PONG expression

[Dan Ebberts]

Try this one:

left = 0;
top = 0;
right = thisComp.width;
bottom = thisComp.height;

minSpeed = 200; //pixels per second
maxSpeed = 500;

minX = left + 20;
maxX = right – 20;
minY = top + 20;
maxY = bottom – 20;

minR = 5;
maxR = 85;

seedRandom(index,true);

// calc start position

pos = random([minX,minY],[maxX,maxY])
quadrent = Math.floor(random(4))*90;
angle = random(minR,maxR) + quadrent;
spd = random(minSpeed,maxSpeed);

// initialize time count;

t = 0;

while(t <= time){ rads = degreesToRadians(angle); xVel = spd*Math.cos(rads); yVel = spd*Math.sin(rads); // see if going up or down if (yVel < 0) yLim = top else yLim = bottom; // see if going right or left if (xVel < 0) xLim = left else xLim = right; timeX = (xLim - pos[0])/xVel; timeY = (yLim - pos[1])/yVel; if (timeX < timeY){ //hit left or right wall if (t + timeX >= time){
deltaT = time – t;
pos += [xVel,yVel]*deltaT;
break;
}else{
pos = [xLim,pos[1] + yVel*timeX];
angle = 180 – angle;
t += timeX;
}
}else{ //hit upper or lower wall
if (t + timeY >= time){
deltaT = time – t;
pos += [xVel,yVel]*deltaT;
break;
}else{
pos = [pos[0] + xVel*timeY,yLim];
angle = 360 – angle;
t += timeY;
}
}
}
pos

Dan

[Jaime Vazquez]

That is an excellent expression Dan. Glad these posts stay up 7 years later. I am trying the same animation but for a screensaver. I would like to know if there is a way to change the object with each bounce. for example if I am bouncing a word, to have it change on every bounce.
Maybe get text from an array?

[Dan Ebberts]

The problem is that this expression, which moves the layer, wouldn’t have any way to cause the text to change when it hits a wall. A text expression would have to do the same calculation, but it can’t generate the same random sequence, because the same seed produces different results for each property. You could do it by generating the random numbers in a Point Control and three sliders, then the position and text versions of the expression could do the same calculation.

The expression would need to be modified to get the values of variables pos, quadrent, angle, and spd from the controls. The text version of the expression would need to bump a counter each time the layer hits a wall and use that counter as the seed to seedRandom() to generate a random index into your array of words. Pretty straight forward. If you give it a try and run into problems, come on back.

Dan

[Jacob Roth]

Hi Dan,

This expression is great, but is there any way for the layer to bounce at its layer edges and not the anchor point?

[Kalleheikki Kannisto]

Change the beginning section to this

content = thisLayer.sourceRectAtTime();
left = content.width/2;
top = content.height/2;
right = thisComp.width-content.width/2;
bottom = thisComp.height-content.height/2;

Note: this expects that the anchor point is in the center of the layer.

Kalleheikki Kannisto
Senior Graphic Designer

[Jacob Roth]

Thanks for the response.

Subbing your suggestions gives me an error at line 65, which is…

t += timeY;

[Jacob Roth]

Sorry, that’s not right. The error is at line 32, and it’s a timeout waiting for the engine.

rads=degreesToRadians(angle);

[Dan Ebberts]

If you’re using the latest version of AE, you’ll need to update the lines that define yLim and xLim:

yLim = (yVel < 0) ? top : bottom;

xLim = (xVel < 0) ? left : right;

Dan

[Jacob Roth]

Now I can’t seem to define xLim. Error at line 46, xLim is missing or does not exist.

content = thisLayer.sourceRectAtTime();
left = content.width/2;
top = content.height/2;
right = thisComp.width-content.width/2;
bottom = thisComp.height-content.height/2;

minSpeed = 100; //pixels per second
maxSpeed = 100;

minX = left + 20;
maxX = right - 20;
minY = top + 20;
maxY = bottom - 20;

minR = 5;
maxR = 85;

seedRandom(index,true);

// calc start position

pos = random([minX,minY],[maxX,maxY])
quadrent = Math.floor(random(4))*90;
angle = random(minR,maxR) + quadrent;
spd = random(minSpeed,maxSpeed);

// initialize time count;

t = 0;

while(t &lt;= time){
rads = degreesToRadians(angle);
xVel = spd*Math.cos(rads);
yVel = spd*Math.sin(rads);

// see if going up or down

if (yVel &lt; 0) yLim = (yVel &lt; 0) ? top : bottom;
// see if going right or left

if (xVel &lt; 0) xLim = (xVel &lt; 0) ? left : right;

timeX = (xLim - pos[0])/xVel;
timeY = (yLim - pos[1])/yVel;

if (timeX < timeY){ //hit left or right wall
if (t + timeX >= time){
deltaT = time - t;
pos += [xVel,yVel]*deltaT;
break;
}else{
pos = [xLim,pos[1] + yVel*timeX];
angle = 180 - angle;
t += timeX;
}
}else{ //hit upper or lower wall
if (t + timeY >= time){
deltaT = time - t;
pos += [xVel,yVel]*deltaT;
break;
}else{
pos = [pos[0] + xVel*timeY,yLim];
angle = 360 - angle;
t += timeY;
}
}
}
pos

[Dan Ebberts]

No, like this:

// see if going up or down

yLim = (yVel < 0) ? top : bottom;
// see if going right or left

xLim = (xVel < 0) ? left : right;

Dan