71. Trees in the Wind

I’ve wanted to get animation for the trees into the game for a while, but could never quite manage it. I’ve tried many different approaches to this, but always the main issue is that the game renders at a fixed low-resolution pixel grid.

Some other pixel art games choose to render the game at a higher internal resolution than that of the actual pixel art, which means that you can rotate sprites without much aliasing. You can see a comparison between a high-res rotation-based animation (left) and how the effect breaks down when you render at a low resolution (right):

I have never liked the look of pixel art games that mix different resolutions, so I chose to render Taiji in a way that would force all effects in the game to be rendered at the same resolution of the base pixel art. But as you can see above, this means that rotating pixel art tends to cause strange artifacts that sort of look like edges sliding across the image. Obviously, this is very unaesthetic looking, and we need to try something else.

One possibility that I tried was to add in some noise to attempt to jitter out the sampling and create a smoother look. This removes the “sliding edges” appearance, but ends up adding in a lot of noise along edges. The effect could perhaps work well with a game that has a more forgiving art-style with a lot of noise built into the graphics.

So, with a couple of failures under my belt, I decided to rule out large motions such as rotating the entire tree, and instead I focused my efforts on animating the leaves on their own. This type of effect can be done fairly easily in a shader by simply adding in a noise offset when you sample the texture for the leaves.

This is certainly an improvement, but the effect is a bit too strong. Also if you look at it closely, it feels more like the tree is underwater than being effected in the wind. We could tone the strength of the distortion down, but then the motion becomes so subtle that it’s almost not worth having.

Another possibility that I attempted was to custom author a secondary texture which would control how the distortion was applied. I tried using a noise texture with leaf pattern built into it. I even did some tests pre-rendering leaves with Blender so that I could use the scene normals of the leaves to modulate the distortion.

I didn’t save this iteration of the shader, but suffice to say that it did not work much better than the purely random noise I was using earlier.

However, I started to think that an approach similar to how I animated the grass would be effective. The grass is essentially just a flat texture on the inside, with all the distortion happening along the outside edges.

So what would it look like if I did the same for the trees?

We’re getting close! This effect is even more pleasing, with a better balance between the details of the original pixel art and significant enough motion to be worthwhile. However, the motion feels a bit unnatural because it is confined completely to the outside edges.

What I chose to do to resolve this was to re-incorporate the idea of having a secondary texture control where the distortion effect can be applied. When used to highlight the internal edges, this forms the final effect. The wind map texture is below on the left. You can see that some interior pixels are colored red, those are the ones that are allowed to be distorted in the final effect on the right:

Overall, I’m pretty happy with how this came out. It adds some much needed motion to the trees, giving those scenes a more dynamic feel, and it doesn’t distort the base pixel art so much that it feels unnatural.

For a fun bonus, remember when I said that the unconstrained effect looked like water? I ended up using the same effect for this reflection in the water:

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