Consolidate Windows bitmap and DC code

skia/ext/skia_utils_win.cc

Index: skia/ext/skia_utils_win.cc
diff --git a/skia/ext/skia_utils_win.cc b/skia/ext/skia_utils_win.cc
index 9873373725705fe6f8e4491a54ebd56916829276..a951a26974236952051c208f831a03785a5b569f 100644
--- a/skia/ext/skia_utils_win.cc
+++ b/skia/ext/skia_utils_win.cc
@@ -7,7 +7,10 @@
 #include <stddef.h>
 #include <windows.h>
 
+#include "base/debug/gdi_debug_util_win.h"
+#include "base/win/win_util.h"
 #include "third_party/skia/include/core/SkRect.h"
+#include "third_party/skia/include/core/SkSurface.h"
 #include "third_party/skia/include/core/SkTypes.h"
 #include "third_party/skia/include/effects/SkGradientShader.h"
 
@@ -23,6 +26,48 @@ static_assert(sizeof(RECT().right) == sizeof(SkIRect().fRight), "o7");
 static_assert(sizeof(RECT().bottom) == sizeof(SkIRect().fBottom), "o8");
 static_assert(sizeof(RECT) == sizeof(SkIRect), "o9");
 
+void CreateBitmapHeaderWithColorDepth(LONG width,
+                                      LONG height,
+                                      WORD color_depth,
+                                      BITMAPINFOHEADER* hdr) {
+  // These values are shared with gfx::PlatformDevice.
+  hdr->biSize = sizeof(BITMAPINFOHEADER);
+  hdr->biWidth = width;
+  hdr->biHeight = -height;  // Minus means top-down bitmap.
+  hdr->biPlanes = 1;
+  hdr->biBitCount = color_depth;
+  hdr->biCompression = BI_RGB;  // No compression.
+  hdr->biSizeImage = 0;
+  hdr->biXPelsPerMeter = 1;
+  hdr->biYPelsPerMeter = 1;
+  hdr->biClrUsed = 0;
+  hdr->biClrImportant = 0;
+}
+
+HBITMAP CreateHBitmap(int width, int height) {
+  // CreateDIBSection fails to allocate anything if we try to create an empty
+  // bitmap, so just create a minimal bitmap.
+  if ((width == 0) || (height == 0)) {
+    width = 1;
+    height = 1;
+  }
+
+  BITMAPINFOHEADER hdr = {0};
+  CreateBitmapHeaderWithColorDepth(width, height, 32, &hdr);
+
+  HBITMAP hbitmap = CreateDIBSection(nullptr,
+                                     reinterpret_cast<BITMAPINFO*>(&hdr),
+                                     0, nullptr, nullptr, 0);
+
+  // If CreateDIBSection() failed, try to get some useful information out
+  // before we crash for post-mortem analysis.
+  if (!hbitmap)
+    base::debug::GDIBitmapAllocFailure(&hdr, nullptr);
+
+  return hbitmap;
+}
+
+
 }  // namespace
 
 namespace skia {
@@ -73,7 +118,7 @@ void InitializeDC(HDC context) {
   SkASSERT(res != 0);
   // As per SetStretchBltMode() documentation, SetBrushOrgEx() must be called
   // right after.
-  res = SetBrushOrgEx(context, 0, 0, NULL);
+  res = SetBrushOrgEx(context, 0, 0, nullptr);
   SkASSERT(res != 0);
 
   // Sets up default orientation.
@@ -97,5 +142,67 @@ void InitializeDC(HDC context) {
   SkASSERT(res != 0);
 }
 
+SkImageInfo PrepareAllocation(HDC context, BITMAP* backing) {
+  HBITMAP backing_handle =
+      static_cast<HBITMAP>(GetCurrentObject(context, OBJ_BITMAP));
+  const size_t backing_size = sizeof(*backing);
+  return (GetObject(backing_handle, backing_size, backing) == backing_size)
+            ? SkImageInfo::MakeN32Premul(backing->bmWidth, backing->bmHeight)
+            : SkImageInfo();
+}
+
+sk_sp<SkSurface> MapPlatformSurface(HDC context) {
+  BITMAP backing;
+  const SkImageInfo size(PrepareAllocation(context, &backing));
+  return size.isEmpty() ? nullptr
+                        : SkSurface::MakeRasterDirect(size, backing.bmBits,
+                                                      backing.bmWidthBytes);
+}
+
+SkBitmap MapPlatformBitmap(HDC context) {
+  BITMAP backing;
+  const SkImageInfo size(PrepareAllocation(context, &backing));
+  SkBitmap bitmap;
+  if (!size.isEmpty())
+    bitmap.installPixels(size, backing.bmBits, size.minRowBytes());
+  return bitmap;
+}
+
+HDC CreateOffscreenSurface(int width, int height) {
+  HBITMAP bitmap = nullptr;
+
+  // If this process doesn't have access to GDI, we'll have to use a shared
+  // memory segment instead.
+  if (!base::win::IsUser32AndGdi32Available())
+    return nullptr;
+
+  bitmap = CreateHBitmap(width, height);
+  if (!bitmap)
+    return nullptr;
+
+  HDC hdc = CreateCompatibleDC(nullptr);

[Peter Kasting, 2016/06/22 23:43:52]

Seems like we could use ScopedCreateDC here to avoid the explicit DeleteObject()
calls on early-exit below (which are verbose and error-prone).

I think the syntax for the final line then is something like "return
scoped_hdc.Take();".

+  if (!hdc)
+    return nullptr;
+  InitializeDC(hdc);
+  HRGN clip = CreateRectRgn(0, 0, width, height);
+  if (SelectClipRgn(hdc, clip) == ERROR) {
+    DeleteObject(hdc);
+    return nullptr;
+  }
+  if (!DeleteObject(clip)) {
+    DeleteObject(hdc);
+    return nullptr;
+  }
+
+  SelectObject(hdc, bitmap);
+
+  // The caller must call DeleteDC(hdc) on this object once done with it.
+  return hdc;
+}
+
+void CreateBitmapHeader(int width, int height, BITMAPINFOHEADER* hdr) {
+  CreateBitmapHeaderWithColorDepth(width, height, 32, hdr);
+}
+
 }  // namespace skia