How to draw a Waveform? - ios

Question

I'm using Superpowered SDK, to play a sound.
It has a function that returns unsigned char** called peakWaveForm.
I wrote a custom uiview and try to draw this values, and my view doesn't have good look. My question, is how should be the values to draw my waveform?.
And what kind of variable. An array?. What should be the normal size for a waveform?. The SDK returns an unsigned char** how can i proceed?
- (void)drawRect:(CGRect)updateRect
{
unsigned i, maxIndex;
maxIndex = floor(CGRectGetMaxX(updateRect));
i = floor(CGRectGetMinX(updateRect));
float firstPoint = (float)mPeakWaveForm[0][i];
UIBezierPath *path = [UIBezierPath bezierPath];
path.lineWidth = 2;
[[UIColor blackColor] setFill];
[path moveToPoint:CGPointMake(i,firstPoint)];
for(i; i <= maxIndex; i++)
{
float nextPoint = (float)mPeakWaveForm[0][i];
[path addLineToPoint:CGPointMake(i, nextPoint)];
}
[path fill];
}

Answer 1

I was in the same situation as you, and solved it this way.
First, the waveform you are getting in only a 1-dimension data array, and we want it 2d to have it in both axis.
So what i did was create an array point instead of drawing the path directly and then drawing the path once and another time mirrored arround x-axis as this:
var points = Array<CGPoint>()
for(i; i <= maxIndex; i++)
{
float nextPoint = (float)mPeakWaveForm[0][i];
points.append(CGPoint(x: CGFloat(i), y: CGFloat(nextPoint)))
}
//Move to the center of the view
var xf = CGAffineTransformIdentity;
xf = CGAffineTransformTranslate(xf, 0, halfHeight)
//Scale it as needed (you can avoid it)
xf = CGAffineTransformScale(xf, xscale, yscale)
let path = CGPathCreateMutable()
//Draw the lines
CGPathAddLines(path, &xf, points, points.count)
//Mirror the drawing and draw them again
xf = CGAffineTransformScale(xf, 1.0, -1.0);
CGPathAddLines(path, &xf, points, points.count);
CGPathCloseSubpath(path)
//Draw the path
let ctx = UIGraphicsGetCurrentContext();
CGContextAddPath(ctx, path);
CGContextSetStrokeColorWithColor(ctx,UIColor.whiteColor().CGColor);
CGContextFillPath(ctx);
Sorry about the code being in swift, but the functions are the same that in Objective-C