Thanks Alessandro
Guessed as much but I'd gone so far down the other path I described
(synthesising a mask) I ploughed on (deadline tomorrow). Will try and
build the RII way later to compare performance/ease.
Someone should right a book with a heap of these kinds of exercises to
explain options (with pros/cons stated) if QC is going to stick around
for a few more years.
Best
Alastair
On 21/04/2012, at 2:22 AM, Alessandro Sabatelli wrote:
The easiest way to do this is to put the whole thing in a constant
sized render in image and mask that.
Sent from my iPad
On Apr 19, 2012, at 11:34 PM, Alastair Leith
<[email protected]> wrote:
Hi List
I'm trying to make an image mask for a Billboard such that the
masked area stays static (relative to Viewer window) while the
image of some text moves up and down (as if) inside the bounds of a
masked window. The problem I am having is that there is no simple
way to give an absolute position for the mask while moving the
image independently, like you say a mask in PS or AE behaves.
Typically the billboard patch scales a rendering-destination-
dimension sized mask image down to be (somehow) relative to the
size of the input image rather than use it as a mask the size of
the rendering destination (Problem 1).
If I use an Image Transform Patch to translate the text image up/
down on the Y-Axis the Billboard patch basically ignores the change
in bounds and just centres the image at the same origin as
determined by X pos, Y pos and image size (Problem 2).
I did make a successful composition that creates a mask the same
size as source image (an Image from String patch output) by
'screen' blending black and white cropped images (doing math for
the crop inputs to get positioning relative white/black correct)
then using a Mask to Alpha patch and inputting it to the Billboard.
By animating several of the cropping offsets and heights and the Y-
Position of the Billboard I can generate the desired animation of
text scrolling up and down inside window bounds. Problem with this
solution is it seems overly complicated, a little CPU hungry on my
old mac anyhow, and because the crop patch uses integer inputs, an
animation that only moves the mask say 33 pixels is noticeably
jerky (only just) as compared to just animating Y Postition of a
billboard with cropping sprites all around it.
Maybe animating a billboard with cropping sprites set to alpha-0%-
black (blend mode: replace) on higher layers inside a RII patch is
the way to go but I'd like to avoid RII patch on principle that's
more overhead. I don't mind using RII patch to construct the mask
if it is static and wont re-evaluate after initialisation but that
just gets me back to Problem 1.
Any assists/demos/thoughts gratefully received. I'm sure some of
you have been here before — I know I have :-)
Alastair Leith
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