Expression to make a boat “ride” on top of generated waves?

[Dan Fredley]

If the waves are consistent then you can just set 2 keyframesat the top and bottom then set the following expression:

(might have to play with ease settings on keyframes)

loopOut(type = "pingpong")

Dan Fredley

[Max Palmer]

Unfortunately, it’s not. The animation is seeded so that it has a natural random feeling.

[Dan Ebberts]

It might be possible to calculate the wave height at any point and time. What are your wave warp settings and expressions? What’s the layer number of the wave layer?

Dan

[Max Palmer]

Dan- first off, love your site. I’ve used the examples several times, and it was actually my first go-to place when trying to figure this particular problem out. Thanks!

Here is a screenshot of my wave setup. I made a small expression with a wiggle, part of which is pickwhipped to a null with some keyframes on it. The reason I did this is so that I could increase the waves later in the animation (a storm will happen).

[Dan Fredley]

change the sampleLayer to your water layer and then try applying the following to the boat position.

L = thisLayer;
targetPosition = L.toWorld(L.anchorPoint);
sampleLayer = thisComp.layer(thisComp.numLayers);
for (i=0; i<thisComp.height;i++) {
alphaCheck = sampleLayer.sampleImage(sampleLayer.fromWorld([targetPosition[0],i]), radius = [.5,.5]);
if (alphaCheck[3]&lt;1) {
continue;
} else {
alphaPosition = [0,i];
break;
}
}
newWorldPos = L.fromWorld(L.toWorld(alphaPosition));
[value[0],newWorldPos[1]]


Dan Fredley

[Dan Fredley]

actually try this–expression got screwed up somehow during copy/paste

L = thisLayer;
targetPosition = L.toWorld(L.anchorPoint);
sampleLayer = thisComp.layer(thisComp.numLayers);
for (i=0; iL = thisLayer;
targetPosition = L.toWorld(L.anchorPoint);
sampleLayer = thisComp.layer(thisComp.numLayers);
for (i=0; i

Dan Fredley

[Dan Fredley]

Let’s try this one more time:

L = thisLayer;
targetPosition = L.toWorld(L.anchorPoint);
sampleLayer = thisComp.layer(thisComp.numLayers);
for (i=0; i < thisComp.height;i++) {
alphaCheck = sampleLayer.sampleImage(sampleLayer.fromWorld([targetPosition[0],i]), radius = [.5,.5]);
if (alphaCheck[3] < 1) {
continue;
} else {
alphaPosition = [0,i];
break;
}
}
newWorldPos = L.fromWorld(L.toWorld(alphaPosition));
[value[0],newWorldPos[1]]

Dan Fredley

[Dan Fredley]

just noticed you have a shape layer. You’ll need to precomp the shape layer with the slider or use a solid instead

Dan Fredley

[Max Palmer]

That works! Amazing. Thank you SO much. My last thing I need to do is find a way to make the boat rotate slightly as it bobs, so in other words, when it bobs up the boat rocks back, and when it bobs back down, it rocks forward. Is that easy to do?

[Dan Fredley]

I wrote a better expression in case the boat layer reaches the edge of the composition. I suggest precomping the boat and water layer in a 2x wide comp to animate the boat across a full comp otherwise the expression won’t work past the edge of the main comp. I hope that makes sense:

Final position expression:

target = thisComp.layer("Controller").effect("Boat")("Layer");
targetWorldPos = target.toWorld(target.anchorPoint);

sample = thisComp.layer("Controller").effect("Ocean")("Layer");

for (i = 0; i < height; i++){
if (sample.sampleImage([clamp(targetWorldPos[0],0,thisComp.width), i], [0.5, 0.5], true)[3] > 0){
top = [0,i];
break;
} else {
top = [0,thisComp.height];
}
}

newWorldPos = target.fromWorld(target.toWorld(top));
[value[0],newWorldPos[1]]

To be able to rock the boat:

Final rotation expression:

target = thisComp.layer("Controller").effect("Boat")("Layer");
targetWorldPos = target.toWorld(target.anchorPoint);

sample = thisComp.layer("Controller").effect("Ocean")("Layer");
offset = -10;

for (i = 0; i < height; i++){
if (sample.sampleImage([clamp(targetWorldPos[0]+offset,0,thisComp.width), i], [0.5, 0.5], true)[3] > 0){
top = [0,i];
break;
} else {
top = [0,thisComp.height];
}
}

newWorldPos = target.fromWorld(target.toWorld(top));
offsetPos = [target.position[0]+offset,newWorldPos[1]];

for (i = 0; i < height; i++){
if (sample.sampleImage([clamp(targetWorldPos[0],0,thisComp.width), i], [0.5, 0.5], true)[3] > 0){
top = [0,i];
break;
} else {
top = [0,thisComp.height];
}
}

targetWorldPos = target.fromWorld(target.toWorld(top));
boatPos = [target.position[0],targetWorldPos[1]];

radians = Math.atan2(boatPos[1] - offsetPos[1],boatPos[0] - offsetPos[0]);
radiansToDegrees(radians);

This is going to be really slow to calculate. You should bake all of these expressions. Then after you bake the rotation put this expression on it otherwise it will be really choppy:

Final baked rotation expression:

smooth(.5,10)

Dan Fredley