hi, thanks for reply and sorry for this
the "suspicious" part is line 16

1.
test= new Rect_line(movex+0.1,height*0.4,movex,height*0.6,wiggle,height*0.5,rect_diam,rect_diam);
if i remove +0.1 from first parameter and first and third then is just movex, then collision is no more detected

2.
now, when line and square collides fill color is randomized but on every frame, i want something to happen just once when collision is detected
so i tried to use boolean touching to achieve this, but then the collision no more works

activate line 47 and see for yourself
//touching= lineRectangleIntersect(lineX1, lineY1, lineX2, lineY2, rectX, rectY, rectWidth, rectHeight);

a bit lost here,don't see where the problem is

here's the full code

1. float movex,a,b,wiggle,wiggle2;
2. float rect_diam=20;
3. boolean maxormin = false;
4. Rect_line test;
5. void setup() {
6.   size(400, 400);
7.   ellipseMode(RADIUS);
8.   smooth();
9. }
10. void draw() {
11.   background(0);
12.  
13.  wiggle=noise(a)*width;
14.  wiggle2=noise(b,20)*height*0.4;
15.  
16. test= new Rect_line(movex+0.1,height*0.4,movex,height*0.6,wiggle,height*0.5,rect_diam,rect_diam);
17.  test.display();
18.  
19.  a+=0.01;
20.  b+=0.03;
21. }
22.  
23. class Rect_line {
24. float lineX1;
25. float lineY1;
26. float lineX2;
27. float lineY2;
28.  
29. float rectX;
30. float rectY;
31. float rectWidth;
32. float rectHeight;
33. float thick;
34. boolean touching;
35. Rect_line(float _lineX1,float _lineY1,float _lineX2,float _lineY2,float _rectX,float _rectY,float _rectWidth,float _rectHeight){
36.  
37. lineX1 = _lineX1;
38. lineY1 = _lineY1;
39. lineX2=_lineX2;
40. lineY2=_lineY2;
41.  
42. rectX = _rectX;
43. rectY = _rectY;
44. rectWidth = _rectWidth;
45. rectHeight = _rectHeight;
46. // breaks the collision detection if activiated
47. //touching= lineRectangleIntersect(lineX1, lineY1, lineX2, lineY2, rectX, rectY, rectWidth, rectHeight);
48.  
49. }
50.  
51.  
52. void display(){
53.   if (lineRectangleIntersect(lineX1, lineY1, lineX2, lineY2, rectX, rectY, rectWidth, rectHeight) == true &&
54.   touching != lineRectangleIntersect(lineX1, lineY1, lineX2, lineY2, rectX, rectY, rectWidth, rectHeight))
55.   {
56.      touching= lineRectangleIntersect(lineX1, lineY1, lineX2, lineY2, rectX, rectY, rectWidth, rectHeight);
57.     fill(random(255));
58.   
59.    
60.   }
61.  
62.  
63.  
64.   else {
65.     fill(0);
66.   touching= lineRectangleIntersect(lineX1, lineY1, lineX2, lineY2, rectX, rectY, rectWidth, rectHeight);
67.   
68.   
69.   };
70.  
71.   stroke(255);
72.   strokeCap(PROJECT);
73.   line(lineX1, lineY1, lineX2, lineY2);
74.   rectMode(CENTER);
75.   strokeWeight(1);
76.   rect(rectX, rectY, rectWidth, rectHeight);
77.   line(0,height/2,width,height/2);
78.  move();
79.  
80. }
81.  
82.  
83.   void move(){
84.     if (movex <= 0) {
85.     maxormin = true;
86.   }
87.   if (movex >= width) {
88.     maxormin = false;
89.   }
90.  
91.   if (maxormin == true) { //if you've hit the min, increase your value
92.     movex +=1;
93.   }
94.   if (maxormin == false) { //if you've hit the max, decremet your value
95.     movex -=1;
96.   }
97.   
98.   }
99.  
100.  
101.  
102.  
103.  
104.  boolean lineRectangleIntersect(float x1, float y1, float x2, float y2,
105.                                float rx, float ry, float rw, float rh) {
106.                                 
107.   float topIntersection;
108.   float bottomIntersection;
109.   float topPoint;
110.   float bottomPoint;
111.  
112.   // Calculate m and c for the equation for the line (y = mx+c)
113.   float m = (y2-y1) / (x2-x1);
114.   float c = y1 -(m*x1);
115.  
116.   // If the line is going up from right to left then the top intersect point is on the left
117.   if(m > 0) {
118.     topIntersection = (m*rx  + c);
119.     bottomIntersection = (m*(rx+rw)  + c);
120.   }
121.   // Otherwise it's on the right
122.   else {
123.     topIntersection = (m*(rx+rw)  + c);
124.     bottomIntersection = (m*rx  + c);
125.   }
126.  
127.   // Work out the top and bottom extents for the triangle
128.   if(y1 < y2) {
129.     topPoint = y1;
130.     bottomPoint = y2;
131.   } else {
132.     topPoint = y2;
133.     bottomPoint = y1;
134.   }
135.  
136.   float topOverlap;
137.   float botOverlap;
138.  
139.   // Calculate the overlap between those two bounds
140.   topOverlap = topIntersection > topPoint ? topIntersection : topPoint;
141.   botOverlap = bottomIntersection < bottomPoint ? bottomIntersection : bottomPoint;
142.  
143.   return (topOverlap<botOverlap) && (!((botOverlap<ry) || (topOverlap>ry+rh)));
144.  
145. }
146.  
147. }

 

i've spend some time on this this morning but i haven't figured out a solution yet.  I did want to stop by to tell you what i believe the problem is so you could at least move past not knowing

The following is unrelated code! However, it deals w/: 

if lineX1 and lineX2 parameters are the same the collision detection don't work anymore changing a bit one of the parameters solves the problem

This is not your fault the problem is with the algorithm to detect an intersection. In fact the problem is with this line :-
float m = (y2-y1) / (x2-x1);

if x1 == x2 then you are attempting to divide a number by zero - which means that m will become INFINITY but the program will attempt to use it anyway

A good line-box intersection algorithm should would for all lines, the code below not only does that, but is also a fast algorithm.

