Use Offscreen Surface for Split Screen

tools/viewer/Viewer.cpp

Index: tools/viewer/Viewer.cpp
diff --git a/tools/viewer/Viewer.cpp b/tools/viewer/Viewer.cpp
index 7052a3ac79244d7ee724ea9f23a900e675ef2b64..29160354328b0a321bb15a7bae5cdfccad32df9b 100644
--- a/tools/viewer/Viewer.cpp
+++ b/tools/viewer/Viewer.cpp
@@ -10,13 +10,17 @@
 #include "GMSlide.h"
 #include "ImageSlide.h"
 #include "SKPSlide.h"
+#include "sk_app/WindowContext.h"
 
+#include "GrRenderTarget.h"
 #include "SkCanvas.h"
 #include "SkCommonFlags.h"
+#include "SkDashPathEffect.h"
 #include "SkMetaData.h"
 #include "SkOSFile.h"
 #include "SkRandom.h"
 #include "SkStream.h"
+#include "SkSurface.h"
 
 using namespace sk_app;
 
@@ -360,9 +364,27 @@ void Viewer::drawSlide(SkCanvas* canvas, bool inSplitScreen) {
     canvas->concat(fDefaultMatrix);
     canvas->concat(computeMatrix());
 
-    canvas->getMetaData().setBool(kImageColorXformMetaData, inSplitScreen);
-    fSlides[fCurrentSlide]->draw(canvas);
+    if (inSplitScreen) {
+        sk_sp<SkSurface> offscreenSurface =
+                fWindow->getContext()->createRenderSurface(nullptr, 0, true, true);
+        fSlides[fCurrentSlide]->draw(offscreenSurface->getCanvas());
+        sk_sp<SkImage> snapshot = offscreenSurface->makeImageSnapshot();
+        canvas->drawImage(snapshot, 0, 0);
+    } else {
+        fSlides[fCurrentSlide]->draw(canvas);
+    }
+
     canvas->restoreToCount(count);
+
+    if (inSplitScreen) {
+        // Draw split line
+        SkPaint paint;
+        SkScalar intervals[] = {10.0f, 5.0f};
+        paint.setPathEffect(SkDashPathEffect::Make(intervals, 2, 0.0f));
+        SkRect contentRect = fWindow->getContentRect();
+        SkScalar middleX = (contentRect.fLeft + contentRect.fRight) * 0.5f;
+        canvas->drawLine(middleX, contentRect.fTop, middleX, contentRect.fBottom, paint);
+    }
 }
 
 void Viewer::onPaint(SkCanvas* canvas) {