In After Effects I can use an alpha matte to make the parts of an object appear gradually until it's fully visible. How can I do that in Blender? Basically, I'd like to make some sort of intro like this.
Path Reveal - (See addendum below)
At first an array of planes was tried and used with the build modifier, but that just plain didn't work.
What did give us a similar result to the video and which would be modifiable to pretty much match the video, was this...
The path (so-called) is simply a large plane subdived 31 times to give us 32 x 32 faces.
To avoid confusion the faces will be referred to as 'Slabs'.
The 'C' circle select was used to select the pathway on the plane by simply 'painting' over those faces in order to highlite a path. (albeit very chunky)
Down at the bottom left of the window the 'Select' menu was opened to choose "Inverse'. This switched the selected faces off and the non-selected on. Those faces once highlited were then deleted to leave just the slab-path.
This is duplicated and moved to layer 10 (0) to give us an original to come back to should things get fouled up.
Another duplicate is sent to layer 2. This will be converted to a wireframe.
Back in layer 1 and the solid slab, add a "Curve-->Nurbs Path" and keep it set to 2D so it doesn't get hilly.
In Edit mode, shape the path to approximately follow the center-line of the solid slab's shape. This is going to be used as a 'dolly' track for our camera.
Set up the Nurbs path's parameters. I've chosen 150 frames for this one.
Add an empty at the same Origin Point as the Nurb's path and give it a "Follow Path" constraint. Select the Nurb's Path as it's "Target". If not already there, position the Empty at the path's starting point.
Position the camera at an approximate location so it's looking from ahead and at the top end of the path. Parent it to the Empty. (child=camera)
The camera (not the empty) can be freely adjusted and keyframed to suit whatever viewpoint you need as it travels down.
What's required now it to separate those faces/slabs that are to be switched visible as the camera moves down the Nurb's path. i.e. have separate meshes which will each be different sized slabs. They can range from one to several faces in size, the more random their appearance the better.
The idea is to have varying sized 'slabs' appearing at varying intervals as the camera moves down, but they must start at the top and follow the cam's travel south.
Had we set up an array of planes and then rows of those, used the "Build" modifier, there would have been a random choice but they'd be appearing all over the place, not constrained to the camera's travel and viewpoint. Had we not chosen 'random', their appearance would still not have achieved the desired result.
Once separated, each slab is made to appear by keyframing their respective EYE icons in the Outliner.
NOTE - All will need to be keyframed OFF at frame 1.
There were 180+ faces in all but only 32 slabs to switch on so the job didn't take long.
Once the appearance switching is done, we turn our attention to the wireframe.
This is setup in Layer 2. The duplicated solid slab inherits the subdivisions. A "Wireframe" modifier is used on this to turn the edges of it's faces into solid mesh and at the same time get rid of the solid face surfaces.
Adjust the modifier's "Thickness" as required and "APPLY" the modifier.
All that's left to do is to reveal the wireframe ahead of the slabs as they come into view. A mask was used for that in this example. It was shapekeyed to shrink and deform (morph) as the camera moves down.
Over the final frames the wireframe's "opacity" in the Material slot was keyframed to fade away.
The wireframe's Mask -
Cycles is not used here and OpenGL rendering was used for the output video.
This allowed OpenGL masking. The mask is just a large 2D plane located a little above the slabs and wireframe. (z axis)
It's set up with a material slot Opacity set to 0.008, no Specular whatever to avoid ghosting and it's diffuse slider set down to about half brightness for the same reason. NOTE - To view the masking effect, deselect everything (press A) and be in the "Material" viewing mode.
For details on this form of masking see here -
Blend file is attached -
Addendum 22nd March 2019 - & 23/3/2019 (added 2nd Blend file)
This is an alternate method. Simply shapekey or slide layer 1's mask down to progressively reveal the solid tiles. (no need to switch them on individually)
Layer 2's mask shapekeys would simply have to see to it that it's own mask reveals the wireframe ahead of Layer 1's.
Each layer would be rendered separately. Layer 2 as an AVI. Layer 1 as an Alpha leyered set of PNG files in another folder.
The VSE would be used to mix both sequences to get the final result.
A sparkly effect using particles could be added to the trailing edge of layer 1's mask such as here - How To Animate A Superhero Zap Into His Super Suit In Blender