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fft_ctrl.js
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fft_ctrl.js
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function __createFFTDataFromCanvas( _canvasId_m, _canvasId_p ) {
var canvas_m = document.getElementById( _canvasId_m );
var canvas_p = document.getElementById( _canvasId_p );
if ( !canvas_m || !canvas_p ) {
return false;
}
var context_m = canvas_m.getContext( '2d' );
var context_p = canvas_p.getContext( '2d' );
if ( !context_m || !context_p ) {
return false;
}
var ww = canvas_m.width;
var hh = canvas_m.height;
var real = new Array();
var imag = new Array();
real.length = ww * hh * 4;
imag.length = ww * hh * 4;
var raw_m = context_m.getImageData( 0, 0, ww, hh );
var result_m = raw_m.data;
var raw_p = context_p.getImageData( 0, 0, ww, hh );
var result_p = raw_p.data;
for ( var pp=0; pp < result_m.length; ++pp ) {
var mag = result_m[ pp ] / 255.0;
var phase = ( result_p[pp] - 128 ) * pi / 128.0;
real[ pp ] = mag * Math.cos( phase );
imag[ pp ] = mag * Math.sin( phase );
}
return {
width: ww,
height: hh,
real: real,
imag: imag,
level: 1
};
}
function __fillCanvasesFromFFTData( _canvasId_m, _canvasId_p, _fftData ) {
var canvas_m = document.getElementById( _canvasId_m );
var canvas_p = document.getElementById( _canvasId_p );
if ( !canvas_m || !canvas_p ) {
return false;
}
var ww = _fftData.width;
var hh = _fftData.height;
var real = _fftData.real;
var imag = _fftData.imag;
canvas_m.width = ww;
canvas_m.height = hh;
canvas_p.width = ww;
canvas_p.height = hh;
var context_m = canvas_m.getContext( '2d' );
var context_p = canvas_p.getContext( '2d' );
if ( !context_m || !context_p ) {
return false;
}
var raw_m = context_m.getImageData( 0, 0, ww, hh );
var result_m = raw_m.data;
var raw_p = context_p.getImageData( 0, 0, ww, hh );
var result_p = raw_p.data;
//
// then, we fill the canvas with the magnitude of
// the complex FFT data
//
for ( var pp=0; pp < result_m.length; pp += 4 ) {
//
// here, we do the red, green, and blue, but just
// hardcode the alpha
//
for ( var kk=0; kk < 3; ++kk ) {
var index = pp + kk;
result_m[ index ] = __clampPixel( real[ index ], imag[ index ] );
result_p[ index ] = __clampPhase( real[ index ], imag[ index ] );
}
result_m[ pp + 3 ] = 255;
result_p[ pp + 3 ] = 255;
}
//
// then, we blit our representation back to the canvas
//
context_m.putImageData( raw_m, 0, 0 );
context_p.putImageData( raw_p, 0, 0 );
return true;
}
function doFFT( _canvasId_m, _canvasId_p, _inverse ) {
if ( !fftData ) {
fftData = __createFFTDataFromCanvas( _canvasId_m, _canvasId_p );
if ( !fftData ) {
return false;
}
}
var success;
if ( _inverse ) {
success = IFFT( fftData );
}
else {
success = FFT( fftData );
}
if ( success ) {
__fillCanvasesFromFFTData( _canvasId_m, _canvasId_p, success );
fftData = success;
}
return success;
}