GLES2 polyline drawn as GL_LINE_STRIP to match GLES3

[lawnjelly]

The behaviour of TYPE_POLYLINE appeared incorrect in GLES2, and inconsistent with GLES3 and the docs, which state that draw_polyline 'Draws interconnected line segments'. Also when drawing with triangles GLES2 draws interconnected segments.

This PR simply changes the primitive from GL_LINES to GL_LINE_STRIP as in GLES3.

Fixes #38703.

Notes

Although this is 'correct', we should also consider that it is a breaking change, that may affect people who have been relying on the bugged behaviour. Do we have a drawlines methods they can change to that does multiple line segments?

It seems Item::Command::TYPE_LINE is for single lines. Maybe we could have some kind of variation of draw_polyline that allows separate segments?

[Calinou]

Do we have a drawlines methods they can change to that does multiple line segments?

Yes, draw_multiline/draw_multiline_colors should do it.

[lawnjelly]

Do we have a drawlines methods they can change to that does multiple line segments?

Yes, draw_multiline/draw_multiline_colors should do it.

Ah, it seem to, you are right, there is a multiline if section in the polyline. The docs are confusing on this to me:

void draw_multiline(points: PoolVector2Array, color: Color, width: float = 1.0, antialiased: bool = false)

Draws multiple, parallel lines with a uniform color. width and antialiased are currently not implemented and have no effect.

I'm not clear on where the parallel bit comes in...

[akien-mga]

There are various issues with draw_polyline/draw_multiline: #16448, #16466, #35878.
Their documentation should also not be taken as reference, it's an educated guess from documentation writers of what this be used for, based on what it actually does and what the code seems to do.

Fixing bugs that would theoretically break compat like here is OK IMO, I don't think we can consider that the previous invalid behavior was a feature/supported.

[akien-mga]

Thanks!