Fixed positioning of tooltips in multi monitor setups.

ui/views/corewm/cursor_height_provider_win.cc

Index: ui/views/corewm/cursor_height_provider_win.cc
diff --git a/ui/views/corewm/cursor_height_provider_win.cc b/ui/views/corewm/cursor_height_provider_win.cc
new file mode 100644
index 0000000000000000000000000000000000000000..f31832282efd53474baab3fda96dc53d75fa10fd
--- /dev/null
+++ b/ui/views/corewm/cursor_height_provider_win.cc
@@ -0,0 +1,144 @@
+// Copyright 2014 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "ui/views/corewm/cursor_height_provider_win.h"
+
+#include <windows.h>
+#include <map>
+
+#include "base/basictypes.h"
+#include "base/memory/scoped_ptr.h"
+#include "base/win/scoped_hdc.h"
+
+namespace {
+typedef scoped_ptr<uint32_t> PixelData;
+typedef std::map<HCURSOR, int> HeightStorage;
+
+const uint32_t kBitsPeruint32 = sizeof(uint32_t) * 8;
+// All bits are 1 for transparent portion of monochromatic mask.
+const uint32_t kTransparentMask = 0xffffffff;
+// This is height of default pointer arrow in Windows 7.
+const int kDefaultHeight = 20;
+// Masks are monochromatic.
+const size_t kNumberOfColors = 2;
+const size_t KHeaderAndPalette =
+      sizeof(BITMAPINFOHEADER) + kNumberOfColors * sizeof(RGBQUAD);
+
+static HeightStorage* g_cached_heights = NULL;

[sky, 2014/05/19 16:12:46]

g_cached_heights -> cached_heights (g_ is for globals, cached_heights is file
local).

+
+// Extracts the pixel data of provided bitmap
+PixelData GetBitmapData(HBITMAP handle, const BITMAPINFO& info, HDC hdc) {
+  PixelData data;
+  // Masks are monochromatic.
+  DCHECK_EQ(info.bmiHeader.biBitCount, 1);
+  if (info.bmiHeader.biBitCount != 1)
+    return data.Pass();
+
+  // When getting pixel data palette is appended to memory pointed by
+  // BITMAPINFO passed so allocate additional memory to store additional data.
+  scoped_ptr<BITMAPINFO> header(
+      reinterpret_cast<BITMAPINFO*>(new char[KHeaderAndPalette]));
+  memcpy(header.get(), &(info.bmiHeader), sizeof(info.bmiHeader));
+
+  data.reset(new uint32_t[info.bmiHeader.biSizeImage / sizeof(uint32_t)]);
+
+  int result = GetDIBits(hdc,
+                         handle,
+                         0,
+                         info.bmiHeader.biHeight,
+                         data.get(),
+                         header.get(),
+                         DIB_RGB_COLORS);
+
+  if (result == 0)
+    data.reset();
+
+  return data.Pass();
+}
+
+// Checks if the specifed row is transparent in provided bitmap.
+bool IsRowTransparent(const PixelData& data,
+                      const uint32_t row_size,
+                      const uint32_t last_byte_mask,
+                      const uint32_t y) {
+  // Set the padding bits to 1 to make mask matching easier.
+  *(data.get() + (y + 1) * row_size - 1) |= last_byte_mask;
+  for (uint32_t i = y * row_size; i < (y + 1) * row_size; ++i) {
+    if (*(data.get() + i) != kTransparentMask)
+      return false;
+  }
+  return true;
+}
+
+// Gets the vertical offset between specified cursor's hotpoint and it's bottom.
+//
+// Gets the cursor image data and extract cursor's visible height.
+// Based on that get's what should be the vertical offset between cursor's
+// hot point and the tooltip.
+int CalculateCursorHeight(HCURSOR cursor_handle) {
+  base::win::ScopedGetDC hdc(NULL);
+
+  ICONINFO icon = {0};
+  GetIconInfo(cursor_handle, &icon);
+
+  BITMAPINFO bitmap_info = {0};
+  bitmap_info.bmiHeader.biSize = sizeof(bitmap_info.bmiHeader);
+  if (GetDIBits(hdc, icon.hbmMask, 0, 0, NULL, &bitmap_info, DIB_RGB_COLORS) ==
+      0)
+    return kDefaultHeight;
+
+  // Rows are padded to full DWORDs. OR with this mask will set them to 1
+  // to simplify matching with |transparent_mask|.
+  uint32_t last_byte_mask = ~0;
+  const unsigned char bits_to_shift = sizeof(last_byte_mask) * 8 -
+      (bitmap_info.bmiHeader.biWidth % kBitsPeruint32);
+  if (bits_to_shift != kBitsPeruint32) {

[sky, 2014/05/19 16:12:46]

nit: no {}

+    last_byte_mask = (last_byte_mask << bits_to_shift);
+  } else {
+    last_byte_mask = 0;
+  }
+
+  const uint32_t row_size =
+      (bitmap_info.bmiHeader.biWidth + kBitsPeruint32 - 1) / kBitsPeruint32;
+  PixelData data(GetBitmapData(icon.hbmMask, bitmap_info, hdc));
+  if (data == NULL)
+    return kDefaultHeight;
+
+  const int cursor_height = GetSystemMetrics(SM_CYCURSOR);
+  int i = bitmap_info.bmiHeader.biHeight - cursor_height;
+  for (; i < bitmap_info.bmiHeader.biHeight; ++i) {
+    if (!IsRowTransparent(data, row_size, last_byte_mask, i)) {
+      i--;

[sky, 2014/05/19 16:12:46]

Might you set i to -1 here?

[Mateusz Szymański, 2014/05/20 09:49:52]

Yes, I believe I can and I believe that would be correct if the cursor is
SM_CYCURSOR high - in that case I have to push the tooltip one pixel lower.

[sky, 2014/05/20 17:19:23]

Might that mean you're going to return a cursor height of -1? That doesn't sound
right.

[Mateusz Szymański, 2014/05/21 08:32:22]

Note that the value returned is
return bitmap_info.bmiHeader.biHeight - i - icon.yHotspot;
in line 116, not i.

+      break;
+    }
+  }
+  return bitmap_info.bmiHeader.biHeight - i - icon.yHotspot;
+}
+
+}  // namespace
+
+namespace views {
+namespace corewm {
+
+int GetCurrentCursorVisibleHeight() {
+  CURSORINFO cursor = {0};
+  cursor.cbSize = sizeof(cursor);
+  GetCursorInfo(&cursor);
+
+  if (g_cached_heights == NULL)
+    g_cached_heights = new HeightStorage;
+
+  HeightStorage::const_iterator cached_height =
+      g_cached_heights->find(cursor.hCursor);
+  if (cached_height != g_cached_heights->end())
+    return cached_height->second;
+
+  const int height = CalculateCursorHeight(cursor.hCursor);
+  (*g_cached_heights)[cursor.hCursor] = height;
+
+  return height;
+}
+
+}  // namespace corewm
+}  // namespace views