Document EffectChain threading considerations.

[movit] / effect_chain.h

diff --git a/effect_chain.h b/effect_chain.h
index ddabad959bb292b7798af46e69c6869ccca1c1c5..db3b87006100b09820687efab1ba0bca6c699484 100644 (file)
--- a/effect_chain.h
+++ b/effect_chain.h
@@ -1,5 +1,21 @@
-#ifndef _EFFECT_CHAIN_H
-#define _EFFECT_CHAIN_H 1
+#ifndef _MOVIT_EFFECT_CHAIN_H
+#define _MOVIT_EFFECT_CHAIN_H 1
+
+// An EffectChain is the largest basic entity in Movit; it contains everything
+// needed to connects a series of effects, from inputs to outputs, and render
+// them. Generally you set up your effect chain once and then call its render
+// functions once per frame; setting one up can be relatively expensive,
+// but rendering is fast.
+//
+// Threading considerations: EffectChain is “thread-compatible”; you can use
+// different EffectChains in multiple threads at the same time (assuming the
+// threads do not use the same OpenGL context, but this is a good idea anyway),
+// but you may not use one EffectChain from multiple threads simultaneously.
+// You _are_ allowed to use one EffectChain from multiple threads as long as
+// you only use it from one at a time (possibly by doing your own locking),
+// but if so, the threads' contexts need to be set up to share resources, since
+// the EffectChain holds textures and other OpenGL objects that are tied to the
+// context.
 
 #include <GL/glew.h>
 #include <stdio.h>
@@ -229,12 +245,10 @@ private:
        Effect *dither_effect;
 
        std::vector<Input *> inputs;  // Also contained in nodes.
-
-       GLuint fbo;
        std::vector<Phase *> phases;
 
        unsigned num_dither_bits;
        bool finalized;
 };
 
-#endif // !defined(_EFFECT_CHAIN_H)
+#endif // !defined(_MOVIT_EFFECT_CHAIN_H)