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Handle blending in RGBM HDR rt

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Hello,

As we know RGBM is a good format for HDR data encoding. But using the alpha channel as the luminance rules out hardware additive blending. So how do you handle blending in RGBM render target? Besides using some off-screen composing technique, are there any alternatives?

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You either do the blending manually in the shader (either by ping-ponging between render targets or by reading back the render target on hardware that supports it) or your resolve to a fp16 target and do your blending with that.

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Hi MJP,

Thanks for the reply~:) Now I am using a technique similar as doing glass refraction(by reading back the render target as you mentioned) and doing a Decode->blending->Encode in my shader. But this trick requires some extra shader code and have some potential problem with depth sorting. So can I just hack into the luminance channel and do some simple additive blending and multiply blending for the RGB channel?

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I don't know of any meaningful hardware blending operations you can do RGBM, asides from multiply blending.

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