Transparency

third_party/WebKit/WebCore/platform/graphics/chromium/FontChromiumWin.cpp

Index: third_party/WebKit/WebCore/platform/graphics/chromium/FontChromiumWin.cpp
===================================================================
--- third_party/WebKit/WebCore/platform/graphics/chromium/FontChromiumWin.cpp	(revision 10194)
+++ third_party/WebKit/WebCore/platform/graphics/chromium/FontChromiumWin.cpp	(working copy)
@@ -39,6 +39,7 @@
 #include "SimpleFontData.h"
 #include "SkiaFontWin.h"
 #include "SkiaUtils.h"
+#include "TransparencyWin.h"
 #include "UniscribeHelperTextRun.h"
 
 #include "skia/ext/platform_canvas_win.h"
@@ -48,6 +49,163 @@
 
 namespace WebCore {
 
+namespace {
+
+bool canvasHasMultipleLayers(const SkCanvas* canvas)
+{
+    SkCanvas::LayerIter iter(const_cast<SkCanvas*>(canvas), false);
+    iter.next();  // There is always at least one layer.
+    return !iter.done();  // There is > 1 layer if the the iterator can stil advance.
+}
+
+// Estimates the bounding box of the given text. This is copied from
+// FontCGWin.cpp, it is possible, but a lot more work, to get the precide
+// bounds.
+IntRect estimateTextBounds(const SimpleFontData* font,
+                           const GlyphBuffer& glyphBuffer,
+                           int from, int numGlyphs,
+                           const FloatPoint& point)
+{
+    int totalWidth = 0;
+    for (int i = 0; i < numGlyphs; i++)
+        totalWidth += lroundf(glyphBuffer.advanceAt(from + i));
+
+    return IntRect(point.x() - (font->ascent() + font->descent()) / 2,
+                   point.y() - font->ascent() - font->lineGap(),
+                   totalWidth + font->ascent() + font->descent(),
+                   font->lineSpacing()); 
+}
+
+class TransparencyAwareFontPainter {
+public:
+    TransparencyAwareFontPainter(GraphicsContext* context,
+                                 const SimpleFontData* font,
+                                 const GlyphBuffer& glyphBuffer,
+                                 int from, int numGlyphs,
+                                 const FloatPoint& point);
+    TransparencyAwareFontPainter(GraphicsContext* context,
+                                 const SimpleFontData* font);
+    ~TransparencyAwareFontPainter();
+
+    // Draws the partial string of glyphs, starting at |startAdvance| to the
+    // left of m_point. We express it this way so that if we're using the Skia
+    // drawing path we can use floating-point positioning, even though we have
+    // to use integer positioning in the GDI path.
+    bool drawGlyphs(int numGlyphs, const WORD* glyphs, const int* advances,
+                    int startAdvance) const;
+
+private:
+    // Use the context from the transparency helper when drawing with GDI. It
+    // may point to a temporary one.
+    GraphicsContext* m_graphicsContext;
+    PlatformGraphicsContext* m_platformContext;
+
+    const SimpleFontData* m_font;
+    FloatPoint m_point;
+
+    // Set when Windows can handle the type of drawing we're doing.
+    bool m_useGDI;
+
+    // These members are valid only when m_useGDI is set.
+    HDC m_hdc;
+    HGDIOBJ m_oldFont;  // For restoring the DC to its original state.
+    TransparencyWin m_transparency;
+    bool m_createdLayer;  // We created a layer to give the font some alpha.
+};
+
+TransparencyAwareFontPainter::TransparencyAwareFontPainter(
+    GraphicsContext* context,
+    const SimpleFontData* font,
+    const GlyphBuffer& glyphBuffer,
+    int from, int numGlyphs,
+    const FloatPoint& point)
+    : m_graphicsContext(context)
+    , m_platformContext(context->platformContext())
+    , m_font(font)
+    , m_point(point)
+    , m_useGDI(windowsCanHandleTextDrawing(context))
+    , m_hdc(0)
+    , m_oldFont(0)
+    , m_createdLayer(false)
+{
+    if (!m_useGDI)
+        return;  // Nothing to do.
+
+    SkColor color = m_platformContext->effectiveFillColor();
+    if (SkColorGetA(color) != 0xFF) {
+        // When the font has some transparency, apply it by creating a new
+        // transparency layer with that opacity applied.
+        m_createdLayer = true;
+        m_graphicsContext->beginTransparencyLayer(SkColorGetA(color) / 255.0f);
+        // The color should be opaque now.
+        color = SkColorSetRGB(SkColorGetR(color), SkColorGetG(color), SkColorGetB(color));
+    }
+
+    TransparencyWin::LayerMode layerMode;
+    IntRect layerRect;
+    if (m_platformContext->isDrawingToImageBuffer()) {
