How to create a ball that remains in a status of uniform motion in a curve line?

Programming Questions

GeoisArt

How to create a ball that remains in a status of uniform motion in a curve line?

in Programming Questions • 7 months ago

Hi everyone,

I use loadStrings() method to load all the discrete X,Y coordinates from a txt file. Then I put them in a string array. If I directly put ellipse(X,Y,10,10) under the draw() method, the ball will not move in a constant speed, because the distance between each sets of coordinates is different. As the ball moves in a high density area, it slows down dramatically; as it moves in a discrete area, it moves fast. Is there any way to make it move in a constant speed in the whole route? or should I use some other shape like to create a curve first before draw()?

Here is my scripts:

String[] lines;
int index=0;
void setup(){
lines=loadStrings("positions.txt");
frameRate(12);
noStroke();
background(0);
}
void draw(){
fill(0,30);
rect(0,0,width,height);
fill(255);
if(index<lines.length){
String[] pieces=split(lines[index],'\t');
if(pieces.length==2){
int x=int(pieces[0]);
int y=int(pieces[1]);
ellipse(x,y,8,8);
}
index++;
}
}

Here is the position.txt:

70 35
69 35
68 39
67 42
66 47
64 51
64 54
63 57
60 60
58 64
51 69
48 72
44 73
39 75
35 75
30 75
25 75
21 75
17 73
13 69
12 66
11 61
11 57
10 49
10 45
10 38
12 32
13 29
16 23
20 19
24 16
27 15
31 13
33 13
37 13
40 15
42 16
45 19
46 21
47 24
48 26
48 29
48 33
47 39
43 45
42 47
38 50
35 51
32 51
30 51
27 50
27 50
26 46
26 41
29 36
30 34
31 33
31 33
32 33
33 33
34 33
34 33
35 33
37 33
39 33
42 32
44 31
46 29
48 29
49 27
52 24
53 23
57 19
61 16
63 14
67 13
69 12
69 12
77 11
77 11
80 11
86 16
90 21
93 25
95 29
95 32
95 33
95 37
94 41
93 44
92 46
91 49
89 51
87 55
85 59
82 62
80 64
79 67
77 69
74 71
68 72
65 73
63 73
62 73
60 72
58 69
57 67
57 66
56 60
56 56
56 54
58 49
60 47
62 47
63 47
67 48
70 52
73 55
74 57
74 58
74 60
74 62
73 65
70 68
67 69
65 70
63 70
62 70
60 68
57 65
55 64
50 62
46 61
40 60
38 60
36 60
32 61
30 62
27 64
26 68
25 71
25 77
25 81
26 84
28 86
31 87
33 88
36 88
39 86
41 85
43 83
44 81
45 76
45 74
45 71
40 67
37 65
34 63
33 61
33 61
32 60
33 49
37 45
41 41
45 39
47 38
51 37
54 37
58 38
61 41
63 44
65 46
66 49
66 51
67 55
67 58
67 60
66 62
64 65
63 66
61 67
60 68
58 68
55 69
54 69
51 69
48 69
46 68
45 66
44 65
44 63
44 61
44 59
44 56
44 55
45 53
47 52
49 50
50 48
51 47
52 46
54 46
55 45
55 45
56 44
57 44

Thanks,

Zhenyang

Replies(5)

Chrisir

Re: How to create a ball that remains in a status of uniform motion in a curve line?

7 months ago

you could use lerp.

If you calculathe dist between the current two points derive amt from the dist.

http://www.processing.org/reference/lerp_.html

GeoisArt

Re: Re: How to create a ball that remains in a status of uniform motion in a curve line?

7 months ago

Hi Chrisir,

Thanks for your answer, but how lerp() could help to solve my question? I want the ball moving along the whole route at the same speed. As in my scripts, everytime draw() refreshes the frame, a new point is drawn, the distance between each set of points is different, but the frameRate, which is the time, is the same, so the speed is different between each set of point. In this case, lerp() only interpolate new points between each two points, which can make the movement look like smooth, but doesn't change the speed to a constant value in the whole route.

Zhenyang

Chrisir

Re: How to create a ball that remains in a status of uniform motion in a curve line?

7 months ago

I didn't test it

which can make the movement look like smooth, but doesn't change the speed to a constant value in the whole route.

amt is the value in the example, but it's not amt really, I mean 10 in the example (my failure):

If your dist is 100 you can use 10 steps,
If your dist is 1000 you can use 100 steps,

to make it look equally fast.

when you change 10 depending on the dist, it could work.

http://www.processing.org/reference/lerp_.html

GeoisArt

Re: Re: How to create a ball that remains in a status of uniform motion in a curve line?

7 months ago

Chrisir,

Thank you for your explanation, I didn't think it through. I tested it, your method works!

Here is the Cpoint class code: //I create a class to generate and collect all the coordinates interpolated by lerp() methods.

class Cpoint{
String[] lines;
ArrayList points;
Cpoint(){
lines=loadStrings("positions.txt");
points=new ArrayList();
}
void makePoint(){
for(int i=0;i<lines.length-1;i++){
String[] pieces1=split(lines[i],'\t');
String[] pieces2=split(lines[i+1],'\t');
if((pieces1.length==2)&&(pieces2.length==2)){
float x1=int(pieces1[0]);
float y1=int(pieces1[1]);
float x2=int(pieces2[0]);
float y2=int(pieces2[1]);
float distance=dist(x1,y1,x2,y2);
for(int j=0;j<distance;j++){
float x=lerp(x1,x2,j*0.1/distance);
float y=lerp(y1,y1,j*0.1/distance);
//println(x);
points.add(new PVector(x,y));
}
}
}
}
}

And then use main to call it:

Cpoint cp;
int index=0;
void setup(){
cp=new Cpoint();
cp.makePoint();
//frameRate(60);
noStroke();
smooth();
background(0);
}
void draw(){
fill(0,5);
rect(0,0,width,height);
fill(255);
if(index<cp.points.size()){
PVector newPoint=(PVector)cp.points.get(index);
float xpos=newPoint.x;
float ypos=newPoint.y;
ellipse(xpos,ypos,8,8);
//println(xpos+", "+ypos);
index++;
}
}

Here comes another question: Is there any way to improve the smoothness of the movement track?

Zhenyang

Chrisir

Re: How to create a ball that remains in a status of uniform motion in a curve line?

7 months ago

Here comes another question: Is there any way to improve the smoothness of the movement track?

I don't know.

I asked that now in another thread.

My only idea is to use some kind of damping.

This means, you don't go to the next point immediately but with a damping / easing:
This means it turns there with a delay.....

I can show you an example for a camera; easing has the value 0.7
so it gets there after some rounds, but not immediately.

Makes it look smooth.

case 3:
// As the last one but with easing
camWhereItShouldBe.set(ball.x+camAdd.x, ball.y+camAdd.y, ball.z+camAdd.z);
camPos.x+= ( camWhereItShouldBe.x - camPos.x ) * easing;
camPos.y+= ( camWhereItShouldBe.y - camPos.y ) * easing;
camPos.z+= ( camWhereItShouldBe.z - camPos.z ) * easing;
camera(camPos.x, camPos.y, camPos.z,
ball.x, ball.y, ball.z,
0.0, 1.0, 0.0);
break;

Greetings, Chrisir

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