path: root/gfx/canvas_skia_win.cc

// Copyright (c) 2010 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 "gfx/canvas_skia.h"

#include <limits>

#include "base/i18n/rtl.h"
#include "gfx/font.h"
#include "gfx/rect.h"
#include "third_party/skia/include/core/SkShader.h"

namespace {

// We make sure that LTR text we draw in an RTL context is modified
// appropriately to make sure it maintains it LTR orientation.
void DoDrawText(HDC hdc, const std::wstring& text,
                RECT* text_bounds, int flags) {
  std::wstring localized_text;
  const wchar_t* string_ptr = text.c_str();
  int string_size = static_cast<int>(text.length());
  // Only adjust string directionality if both of the following are true:
  // 1. The current locale is RTL.
  // 2. The string itself has RTL directionality.
  if (flags & DT_RTLREADING) {
    if (base::i18n::AdjustStringForLocaleDirection(text, &localized_text)) {
      string_ptr = localized_text.c_str();
      string_size = static_cast<int>(localized_text.length());
    }
  }

  DrawText(hdc, string_ptr, string_size, text_bounds, flags);
}

// Compute the windows flags necessary to implement the provided text Canvas
// flags.
int ComputeFormatFlags(int flags, const std::wstring& text) {
  // Setting the text alignment explicitly in case it hasn't already been set.
  // This will make sure that we don't align text to the left on RTL locales
  // just because no alignment flag was passed to DrawStringInt().
  if (!(flags & (gfx::Canvas::TEXT_ALIGN_CENTER |
                 gfx::Canvas::TEXT_ALIGN_RIGHT |
                 gfx::Canvas::TEXT_ALIGN_LEFT))) {
    flags |= gfx::CanvasSkia::DefaultCanvasTextAlignment();
  }

  // horizontal alignment
  int f = 0;
  if (flags & gfx::Canvas::TEXT_ALIGN_CENTER)
    f |= DT_CENTER;
  else if (flags & gfx::Canvas::TEXT_ALIGN_RIGHT)
    f |= DT_RIGHT;
  else
    f |= DT_LEFT;

  // vertical alignment
  if (flags & gfx::Canvas::TEXT_VALIGN_TOP)
    f |= DT_TOP;
  else if (flags & gfx::Canvas::TEXT_VALIGN_BOTTOM)
    f |= DT_BOTTOM;
  else
    f |= DT_VCENTER;

  if (flags & gfx::Canvas::MULTI_LINE) {
    f |= DT_WORDBREAK;
    if (flags & gfx::Canvas::CHARACTER_BREAK)
      f |= DT_EDITCONTROL;  // Turns on character breaking (not documented)
    else if (!(flags & gfx::Canvas::NO_ELLIPSIS))
      f |= DT_WORD_ELLIPSIS;
  } else {
    f |= DT_SINGLELINE;
  }

  if (flags & gfx::Canvas::HIDE_PREFIX)
    f |= DT_HIDEPREFIX;
  else if ((flags & gfx::Canvas::SHOW_PREFIX) == 0)
    f |= DT_NOPREFIX;

  if (!(flags & gfx::Canvas::NO_ELLIPSIS))
    f |= DT_END_ELLIPSIS;

  // In order to make sure RTL/BiDi strings are rendered correctly, we must
  // pass the flag DT_RTLREADING to DrawText (when the locale's language is
  // a right-to-left language) so that Windows does the right thing.
  //
  // In addition to correctly displaying text containing both RTL and LTR
  // elements (for example, a string containing a telephone number within a
  // sentence in Hebrew, or a sentence in Hebrew that contains a word in
  // English) this flag also makes sure that if there is not enough space to
  // display the entire string, the ellipsis is displayed on the left hand side
  // of the truncated string and not on the right hand side.
  //
  // We make a distinction between Chrome UI strings and text coming from a web
  // page.
  //
  // For text coming from a web page we determine the alignment based on the
  // first character with strong directionality. If the directionality of the
  // first character with strong directionality in the text is LTR, the
  // alignment is set to DT_LEFT, and the directionality should not be set as
  // DT_RTLREADING.
  //
  // This heuristic doesn't work for Chrome UI strings since even in RTL
  // locales, some of those might start with English text but we know they're
  // localized so we always want them to be right aligned, and their
  // directionality should be set as DT_RTLREADING.
  //
  // Caveat: If the string is purely LTR, don't set DTL_RTLREADING since when
  // the flag is set, LRE-PDF don't have the desired effect of rendering
  // multiline English-only text as LTR.
  //
  // Note that if the caller is explicitly requesting displaying the text
  // using RTL directionality then we respect that and pass DT_RTLREADING to
  // ::DrawText even if the locale is LTR.
  if ((flags & gfx::Canvas::FORCE_RTL_DIRECTIONALITY) ||
      (base::i18n::IsRTL() &&
       (f & DT_RIGHT) && base::i18n::StringContainsStrongRTLChars(text))) {
    f |= DT_RTLREADING;
  }