+        // Assume if we're drawing to an image buffer that the background
+        // is not opaque and we have to undo ClearType. We may want to
+        // enhance this to actually check, since it will often be opaque
+        // and we could do ClearType in that case.
+        layerMode = TransparencyWin::TextComposite;
+        layerRect = estimateTextBounds(m_font, glyphBuffer, from, numGlyphs, point);
+
+        // The transparency helper requires that we draw text in black in
+        // this mode and it will apply the color.
+        m_transparency.setTextCompositeColor(color);
+        color = SkColorSetRGB(0, 0, 0);
+    } else if (canvasHasMultipleLayers(m_platformContext->canvas())) {
+        // When we're drawing a web page, we know the background is opaque,
+        // but if we're drawing to a layer, we still need extra work.
+        layerMode = TransparencyWin::OpaqueCompositeLayer;
+        layerRect = estimateTextBounds(m_font, glyphBuffer, from, numGlyphs, point);
+    } else {
+        // Common case of drawing onto the bottom layer of a web page: we
+        // know everything is opaque so don't need to do anything special.
+        layerMode = TransparencyWin::NoLayer;
+    }
+    m_transparency.init(m_graphicsContext, layerMode, TransparencyWin::KeepTransform, layerRect);
+
+    // Set up the DC, using the one from the transparency helper.
+    m_hdc = m_transparency.platformContext()->canvas()->beginPlatformPaint();
+    m_oldFont = ::SelectObject(m_hdc, m_font->platformData().hfont());
+    SetTextColor(m_hdc, skia::SkColorToCOLORREF(color));
+    SetBkMode(m_hdc, TRANSPARENT);
+}
+
+TransparencyAwareFontPainter::~TransparencyAwareFontPainter()
+{
+    if (!m_useGDI)
+        return;  // Nothing to do.
+    if (m_createdLayer)
+        m_graphicsContext->endTransparencyLayer();
+
+    ::SelectObject(m_hdc, m_oldFont);
+    m_platformContext->canvas()->endPlatformPaint();
+}
+
+bool TransparencyAwareFontPainter::drawGlyphs(int numGlyphs,
+                                              const WORD* glyphs,
+                                              const int* advances,
+                                              int startAdvance) const
+{
+    if (!m_useGDI) {
+        SkPoint origin = { SkFloatToScalar(m_point.x() + startAdvance),
+                           SkFloatToScalar(m_point.y()) };
+        return paintSkiaText(m_platformContext, m_font->platformData().hfont(),
+                             numGlyphs, glyphs, advances, 0, &origin);
+    }
+
+    // Windows' origin is the top-left of the bounding box, so we have
+    // to subtract off the font ascent to get it.
+    int x = lroundf(m_point.x() + startAdvance);
+    int y = lroundf(m_point.y() - m_font->ascent());
+    return !!ExtTextOut(m_hdc, x, y, ETO_GLYPH_INDEX, 0, reinterpret_cast<const wchar_t*>(&glyphs[0]), numGlyphs, &advances[0]);
+}
+
+}  // namespace
+
 void Font::drawGlyphs(GraphicsContext* graphicsContext,
                       const SimpleFontData* font,
                       const GlyphBuffer& glyphBuffer,
@@ -55,62 +213,27 @@
                       int numGlyphs,
                       const FloatPoint& point) const
 {
-    PlatformGraphicsContext* context = graphicsContext->platformContext();
-
-    bool canUseGDI = windowsCanHandleTextDrawing(graphicsContext);
-    bool createdLayer = false;
-
-    if (canUseGDI && context->isDrawingToImageBuffer()) {
-        // We're drawing to an image buffer and about to render text with GDI.
-        // We need to start a layer here, otherwise the alpha values rendered
-        // by GDI are never correctly updated.
-        // NOTE: this doesn't handle clear type well and should be removed when
-        // we have better text handling code.
-        graphicsContext->beginTransparencyLayer(1.0);
-        createdLayer = true;
-    }
-
-    // Max buffer length passed to the underlying windows API.
-    const int kMaxBufferLength = 1024;
-    // Default size for the buffer. It should be enough for most of cases.
-    const int kDefaultBufferLength = 256;
-
-    SkColor color = context->effectiveFillColor();
+    SkColor color = graphicsContext->platformContext()->effectiveFillColor();
     unsigned char alpha = SkColorGetA(color);
     // Skip 100% transparent text; no need to draw anything.
-    if (!alpha && context->getStrokeStyle() == NoStroke)
+    if (!alpha && graphicsContext->platformContext()->getStrokeStyle() == NoStroke)
         return;
 
