Bug 1457110: Restore behavior of maintaining width/height when one of the two is exactly zero. r=jrmuizel

MozReview-Commit-ID: 5OpjfTnJQxe

gfx/2d/BaseRect.h

@@ -124,7 +124,9 @@ struct BaseRect {
     result.y = std::max<T>(y, aRect.y);
     result.width = std::min<T>(x - result.x + width, aRect.x - result.x + aRect.width);
     result.height = std::min<T>(y - result.y + height, aRect.y - result.y + aRect.height);
-    if (result.width <= 0 || result.height <= 0) {
+    // See bug 1457110, this function expects to -only- size to 0,0 if the width/height
+    // is explicitly negative.
+    if (result.width < 0 || result.height < 0) {
       result.SizeTo(0, 0);
     }
     return result;
@@ -137,8 +139,17 @@ struct BaseRect {
   // 'this' can be the same object as either aRect1 or aRect2
   bool IntersectRect(const Sub& aRect1, const Sub& aRect2)
   {
-    *static_cast<Sub*>(this) = aRect1.Intersect(aRect2);
-    return !IsEmpty();
+    T newX = std::max<T>(aRect1.x, aRect2.x);
+    T newY = std::max<T>(aRect1.y, aRect2.y);
+    width = std::min<T>(aRect1.x - newX + aRect1.width, aRect2.x - newX + aRect2.width);
+    height = std::min<T>(aRect1.y - newY + aRect1.height, aRect2.y - newY + aRect2.height);
+    x = newX;
+    y = newY;
+    if (width <= 0 || height <= 0) {
+      SizeTo(0, 0);
+      return false;
+    }
+    return true;
   }
 
   // Returns the smallest rectangle that contains both the area of both

gfx/src/nsRect.h

@@ -150,7 +150,7 @@ struct nsRect :
 
       resultRect = _mm_blend_epi16(resultRect, widthheight, 0xF0); // xr, yr, wr, hr
 
-      if ((_mm_movemask_ps(_mm_castsi128_ps(_mm_cmpgt_epi32(resultRect, _mm_setzero_si128()))) & 0xC) != 0xC) {
+      if ((_mm_movemask_ps(_mm_castsi128_ps(_mm_cmplt_epi32(resultRect, _mm_setzero_si128()))) & 0xC) != 0) {
         // It's potentially more efficient to store all 0s. But the non SSE4 code leaves x/y intact
         // so let's do the same here.
         resultRect = _mm_and_si128(resultRect, _mm_set_epi32(0, 0, 0xFFFFFFFF, 0xFFFFFFFF));
@@ -165,7 +165,7 @@ struct nsRect :
     result.y = std::max<int32_t>(y, aRect.y);
     result.width = std::min<int32_t>(x - result.x + width, aRect.x - result.x + aRect.width);
     result.height = std::min<int32_t>(y - result.y + height, aRect.y - result.y + aRect.height);
-    if (result.width <= 0 || result.height <= 0) {
+    if (result.width < 0 || result.height < 0) {
       result.SizeTo(0, 0);
     }
     return result;
@@ -198,8 +198,18 @@ struct nsRect :
 
       return true;
     }
-    *static_cast<nsRect*>(this) = aRect1.Intersect(aRect2);
-    return !IsEmpty();
+
+    int32_t newX = std::max<int32_t>(aRect1.x, aRect2.x);
+    int32_t newY = std::max<int32_t>(aRect1.y, aRect2.y);
+    width = std::min<int32_t>(aRect1.x - newX + aRect1.width, aRect2.x - newX + aRect2.width);
+    height = std::min<int32_t>(aRect1.y - newY + aRect1.height, aRect2.y - newY + aRect2.height);
+    x = newX;
+    y = newY;
+    if (width <= 0 || height <= 0) {
+      SizeTo(0, 0);
+      return false;
+    }
+    return true;
   }
 #endif
 #endif