Unexpected error when terrain is loading when `setStyle` is called

[ztzthu]

maplibre-gl-js version: 5.14.0 (latest)

browser: All browsers i believe

Steps to Trigger Behavior

1. Set a map with terrain.
2. Let the map flying or zoom in.
3. When flying or zoom in is still happening, use map.setStyle() to set a new style with terrain.

Link to Demonstration

Example

To use this example:

1. Click the compass button to let the map move.
2. Before map move is finished, set the map to another style.
3. Error occurs.

Expected Behavior

No error and the map is able to set a new style with terrain.

Actual Behavior

There is an error:

Uncaught TypeError: Cannot read properties of undefined (reading 'shaderPreludeCode')
useProgram	@	painter.ts:729
(anonymous)	@	draw_terrain.ts:23
maybeDrawDepthAndCoords	@	painter.ts:653
render	@	painter.ts:519
_render	@	map.ts:3483
(anonymous)	@	map.ts:3617
(anonymous)

Use-case

Users should be able to change basemap layers freely no matter the terrain is ready or not.

Explanation

I belive that when map.setStyle() is called, the map.painter.style.projection is immediately set to undefined at initialization untill the correct projection is set. As a result, if the terrain is still drawing, in the Painter.useprogram() implementation, this following line will lead to an error

const projectionPrelude = forceSimpleProjection ? shaders.projectionMercator : projection.shaderPreludeCode;

I'm new to maplibre internal implementation so lmk if I'm wrong.

Might be related to #6184 and #6817

Solution

Change the following line in Painter.maybeDrawDepthAndCoords():

-        if (!this.style || !this.style.map || !this.style.map.terrain) {
+        if (!this.style || !this.style.map || !this.style.map.terrain || !this.style.projection) {

I could create a PR but I need to learn how to properly write tests as per the contribution guideline and see if it breaks anything else..

[HarelM]

Thanks for taking the time to report this issue!
Is there a version prior to 5.14 that this does not happen?

[ztzthu]

I tested multiple versions just now and it seems that I can reproduce the issue on 5.1 but not 5.0.

[HarelM]

Consider checking the changelog, maybe one of the PRs will look suspicious...