fix: max hold for various corner cases

max hold needs to work, even when the data is always negative, but this complicates things because the ypoint array is initialized to zeros prior to the first push of data. The new code will wait until an entire frame of data is pushed (since you can push partial frames) and then initialize max hold to -Infinity.

Author: maihde

js/sigplot.layer1d.js

@@ -228,7 +228,16 @@
  }
 
  // update the position
- this.position = (this.position + tle) % this.size;
+ this.position = (this.position + tle);
+ // after we get one full buffer of data we can initialize maxhold and
+ // no longer rescale on first push
+ if ((this.position >= this.size) && (this.firstpush === false)) {
+ this.firstpush = true;
+ if (this.mhpoint) {
+ this.mhpoint.fill(-Infinity);
+ }
+ }
+ this.position = this.position % this.size;
 
  if (this.tle === undefined) {
  tle = Math.floor(m.pavail(this.hcb)) / this.hcb.spa;
@@ -325,12 +334,12 @@
  this.maxhold.decay = 0;
  }
  if (this.mhpoint) {
- // clear the maxhold buffer by setting to the current ypoint
- this.mhpoint.set(this.ypoint);
+ // clear the maxhold buffer by setting to negative Infinity
+ this.mhpoint.fill(-Infinity);
  } else {
  this.mhptr = new ArrayBuffer(this.pointbufsize);
  this.mhpoint = new m.PointArray(this.mhptr);
- this.mhpoint.set(this.ypoint);
+ this.mhpoint.fill(-Infinity);
  }
  } else if (settings.maxhold === null) {
  this.maxhold = undefined;
@@ -349,6 +358,7 @@
  if (this.maxhold) {
  this.mhptr = new ArrayBuffer(this.pointbufsize);
  this.mhpoint = new m.PointArray(this.mhptr);
+ this.mhpoint.fill(-Infinity);
  }
  }
 
@@ -420,6 +430,7 @@
  this.ymin = null;
  this.ymax = null;
  }
+ this.firstpush = false;
  }
 
  this.xdelta = this.hcb.xdelta;
@@ -436,7 +447,6 @@
 
  // if this is the first push of data, request a rescale
  if (this.firstpush === false) {
- this.firstpush = true;
  hdrmod = true;
  }
  return hdrmod ? true : false;
@@ -470,9 +480,13 @@
  this.yptr = new ArrayBuffer(this.pointbufsize);
  this.xpoint = new m.PointArray(this.xptr);
  this.ypoint = new m.PointArray(this.yptr);
+ // invalidate max hold buffers
+ this.mhptr = null;
+ this.mhpoint = null;
  if (this.maxhold) {
  this.mhptr = new ArrayBuffer(this.pointbufsize);
  this.mhpoint = new m.PointArray(this.mhptr);
+ this.mhpoint.fill(-Infinity);
  }
  }