Copy the code into your sketch and use either method depending on how the box co-ordinates are specified.

NOTE if the line is completey inside the box (i.e. both start and end points are inside the box) then these methods return true.

1. /**
2.  * Determine whether a line intersects with a box. <br>
3.  * The box is represented by the top-left and
4.  * bottom-right corner coordinates.
5.  * @param lx0
6.  * @param ly0
7.  * @param lx1
8.  * @param ly1
9.  * @param rx0
10.  * @param ry0
11.  * @param rx1
12.  * @param ry1
13.  * @return true if they intersect else false
14.  */
15. boolean line_box_xyxy(float lx0, float ly0, float lx1, float ly1, float rx0, float ry0, float rx1, float ry1) {
16.   int out1, out2;
17.   float rectWidth = rx1 - rx0;
18.   float rectHeight = ry1 - ry0;
19.   if ((out2 = outcode(lx1, ly1, rx0, ry0, rectWidth, rectHeight)) == 0) {
20.     return true;
21.   }
22.   while ( (out1 = outcode (lx0, ly0, rx0, ry0, rectWidth, rectHeight)) != 0) {
23.     if ((out1 & out2) != 0) {
24.       return false;
25.     }
26.     if ((out1 & (OUT_LEFT | OUT_RIGHT)) != 0) {
27.       float x = rx0;
28.       if ((out1 & OUT_RIGHT) != 0) {
29.         x += rectWidth;
30.       }
31.       ly0 = ly0 + (x - lx0) * (ly1 - ly0) / (lx1 - lx0);
32.       lx0 = x;
33.     } else {
34.       float y = ry0;
35.       if ((out1 & OUT_BOTTOM) != 0) {
36.         y += rectHeight;
37.       }
38.       lx0 = lx0 + (y - ly0) * (lx1 - lx0) / (ly1 - ly0);
39.       ly0 = y;
40.     }
41.   }
42.   return true;
43. }
44. 
    
45. /**
46.  * Determine whether a line intersects with a box. <br>
47.  * The box is represented by the top-left corner coordinates
48.  * and the box width and height.
49.  * @param lx0
50.  * @param ly0
51.  * @param lx1
52.  * @param ly1
53.  * @param rx0
54.  * @param ry0
55.  * @param rWidth
56.  * @param rHeight
57.  * @return true if they intersect else false
58.  */
59. boolean line_box_xywh(float lx0, float ly0, float lx1, float ly1, float rx0, float ry0, float rWidth, float rHeight) {
60.   int out1, out2;
61.   if ((out2 = outcode(lx1, ly1, rx0, ry0, rWidth, rHeight)) == 0) {
62.     return true;
63.   }
64.   while ( (out1 = outcode (lx0, ly0, rx0, ry0, rWidth, rHeight)) != 0) {
65.     if ((out1 & out2) != 0) {
66.       return false;
67.     }
68.     if ((out1 & (OUT_LEFT | OUT_RIGHT)) != 0) {
69.       float x = rx0;
70.       if ((out1 & OUT_RIGHT) != 0) {
71.         x += rWidth;
72.       }
73.       ly0 = ly0 + (x - lx0) * (ly1 - ly0) / (lx1 - lx0);
74.       lx0 = x;
75.     } else {
76.       float y = ry0;
77.       if ((out1 & OUT_BOTTOM) != 0) {
78.         y += rHeight;
79.       }
80.       lx0 = lx0 + (y - ly0) * (lx1 - lx0) / (ly1 - ly0);
81.       ly0 = y;
82.     }
83.   }
84.   return true;
85. }
86. 
    
87. /*
88.  * Used by line - box intersection algorithm
89.  */
90. int outcode(float pX, float pY, float rectX, float rectY, float rectWidth, float rectHeight) {
91.   int out = 0;
92.   if (rectWidth <= 0) {
93.     out |= OUT_LEFT | OUT_RIGHT;
94.   } else if (pX < rectX) {
95.     out |= OUT_LEFT;
96.   } else if (pX > rectX + rectWidth) {
97.     out |= OUT_RIGHT;
98.   }
99.   if (rectHeight <= 0) {
100.     out |= OUT_TOP | OUT_BOTTOM;
101.   } else if (pY < rectY) {
102.     out |= OUT_TOP;
103.   } else if (pY > rectY + rectHeight) {
104.     out |= OUT_BOTTOM;
105.   }
106.   return out;
107. }
108. 
     
109. // Used in line-box intersection test
110. final int OUT_LEFT    = 1;
111. final int OUT_TOP     = 2;
112. final int OUT_RIGHT   = 4;
113. final int OUT_BOTTOM  = 8;

thanx a lot guys for answers but i am too stupid to put it all together now and need it to work asap
can somebody be so kind and update the code please?