projector: draw transparent sprites correctly

[canbakiskan]

• Motivation for features / changes

In projector view, when the image sprites are transparent, transparent pixels are not rendered correctly. See images below. This change fixes this rendering issue.

Proper rendering of transparent pixels also allow users to display non-square images as sprites, as long as they pad their image with transparent pixels.

• Technical description of changes

Added a condition to fragment shader that checks if a the texture to be rendered is transparent at that coordinate; if so, it discards the texture.

• Screenshots of UI changes

Before:

After:

• Detailed steps to verify changes work correctly (as executed by you)

Make some pixels in the sprites transparent.

• Alternate designs / implementations considered

I tried changing the depthTest, depthWrite, and blending fields of THREE.ShaderMaterial but nothing really worked, either there were z-index issues or transparent pixels were showing up as gray,

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[canbakiskan]

It doesn't accept my CLA acceptance because I can only sign it with my gmail address which is different from my regular email address I have on record. No idea how to resolve it, can't edit the email address in the signing area of CLA. Ok, changed commit email address.

Isn't it a bit presumptuous to assume everyone uses gmail for git?

[bileschi]

@canbakiskan Thanks for the PR! Sorry about the trouble with the CLA bot.

[nfelt]

Thanks for the contribution!

Isn't it a bit presumptuous to assume everyone uses gmail for git?

For what it's worth - I haven't tried this myself, but I believe the CLA just requires a Google account, and that account can be associated with non-gmail email addresses. Specifically the page at https://cla.developers.google.com/about says "Ensure you submitted your contribution using one of the email addresses associated with the account you're signed in to" (I'm assuming they mean Google account here; I agree it could be clearer) and links to the page https://security.google.com/settings/email where you can add additional email addresses. So it might be the case that if you added your .edu email address to that account that would satisfy the CLA bot going forward.