Simplify mask/clip intersection, making sure to explicitly check for an empty mask.

src/core/SkDraw.cpp

 /*
  * Copyright 2006 The Android Open Source Project
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 #define __STDC_LIMIT_MACROS
 
 #include "SkDraw.h"
 #include "SkBlitter.h"
@@ skipping 1439 matching lines @@
         , fGlyphCache(cache)
         , fBlitter(blitter)
         , fClip(fUseRegionToDraw ? &draw.fRC->bwRgn() : nullptr)
         , fDraw(draw)
         , fPaint(paint)
         , fClipBounds(PickClipBounds(draw)) { }
 
     void operator()(const SkGlyph& glyph, SkPoint position, SkPoint rounding) {
         position += rounding;
         // Prevent glyphs from being drawn outside of or straddling the edge of device space.
-        if (position.fX > INT_MAX - (INT16_MAX + UINT16_MAX) ||
-            position.fX < INT_MIN - (INT16_MIN + 0 /*UINT16_MIN*/) ||
-            position.fY > INT_MAX - (INT16_MAX + UINT16_MAX) ||
-            position.fY < INT_MIN - (INT16_MIN + 0 /*UINT16_MIN*/)) {
+        // Comparisons written a little weirdly so that NaN coordinates are treated safely.
+        auto gt = [](float a, int b) { return !(a <= (float)b); };
+        auto lt = [](float a, int b) { return !(a >= (float)b); };
+        if (gt(position.fX, INT_MAX - (INT16_MAX + UINT16_MAX)) ||
+            lt(position.fX, INT_MIN - (INT16_MIN + 0 /*UINT16_MIN*/)) ||
+            gt(position.fY, INT_MAX - (INT16_MAX + UINT16_MAX)) ||
+            lt(position.fY, INT_MIN - (INT16_MIN + 0 /*UINT16_MIN*/))) {
             return;
         }
 
         int left = SkScalarFloorToInt(position.fX);
         int top  = SkScalarFloorToInt(position.fY);
         SkASSERT(glyph.fWidth > 0 && glyph.fHeight > 0);
 
         left += glyph.fLeft;
         top  += glyph.fTop;
 
         int right   = left + glyph.fWidth;
         int bottom  = top  + glyph.fHeight;
 
         SkMask mask;
         mask.fBounds.set(left, top, right, bottom);
+        SkASSERT(!mask.fBounds.isEmpty());
 
         if (fUseRegionToDraw) {
             SkRegion::Cliperator clipper(*fClip, mask.fBounds);
 
             if (!clipper.done() && this->getImageData(glyph, &mask)) {
                 const SkIRect& cr = clipper.rect();
                 do {
                     this->blitMask(mask, cr);
                     clipper.next();
                 } while (!clipper.done());
@@ skipping 587 matching lines @@
         mask->fImage = SkMask::AllocImage(size);
         memset(mask->fImage, 0, mask->computeImageSize());
     }
 
     if (SkMask::kJustComputeBounds_CreateMode != mode) {
         draw_into_mask(*mask, devPath, style);
     }
 
     return true;
 }