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reduce symbol overlap when zooming out quickly #8628

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merged 3 commits into from
Sep 30, 2019
Merged

reduce symbol overlap when zooming out quickly #8628

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0e26fbd
fix #8627
ansis Aug 13, 2019
5590c8b
use the zoom from when the placement started, not the commit zoom
ansis Aug 14, 2019
26cd733
improve zoom fading in several ways:
ansis Sep 25, 2019
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2 changes: 1 addition & 1 deletion src/style/style.js
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Original file line number Diff line number Diff line change
Expand Up @@ -1200,7 +1200,7 @@ class Style extends Evented {
// tiles will fully display symbols in their first frame
const forceFullPlacement = this._layerOrderChanged || fadeDuration === 0;

if (forceFullPlacement || !this.pauseablePlacement || (this.pauseablePlacement.isDone() && !this.placement.stillRecent(browser.now()))) {
if (forceFullPlacement || !this.pauseablePlacement || (this.pauseablePlacement.isDone() && !this.placement.stillRecent(browser.now(), transform.zoom))) {
this.pauseablePlacement = new PauseablePlacement(transform, this._order, forceFullPlacement, showCollisionBoxes, fadeDuration, crossSourceCollisions, this.placement);
this._layerOrderChanged = false;
}
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30 changes: 24 additions & 6 deletions src/symbol/placement.js
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Expand Up @@ -167,12 +167,14 @@ export class Placement {
variableOffsets: {[CrossTileID]: VariableOffset };
placedOrientations: {[CrossTileID]: number };
commitTime: number;
prevZoomAdjustment: number;
lastPlacementChangeTime: number;
stale: boolean;
fadeDuration: number;
retainedQueryData: {[number]: RetainedQueryData};
collisionGroups: CollisionGroups;
prevPlacement: ?Placement;
zoomAtLastRecencyCheck: number;

constructor(transform: Transform, fadeDuration: number, crossSourceCollisions: boolean, prevPlacement?: Placement) {
this.transform = transform.clone();
Expand Down Expand Up @@ -636,13 +638,13 @@ export class Placement {

commit(now: number): void {
this.commitTime = now;
this.zoomAtLastRecencyCheck = this.transform.zoom;

const prevPlacement = this.prevPlacement;
let placementChanged = false;

const increment = (prevPlacement && this.fadeDuration !== 0) ?
(this.commitTime - prevPlacement.commitTime) / this.fadeDuration :
1;
this.prevZoomAdjustment = prevPlacement ? prevPlacement.zoomAdjustment(this.transform.zoom) : 0;
const increment = prevPlacement ? prevPlacement.symbolFadeChange(now) : 1;

const prevOpacities = prevPlacement ? prevPlacement.opacities : {};
const prevOffsets = prevPlacement ? prevPlacement.variableOffsets : {};
Expand Down Expand Up @@ -893,16 +895,32 @@ export class Placement {
symbolFadeChange(now: number) {
return this.fadeDuration === 0 ?
1 :
(now - this.commitTime) / this.fadeDuration;
((now - this.commitTime) / this.fadeDuration + this.prevZoomAdjustment);
}

zoomAdjustment(zoom: number) {
// When zooming out quickly, labels can overlap each other. This
// adjustment is used to reduce the interval between placement calculations
// and to reduce the fade duration when zooming out quickly. Discovering the
// collisions more quickly and fading them more quickly reduces the unwanted effect.
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Discovering the collisions more quickly and fading them more quickly reduces the unwanted effect.

nit: This part of the comment can be removed, or make it clearer. It is not clear how zoomAdjustment results in discovering the collisions more quickly.

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It is not clear how zoomAdjustment results in discovering the collisions more quickly.

+1 to this - it took me reading through all the code to understand how the adjustment works. Perhaps merging the "Discovering" sentence into the previous one would make it clearer, something like:

"This adjustment is applied when zooming out quickly to reduce the interval between placement calculations so we can discover & correct label collisions sooner, and also to reduce the fade duration so that overlapping labels fade out more quickly."

Just a suggestion, not sure if that wording would make it any clearer to someone else.

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As is, it seems relatively clear to me that "reducing the interval between placement calculations" discovers collisions more quickly and "reducing the fade duration" fades them more quickly. I agree with @vakila that keeping the order of the clauses in the last sentence parallel to the previous sentence would improve clarity. I think shorter and simpler sentences are generally easier to follow than longer ones.

        // When zooming out quickly, labels can overlap each other. This
        // adjustment is used to reduce the interval between placement calculations
        // and to reduce the fade duration when zooming out quickly. Discovering the
        // collisions more quickly and fading them more quickly reduces the unwanted effect.

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Thanks for all the suggestions on how to make this better! I've committed chloe's version with shorter sentences.

return Math.max(0, (this.transform.zoom - zoom) / 1.5);
}

hasTransitions(now: number) {
return this.stale ||
now - this.lastPlacementChangeTime < this.fadeDuration;
}

stillRecent(now: number) {
return this.commitTime + this.fadeDuration > now;
stillRecent(now: number, zoom: number) {
// The adjustment makes placement more frequent when zooming.
// This condition applies the adjustment only after the map has
// stopped zooming. This avoids adding extra jank while zooming.
const durationAdjustment = this.zoomAtLastRecencyCheck === zoom ?
(1 - this.zoomAdjustment(zoom)) :
1;
this.zoomAtLastRecencyCheck = zoom;

return this.commitTime + this.fadeDuration * durationAdjustment > now;
}

setStale() {
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