clearer pitched line antialiasing

Project the extrusion and compare it's projected pixel length with the
actual pixel length and adjust antialiasing accordingly.

The previous approach calculated the adjustment much more indirectly and
had no intuitive explanation.

js/geo/transform.js

@@ -439,16 +439,6 @@ class Transform {
         if (!m) throw new Error("failed to invert matrix");
         this.pixelMatrixInverse = m;
 
-        // line antialiasing matrix
-        m = mat2.create();
-        mat2.scale(m, m, [1, Math.cos(this._pitch)]);
-        mat2.rotate(m, m, this.angle);
-        this.lineAntialiasingMatrix = m;
-
-        // calculate how much longer the real world distance is at the top of the screen
-        // than at the middle of the screen.
-        const topEdgeLength = Math.sqrt((this.height * this.height + this.cameraToCenterDistance * this.cameraToCenterDistance) / 4);
-        this.lineStretch = (this.height / 2 * Math.tan(this._pitch)) / topEdgeLength;
     }
 }
 

js/render/draw_line.js

@@ -80,6 +80,8 @@ function drawLineTile(program, painter, tile, buffers, layer, coord, layerData,
             gl.uniform2f(program.u_pattern_size_a, imagePosA.size[0] * image.fromScale / tileRatio, imagePosB.size[1]);
             gl.uniform2f(program.u_pattern_size_b, imagePosB.size[0] * image.toScale / tileRatio, imagePosB.size[1]);
         }
+
+        gl.uniform2f(program.u_gl_units_to_pixels, 1 / painter.transform.pixelsToGLUnits[0], 1 / painter.transform.pixelsToGLUnits[1]);
     }
 
     if (programChanged) {
@@ -105,9 +107,6 @@ function drawLineTile(program, painter, tile, buffers, layer, coord, layerData,
             gl.uniform1f(program.u_fade, image.t);
         }
         gl.uniform1f(program.u_width, layer.paint['line-width']);
-
-        gl.uniformMatrix2fv(program.u_antialiasingmatrix, false, painter.transform.lineAntialiasingMatrix);
-        gl.uniform1f(program.u_extra, painter.transform.lineStretch);
     }
 
     painter.enableTileClippingMask(coord);

package.json

@@ -21,7 +21,7 @@
     "geojson-vt": "^2.4.0",
     "grid-index": "^1.0.0",
     "mapbox-gl-function": "mapbox/mapbox-gl-function#41c6724e2bbd7bd1eb5991451bbf118b7d02b525",
-    "mapbox-gl-shaders": "mapbox/mapbox-gl-shaders#69a834aa6b3c58e0ee60335590b443ac7742ed8d",
+    "mapbox-gl-shaders": "mapbox/mapbox-gl-shaders#a5401d074f2fb7a127f3fb4caff530ed2c6ad5a1",
     "mapbox-gl-style-spec": "mapbox/mapbox-gl-style-spec#e85407a377510acb647161de6be6357ab4f606dd",
     "mapbox-gl-supported": "^1.2.0",
     "package-json-versionify": "^1.0.2",