Deduplicate perspective ratio math

Author: mpulkki-mapbox

src/render/draw_symbol.js

@@ -156,7 +156,7 @@ function updateVariableAnchorsForBucket(bucket, rotateWithMap, pitchWithMap, var
         } else  {
             const tileAnchor = new Point(symbol.anchorX, symbol.anchorY);
             const projectedAnchor = symbolProjection.project(tileAnchor, pitchWithMap ? posMatrix : labelPlaneMatrix);
-            const perspectiveRatio = 0.5 + 0.5 * (transform.cameraToCenterDistance / projectedAnchor.signedDistanceFromCamera);
+            const perspectiveRatio = symbolProjection.getPerspectiveRatio(transform.cameraToCenterDistance, projectedAnchor.signedDistanceFromCamera);
             let renderTextSize = symbolSize.evaluateSizeForFeature(bucket.textSizeData, size, symbol) * perspectiveRatio / ONE_EM;
             if (pitchWithMap) {
                 // Go from size in pixels to equivalent size in tile units

src/symbol/collision_index.js

@@ -103,11 +103,12 @@ class CollisionIndex {
                           textPixelPadding: number): { circles: Array<number>, offscreen: boolean, collisionDetected: boolean } {
         const placedCollisionCircles = [];
 
-        const perspectiveRatio = this.projectAnchor(posMatrix, symbol.anchorX, symbol.anchorY).perspectiveRatio;
+        const tileUnitAnchorPoint = new Point(symbol.anchorX, symbol.anchorY);
+        const screenAnchorPoint = projection.project(tileUnitAnchorPoint, posMatrix);
+        const perspectiveRatio = projection.getPerspectiveRatio(this.transform.cameraToCenterDistance, screenAnchorPoint.signedDistanceFromCamera);
         const labelPlaneFontSize = pitchWithMap ? fontSize / perspectiveRatio : fontSize * perspectiveRatio;
         const labelPlaneFontScale = labelPlaneFontSize / ONE_EM;
 
-        const tileUnitAnchorPoint = new Point(symbol.anchorX, symbol.anchorY);
         const labelPlaneAnchorPoint = projection.project(tileUnitAnchorPoint, labelPlaneMatrix).point;
 
         const projectionCache = {};
@@ -330,15 +331,6 @@ class CollisionIndex {
         }
     }
 
-    projectAnchor(posMatrix: mat4, x: number, y: number) {
-        const p = [x, y, 0, 1];
-        projection.xyTransformMat4(p, p, posMatrix);
-        return {
-            perspectiveRatio: 0.5 + 0.5 * (this.transform.cameraToCenterDistance / p[3]),
-            cameraDistance: p[3]
-        };
-    }
-
     projectPoint(posMatrix: mat4, x: number, y: number) {
         const p = [x, y, 0, 1];
         projection.xyTransformMat4(p, p, posMatrix);

src/symbol/projection.js

@@ -16,7 +16,7 @@ import type {
 } from '../data/array_types';
 import {WritingMode} from '../symbol/shaping';
 
-export {updateLineLabels, hideGlyphs, getLabelPlaneMatrix, getGlCoordMatrix, project, placeFirstAndLastGlyph, placeGlyphAlongLine, xyTransformMat4};
+export {updateLineLabels, hideGlyphs, getLabelPlaneMatrix, getGlCoordMatrix, project, getPerspectiveRatio, placeFirstAndLastGlyph, placeGlyphAlongLine, xyTransformMat4};
 
 /*
  * # Overview of coordinate spaces
@@ -113,6 +113,10 @@ function project(point: Point, matrix: mat4) {
     };
 }
 
+function getPerspectiveRatio(cameraToCenterDistance: number, signedDistanceFromCamera: number): number {
+    return 0.5 + 0.5 * (cameraToCenterDistance / signedDistanceFromCamera);
+}
+
 function isVisible(anchorPos: [number, number, number, number],
                    clippingBuffer: [number, number]) {
     const x = anchorPos[0] / anchorPos[3];
@@ -178,7 +182,7 @@ function updateLineLabels(bucket: SymbolBucket,
         }
 
         const cameraToAnchorDistance = anchorPos[3];
-        const perspectiveRatio = 0.5 + 0.5 * (painter.transform.cameraToCenterDistance / cameraToAnchorDistance);
+        const perspectiveRatio = getPerspectiveRatio(painter.transform.cameraToCenterDistance, cameraToAnchorDistance);
 
         const fontSize = symbolSize.evaluateSizeForFeature(sizeData, partiallyEvaluatedSize, symbol);
         const pitchScaledFontSize = pitchWithMap ? fontSize / perspectiveRatio : fontSize * perspectiveRatio;