do not hide icons if text is an empty string

[ansis]

fix #6160

Empty text strings do not have any collision boxes so the collision index check was never done and the text was not counted as "placed". This fixes that by making "placed" the default when the feature has text.

Alternative fix

Another possibility would be to create zero-sized collision boxes for empty strings. If we did this, should these zero-size boxes collide with other boxes if they are contained within them?

Launch Checklist

• briefly describe the changes in this PR
• write tests for all new functionality
• [N/A] document any changes to public APIs
• [N/A] post benchmark scores
• manually test the debug page

[mb12]

@ansis Can you please clarify when should one use 'text-optional' and 'icon-optional' layout properties? Shouldn't this require setting text-optional to true in the corresponding style?

[ChrisLoer]

Yeah this looks right to me.

@mb12 I was confused by the same thing regarding text/icon-optional. The difference is that text-optional means "show this icon even if its corresponding text has been hidden because of a collision". It doesn't have anything to do with whether the corresponding text is defined/empty. So in this case even though the text is empty, text-optional still shouldn't be necessary (because the text isn't colliding with anything either).

[dagjomar]

Would this also fix the inverse case, "do not hide text if icon is an empty string" ?

[ChrisLoer]

@dagjomar Mostly I think yes... from the point of view of the code, there's nothing special about an icon-image that evaluates to an empty string: it will be just the same as any other icon-image that's not available in the sprite sheet. Here's the relevant logic:

mapbox-gl-js/src/symbol/symbol_layout.js

Lines 124 to 147 in 25f9afa

	let shapedIcon;
	if (feature.icon) {
	const image = imageMap[feature.icon];
	if (image) {
	shapedIcon = shapeIcon(
	imagePositions[feature.icon],
	layout.get('icon-offset').evaluate(feature),
	layout.get('icon-anchor').evaluate(feature));
	if (bucket.sdfIcons === undefined) {
	bucket.sdfIcons = image.sdf;
	} else if (bucket.sdfIcons !== image.sdf) {
	warnOnce('Style sheet warning: Cannot mix SDF and non-SDF icons in one buffer');
	}
	if (image.pixelRatio !== bucket.pixelRatio) {
	bucket.iconsNeedLinear = true;
	} else if (layout.get('icon-rotate').constantOr(1) !== 0) {
	bucket.iconsNeedLinear = true;
	}
	}
	}
	if (shapedTextOrientations.horizontal || shapedIcon) {
	addFeature(bucket, feature, shapedTextOrientations, shapedIcon, glyphPositionMap, sizes);
	}

Along with:

mapbox-gl-js/src/symbol/placement.js

Line 162 in 25f9afa

let placeIcon = symbolInstance.feature.icon !== undefined;

So what that means is something like: "If the feature has an icon, but that icon's image is not in the image map, we won't create a shapedIcon and we won't add a symbol instance for just that icon. But if the same feature also has text, we'll bring the icon along for the ride, and placeIcon will default to true even though there's no collision feature for the empty icon"

[AzadehY-Dev]

hi. i have an apposite problem. when i add a text field the symbols disappear. i searched a lot and i used a lot of suggestions. but none of them didn't work for me. please help me. that's my code:
`
private void addSymbolToMap(String name, LatLng point) {
mapStyle.addImage(name, getResources().getDrawable(R.drawable.mapbox_marker_icon_default));
SymbolManager sampleSymbolManager = new SymbolManager(mapView, map, mapStyle);
sampleSymbolManager.setIconAllowOverlap(true);
sampleSymbolManager.setTextAllowOverlap(true);
sampleSymbolManager.setIconRotationAlignment(ICON_ROTATION_ALIGNMENT_VIEWPORT);
SymbolOptions sampleSymbolOptions = new SymbolOptions()
.withLatLng(point)
.withIconImage(name)
.withIconSize(1.5f);
.withTextField("test")
.withTextFont(new String[] { "Arial Unicode MS Regular"});
Symbol sampleSymbol = sampleSymbolManager.create(sampleSymbolOptions);
}

`