I need effect like reverse-build. Plain build just imitates object construction (following edge loops or randomly), and I need to imitate object destruction. For example in frame 0 I have solid object and in frame 50 I have just few faces. It is possible to achieve this somehow? (without hardcore workarounds, if possible)
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Sure - if you go into the IPO window for the object, and make a linear ‘Time’ IPO with a negative gradient, time will go backwards for the object.
Indigomonkey, can you describe it step-by-step how to do this?
The method is :
- Select your object and put the Build Modifier in the Modifier stack.
- Open a IPO window and on the right side of this window, at the same place than “LocX, Loc Y …”, select “Time”.
- Create a new Curve with Ctrl + Click.
- On the first frame of your animation, enter a value of 10. And on the last frame, enter a value of 0. You can edit each point of the curve by pressing “N” : for the first frame Vertex Y should be = 1, and for the last frame, Vertex Y should be = 0.
- If you want a linear build effect, in edit mode, in the IPO window, press “V”.
- Et voilà.
Step 3. is what i didn’t knew. Thanks a lot!
OK, I’ll try! 
Make sure your object is selected, and has the build modifier.
Hit Shift-F6 to enter the IPO window.
Select ‘Time’ on the right-hand side.
Shift-leftclick on any point on the graph. An IPO line will appear, with a vertex at the point you clicked.
On the Curve menu, select Interpolation Method->Linear.
Hit Tab to enter Edit Mode for the line. Make sure the vertex is selected with right-click.
Press N to view the properties of the line. Set vertexX to 1, and vertexY to 10. (for some reason this corresponds to 100 frames, as you can see from the scale on the left).
Shift-leftclick at any point on the graph again, making another vertex.
In its properties, set vertexX to 100, and vertexY to 0.1.
You should now have a graph with a negative gradient between frames 1 and 100, for the Time IPO. This basically means that anything that usually happens at the frame denoted by the Y-axis will instead happen at the frame denoted by the X-axis. So time will move backwards for the object!
You can of course mess around with this to change the amount of frames the build takes to however long you like.
[EDIT]Dammit, just too late… [/EDIT]
Go to IPO window, select Time from the menu on the right side of the screen. While hovering mouse over IPO window press “N” key. In the window that pops up press the button labeled “Add Driver”. Still hovering mouse over IPO window press “I” key and text will pop up asking “Insert default one to one mapping?” Click on the text and you will see the time IPO appear as a diagonal line across the window. Now in the popup window from “N” key press remove driver. The values on the left side of the IPO window are percentages. Open a timeline window, set animation to first frame. With mouse hovering in IPO window press “Tab” key. Now select first point and press Shift+S key+4 key. This will cause the selected point to snap to the current frame. Press G key+ middle mouse button and drag upward to move point from zero% to 100 %. Go to last frame of animation and reverse the process for the last point on the IPO. Your time will now be reversed. Lots of ways to do it, eh?
wow time remapping in blender? who knew. this would be sick for syncing animation clips to audio.
Thanks guys, I did what I wanted. Suzanne destruction (1.8MB). For better effect whole “destruction” must last just 2 or 3 frames, and now it lasts 10 frames, so you can see it clearer. I’m planning to write a tutorial about it.
Indeed, there are serious problems with reverse time when you have complex or even moving object - you must reverse all the animation. Fortunately i made just static object, and it worked for me. It would be nice to have option in build effect to have just “reverse” or “invert” button, but I don’t know is it worth changing.
Wow, I like that - how did you do it?
How to do thing like that:
I had two identical suzannes.
First one has build effect (reverse) that starts at frame 90 and ends at frame 100.
Second is just a particle emitter, starts emit particles at frame 90 and ends at frame 100, it has parented litle plane and dupliverts enabled (particle count ~1500, 0,10 speed from normals, a bit random). Both suzannes are at the same position.
In the centre of suzanne add an empty and make it vortex field with enough strenght and falloff enabled (for particle spinning).
Just turn around the camera and animate frames from 0 to 200 :]
BTW, it would be cool to change little planes to flying birds or bats ;] But with moving objects and complex animation its still easier to code reverse build effect with python - then it wont break animation logic
If you parrent all objects in your scene to an empty and add the time IPO to that empty then you will only have to apply the IPO once. Press spacebar>empty, then “A” key to select all objects, then right click on the empty which will bring it to the top of the heirarchy (you can tell because it will be highlighted in a lighter shade of pink), then press"CTRL"+“P” key to make it the parrent of all objects. You may want to consider omitting the camera from this parrented group so that you can animate it seperately.