Tubes disappear when meshgrid is too fine

[etpinard]

@kig try

var s0 = -5, s1 = 6, ds = 0.5
var s = [];

for (var i = 0; i < (s1 - s0) / ds; i++) {
  s.push(s0 + ds * i)
} 

var x = s, y = s, z = s;
    
var len = x.length * y.length * z.length;
var u=[],v=[],w=[]; 
for (var i=0; i<len; i++) { 
   u.push(1+Math.sin(i)); 
   v.push(Math.cos(i));
   w.push(Math.sin(i*0.3)*0.3);
}

var cx=[],cy=[],cz=[];
for (var i=0; i<7; i++) { 
  for(var j=0; j<7; j++) { 
    cx.push(-5); cy.push(i-3); cz.push(j-3);
  }
}

    Plotly.newPlot(gd, [{
      type: 'streamtube',
      startx: cx, starty: cy, startz: cz,
      u: u, v: v, w: w,
      x: x, y: y, z: z,
      colorscale: 'Viridis'
    }], {
       scene: {
         xaxis: {range: [-5,5]},
         yaxis: {range: [-5,5]},
         zaxis: {range: [-5,5]}
       }
    })

off the latest commit off plotly/plotly.js#2658,

I'm getting a blank scene:

whereas for ds values >= 0.6, things appear to work ok. For example with ds: 0.6:

[etpinard]

Post plotly/plotly.js#2658 (comment), this might be a non-issue, as meshgrid are on their way out (at least for the plotly.js v1 integration).

[kig]

I think this is because the starting points are right at the edge of the meshgrid, and sampling outside the meshgrid results in zero vectors and no streams. I changed the cx value to -4.9 and that got me tubes whereas -5 came up empty.