720, 576, 6,171,170,5,91,161,0,28,54).Subtitle("Deep Ocean", align=2,text_color=$FFFFFF)#Deep Ocean
last+Gradient(720, 576,217,204,143,109,140,42,37,64,25).Subtitle("Grassy Fields", align=2,text_color=$FFFFFF)#Grassy Fields
last+Gradient(720, 576,103,57,15,217,139,43,42,23,12).Subtitle("Brown", align=2,text_color=$FFFFFF)#Brown
last+Gradient(720, 576,178,150,82,255,94,53,166,222,161).Subtitle("Orange Green", align=2,text_color=$FFFFFF)#OrangeGreen
last+Gradient(720, 576,249,209,147,75,83,106,193,90,55).Subtitle("Blue Evening", align=2,text_color=$FFFFFF)#Blue Evening
last+GradientNoSpline(720, 576,121,121,59,216,186,72,51,7,6).Subtitle("Red jungle", align=2,text_color=$FFFFFF)#Red jungle

The next big challenge is how to make a smooth gradient in yv12.

[Gavino]

Originally Posted by tin3tin

The next big challenge is how to make a smooth gradient in yv12.

I suppose you mean something other than just adding ConvertToYV12()?
Perhaps starting out with yuv values as the arguments instead of rgb?

Note that BlankClip has a color_yuv parameter, so I think you can just do something similar to the rgb version, using pixel_type="YUY2", and convert to YV12 after the resize.