[Command buffer] Feedback loop detection between texture and framebuffer attachments

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 c032dff22ae14ad9a95fdad3815abc464779af5b..f35c5770937a899b218ed24c83616d3e6c85c1d0 100644
--- a/gpu/command_buffer/service/gles2_cmd_decoder.cc
+++ b/gpu/command_buffer/service/gles2_cmd_decoder.cc
@@ -1321,6 +1321,11 @@ class GLES2DecoderImpl : public GLES2Decoder, public ErrorStateClient {
   // of the draw operation are the same.
   bool CheckDrawingFeedbackLoops();
 
+  // Helper for CheckDrawingFeedbackLoops. Returns true if the attachment is
+  // the same one where it samples from during drawing.
+  bool CheckDrawingFeedbackLoopsHelper(
+    const Framebuffer::Attachment* attachment);
+
   bool SupportsDrawBuffers() const;
 
   // Checks if a draw buffer's format and its corresponding fragment shader
@@ -8645,15 +8650,8 @@ bool GLES2DecoderImpl::CheckCurrentProgramForUniform(
       location);
 }
 
-bool GLES2DecoderImpl::CheckDrawingFeedbackLoops() {
-  Framebuffer* framebuffer = GetFramebufferInfoForTarget(GL_FRAMEBUFFER);
-  if (!framebuffer)
-    return false;
-  const Framebuffer::Attachment* attachment =
-      framebuffer->GetAttachment(GL_COLOR_ATTACHMENT0);
-  if (!attachment)
-    return false;
-
+bool GLES2DecoderImpl::CheckDrawingFeedbackLoopsHelper(
+    const Framebuffer::Attachment* attachment) {
   DCHECK(state_.current_program.get());
   const Program::SamplerIndices& sampler_indices =
       state_.current_program->sampler_indices();
@@ -8675,6 +8673,36 @@ bool GLES2DecoderImpl::CheckDrawingFeedbackLoops() {
   return false;
 }
 
+bool GLES2DecoderImpl::CheckDrawingFeedbackLoops() {
+  if (!SupportsDrawBuffers()) {
+    Framebuffer* framebuffer = GetFramebufferInfoForTarget(GL_FRAMEBUFFER);
+    if (!framebuffer)
+      return false;
+    const Framebuffer::Attachment* attachment =
+        framebuffer->GetAttachment(GL_COLOR_ATTACHMENT0);
+    if (!attachment)
+      return false;
+    return CheckDrawingFeedbackLoopsHelper(attachment);
+  } else {
+    Framebuffer* framebuffer = GetFramebufferInfoForTarget(GL_DRAW_FRAMEBUFFER);
+    if (!framebuffer)
+      return false;
+    for (uint32_t ii = 0; ii < group_->max_draw_buffers(); ++ii) {
+      GLenum drawbuffer = static_cast<GLenum>(GL_DRAW_BUFFER0 + ii);
+      if (framebuffer->GetDrawBuffer(drawbuffer) == GL_NONE)
+        continue;
+      GLenum attachment = static_cast<GLenum>(GL_COLOR_ATTACHMENT0 + ii);
+      const Framebuffer::Attachment* draw_buffer =
+          framebuffer->GetAttachment(attachment);
+      if (!draw_buffer)
+        continue;
+      if (CheckDrawingFeedbackLoopsHelper(draw_buffer))
+        return true;
+    }
+    return false;
+  }
+}
+
 bool GLES2DecoderImpl::SupportsDrawBuffers() const {
   return feature_info_->IsWebGL1OrES2Context() ?
       feature_info_->feature_flags().ext_draw_buffers : true;