  return f;
}

}  // anonymous namespace

namespace gfx {

CanvasSkia::CanvasSkia(int width, int height, bool is_opaque)
    : skia::PlatformCanvas(width, height, is_opaque) {
}

CanvasSkia::CanvasSkia() : skia::PlatformCanvas() {
}

CanvasSkia::~CanvasSkia() {
}

// static
void CanvasSkia::SizeStringInt(const std::wstring& text,
                               const gfx::Font& font,
                               int* width, int* height, int flags) {
  // Clamp the max amount of text we'll measure to 2K.  When the string is
  // actually drawn, it will be clipped to whatever size box is provided, and
  // the time to do that doesn't depend on the length being clipped off.
  const int kMaxStringLength = 2048 - 1;  // So the trailing \0 fits in 2K.
  std::wstring clamped_string(text.substr(0, kMaxStringLength));

  if (*width == 0) {
    // If multi-line + character break are on, the computed width will be one
    // character wide (useless).  Furthermore, if in this case the provided text
    // contains very long "words" (substrings without a word-breaking point),
    // DrawText() can run extremely slowly (e.g. several seconds).  So in this
    // case, we turn character breaking off to get a more accurate "desired"
    // width and avoid the slowdown.
    if (flags & (gfx::Canvas::MULTI_LINE | gfx::Canvas::CHARACTER_BREAK))
      flags &= ~gfx::Canvas::CHARACTER_BREAK;

    // Weird undocumented behavior: if the width is 0, DoDrawText() won't
    // calculate a size at all.  So set it to 1, which it will then change.
    if (!text.empty())
      *width = 1;
  }
  RECT r = { 0, 0, *width, *height };

  HDC dc = GetDC(NULL);
  HFONT old_font = static_cast<HFONT>(SelectObject(dc, font.GetNativeFont()));
  DoDrawText(dc, clamped_string, &r,
             ComputeFormatFlags(flags, clamped_string) | DT_CALCRECT);
  SelectObject(dc, old_font);
  ReleaseDC(NULL, dc);

  *width = r.right;
  *height = r.bottom;
}

void CanvasSkia::DrawStringInt(const std::wstring& text, HFONT font,
                               const SkColor& color, int x, int y, int w, int h,
                               int flags) {
  if (!IntersectsClipRectInt(x, y, w, h))
    return;

  // Clamp the max amount of text we'll draw to 32K.  There seem to be bugs in
  // DrawText() if you e.g. ask it to character-break a no-whitespace string of
  // length > 43680 (for which it draws nothing), and since we clamped to 2K in
  // SizeStringInt() we're unlikely to be able to display this much anyway.
  const int kMaxStringLength = 32768 - 1;  // So the trailing \0 fits in 32K.
  std::wstring clamped_string(text.substr(0, kMaxStringLength));

  RECT text_bounds = { x, y, x + w, y + h };
  HDC dc = beginPlatformPaint();
  SetBkMode(dc, TRANSPARENT);
  HFONT old_font = (HFONT)SelectObject(dc, font);
  COLORREF brush_color = RGB(SkColorGetR(color), SkColorGetG(color),
                             SkColorGetB(color));
  SetTextColor(dc, brush_color);

  int f = ComputeFormatFlags(flags, clamped_string);
  DoDrawText(dc, clamped_string, &text_bounds, f);
  endPlatformPaint();

  // Restore the old font. This way we don't have to worry if the caller
  // deletes the font and the DC lives longer.
  SelectObject(dc, old_font);

