blitz-research
107 lines
3.5 KiB
HTML
107 lines
3.5 KiB
HTML
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<title>Blitz3D Docs</title>
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<link rel=stylesheet href=../css/commands.css type=text/css>
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<body>
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<h1>Sin# ( degrees# )</h1>
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<h1>Parameters</h1>
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<table>
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<tr>
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<td>
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degrees# = angle in degrees.
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</td>
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</tr>
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</table>
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<h1>Description</h1>
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<table>
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Sine of an angle. The angle is measured in degrees.
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For angles between 0 and 90 degrees this is defined by the sides of a right triangle. The sine is the side opposite the angle divided by the hypotenuse.
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Outside of 0 to 90 the definition uses a circle with radius=1. The angle is placed at the center of the circle, with one side on the positive x-axis. The other side hits the circle at some point. The y coordinate of this point is the sine of the angle.
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The positive y-axis corresonds to +90 degrees. This is a common source of confusion in Blitz. With screen coordinates ( pixels ) the y-axis points downward. But in the 3d world the y-axis typically points upward.
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Another possible snag is the size of the angle. In principle, the sine function repeats every 360 degrees. So Sin(-360), Sin(0), Sin(360), Sin(720) etc. should all be exactly the same. But in practice the accuracy decreases as the angle gets farther away from zero.
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See also ASin, Cos, ACos, Tan, Atan, ATan2
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</td>
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</tr>
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</table>
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<h1><a href=../2d_examples/Sin.bb>Example</a></h1>
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<table>
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; Sin / Cos / Tan example.
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; Left/Right arrow keys change angle. Escape quits.
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Const width = 640, height = 480
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Const radius# = .2 * height
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Const KEY_ESC = 1, KEY_LEFT = 203, KEY_RIGHT = 205
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Graphics width, height
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SetBuffer BackBuffer( )
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Origin width / 3, height / 2
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angle# = 0.0
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While Not KeyDown( KEY_ESC )
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; NOTE: It is usually best to avoid very large angles.
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; The 'If angle...' lines show one way to do this.
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; Mod is another possibility.
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If KeyDown( KEY_LEFT ) Then angle = angle - .5
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; If angle < 0.0 Then angle = angle + 360
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If KeyDown( KEY_RIGHT ) Then angle = angle + .5
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; If angle >= 360.0 Then angle = angle - 360
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Cls
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Color 80, 80, 0 ; pale yellow circle
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Oval -radius, -radius, 2 * radius, 2 * radius, False
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For a# = 0.0 To Abs( angle Mod 360 ) Step .5
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x# = radius * Cos( a ) ; (x,y) is a point on the circle
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y# = radius * Sin( a ) ; corresponding to angle a.
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If ( angle Mod 360 < 0 ) Then y = -y ; reverse for negative angle
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WritePixel x, y, $ffff00 ; bright yellow
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Next
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Color 255, 255, 0 ; yellow
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Line 0, 0, radius * Cos( angle ), radius * Sin( angle )
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Color 0, 255, 0 ; green
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Line 0, 0, radius * Cos( angle ), 0
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Text radius * 1.5, 10, "Cos( angle ) = " + Cos( angle )
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Color 255, 0, 0 ; red
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Line radius * Cos( angle ), 0, radius * Cos( angle ), radius * Sin( angle )
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Text radius * 1.5, -10, "Sin( angle ) = " + Sin( angle )
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Color 255, 255, 255
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Text radius * 1.5, -30, " angle = " + angle
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Text radius * 1.5, 30, "Tan( angle ) = " + Tan( angle )
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Flip
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Wend
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End
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</td>
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</tr>
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</table>
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<br>
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<a target=_top href=../index.htm>Index</a><br>
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<br>
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Click <a href=http://www.blitzbasic.co.nz/b3ddocs/command.php?name=Sin&ref=comments target=_blank>here</a> to view the latest version of this page online</body>
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</html>
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