Random layer position constrained by another layer's alpha

	Re: Random layer position constrained by another layer's alpha by Mike Clasby on Jan 6, 2008 at 6:26:45 am This modified Dan Ebberts' expression is a good place to start. It goes on Position. minX = 0;//Minimum x depth value maxX = 500;//Maximum x depth value minZ = 0;//Minimum z depth value maxZ = 1000;//Maximum z depth value op = thisComp.layer("opLeader").opacity; opX = linear(op,0,100,minX,maxX); opZ = linear(op,0,100,minZ,maxZ); seedRandom(index, true); x = Math.round(random(opX)); z = Math.round(random(opZ)); [x, position[1], z] Change the min/max X and Z as needed. All the Y's are the same, I'm assuming you have a Floor if you want to cast shadows, so you Y needs to be at (or near) the Floor. Is this close to what you want? Respond to this post   •   Return to posts index

	Re: Random layer position constrained by another layer's alpha by Mike Clasby on Jan 6, 2008 at 8:10:49 am Oh, I see what you're trying to do. Yes, you probably can, err, maybe Dan can, ask over at the Cow Expression Forum: http://forums.creativecow.net/viewforum/227 I think if you combine this position expression from Colin: minX = 0;//Minimum x depth value maxX = 1000;//Maximum x depth value minZ = 0;//Minimum z depth value maxZ = 2000;//Maximum z depth value seedRandom(index, true); x = random(minX,maxX); z = random(minZ, maxZ); [Math.round( x), position[1], Math.round( z )] With an Opacity expression that is 100 when there is a Collision Detection, and 0 when not, from Dan's page: http://www.motionscript.com/design-guide/collision.html But I don't have AE CS3 or the expression finesse to do it. Alternatively, you could just use Colin's Position expression above, with the min/max set to hit the island, and then turn off the eyeballs of all trees landing off-island, and shy them so they don't clutter up the stack. That way no collision detection necessary... er, actually you would be performing the collision detection, manually. Respond to this post   •   Return to posts index

	Re: Random layer position constrained by another layer's alpha by Darby Edelen on Jan 7, 2008 at 6:07:19 am The way I would approach this is by looping through random points on the layer, sampling its alpha and stopping the loop when the sample point is over a threshold of alpha value. I should note that I haven't error checked this code at all, I don't have AE on this computer so I'm writing this from memory (and the online documentation) =) l = thisComp.layer("Island.psd"); //The 'island' layer w = l.width; //The island layer's width h = l.height; //The island layer's height thresh = 0.9; //Threshold for alpha value on the island layer seedRandom(index, true); //Seed our random numbers and don't update them based on time (timeless) p = random([0,0], [w,h]); //'p' is a random point in the layer space of the island layer alpha = l.sampleImage(p)[4]; //The alpha value at the point 'p' on the island layer (values range from 0-1) //While the alpha value is below our threshold... while(alpha < thresh){ p = random([0,0], [w,h]); //Pick a new random point on the island layer alpha = l.sampleImage(p)[4]; //Update the alpha value at the point } l.toWorld(p); //Transforms the point 'p' from layer space to world space This will return a point in 3D space that should correspond to a random point on the island layer that has an alpha value greater than or equal to 0.9 (0 is fully transparent, 1 is fully opaque), so make sure you have your anchor point on your tree layer set to the base of the trunk (where it will meet the island) and apply this expression to each tree's position property. Let me know if there are problems with this code, I can check it tomorrow for errors. Darby Edelen Designer Left Coast Digital Santa Cruz, CA Respond to this post   •   Return to posts index