Hi List
I'm trying to make an image mask for a billboard such that the masked
area stays static 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 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 keep re-evaluating but that 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
The machine does not isolate man from the great problems of nature but
plunges him more deeply into them.
Antoine de Saint-Exupery
_______________________________________________
Do not post admin requests to the list. They will be ignored.
Quartzcomposer-dev mailing list (Quartzcomposer-dev@lists.apple.com)
Help/Unsubscribe/Update your Subscription:
https://lists.apple.com/mailman/options/quartzcomposer-dev/archive%40mail-archive.com
This email sent to arch...@mail-archive.com