-    // Set up our graphics context.
-    HDC hdc = context->canvas()->beginPlatformPaint();
-    HGDIOBJ oldFont = SelectObject(hdc, font->platformData().hfont());
+    TransparencyAwareFontPainter helper(graphicsContext, font, glyphBuffer, from, numGlyphs, point);
 
-    // TODO(maruel): http://b/700464 SetTextColor doesn't support transparency.
-    // Enforce non-transparent color.
-    color = SkColorSetRGB(SkColorGetR(color), SkColorGetG(color), SkColorGetB(color));
-    SetTextColor(hdc, skia::SkColorToCOLORREF(color));
-    SetBkMode(hdc, TRANSPARENT);
-
-    // Windows needs the characters and the advances in nice contiguous
-    // buffers, which we build here.
-    Vector<WORD, kDefaultBufferLength> glyphs;
-    Vector<int, kDefaultBufferLength> advances;
-
-    // Compute the coordinate. The 'origin' represents the baseline, so we need
-    // to move it up to the top of the bounding square.
-    int x = static_cast<int>(point.x());
-    int lineTop = static_cast<int>(point.y()) - font->ascent();
-
     // We draw the glyphs in chunks to avoid having to do a heap allocation for
     // the arrays of characters and advances. Since ExtTextOut is the
     // lowest-level text output function on Windows, there should be little
     // penalty for splitting up the text. On the other hand, the buffer cannot
     // be bigger than 4094 or the function will fail.
-    int glyphIndex = 0;
+    const int kMaxBufferLength = 256;
+    Vector<WORD, kMaxBufferLength> glyphs;
+    Vector<int, kMaxBufferLength> advances;
+    int glyphIndex = 0;  // The starting glyph of the current chunk.
+    int curAdvance = 0;  // How far from the left the current chunk is.
     while (glyphIndex < numGlyphs) {
-        // how many chars will be in this chunk?
+        // How many chars will be in this chunk?
         int curLen = std::min(kMaxBufferLength, numGlyphs - glyphIndex);
-
         glyphs.resize(curLen);
         advances.resize(curLen);
 
@@ -121,21 +244,10 @@
             curWidth += advances[i];
         }
 
+        // Actually draw the glyphs (with retry on failure).
         bool success = false;
         for (int executions = 0; executions < 2; ++executions) {
-            if (canUseGDI)
-                success = !!ExtTextOut(hdc, x, lineTop, ETO_GLYPH_INDEX, 0,
-                        reinterpret_cast<const wchar_t*>(&glyphs[0]),
-                        curLen, &advances[0]);
-            else {
-                // Skia's text drawing origin is the baseline, like WebKit, not
-                // the top, like Windows.
-                SkPoint origin = { x, point.y() };
-                success = paintSkiaText(context, font->platformData().hfont(),
-                        numGlyphs, reinterpret_cast<const WORD*>(&glyphs[0]),
-                        &advances[0], 0, &origin);
-            }
-
+            success = helper.drawGlyphs(curLen, &glyphs[0], &advances[0], curAdvance);
             if (!success && executions == 0) {
                 // Ask the browser to load the font for us and retry.
                 ChromiumBridge::ensureFontLoaded(font->platformData().hfont());
@@ -145,14 +257,8 @@
         }
 
         ASSERT(success);
-
-        x += curWidth;
+        curAdvance += curWidth;
     }
-
-    SelectObject(hdc, oldFont);
-    if (createdLayer)
-        graphicsContext->endTransparencyLayer();
-    context->canvas()->endPlatformPaint();
 }
 
 FloatRect Font::selectionRectForComplexText(const TextRun& run,