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So we've been banging at this for a few hours now.

All transparent textures we use, regardless of format we've tried (TGA, PNG, etc.) exhibit a solid outline where the alpha channel begins to fade in; like a 1-bit alpha mask (think hard outline). It's not a border around the image, just a hard silhouette around where any alpha blending occurs, and nothing else. No real blending happening.

We've tried every manner of blend function combination referenced online for proper alpha blending without avail. They all change the blending style, but nothing makes the lost information (for blending gradations) appear.

Even using the blend functions listed in the solution here:

Metal MTLTexture replaces semi-transparent areas with black when alpha values that aren't 1 or 0

doesn't help it.

Thoughts? Thanks!

Community
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Bob Jones
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  • Are you sorting your drawcalls based on distance from camera? What you describe sounds a lot like drawing unsorted transparency with alphatest. Reference: http://nsa33.casimages.com/img/2013/06/10/130610122758421435.jpg (Also I've no knowledge of metal, so maybe this is a stupid answer) – Henk De Boer Aug 29 '15 at 08:06
  • This is interesting. Would this explain why all my additive textures work without problem, but blenders don't? – Bob Jones Aug 29 '15 at 08:26
  • Well, you're the only one who can answer that question I think :) Just draw a couple of manually sorted sprites, the artifacts should appear when viewing from one direction, but not when viewing from the opposite direction. – Henk De Boer Aug 29 '15 at 08:54
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    Pre-multiplied alpha is designed for this purpose. It's a problem (the fringing you discussed) caused by interpolation of the alpha channel independent from the color. The blend equation you linked to is absolutely not appropriate for pre-multiplied alpha. You'd use Src * ONE + Dst * ONE_MINUS_SRC_ALPHA once you get the alpha and color channels in your texture setup appropriately. – Andon M. Coleman Aug 29 '15 at 15:09

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