Update Texture dirty bits documentation.

src/libANGLE/Program.cpp

@@ -2968,13 +2968,14 @@ void Program::updateSamplerUniform(const VariableLocation &locationInfo,
                                    GLsizei clampedCount,
                                    const GLint *v)
 {
-    // Invalidate the validation cache only if we modify the sampler data.
     ASSERT(mState.isSamplerUniformIndex(locationInfo.index));
     GLuint samplerIndex = mState.getSamplerIndexFromUniformIndex(locationInfo.index);
     std::vector<GLuint> *boundTextureUnits =
         &mState.mSamplerBindings[samplerIndex].boundTextureUnits;
 
     std::copy(v, v + clampedCount, boundTextureUnits->begin() + locationInfo.element);
+
+    // Invalidate the validation cache.
     mCachedValidateSamplersResult.reset();
 }
 

src/libANGLE/State.h

@@ -536,6 +536,18 @@ class State : public OnAttachmentDirtyReceiver, angle::NonCopyable
     typedef std::map<GLenum, TextureBindingVector> TextureBindingMap;
     TextureBindingMap mSamplerTextures;
 
+    // Texture Completeness Caching
+    // ----------------------------
+    // The texture completeness cache uses dirty bits to avoid having to scan the list
+    // of textures each draw call. This gl::State class implements OnAttachmentDirtyReceiver,
+    // and keeps an array of bindings to the Texture class. When the Textures are marked dirty,
+    // they send messages to the State class (and any Framebuffers they're attached to) via the
+    // State::signal method (see above). Internally this then invalidates the completeness cache.
+    //
+    // Note this requires that we also invalidate the completeness cache manually on events like
+    // re-binding textures/samplers or a change in the program. For more information see the
+    // signal_utils.h header and the design doc linked there.
+
     // A cache of complete textures. nullptr indicates unbound or incomplete.
     // Don't use BindingPointer because this cache is only valid within a draw call.
     // Also stores a notification channel to the texture itself to handle texture change events.

src/libANGLE/signal_utils.h

@@ -6,6 +6,8 @@
 // signal_utils:
 //   Helper classes for tracking dependent state changes between objects.
 //   These changes are signaled to the dependent class via channels.
+//   See design document:
+//   https://docs.google.com/document/d/15Edfotqg6_l1skTEL8ADQudF_oIdNa7i8Po43k6jMd4/
 
 #ifndef LIBANGLE_SIGNAL_UTILS_H_
 #define LIBANGLE_SIGNAL_UTILS_H_