Tag Archives: flash

Calculate Slope of a Line

By Zevan | June 2, 2009
CLICK HERE TO COPY
Actionscript:
  1. // calculate the slope of a line
  2. function calculateSlope(x1:Number, y1:Number, x2:Number, y2:Number):Number {
  3.         // rise over run
  4.     var s:Number = (y1 - y2) / (x1 - x2);
  5.     /*if (x1==x2) {
  6.         // slope is Infinity or -Infinity
  7.     }*/
  8.     return s;
  9. }
  10.  
  11. /**
  12.  Test it out
  13. */
  14. function draw(x1:Number, y1:Number, x2:Number, y2:Number):void {
  15.     graphics.moveTo(x1, y1);
  16.     graphics.lineTo(x2, y2)
  17.     var txt:TextField =TextField(addChild(new TextField()));
  18.     txt.text = calculateSlope(x1, y1, x2, y2).toFixed(2);
  19.     txt.x = x2, txt.y = y2;
  20. }
  21.  
  22. graphics.lineStyle(0,0xFF0000);
  23. draw (100, 100, 200, 200);
  24.  
  25. draw(100, 100, 200, 150);
  26.  
  27. draw(100, 100, 200, 100);
  28.  
  29. draw(100, 100, 99, 200);

This snippet shows how to calculate the slope of a line ... It demos the function by drawing a few lines and showing the corresponding slope of each.

It will draw this:

If (x1 == x2), the slope will be -Infinity or Infinity... depending on where you're using this calculation you may want to reset the s variable to something else, return null etc... I commented it out for simplicity.

Posted in Math, misc | Also tagged , | Leave a comment

for loop Fun

By Zevan | June 1, 2009
CLICK HERE TO COPY
Actionscript:
  1. var leng:int = 10;
  2. for (var i:int = 0, j:int = leng;  i <leng; i++, j = leng - i){
  3.     trace(i, j);
  4. }
  5.  
  6. /*outputs
  7. 0 10
  8. 1 9
  9. 2 8
  10. 3 7
  11. 4 6
  12. 5 5
  13. 6 4
  14. 7 3
  15. 8 2
  16. 9 1
  17. */

Looping backwards and forwards.

Posted in Math, misc, one-liners | Also tagged | Leave a comment

QuickBox2D Groups

By Zevan | May 31, 2009
CLICK HERE TO COPY
Actionscript:
  1. import com.actionsnippet.qbox.*;
  2.  
  3. [SWF (backgroundColor=0xAA0000, width=700, height=600, frameRate=60)]
  4.  
  5. var sim:QuickBox2D = new QuickBox2D(this);
  6.  
  7. sim.createStageWalls();
  8.  
  9. /**
  10. create a dancing pill
  11. */
  12. // all x and y coords are relative to the center of the group
  13. var partA:QuickObject = sim.addCircle({x:-1, y:0, radius:0.5, restitution:.9});
  14. var partB:QuickObject = sim.addCircle({x:1, y:0, radius:0.5, restitution:.9});
  15. var partC:QuickObject = sim.addBox({x:0, y:0, width:2, height:1});
  16. // all the parts are passed into the objects array
  17. // addGroup() groups the parts together into one rigid body
  18. var pill:QuickObject = sim.addGroup({objects:[partA, partB, partC], x:3, y:3, angle:0.3});
  19.  
  20. /**
  21. create another group
  22. */
  23. partA = sim.addCircle({x:0, y:0, radius:1});
  24. partB = sim.addBox({x:0, y:1, width:1, height:1, fillColor:0x666666});
  25. partC = sim.addBox({x:0, y:-1, width:1, height:1, fillColor:0x666666});
  26. sim.addGroup({objects:[partA, partB, partC], x:8, y:3, angle:0.3});
  27.  
  28. /**
  29. create two circles linked together by a stretchy joint
  30. */
  31. partA = sim.addCircle({x:15, y:3, fillColor:0x000000, anglularDamping:1});
  32. partB = sim.addCircle({x:17, y:3, fillColor:0xFFFFFF, anglularDamping:1});
  33. // if x1, y1, x2 and y2 properties are not set, the joint is automatically placed
  34. // at the b2Body's center
  35. sim.addJoint({a:partA.body, b:partB.body, frequencyHz:1});
  36.  
  37. sim.start();
  38. sim.mouseDrag();

You'll need QuickBox2D Alpha 106 to run this... This snippet demo's the addGroup() method, which allows for easy grouping of shapes. I updated the docs today to feature a simple explanation of how this works.


Have a look at the swf here...

Posted in Box2D, QuickBox2D, motion | Also tagged , | 3 Comments

QuickBox2D Polys

By Zevan | May 30, 2009
CLICK HERE TO COPY
Actionscript:
  1. import com.actionsnippet.qbox.*;
  2.  
  3. [SWF(backgroundColor=0x000000, width=700, height=600)]
  4.  
  5. var sim:QuickBox2D = new QuickBox2D(this);
  6.  
  7. sim.setDefault({fillColor:0x003366, lineColor:0x2B80D5});
  8. sim.createStageWalls();
  9.  
  10. var i:int = 0;
  11. for (i= 0; i<10; i++){
  12.   sim.addCircle({x:5 + i, y:7, radius:0.3, linearDamping:1, angularDamping:1, fillColor:0x78B4C2, isBullet:true}); 
  13. }
  14.  
  15. for (i= 0; i<2; i++){
  16.     var poly:Array = [];
  17.     var r:Number = 3;
  18.     var step:Number = Math.PI / 6;
  19.     for (var t:Number = 0; t<=Math.PI; t+=step){
  20.         poly.push(r * Math.cos(t));
  21.         poly.push(r * Math.sin(t));
  22.     }
  23.     r = 2;
  24.     for (t = Math.PI; t>= -step; t-=step){
  25.         poly.push(r * Math.cos(t));
  26.         poly.push(r * Math.sin(t));
  27.     }
  28.     // using points instead of verts causes QuickBox2D to triangulate the polygon
  29.     // the wireframe boolean changes rendering style for polys
  30.     sim.addPoly({x:4 + i *7, y:16, points:poly, wireframe:Boolean(i), linearDamping:1.5, angularDamping:1});
  31. }
  32.  
  33. sim.start();
  34. sim.mouseDrag();

I just uploaded QuickBox2D Alpha 106 which includes a few bug fixes and support for compound shapes and easier polys. I used the algorithm from yesterdays post to significantly simplify the way QuickBox2D handles the description of polygons.

You'll need QuickBox2D Alpha 106 or greater, if you want to test this....


or just have a look at the demo here.

This triangulation is really better suited for 3D stuff - Box2D supports multiple convex polygons in one rigid body... this algorithm makes more shapes (triangles) than Box2D needs - I'll probably swap out the algorithm in the near future.

Tomorrow I'll be posting a demo about the way QuickBox2D simplifies compound shapes. I have yet to update the docs to include the new features of Alpha 106. That will happen along with tomorrows post.

Posted in Box2D, QuickBox2D, motion | Also tagged | 7 Comments