  // Windows will have cleared the alpha channel of the text we drew. Assume
  // we're drawing to an opaque surface, or at least the text rect area is
  // opaque.
  getTopPlatformDevice().makeOpaque(x, y, w, h);
}

void CanvasSkia::DrawStringInt(const std::wstring& text,
                               const gfx::Font& font,
                               const SkColor& color,
                               int x, int y, int w, int h, int flags) {
  DrawStringInt(text, font.GetNativeFont(), color, x, y, w, h, flags);
}

// Checks each pixel immediately adjacent to the given pixel in the bitmap. If
// any of them are not the halo color, returns true. This defines the halo of
// pixels that will appear around the text. Note that we have to check each
// pixel against both the halo color and transparent since DrawStringWithHalo
// will modify the bitmap as it goes, and clears pixels shouldn't count as
// changed.
static bool pixelShouldGetHalo(const SkBitmap& bitmap, int x, int y,
                               SkColor halo_color) {
  if (x > 0 &&
      *bitmap.getAddr32(x - 1, y) != halo_color &&
      *bitmap.getAddr32(x - 1, y) != 0)
    return true;  // Touched pixel to the left.
  if (x < bitmap.width() - 1 &&
      *bitmap.getAddr32(x + 1, y) != halo_color &&
      *bitmap.getAddr32(x + 1, y) != 0)
    return true;  // Touched pixel to the right.
  if (y > 0 &&
      *bitmap.getAddr32(x, y - 1) != halo_color &&
      *bitmap.getAddr32(x, y - 1) != 0)
    return true;  // Touched pixel above.
  if (y < bitmap.height() - 1 &&
      *bitmap.getAddr32(x, y + 1) != halo_color &&
      *bitmap.getAddr32(x, y + 1) != 0)
    return true;  // Touched pixel below.
  return false;
}

void CanvasSkia::DrawStringWithHalo(const std::wstring& text,
                                    const gfx::Font& font,
                                    const SkColor& text_color,
                                    const SkColor& halo_color_in,
                                    int x, int y, int w, int h,
                                    int flags) {
  // Some callers will have semitransparent halo colors, which we don't handle
  // (since the resulting image can have 1-bit transparency only).
  SkColor halo_color = halo_color_in | 0xFF000000;

  // Create a temporary buffer filled with the halo color. It must leave room
  // for the 1-pixel border around the text.
  CanvasSkia text_canvas(w + 2, h + 2, true);
  SkPaint bkgnd_paint;
  bkgnd_paint.setColor(halo_color);
  text_canvas.FillRectInt(0, 0, w + 2, h + 2, bkgnd_paint);

  // Draw the text into the temporary buffer. This will have correct
  // ClearType since the background color is the same as the halo color.
  text_canvas.DrawStringInt(text, font, text_color, 1, 1, w, h, flags);

  // Windows will have cleared the alpha channel for the pixels it drew. Make it
  // opaque. We have to do this first since pixelShouldGetHalo will check for
  // 0 to see if a pixel has been modified to transparent, and black text that
  // Windows draw will look transparent to it!
  text_canvas.getTopPlatformDevice().makeOpaque(0, 0, w + 2, h + 2);

  uint32_t halo_premul = SkPreMultiplyColor(halo_color);
  SkBitmap& text_bitmap = const_cast<SkBitmap&>(
      text_canvas.getTopPlatformDevice().accessBitmap(true));
  for (int cur_y = 0; cur_y < h + 2; cur_y++) {
    uint32_t* text_row = text_bitmap.getAddr32(0, cur_y);
    for (int cur_x = 0; cur_x < w + 2; cur_x++) {
      if (text_row[cur_x] == halo_premul) {
        // This pixel was not touched by the text routines. See if it borders
        // a touched pixel in any of the 4 directions (not diagonally).
        if (!pixelShouldGetHalo(text_bitmap, cur_x, cur_y, halo_premul))
          text_row[cur_x] = 0;  // Make transparent.
      } else {
        text_row[cur_x] |= 0xff << SK_A32_SHIFT;  // Make opaque.
      }
    }
  }

  // Draw the halo bitmap with blur.
  drawBitmap(text_bitmap, SkIntToScalar(x - 1), SkIntToScalar(y - 1));
}

}  // namespace gfx