fix zero-width line rendering

src/render/draw_line.js

@@ -16,7 +16,8 @@ export default function drawLine(painter: Painter, sourceCache: SourceCache, lay
     if (painter.renderPass !== 'translucent') return;
 
     const opacity = layer.paint.get('line-opacity');
-    if (opacity.constantOr(1) === 0) return;
+    const width = layer.paint.get('line-width');
+    if (opacity.constantOr(1) === 0 || width.constantOr(1) === 0) return;
 
     const context = painter.context;
 

src/shaders/line.vertex.glsl

@@ -58,7 +58,7 @@ void main() {
     offset = -1.0 * offset;
 
     float inset = gapwidth + (gapwidth > 0.0 ? ANTIALIASING : 0.0);
-    float outset = gapwidth + halfwidth * (gapwidth > 0.0 ? 2.0 : 1.0) + ANTIALIASING;
+    float outset = gapwidth + halfwidth * (gapwidth > 0.0 ? 2.0 : 1.0) + (halfwidth == 0.0 ? 0.0 : ANTIALIASING);
 
     // Scale the extrusion vector down to a normal and then up by the line width
     // of this vertex.

test/integration/render-tests/line-width/zero-width-function/style.json

@@ -0,0 +1,75 @@
+{
+  "version": 8,
+  "metadata": {
+    "test": {
+      "width": 100,
+      "height": 100,
+      "diff": 0.00075
+    }
+  },
+  "zoom": 2,
+  "sources": {
+    "linesource": {
+      "type": "geojson",
+      "data": {
+        "type": "Feature",
+        "properties": {
+          "width": 0
+        },
+        "geometry": {
+          "type": "LineString",
+          "coordinates": [
+            [
+              -1,
+              8
+            ],
+            [
+              8,
+              1
+            ],
+            [
+              1,
+              -8
+            ],
+            [
+              -8,
+              -1
+            ],
+            [
+              1,
+              4
+            ],
+            [
+              4,
+              -1
+            ],
+            [
+              -1,
+              -4
+            ],
+            [
+              -2,
+              0
+            ]
+          ]
+        }
+      },
+      "lineMetrics": true
+    }
+  },
+  "layers": [
+    {
+      "id": "line",
+      "type": "line",
+      "source": "linesource",
+      "layout": {
+        "line-cap": "round",
+        "line-join": "round"
+      },
+      "paint": {
+        "line-width": ["get", "width"],
+        "line-color": "red"
+      }
+    }
+  ]
+}

test/integration/render-tests/line-width/zero-width/style.json

@@ -0,0 +1,73 @@
+{
+  "version": 8,
+  "metadata": {
+    "test": {
+      "width": 100,
+      "height": 100,
+      "diff": 0.00075
+    }
+  },
+  "zoom": 2,
+  "sources": {
+    "linesource": {
+      "type": "geojson",
+      "data": {
+        "type": "Feature",
+        "properties": {},
+        "geometry": {
+          "type": "LineString",
+          "coordinates": [
+            [
+              -1,
+              8
+            ],
+            [
+              8,
+              1
+            ],
+            [
+              1,
+              -8
+            ],
+            [
+              -8,
+              -1
+            ],
+            [
+              1,
+              4
+            ],
+            [
+              4,
+              -1
+            ],
+            [
+              -1,
+              -4
+            ],
+            [
+              -2,
+              0
+            ]
+          ]
+        }
+      },
+      "lineMetrics": true
+    }
+  },
+  "layers": [
+    {
+      "id": "line",
+      "type": "line",
+      "source": "linesource",
+      "layout": {
+        "line-cap": "round",
+        "line-join": "round"
+      },
+      "paint": {
+        "line-width": 0,
+        "line-color": "red"
+      }
+    }
+  ]
+}