Add a function to scroll a platform canvas. This uses the platform scroll...

gfx/blit.cc

Index: gfx/blit.cc
===================================================================
--- gfx/blit.cc	(revision 52180)
+++ gfx/blit.cc	(working copy)
@@ -4,20 +4,50 @@
 
 #include "gfx/blit.h"
 
-#if defined(OS_POSIX) && !defined(OS_MACOSX)
+#include "base/logging.h"
+#include "build/build_config.h"
+#include "gfx/point.h"
+#include "gfx/rect.h"
+#include "skia/ext/platform_canvas.h"
+#include "skia/ext/platform_device.h"
+
+#if defined(TOOLKIT_GTK)
 #include <cairo/cairo.h>
 #endif
 
 #if defined(OS_MACOSX)
+#include "base/mac_util.h"
 #include "base/scoped_cftyperef.h"
 #endif
-#include "gfx/point.h"
-#include "gfx/rect.h"
-#include "skia/ext/platform_canvas.h"
-#include "skia/ext/platform_device.h"
 
 namespace gfx {
 
+namespace {
+
+// Returns true if the given canvas has any part of itself clipped out or
+// any non-identity tranform.
+bool HasClipOrTransform(const skia::PlatformCanvas& canvas) {
+  if (!canvas.getTotalMatrix().isIdentity())
+    return true;
+
+  const SkRegion& clip_region = canvas.getTotalClip();
+  if (clip_region.isEmpty() || clip_region.isComplex())
+    return true;
+
+  // Now we know the clip is a regular rectangle, make sure it covers the
+  // entire canvas.
+  const SkBitmap& bitmap = canvas.getTopPlatformDevice().accessBitmap(false);
+  const SkIRect& clip_bounds = clip_region.getBounds();
+  if (clip_bounds.fLeft != 0 || clip_bounds.fTop != 0 ||
+      clip_bounds.fRight != bitmap.width() ||
+      clip_bounds.fBottom != bitmap.height())
+    return true;
+
+  return false;
+}
+
+}  // namespace
+
 void BlitContextToContext(NativeDrawingContext dst_context,
                           const Rect& dst_rect,
                           NativeDrawingContext src_context,
@@ -98,4 +128,76 @@
                        GetContextFromCanvas(src_canvas), src_origin);
 }
 
+#if defined(OS_WIN)
+
+void ScrollCanvas(skia::PlatformCanvas* canvas,
+                  const gfx::Rect& clip,
+                  const gfx::Point& amount) {
+  DCHECK(!HasClipOrTransform(*canvas));  // Don't support special stuff.
+  HDC hdc = canvas->beginPlatformPaint();
+
+  RECT damaged_rect;
+  RECT r = clip.ToRECT();
+  ScrollDC(hdc, dx, dy, NULL, &r, NULL, &damaged_rect);
+
+  canvas->endPlatformPaint();
+}
+
+#elif defined(OS_POSIX)
+// Cairo has no nice scroll function so we do our own. On Mac it's possible to
+// use platform scroll code, but it's complex so we just use the same path
+// here. Either way it will be software-only, so it shouldn't matter much.
+
+void ScrollCanvas(skia::PlatformCanvas* canvas,
+                  const gfx::Rect& in_clip,
+                  const gfx::Point& amount) {
+  DCHECK(!HasClipOrTransform(*canvas));  // Don't support special stuff.
+  SkBitmap& bitmap = const_cast<SkBitmap&>(
+      canvas->getTopPlatformDevice().accessBitmap(true));
+  SkAutoLockPixels lock(bitmap);
+
+  // We expect all coords to be inside the canvas, so clip here.
+  gfx::Rect clip = in_clip.Intersect(
+      gfx::Rect(0, 0, bitmap.width(), bitmap.height()));
+
+  // Compute the set of pixels we'll actually end up painting.
+  gfx::Rect dest_rect = clip;
+  dest_rect.Offset(amount);
+  dest_rect = dest_rect.Intersect(clip);
+  if (dest_rect.size() == gfx::Size())
+    return;  // Nothing to do.
+
+  // Compute the source pixels that will map to the dest_rect
+  gfx::Rect src_rect = dest_rect;
+  src_rect.Offset(-amount.x(), -amount.y());
+
+  size_t row_bytes = dest_rect.width() * 4;
+  if (amount.y() > 0) {
+    // Data is moving down, copy from the bottom up.
+    for (int y = dest_rect.height() - 1; y >= 0; y--) {
+      memcpy(bitmap.getAddr32(dest_rect.x(), dest_rect.y() + y),
+             bitmap.getAddr32(src_rect.x(), src_rect.y() + y),
+             row_bytes);
+    }
+  } else if (amount.y() < 0) {
+    // Data is moving up, copy from the top down.
+    for (int y = 0; y < dest_rect.height(); y++) {
+      memcpy(bitmap.getAddr32(dest_rect.x(), dest_rect.y() + y),
+             bitmap.getAddr32(src_rect.x(), src_rect.y() + y),
+             row_bytes);
+    }
+  } else if (amount.x() != 0) {
+    // Horizontal-only scroll. We can do it in either top-to-bottom or bottom-
+    // to-top, but have to be careful about the order for copying each row.
+    // Fortunately, memmove already handles this for us.
+    for (int y = 0; y < dest_rect.height(); y++) {
+      memmove(bitmap.getAddr32(dest_rect.x(), dest_rect.y() + y),
+              bitmap.getAddr32(src_rect.x(), src_rect.y() + y),
+              row_bytes);
+    }
+  }
+}
+
+#endif
+
 }  // namespace gfx