allow createScalerContext to return null, and then have the GDI backend trigger that if we fail to …

src/ports/SkFontHost_win.cpp

Index: src/ports/SkFontHost_win.cpp
diff --git a/src/ports/SkFontHost_win.cpp b/src/ports/SkFontHost_win.cpp
index 0874e3b9c376e463274dd7dce7d89deded3728cb..06d56aaa2e053f844563c203bf0ecc6e985e7d36 100755
--- a/src/ports/SkFontHost_win.cpp
+++ b/src/ports/SkFontHost_win.cpp
@@ -508,6 +508,10 @@ public:
     SkScalerContext_Windows(SkTypeface*, const SkDescriptor* desc);
     virtual ~SkScalerContext_Windows();
 
+    // Returns true if the constructor was able to complete all of its
+    // initializations (which may include calling GDI).
+    bool isValid() const;
+
 protected:
     virtual unsigned generateGlyphCount() SK_OVERRIDE;
     virtual uint16_t generateCharToGlyph(SkUnichar uni) SK_OVERRIDE;
@@ -583,6 +587,10 @@ SkScalerContext_Windows::SkScalerContext_Windows(SkTypeface* rawTypeface,
     LogFontTypeface* typeface = reinterpret_cast<LogFontTypeface*>(rawTypeface);
 
     fDDC = ::CreateCompatibleDC(NULL);
+    if (!fDDC) {
+        return;
+    }
+
     SetGraphicsMode(fDDC, GM_ADVANCED);
     SetBkMode(fDDC, TRANSPARENT);
 
@@ -592,6 +600,9 @@ SkScalerContext_Windows::SkScalerContext_Windows(SkTypeface* rawTypeface,
     lf.lfHeight = -gCanonicalTextSize;
     lf.lfQuality = compute_quality(fRec);
     fFont = CreateFontIndirect(&lf);
+    if (!fFont) {
+        return;
+    }
 
     // if we're rotated, or want fractional widths, create a hires font
     fHiResFont = 0;
@@ -702,6 +713,10 @@ SkScalerContext_Windows::~SkScalerContext_Windows() {
     }
 }
 
+bool SkScalerContext_Windows::isValid() const {
+    return fDDC && fFont;
+}
+
 unsigned SkScalerContext_Windows::generateGlyphCount() {
     if (fGlyphCount < 0) {
         if (fType == SkScalerContext_Windows::kBitmap_Type) {
@@ -1665,7 +1680,13 @@ SkStream* LogFontTypeface::onOpenStream(int* ttcIndex) const {
 }
 
 SkScalerContext* LogFontTypeface::onCreateScalerContext(const SkDescriptor* desc) const {
-    return SkNEW_ARGS(SkScalerContext_Windows, (const_cast<LogFontTypeface*>(this), desc));
+    SkScalerContext_Windows* ctx = SkNEW_ARGS(SkScalerContext_Windows,

[bungeman-skia, 2013/07/09 22:45:37]

It may be easier to understand the intent with something like:

SkAutoTDelete<SkScalerContext_Windows> ctx(SkNEW_ARGS(SkScalerContext_Windows,
(const_cast<LogFontTypeface*>(this), desc)));

return ctx->isValid() ? ctx.detach() : NULL;

[reed1, 2013/07/10 13:59:04]

Probably a matter of taste, as I find the current way clearer, but I'll make the
change.

+                                                (const_cast<LogFontTypeface*>(this), desc));
+    if (!ctx->isValid()) {
+        SkDELETE(ctx);
+        ctx = NULL;
+    }
+    return ctx;
 }
 
 /** Return the closest matching typeface given either an existing family