Use NV_draw_buffers to implement EXT_draw_buffers

gpu/command_buffer/service/feature_info.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/feature_info.h"
 
 #include <set>
 
 #include "base/command_line.h"
 #include "base/macros.h"
@@ skipping 114 matching lines @@
       arb_texture_rectangle(false),
       angle_instanced_arrays(false),
       occlusion_query_boolean(false),
       use_arb_occlusion_query2_for_occlusion_query_boolean(false),
       use_arb_occlusion_query_for_occlusion_query_boolean(false),
       native_vertex_array_object(false),
       ext_texture_format_bgra8888(false),
       enable_shader_name_hashing(false),
       enable_samplers(false),
       ext_draw_buffers(false),
+      nv_draw_buffers(false),
       ext_frag_depth(false),
       ext_shader_texture_lod(false),
       use_async_readpixels(false),
       map_buffer_range(false),
       ext_discard_framebuffer(false),
       angle_depth_texture(false),
       is_angle(false),
       is_swiftshader(false),
       angle_texture_usage(false),
       ext_texture_storage(false),
@@ skipping 608 matching lines @@
   if (!workarounds_.disable_angle_instanced_arrays &&
       (extensions.Contains("GL_ANGLE_instanced_arrays") ||
        (extensions.Contains("GL_ARB_instanced_arrays") &&
         extensions.Contains("GL_ARB_draw_instanced")) ||
        is_es3)) {
     AddExtensionString("GL_ANGLE_instanced_arrays");
     feature_flags_.angle_instanced_arrays = true;
     validators_.vertex_attribute.AddValue(GL_VERTEX_ATTRIB_ARRAY_DIVISOR_ANGLE);
   }
 
+  bool vendor_agnostic_draw_buffers =
+      extensions.Contains("GL_ARB_draw_buffers") ||
+      extensions.Contains("GL_EXT_draw_buffers");
   if (!workarounds_.disable_ext_draw_buffers &&
-      (extensions.Contains("GL_ARB_draw_buffers") ||
-       extensions.Contains("GL_EXT_draw_buffers"))) {
+      (vendor_agnostic_draw_buffers ||
+       (extensions.Contains("GL_NV_draw_buffers") && is_es3))) {
     AddExtensionString("GL_EXT_draw_buffers");
     feature_flags_.ext_draw_buffers = true;
 
+    // This flag is set to enable emulation of EXT_draw_buffers when we're
+    // running on GLES 3.0+, NV_draw_buffers extension is supported and
+    // glDrawBuffers from GLES 3.0 core has been bound. It toggles using the
+    // NV_draw_buffers extension directive instead of EXT_draw_buffers extension
+    // directive in ESSL 100 shaders translated by ANGLE, enabling them to write
+    // into multiple gl_FragData values, which is not by default possible in
+    // ESSL 100 with core GLES 3.0. For more information, see the
+    // NV_draw_buffers specification.
+    feature_flags_.nv_draw_buffers = !vendor_agnostic_draw_buffers;
+
     GLint max_color_attachments = 0;
     glGetIntegerv(GL_MAX_COLOR_ATTACHMENTS_EXT, &max_color_attachments);
     for (GLenum i = GL_COLOR_ATTACHMENT1_EXT;
          i < static_cast<GLenum>(GL_COLOR_ATTACHMENT0 + max_color_attachments);
          ++i) {
       validators_.attachment.AddValue(i);
     }
     COMPILE_ASSERT(GL_COLOR_ATTACHMENT0_EXT == GL_COLOR_ATTACHMENT0,
                    color_attachment0_variation_must_match);
 
@@ skipping 93 matching lines @@
   if (pos == std::string::npos) {
     extensions_ += (extensions_.empty() ? "" : " ") + str;
   }
 }
 
 FeatureInfo::~FeatureInfo() {
 }
 
 }  // namespace gles2
 }  // namespace gpu