-
A Simple Motion Problem?
My After Effects CS3 seems to ignore the most basic rules of mathematics. I need to create a smooth motion of an object with 100px/s in a 25fps composition. It’s a linear motion without any variations. But somehow the calculation always gets wrong.
Example:
Setting up two position-keyframes with, let’s say, “3000” and “3016” and three frames in between always creates values like “3004,0002”, “3007,9996” or “3012,0008” instead of 3004, 3008 and 3012.Some rounding can’t be that hard. But even between two position-keyframes with “0” and “8” I always get something like “4,0006”. I just don’t get it
-
3 Replies
-
After Effects handles interpolating properties outside of a frame based structure internally, that is to say that there can be unique values at a subframe level. This may be what is causing your subtle ’rounding errors.’ If you need each element of the vector to be an integer at each frame try applying this expression to the position property:
x = Math.floor(value[0]);
y = Math.floor(value[1]);
[x,y]Darby Edelen
Designer
Left Coast Digital
Santa Cruz, CA -
I get accurate results. Pal square pixel comp, square pixel solid, starting position at 1 second is 100, 288. Set keytframe, then moved to 4 seconds and set position keyframe at 1000, 288.
layer moves 900 pixels in x in 3 seconds or 300 pixels per second.
Checking position at 2 seconds it’s exactly 200, 288.
Change the comp to non square pixels and the results are the same.
If you’ve got any easing applied or your keyframes don’t look like ◊ in the timeline then you won’t get exact numbers.
If you motion isn’t just in x or just in y then you won’t get exact numbers either. If your movement must be exactly 300 pixels per second try adding this expression to the position.
x = position[1] + (time * 300);
y = position[0];
[x, y]this moves 300 pixels per second from left to right. Want to move from right to left then change the + to a minus. Want to move up or down, change the y to x and the x to y, then change the zero to one and the one to zero.
hope this helps….
-
Here’s another question: how are you creating your position keyframes? If you drag the layer in the comp window then you can easily end up with position keyframes with subpixel values, if you want an exact integer you need to type it into the position property field.
Darby Edelen
Designer
Left Coast Digital
Santa Cruz, CA
Reply to this Discussion! Login or Sign Up