Add warning if attribute with divisor present but no instance count provided

[vorg]

Due to how we detect instancing it is possible to have a geometry with offsets and no instances count and no instanced shader present yet still attempt to render instances resulting in no draw call const instanced = Object.values(cmd.attributes || cmd.vertexArray.attributes).some(attrib => attrib.divisor); https://github.com/pex-gl/pex-context/blame/v3/index.js#L1072

https://github.com/pex-gl/pex-context/blame/v3/index.js#L1094.

Maybe a warning would be good?

[dmnsgn]

Would checking && (Number.isFinite(cmd.instances) && cmd.instances > 1) be too much automagic?

[vorg]

I think it should be the default. Not sure what's the point of checking divisor if no instanced count is provided. Your version using .some() is just refactor of my attribute by attribute checks. Happy to go ahead with

const instanced = Number.isFinite(cmd.instances) && cmd.instances >= 1)

[vorg]

Turns out the point is that when we animating sth there might be zero instances of a cube which is a valid draw call. Checking for Number.isFinite(cmd.instances) introduced a bug where vertex array for instanced attributes were being enabled but they had no data and drawElements call was causing Context Loss.

Note: simply not enabling those attributes with divisor if instances==0 doesn't seem to work. I would expect one cube to be drawn in the center of the scene but nothing happens probably becase pex-renderer already assigned shader with instanced attributres???

[dmnsgn]

Reverted in 266287217840a46adf19df79746455c943bd2c54 for 3.0.0-alpha.5