VrShell: Allow native control of UI element opacity.

chrome/browser/android/vr_shell/vr_shell_gl.cc

Index: chrome/browser/android/vr_shell/vr_shell_gl.cc
diff --git a/chrome/browser/android/vr_shell/vr_shell_gl.cc b/chrome/browser/android/vr_shell/vr_shell_gl.cc
index effea8744a33b0116316f64481f8d79c751d5497..2e0ee4ddd42b730b19495fb47ddde8006572bde4 100644
--- a/chrome/browser/android/vr_shell/vr_shell_gl.cc
+++ b/chrome/browser/android/vr_shell/vr_shell_gl.cc
@@ -487,7 +487,8 @@ void VrShellGl::UpdateController(const gvr::Vec3f& forward_vector) {
   InputTarget input_target = InputTarget::NONE;
 
   for (const auto& plane : scene_->GetUiElements()) {
-    if (!plane->visible || !plane->hit_testable) {
+    if (!plane->visible || plane->computed_opacity == 0.0f ||

[cjgrant, 2017/01/11 16:45:47]

Checking opacity here relieves the HTML UI of having to manage both visibility
and opacity (it can use one or the other).  I stopped short of removing the
visibility toggle though, because in most cases, the toggle is more analogous to
"enabled".

[mthiesse, 2017/01/11 18:33:04]

Maybe add a function IsVisible() to ContentRectangle?

[cjgrant, 2017/01/11 20:58:42]

Done.

+        !plane->hit_testable) {
       continue;
     }
     float distance_to_plane = plane->GetRayDistance(kOrigin, eye_to_target);
@@ -701,7 +702,7 @@ void VrShellGl::DrawVrShell(const gvr::Mat4f& head_pose,
   std::vector<const ContentRectangle*> head_locked_elements;
   std::vector<const ContentRectangle*> world_elements;
   for (const auto& rect : scene_->GetUiElements()) {
-    if (!rect->visible) {
+    if (!rect->visible || rect->computed_opacity == 0.0f) {
       continue;
     }
     if (rect->lock_to_fov) {
@@ -813,7 +814,7 @@ void VrShellGl::DrawElements(
     }
     gvr::Mat4f transform = MatrixMul(render_matrix, rect->transform.to_world);
     vr_shell_renderer_->GetTexturedQuadRenderer()->Draw(
-        texture_handle, transform, copy_rect);
+        texture_handle, transform, copy_rect, rect->computed_opacity);
   }
 }