fix line-pattern sampling from outside icon tex coords

src/render/draw_line.js

@@ -75,7 +75,7 @@ function drawLineTile(program, painter, tile, bucket, layer, coord, programConfi
             imagePosB = painter.imageManager.getPattern(image.to);
             if (!imagePosA || !imagePosB) return;
 
-            gl.uniform2f(program.uniforms.u_pattern_size_a, imagePosA.displaySize[0] * image.fromScale / tileRatio, imagePosB.displaySize[1]);
+            gl.uniform2f(program.uniforms.u_pattern_size_a, imagePosA.displaySize[0] * image.fromScale / tileRatio, imagePosA.displaySize[1]);
             gl.uniform2f(program.uniforms.u_pattern_size_b, imagePosB.displaySize[0] * image.toScale / tileRatio, imagePosB.displaySize[1]);
 
             const {width, height} = painter.imageManager.getPixelSize();

src/shaders/line_pattern.fragment.glsl

@@ -32,8 +32,14 @@ void main() {
 
     float x_a = mod(v_linesofar / u_pattern_size_a.x, 1.0);
     float x_b = mod(v_linesofar / u_pattern_size_b.x, 1.0);
-    float y_a = 0.5 + (v_normal.y * v_width2.s / u_pattern_size_a.y);
-    float y_b = 0.5 + (v_normal.y * v_width2.s / u_pattern_size_b.y);
+
+    // v_normal.y is 0 at the midpoint of the line, -1 at the lower edge, 1 at the upper edge
+    // we clamp the line width outset to be between 0 and half the pattern height plus padding (2.0)
+    // to ensure we don't sample outside the designated symbol on the sprite sheet.
+    // 0.5 is added to shift the component to be bounded between 0 and 1 for interpolation of
+    // the texture coordinate
+    float y_a = 0.5 + (v_normal.y * clamp(v_width2.s, 0.0, (u_pattern_size_a.y + 2.0) / 2.0) / u_pattern_size_a.y);
+    float y_b = 0.5 + (v_normal.y * clamp(v_width2.s, 0.0, (u_pattern_size_b.y + 2.0) / 2.0) / u_pattern_size_b.y);
     vec2 pos_a = mix(u_pattern_tl_a / u_texsize, u_pattern_br_a / u_texsize, vec2(x_a, y_a));
     vec2 pos_b = mix(u_pattern_tl_b / u_texsize, u_pattern_br_b / u_texsize, vec2(x_b, y_b));
 

test/integration/render-tests/regressions/mapbox-gl-js#5978/style.json

@@ -0,0 +1,64 @@
+{
+  "version": 8,
+  "metadata": {
+    "test": {
+      "width": 64,
+      "height": 64
+    }
+  },
+  "sprite": "local://sprites/emerald",
+  "sources": {
+    "a": {
+      "type": "geojson",
+      "data": {
+        "type": "LineString",
+        "coordinates": [
+          [
+            -180,
+            10
+          ],
+          [
+            180,
+            10
+          ]
+        ]
+      }
+    },
+    "b": {
+      "type": "geojson",
+      "data": {
+        "type": "LineString",
+        "coordinates": [
+          [
+            -180,
+            -10
+          ],
+          [
+            180,
+            -10
+          ]
+        ]
+      }
+    }
+  },
+  "layers": [
+    {
+      "id": "a",
+      "type": "line",
+      "source": "a",
+      "paint": {
+        "line-width": 4,
+        "line-pattern": "oneway_road"
+      }
+    },
+    {
+      "id": "b",
+      "type": "line",
+      "source": "b",
+      "paint": {
+        "line-width": 30,
+        "line-pattern": "default_3"
+      }
+    }
+  ]
+}