Fix some viewer crashes when switching color mode

The whole idea of immediate mode GUIs is to put your GUI code and the
resulting action close together. Unfortunately, for actions that tear
down the backend (possibly freeing the surfaces we're drawing to), we
can't do that. So defer that action until the next frame (really, the
next idle). Only required when an action might call setDisplayParams.

BUG=skia:

Change-Id: I3eb95fdb462526cb6d95819612ad2725c6f1050b
Reviewed-on: https://skia-review.googlesource.com/8953
Reviewed-by: Jim Van Verth <jvanverth@google.com>
Commit-Queue: Brian Osman <brianosman@google.com>

2 files changed, 13 insertions, 2 deletions

diff --git a/tools/viewer/Viewer.cpp b/tools/viewer/Viewer.cpp
index 535ece8b9e..e056b43ec4 100644
--- a/tools/viewer/Viewer.cpp
+++ b/tools/viewer/Viewer.cpp
@@ -934,8 +934,12 @@ void Viewer::drawImGui(SkCanvas* canvas) {
                 ImGui::RadioButton("Color Managed 8888", &newMode, 1);
                 ImGui::RadioButton("Color Managed F16", &newMode, 2);
                 if (newMode != oldMode) {
-                    this->setColorMode(2 == newMode ? kRGBA_F16_SkColorType : kN32_SkColorType,
-                                       0 != newMode);
+                    // It isn't safe to switch color mode now (in the middle of painting). We might
+                    // tear down the back-end, etc... Defer this change until the next onIdle.
+                    fDeferredActions.push_back([=]() {
+                        this->setColorMode(2 == newMode ? kRGBA_F16_SkColorType : kN32_SkColorType,
+                                           0 != newMode);
+                    });
                 }
 
                 // Pick from common gamuts:
@@ -1038,6 +1042,11 @@ void Viewer::drawImGui(SkCanvas* canvas) {
 }
 
 void Viewer::onIdle() {
+    for (int i = 0; i < fDeferredActions.count(); ++i) {
+        fDeferredActions[i]();
+    }
+    fDeferredActions.reset();
+
     double startTime = SkTime::GetMSecs();
     fAnimTimer.updateTime();
     bool animateWantsInval = fSlides[fCurrentSlide]->animate(fAnimTimer);
diff --git a/tools/viewer/Viewer.h b/tools/viewer/Viewer.h
index b17bd250db..1364592300 100644
--- a/tools/viewer/Viewer.h
+++ b/tools/viewer/Viewer.h
@@ -92,6 +92,8 @@ private:
     SkMatrix               fDefaultMatrix;
     SkMatrix               fDefaultMatrixInv;
 
+    SkTArray<std::function<void(void)>> fDeferredActions;
+
     Json::Value            fAllSlideNames; // cache all slide names for fast updateUIState
 };