Choose Largest DrawQuad Type No Longer Depended on Compiler Flag

cc/quads/largest_draw_quad.h

 // Copyright 2014 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.
 
 #ifndef CC_QUADS_LARGEST_DRAW_QUAD_H_
 #define CC_QUADS_LARGEST_DRAW_QUAD_H_
 
+#include "cc/quads/render_pass_draw_quad.h"

[danakj, 2014/11/03 18:14:21]

including this includes GL headers which was breaking the build before. is this
going to be okay? Or should we make a helper function and move all this to a .cc
file instead?

[weiliangc, 2014/11/03 18:42:46]

Have to include for sizeof(). I don't think it can be moved to source file
because that would move entire definition of kLargestDrawQuad.

[jbroman, 2014/11/03 18:44:27]

I'm curious how this broke the build before; do you have a link?

Anyone who included this header (before this change, even) would need to also
include render_pass_draw_quad.h (in order to have a complete definition of
RenderPassDrawQuad, which it would need to evaluate its size).

[danakj, 2014/11/03 18:50:36]

It was a matter of include files including include files and somewhere including
a GL header than conflicts with what this included on mac builds I think. We hit
it again on one of wei's patches maybe she can find the patch set. But if you
include this header in render_pass.h you can see it on trybots for yourself.

[danakj, 2014/11/03 18:50:36]

Ya, it would mean a function returning a size instead of a type. Similar to what
Jeremy suggested, though I guess you can just use std::max instead of a
templated magics.

+#include "cc/quads/stream_video_draw_quad.h"
+
 namespace cc {
-class StreamVideoDrawQuad;
-class RenderPassDrawQuad;
 
-#if defined(ARCH_CPU_64_BITS)
-typedef RenderPassDrawQuad kLargestDrawQuad;
-#else
-typedef StreamVideoDrawQuad kLargestDrawQuad;
-#endif
+// The largest quad is either a RenderPassDrawQuad or a StreamVideoDrawQuad
+// depends on hardware structure, so use a template to determine which is
+// larger.

[danakj, 2014/11/03 18:14:21]

TODO to use std::conditional when we can do that :)

+template <bool RenderPassDrawQuadLarger>

[danakj, 2014/11/03 18:14:21]

render_pass_draw_quad_is_larger

+struct LargerQuadOfEitherRenderPassOrStreamVideo {
+  typedef RenderPassDrawQuad Type;

[danakj, 2014/11/03 18:14:21]

using Type = RenderPassDrawQuad

[jbroman, 2014/11/03 18:28:25]

If you don't mind drive-by...

Since you only ever need the size of this, not the type itself (as far as I can
tell), why not have the template provide the size rather than the type, and put
"size_t Value = sizeof(RenderPassDrawQuad)" here, and similar below?

Considering one step further, with optimizations on, the following even has no
runtime cost (with optimizations off it may emit a static initializer, at least
until C++14 where this could be constexpr):

#include <algorithm>
const size_t kLargestDrawQuadSize = std::max(sizeof(RenderPassDrawQuad),
sizeof(StreamVideoDrawQuad));

If you were concerned about the static initializer in non-release builds, you
could instead write a function with this as its body (which would be trivially
inlined in optimized builds).

+};
+
+template <>
+struct LargerQuadOfEitherRenderPassOrStreamVideo<false> {
+  typedef StreamVideoDrawQuad Type;

[danakj, 2014/11/03 18:14:21]

using Type = StreamVideoDrawQuad

+};
+
+typedef LargerQuadOfEitherRenderPassOrStreamVideo<(

[danakj, 2014/11/03 18:14:21]

using kLargestDrawQuad = ...

+    sizeof(RenderPassDrawQuad) > sizeof(StreamVideoDrawQuad))>::Type
+    kLargestDrawQuad;
 
 }  // namespace cc
 
 #endif  // CC_QUADS_LARGEST_DRAW_QUAD_H_