J'ai travaillé sur la création de beaux graphiques transparents en couches sur un canevas html5 et j'ai rencontré une erreur ennuyeuse uniquement sur Chrome. Il met en évidence les bords des sections de ligne de chaque graphique créant des lignes verticales laides. Voir image ci-dessous :

enter image description here

Le code qui dessine ces lignes est :

var graphs = // [[points...],[points...],...]
var canvas = document.getElementById('canvas');
var ctx = canvas.getContext('2d');
canvas.width = 926;
canvas.height = 418;

ctx.lineWidth = 1;
ctx.strokeStyle = "rgba(155,155,255, .3)"

for(var j = 0; j < graphs.length; j++) {
  var graph = graphs[j]

  var path = new Path2D()

  for(var i = 0; i < graph.length; i = i + 2) {
    // i = x, i+1 = y
    if(i === 0) 
      path.moveTo(graph[i], graph[i+1])
    else 
      path.lineTo(graph[i], graph[i+1])
  }

  ctx.stroke(path);  
}

Codepen : voir exemple de travail

Il fonctionne sur Firefox, Safari, Edge. Ne fonctionne pas sur Chrome sur Mac et Windows.

Une idée de ce qui cause cela ???

1
miqueloi 8 mars 2019 à 17:44

2 réponses

Meilleure réponse

Bug intéressant en effet, vous voudrez peut-être ouvrir un problème sur leur bug tracker.

Pour une solution de contournement, vous pouvez simplement changer légèrement lineWidth en 1.1 et le bogue d'anticrénelage disparaîtra :

function draw(graphs) {
  var canvas = document.getElementById('canvas');
  var ctx = canvas.getContext('2d');
  canvas.width = 926;
  canvas.height = 418;

  ctx.lineWidth = 1.1;
  ctx.strokeStyle = "rgba(155,155,255, .3)"

  for (var j = 0; j < graphs.length; j++) {
    var graph = graphs[j]

    var path = new Path2D()

    for (var i = 0; i < graph.length; i = i + 2) {
      // i = x, i+1 = y
      if (i === 0)
        path.moveTo(graph[i], graph[i + 1])
      else
        path.lineTo(graph[i], graph[i + 1])
    }

    ctx.stroke(path);
  }
}

//reduced the dataset so it can fit in the answer
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2
Kaiido 8 mars 2019 à 15:06

Ceci est dû à l'utilisation de coordonnées à virgule flottante, MDN recommande de l'éviter, vous pouvez atténuer le problème en utilisant une largeur de ligne de nombre à virgule flottante, ctx.lineWidth = 1.5;.

1
marc_s 22 mars 2019 à 21:44