Brain Fart of This Week - Multiply Blend "Op"

Pope Kim Jan 15, 2011

I absolutely love my darn stupidity. :) So I had to use the multiply blend op this week at work to implement some kinda per-geometry glow effect that our FE artist mocked up in Photoshop. Unfortunately, he didn't have the PSD file around anymore, so I had to believe what he said: it is using a additive blend layer in Photoshop + outer glow.

I was not planning to implement a real glow pass, so I decided to support that additive blend only and let our HDR bloom pickup the over-saturated value and do the "outer glow" for me. So I simple re-submitted those glow geometries with a simple color shader after turning on the additive blend……

The result was not great.. sure… It turns out to be he didn't use the additive blend in Photoshop; it was actually the multiply blend…….. and guess what? I totally forgot the Photoshop doesn't even have a blend mode called ADDITIVE to begin with… uh.. first brain fart…but still not the best part :)

Then 2nd brain fart was even more fun… I thought I could quickly turn on the multiply blend on D3D and show the result to him.. but I couldn't find D3DBLENDOP_MULTIPLY, so I was like.. "hmm really? multiply blend mode is not supported on PC.. maybe it's only supported on X360 and PS3…" Then later my lead reminded me that multiply blend can be done by using dest color as source blend alpha… uh… awesome brain fart.. I knew this.. but I completely forgot yesterday…

oh well, story of my life… :)

ps. the blend mode supported by Photoshop: