Added MSAA selection to viewer GUI

On Windows, we need to reconstruct the window to allow setting a new
pixel format with a different sample count.

Added some code that maintains window size/position across these changes.
Previously, just cycling through backends would cause the window to move,
as the "default" position would cycle across the screen. Now it's pinned.

BUG=skia:

Change-Id: Iecbe7a490577382043ffe5a88c910b4c0be2ed5c
Reviewed-on: https://skia-review.googlesource.com/9085
Commit-Queue: Brian Osman <brianosman@google.com>
Reviewed-by: Brian Salomon <bsalomon@google.com>

tools/viewer/Viewer.cpp

@@ -1013,6 +1013,20 @@ void Viewer::drawImGui(SkCanvas* canvas) {
                     paramsChanged = true;
                 }
 
+                if (ctx) {
+                    int sampleCount = fWindow->sampleCount();
+                    ImGui::Text("MSAA: "); ImGui::SameLine();
+                    ImGui::RadioButton("0", &sampleCount, 0); ImGui::SameLine();
+                    ImGui::RadioButton("4", &sampleCount, 4); ImGui::SameLine();
+                    ImGui::RadioButton("8", &sampleCount, 8); ImGui::SameLine();
+                    ImGui::RadioButton("16", &sampleCount, 16);
+
+                    if (sampleCount != params.fMSAASampleCount) {
+                        params.fMSAASampleCount = sampleCount;
+                        paramsChanged = true;
+                    }
+                }
+
                 if (ImGui::TreeNode("Path Renderers")) {
                     GpuPathRenderers prevPr = params.fGrContextOptions.fGpuPathRenderers;
                     auto prButton = [&](GpuPathRenderers x) {

tools/viewer/sk_app/Window.h

@@ -193,7 +193,7 @@ public:
     int height();
 
     virtual const DisplayParams& getRequestedDisplayParams() { return fRequestedDisplayParams; }
-    void setRequestedDisplayParams(const DisplayParams&);
+    virtual void setRequestedDisplayParams(const DisplayParams&);
 
     // Actual parameters in effect, obtained from the native window.
     int sampleCount() const;

tools/viewer/sk_app/win/Window_win.cpp

@@ -12,6 +12,7 @@
 #include <windowsx.h>
 
 #include "SkUtils.h"
+#include "../WindowContext.h"
 #include "WindowContextFactory_win.h"
 #ifdef SK_VULKAN
 #include "../VulkanWindowContext.h"
@@ -36,7 +37,7 @@ Window* Window::CreateNativeWindow(void* platformData) {
     return window;
 }
 
-Window_win::~Window_win() {
+void Window_win::closeWindow() {
     RECT r;
     if (GetWindowRect(fHWnd, &r)) {
         gWindowX = r.left;
@@ -47,6 +48,10 @@ Window_win::~Window_win() {
     DestroyWindow(fHWnd);
 }
 
+Window_win::~Window_win() {
+    this->closeWindow();
+}
+
 LRESULT CALLBACK WndProc(HWND hWnd, UINT message, WPARAM wParam, LPARAM lParam);
 
 
@@ -308,6 +313,8 @@ void Window_win::show() {
 
 
 bool Window_win::attach(BackendType attachType) {
+    fBackend = attachType;
+
     switch (attachType) {
         case kNativeGL_BackendType:
             fWindowContext = window_context_factory::NewGLForWin(fHWnd, fRequestedDisplayParams);
@@ -332,4 +339,19 @@ void Window_win::onInval() {
     InvalidateRect(fHWnd, nullptr, false);
 }
 
+void Window_win::setRequestedDisplayParams(const DisplayParams& params) {
+    // GL on Windows doesn't let us change MSAA after the window is created
+    if (params.fMSAASampleCount != this->getRequestedDisplayParams().fMSAASampleCount) {
+        // Need to change these early, so attach() creates the window context correctly
+        fRequestedDisplayParams = params;
+
+        delete fWindowContext;
+        this->closeWindow();
+        this->init(fHInstance);
+        this->attach(fBackend);
+    }
+
+    INHERITED::setRequestedDisplayParams(params);
+}
+
 }   // namespace sk_app

tools/viewer/sk_app/win/Window_win.h

@@ -27,9 +27,16 @@ public:
 
     void onInval() override;
 
+    void setRequestedDisplayParams(const DisplayParams&) override;
+
 private:
+    void closeWindow();
+
     HINSTANCE fHInstance;
     HWND      fHWnd;
+    BackendType fBackend;
+
+    typedef Window INHERITED;
 };
 
 }   // namespace sk_app