Disallow drawing feedback loops.

gpu/command_buffer/service/gles2_cmd_decoder.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "gpu/command_buffer/service/gles2_cmd_decoder.h"
 
 #include <stdio.h>
 
 #include <algorithm>
 #include <list>
@@ skipping 1184 matching lines @@
   // appropriate GL error.  Returns true if the current program is in a usable
   // state.
   bool CheckCurrentProgram(const char* function_name);
 
   // Checks if the current program exists and is valid and that location is not
   // -1. If the current program is not valid generates the appropriate GL
   // error. Returns true if the current program is in a usable state and
   // 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
   // does not overflow the uniform.
   bool PrepForSetUniformByLocation(GLint fake_location,
                                    const char* function_name,
                                    Program::UniformApiType api_type,
                                    GLint* real_location,
                                    GLenum* type,
                                    GLsizei* count);
@@ skipping 4533 matching lines @@
 }
 
 bool GLES2DecoderImpl::CheckCurrentProgramForUniform(
     GLint location, const char* function_name) {
   if (!CheckCurrentProgram(function_name)) {
     return false;
   }
   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,
     Program::UniformApiType api_type,
     GLint* real_location,
     GLenum* type,
     GLsizei* count) {
   DCHECK(type);
   DCHECK(count);
   DCHECK(real_location);
@@ skipping 476 matching lines @@
   // it could never be invalid since glUseProgram would have failed. While
   // glLinkProgram could later mark the program as invalid the previous
   // valid program will still function if it is still the current program.
   if (!state_.current_program.get()) {
     // The program does not exist.
     // But GL says no ERROR.
     LOCAL_RENDER_WARNING("Drawing with no current shader program.");
     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,
                          feature_info_.get(),
                          state_.current_program.get(),
                          max_vertex_accessed,
                          instanced,
                          primcount);
 }
 
@@ skipping 4925 matching lines @@
   }
 }
 
 // Include the auto-generated part of this file. We split this because it means
 // we can easily edit the non-auto generated parts right here in this file
 // instead of having to edit some template or the code generator.
 #include "gpu/command_buffer/service/gles2_cmd_decoder_autogen.h"
 
 }  // namespace gles2
 }  // namespace gpu