Fix opacity calculation on chrome

nummi/history/templates/history/plot.html

@@ -102,8 +102,7 @@
                         {% endif %}
                         {% if m %}
                             <td class="{% if m.sum > 0 %}p{% else %}m{% endif %}"
-                                style="opacity: calc( sin( abs({% widthratio m.sum history.years_max 100 %}) / 400 * 1turn ) )">
-                            </td>
+                                style="opacity: {% opacity m.sum history.years_max %}"></td>
                         {% else %}
                             <td></td>
                         {% endif %}

nummi/main/templatetags/main_extras.py

@@ -1,3 +1,5 @@
+import math
+
 from django import template
 from django.templatetags.static import static
 from django.utils import formats
@@ -67,3 +69,8 @@ def css(href):
     return mark_safe(
         f"""<link rel="stylesheet" href="{static(href)}" type="text/css">"""
     )
+
+
+@register.simple_tag
+def opacity(v, vmax):
+    return f"{math.sin(math.fabs(v/vmax)*math.pi/2):.2f}"