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ATan2.htm

ATan2.htm 2.1 KB
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  1. <html>
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  2. <head>
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  3. <title>Blitz3D Docs</title>
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  4. <link rel=stylesheet href=../css/commands.css type=text/css>
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  5. </head>
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  6. <body>
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  7. <h1>ATan2# ( y#, x# )</h1>
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  8. <h1>Parameters</h1>
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  9. <table>
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  10. <tr>
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  11. <td>
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  12. y, x are any numbers.
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  14. They are interpreted as corresponding to a point ( x, y ).
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  15. </td>
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  16. </tr>
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  17. </table>
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  18. <h1>Description</h1>
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  19. <table>
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  20. <tr>
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  22. ATan2 gives the angle between the positive x-axis and a vector from the point (0,0) to the point (x,y).

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  23. 
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  24. One common use is in 2d graphics. Suppose you have two objects and you want to aim the first at the second.

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  25. 
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  26. ATan2( y2 - y1, x2 - x1 ) gives the proper orientation for object1.

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  27. You can use this angle to select an appropriately rotated image.

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  28. 
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  29. Notice the reverse order, ATan2( y, x ) rather than ATan2( x, y).

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  30. ATan2( y, x ) is analogous to ATan( y / x), but covers 360 degrees.

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  31. 
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  32. The angle satisfies:  -180 < ATan2 <= +180
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  33. </td>
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  34. </tr>
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  35. </table>
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  36. <h1><a href=../2d_examples/ATan2.bb>Example</a></h1>
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  37. <table>
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  38. <tr>
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  39. <td>
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  40. ; ATan2 example.
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  41. 
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  42. ; Move mouse. Escape quits.
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  43. 
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  44. Const width = 640, height = 480
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  45. Const radius# = .2 * height
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  46. Const KEY_ESC = 1
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  47. 
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  48. Graphics width, height
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  49. SetBuffer BackBuffer( )
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  50. Origin width / 2, height / 2
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  51. HidePointer 
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  52. MoveMouse .75 * width, height / 2
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  53. 
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  54. While Not KeyDown( KEY_ESC )
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  55. 
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  56. Cls
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  57. 
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  58. Color 255, 255, 0
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  59. Line 0, 0, width / 2, 0   ; positive x-axis
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  60. 
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  61. x = MouseX() -  width / 2
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  62. y = MouseY() - height / 2
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  63. 
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  64. Oval x - 3, y - 3, 7, 7, True
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  65. Line 0, 0, x, y
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  66. 
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  67. Text .35 * width, -80, "x = " + x
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  68. Text .35 * width, -60, "y = " + y
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  69. 
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  70. Text .35 * width - 96, -40, "ATan2( y, x ) = " + ATan2( y, x )
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  71. 
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  72. Flip
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  73. 
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  74. Wend
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  75. 
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  76. End
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  77. </td>
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  78. </tr>
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  79. </table>
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  80. <br>
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  81. <a target=_top href=../index.htm>Index</a><br>
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  82. <br>
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  83. Click <a href=http://www.blitzbasic.co.nz/b3ddocs/command.php?name=ATan2&ref=comments target=_blank>here</a> to view the latest version of this page online</body>
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  84. </html>
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