Add the rest of the files for the premultiplied alpha commit.

[movit] / effect.h

diff --git a/effect.h b/effect.h
index 235558f8e1c4cf9f480361f0f428916885b1e0e5..39c612601a36a4e4a9ed9d755c11233d298d2479 100644 (file)
--- a/effect.h
+++ b/effect.h
@@ -78,6 +78,49 @@ public:
        // in a linear fashion.
        virtual bool needs_srgb_primaries() const { return true; }
 
+       // How this effect handles alpha, ie. what it outputs in its
+       // alpha channel. The choices are basically blank (alpha is always 1.0),
+       // premultiplied and postmultiplied.
+       //
+       // Premultiplied alpha is when the alpha value has been be multiplied
+       // into the three color components, so e.g. 100% red at 50% alpha
+       // would be (0.5, 0.0, 0.0, 0.5) instead of (1.0, 0.0, 0.0, 0.5)
+       // as it is stored in most image formats (postmultiplied alpha).
+       // The multiplication is taken to have happened in linear light.
+       // This is the most natural format for processing, and the default in
+       // most of Movit (just like linear light is).
+       //
+       // If you set INPUT_AND_OUTPUT_ALPHA_PREMULTIPLIED, all of your inputs
+       // (if any) are guaranteed to also be in premultiplied alpha.
+       // Otherwise, you can get postmultiplied or premultiplied alpha;
+       // you won't know. If you have multiple inputs, you will get the same
+       // (pre- or postmultiplied) for all inputs, although most likely,
+       // you will want to combine them in a premultiplied fashion anyway
+       // in that case.
+       enum AlphaHandling {
+               // Always outputs blank alpha (ie. alpha=1.0). Only appropriate
+               // for inputs that do not output an alpha channel.
+               // Blank alpha is special in that it can be treated as both
+               // pre- and postmultiplied.
+               OUTPUT_BLANK_ALPHA,
+
+               // Always outputs premultiplied alpha. As noted above,
+               // you will then also get all inputs in premultiplied alpha.
+               // If you set this, you should also set needs_linear_light().
+               INPUT_AND_OUTPUT_ALPHA_PREMULTIPLIED,
+
+               // Always outputs postmultiplied alpha. Only appropriate for inputs.
+               OUTPUT_ALPHA_POSTMULTIPLIED,
+
+               // Keeps the type of alpha unchanged from input to output.
+               // Usually appropriate if you process all color channels
+               // in a linear fashion, and do not change alpha.
+               //
+               // Does not make sense for inputs.
+               DONT_CARE_ALPHA_TYPE,
+       };
+       virtual AlphaHandling alpha_handling() const { return INPUT_AND_OUTPUT_ALPHA_PREMULTIPLIED; }
+
        // Whether this effect expects its input to come directly from
        // a texture. If this is true, the framework will not chain the
        // input from other effects, but will store the results of the