Disallow drawing feedback loops.

gpu/command_buffer/service/gles2_cmd_decoder.cc

Index: gpu/command_buffer/service/gles2_cmd_decoder.cc
diff --git a/gpu/command_buffer/service/gles2_cmd_decoder.cc b/gpu/command_buffer/service/gles2_cmd_decoder.cc
index 20c4da8efce5dea9ded6e230dde087e69c9cf0b9..dbfbccf47229b6f4508658c548133146efa14a4c 100644
--- a/gpu/command_buffer/service/gles2_cmd_decoder.cc
+++ b/gpu/command_buffer/service/gles2_cmd_decoder.cc
@@ -1202,6 +1202,11 @@ class GLES2DecoderImpl : public GLES2Decoder,
   // location is not -1.
   bool CheckCurrentProgramForUniform(GLint location, const char* function_name);
 
+  // Checks if the current program samples a texture that is also the color
+  // image of the current bound framebuffer, i.e., the source and destination
+  // of the draw operation are the same.
+  bool CheckDrawingFeedbackLoops();
+
   // Gets the type of a uniform for a location in the current program. Sets GL
   // errors if the current program is not valid. Returns true if the current
   // program is valid and the location exists. Adjusts count so it
@@ -5755,6 +5760,38 @@ bool GLES2DecoderImpl::CheckCurrentProgramForUniform(
   return location != -1;
 }
 
+bool GLES2DecoderImpl::CheckDrawingFeedbackLoops() {

[Ken Russell (switch to Gerrit), 2014/10/16 21:08:30]

Have you checked any benchmarks -- e.g.
http://webglsamples.googlecode.com/hg/lots-o-objects/ ,
http://webglsamples.googlecode.com/hg/google-io/2011/ -- to see how much
overhead this new check adds? It could be significant.

+  Framebuffer* framebuffer = GetFramebufferInfoForTarget(GL_FRAMEBUFFER);
+  if (!framebuffer)
+    return false;
+  const Framebuffer::Attachment* attachment =
+      framebuffer->GetAttachment(GL_COLOR_ATTACHMENT0);
+  if (!attachment)
+    return false;
+
+  DCHECK(state_.current_program.get());
+  const Program::SamplerIndices& sampler_indices =
+      state_.current_program->sampler_indices();
+  for (size_t ii = 0; ii < sampler_indices.size(); ++ii) {
+    const Program::UniformInfo* uniform_info =
+        state_.current_program->GetUniformInfo(sampler_indices[ii]);
+    DCHECK(uniform_info);
+    if (uniform_info->type != GL_SAMPLER_2D)
+      continue;
+    for (size_t jj = 0; jj < uniform_info->texture_units.size(); ++jj) {
+      GLuint texture_unit_index = uniform_info->texture_units[jj];
+      if (texture_unit_index >= state_.texture_units.size())
+        continue;
+      TextureUnit& texture_unit = state_.texture_units[texture_unit_index];
+      TextureRef* texture_ref =
+          texture_unit.GetInfoForSamplerType(GL_SAMPLER_2D).get();
+      if (attachment->IsTexture(texture_ref))
+        return true;
+    }
+  }
+  return false;
+}
+
 bool GLES2DecoderImpl::PrepForSetUniformByLocation(
     GLint fake_location,
     const char* function_name,
@@ -6251,6 +6288,13 @@ bool GLES2DecoderImpl::IsDrawValid(
     return false;
   }
 
+  if (CheckDrawingFeedbackLoops()) {
+    LOCAL_SET_GL_ERROR(
+        GL_INVALID_OPERATION, function_name,
+        "Source and destination textures of the draw are the same.");
+    return false;
+  }
+
   return state_.vertex_attrib_manager
       ->ValidateBindings(function_name,
                          this,