Tuesday, 29 April 2014

Scale a texture from the centre.

Nice and easy today.
We're starting off with this texture, which is clamped. 

When you scale it down (= tile it at a value greater than 1) it moves to the upper left corner. That's because 0,0 is in this corner.

With the following setup, you'll scale the texture from the visual centre of the material:

What is happening exactly?

First we subtract 0.5,0.5 to our texture coordinates. We're shifting the texture and bringing 0,0 to the centre.

Then we scale it.

Finally we add 0.5, 0.5 to bring the texture back to the original position. Simple :)

This was used in Enslaved in the dragonfly scan post process. The values subtracted/added back were exposed and so was the scaling factor, so that the glowy reticle could be animated in matinee.

A screenshot won't tell you much about it but you can see in it in my enslaved showreel from 2:00. It's super short but I couldn't find any specific youtube video. Well, gotta play Enslaved to see it at its best ;)

Now, that was a bit short so let's talk some more.
When reducing the size of a clamped texture a lot, you can come across mipmap artifacts.

One fix is the Preserve Border option.
The tooltip says: ‘If true, the color border pixels are preserved by mipmap generation. One flag per color channel.’

Now the result is much better, but we can still see some artifacts.

Here is the texture I created. The last two pixels are plain black but pixel 3 and 4 start to be white. The dxt compression is done with blocks of 4 pixels so since I've got both black and white in a 4 pixel group, my mipmaps get messed up.

I reimported the texture and made sure I've got a clean 4 pixels border. Even with preserve border off, I don't get any artifacts.

They will appear at a lower mipmap though, but won't ever appear with a correct border and the preserve border option.

Maya tip: clear particles initial state.

Today I wanted to clear an initial state on particles in maya but didn't know how to. I found my answer here:

Here's the MEL command you need to enter:
clearParticleStartState <particleObjectName>

which typically will be
clearParticleStartState particle1

(and… I've got my copy/paste ready to use.)

Monday, 14 April 2014

Super simple manual flipbook.

Say you want to manually animate a flipbook in matinee.
Here's a very simplified setup for it. The downside is: is has to be one single row but you can modify the amount of columns as you wish.

There could be less instructions but the idea is to make it easy to instance. In the material instance, you just have to modify the FramesAmount parameter and you can animate the FrameIndex parameter in matinee with everything working fine.

What's happening there?
You simple tile and shift your texture.


In this case, one tile is a forth of the texture size. So you divide 1 by the amount of horizontal frames in your texture and multiply only the U of your texture coordinates.
You've got the correct tile size.


To display the correct frame at the right moment, you'll just need to move the texture horizontally.
The amount by which you need to shift the texture to reach the next frame is one nth of your texture, n being th amount of horizontal frames. (4 in this case)
The FrameIndex value (animated from matinee) multiplies this to find how many times you need to shift it.

The floor node is there to ensure you only display full frames.
Since the frame index is floored, your index will be starting at 0, remember this when you control the value in matinee. To animate a four-frames texture, the value will have to interpolate between 0 and 3. (If your texture is set to wrap, a FrameIndex of four will get you back to displaying frame 0.)

Not super clean or flexible but definitely super simple.

Wednesday, 9 April 2014

Fixed rotator

What's on today:
  • Fixed rotator.
  • Fixed rotator with steps.
  • Quick look at vector graphics textures in after effect.

Fixed rotator.

How to rotate a texture by a certain fixed angle?

Just input a constant value in the time pin of your rotator. The constant value is like saying ‘this is where the rotator would get you in that much time’. (I mean, not technically since the unit is not seconds but it's sort of a way of seeing it.)

What to expect from that value? First thing, set your rotator speed to 1. Then you have to know that unreal uses radians as a rotation unit.
180 degrees = π (pi, the maths symbol equal to 3.14159 and so on).

Therefore, 90 degrees is going to be π / 2.
Good thing to know: you can do maths in input fields. In your constant input, you can simply type in 3.14159/2.


You could use a fixed rotator to represent a circular gauge for instance. Most likely, the gameplay code is going to provide you with some normalized parameter. (Frankly that’s the best option. Sure modifying the value to fill your needs will add a few instructions but it gives you the flexibility to easily do anything you want with it, rather than having to go bug a coder so he changes the value he's hard coded for you.)

Modify the input to the range you are interested in (say 0 to 90 degrees), plug it into the rotator, and then into a mask that multiplies your gauge.

You’ll notice that I’ve just multiplied my normalised value; since my min is 0, I don’t need to use a lerp which would add more instructions for the same result.

Fixed rotator with steps.

We can go one step further.
In Enslaved, Trip has an emp gauge which recharges over time and is split in several chunks which appear one at a time.

I used a similar setting, with a rotating mask that multiplied my texture, only this time the rotation value had to be contained until it reached the next step.

In the following example our gauge value is at 0.5, that's half filled. The gauge is split into 5 chunks, so each step is 0.2.

We check: our many steps are there in our current value ? That's 0.5 / 0.2 = 2.5. We're only interested in full steps so we floor it.
We've then got two full steps, the step size is 0.2 that's 0.2*2, our output value is 0.4.
The floor node is going to keep the value contained at 0.4 until the next integer is reached. When we get to 3 full steps, the output will suddenly jump to 0.6 and so on.

The input value is divided by your step size, floored and then multiplied by your step size.
Credit for this little setup goes to Gavin Costello, currently Lead Programmer at Ninja Theory and full time graphics programming genius.

Vector graphics textures in after effect.

 I've got a thing for after effects in general, and I find it excellent for vector graphics in particular. It's very flexible, the textures are easily scaled and iterated. Illustrator could do the same but with after effects you can also animate everything for previs and/or flipbook generation. (Which is exactly how I worked during Enslaved. My previs and textures were the same assets.)

Here's the way I made the previous gauge for instance, using shape layers:

2 ellipses, 6 rectangles, a subtract merge to cut out the inner circle and the rectangles, another rectangle and an intersect merge to extract the bottom left quarter. And finally a white fill of course.

I like to use expressions even with these sort of very simple shapes. It is a small time saver as you make the texture and might be a massive one along the project as you iterate on your texture.

Right there for instance, I link the anchor point to my rectangle size for the anchor to be at the end of the rectangle rather than in the default centre. Sure I could have done it by hand but I find it better when automated. I was a bit lasy in this case so I stopped there but if I had created this texture for production, I would have also:
  • linked the size of every rectangle to the first rectangle (or even neater, to a slider control)
  • linked the rotation of every rectangle to a slider control (and multiplied it by 2, 3, 4 etc. for each next rectangle)
  • and maybe controlled the radius of each ellipse from a slider parameter too, just so as to modify everything for one single place and not have to open up the content properties