Fix radial shading when center of start point is on the border of an end circle.

Radial shading is done between two circles with their own centers and
radii. When one has a radius of 0 and is located on or very close to
the border of the other circle, a should be 0, but is not due to
rounding errors unless the circles are aligned in x or y.

Bug: pdfium:1140
Change-Id: Ief2efa91f3f16f7bed439aa471b258fa4d680acf
Reviewed-on: https://pdfium-review.googlesource.com/41590
Reviewed-by: Ryan Harrison <rharrison@chromium.org>
Commit-Queue: Henrique Nakashima <hnakashima@chromium.org>

1 files changed, 5 insertions, 1 deletions

diff --git a/core/fpdfapi/render/cpdf_renderstatus.cpp b/core/fpdfapi/render/cpdf_renderstatus.cpp
index 9965cbb945..95d3cbe5de 100644
--- a/core/fpdfapi/render/cpdf_renderstatus.cpp
+++ b/core/fpdfapi/render/cpdf_renderstatus.cpp
@@ -50,6 +50,7 @@
 #include "core/fpdfdoc/cpdf_occontext.h"
 #include "core/fxcrt/autorestorer.h"
 #include "core/fxcrt/fx_safe_types.h"
+#include "core/fxcrt/fx_system.h"
 #include "core/fxcrt/maybe_owned.h"
 #include "core/fxge/cfx_defaultrenderdevice.h"
 #include "core/fxge/cfx_graphstatedata.h"
@@ -262,6 +263,9 @@ void DrawRadialShading(const RetainPtr<CFX_DIBitmap>& pBitmap,
   float a = ((start_x - end_x) * (start_x - end_x)) +
             ((start_y - end_y) * (start_y - end_y)) -
             ((start_r - end_r) * (start_r - end_r));
+  if (IsFloatZero(a))
+    a = 0.0f;
+
   int width = pBitmap->GetWidth();
   int height = pBitmap->GetHeight();
   int pitch = pBitmap->GetPitch();
@@ -285,7 +289,7 @@ void DrawRadialShading(const RetainPtr<CFX_DIBitmap>& pBitmap,
       float c = ((pos.x - start_x) * (pos.x - start_x)) +
                 ((pos.y - start_y) * (pos.y - start_y)) - (start_r * start_r);
       float s;
-      if (a == 0) {
+      if (a == 0.0f) {
         s = -c / b;
       } else {
         float b2_4ac = (b * b) - 4 * (a * c);