From d176b30156f3e215df74eaa0c2494f0c267beb5f Mon Sep 17 00:00:00 2001
From: Vadim Zeitlin <vadim@wxwidgets.org>
Date: Thu, 28 Oct 2010 14:23:18 +0000
Subject: [PATCH] Use floating point arithmetic in
 wxDC::GradientFillConcentric().

Use doubles to avoid accumulated rounding errors from using integers in the
generic implementation of wxDC::GradientFillConcentric(). This results in
smoother gradient.

Also avoid using the expensive pow() function inside the inner loop when we
just need to calculate a square.

Closes #12337.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@65944 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775
---
 src/common/dcbase.cpp | 43 ++++++++++++++++++++++++++-----------------
 1 file changed, 26 insertions(+), 17 deletions(-)

diff --git a/src/common/dcbase.cpp b/src/common/dcbase.cpp
index df11b95eea..fdb0a2f1b7 100644
--- a/src/common/dcbase.cpp
+++ b/src/common/dcbase.cpp
@@ -1075,37 +1075,46 @@ void wxDCImpl::DoGradientFillConcentric(const wxRect& rect,
 
 
     //Radius
-    wxInt32 cx = rect.GetWidth() / 2;
-    wxInt32 cy = rect.GetHeight() / 2;
-    wxInt32 nRadius;
+    double cx = rect.GetWidth() / 2;
+    double cy = rect.GetHeight() / 2;
+    double dRadius;
     if (cx < cy)
-        nRadius = cx;
+        dRadius = cx;
     else
-        nRadius = cy;
+        dRadius = cy;
 
     //Offset of circle
-    wxInt32 nCircleOffX = circleCenter.x - (rect.GetWidth() / 2);
-    wxInt32 nCircleOffY = circleCenter.y - (rect.GetHeight() / 2);
+    double ptX, ptY;
+    ptX = circleCenter.x;
+    ptY = circleCenter.y;
+    double nCircleOffX = ptX - cx;
+    double nCircleOffY = ptY - cy;
+
+    double dGradient;
+    double dx, dy;
 
     for ( wxInt32 x = 0; x < rect.GetWidth(); x++ )
     {
         for ( wxInt32 y = 0; y < rect.GetHeight(); y++ )
         {
             //get color difference
-            wxInt32 nGradient = ((nRadius -
-                                  (wxInt32)sqrt(
-                                    pow((double)(x - cx - nCircleOffX), 2) +
-                                    pow((double)(y - cy - nCircleOffY), 2)
-                                  )) * 100) / nRadius;
+            dx = x;
+            dy = y;
+
+            dGradient = ((dRadius - sqrt(  (dx - cx - nCircleOffX) * (dx - cx - nCircleOffX)
+                                          +(dy - cy - nCircleOffY) * (dy - cy - nCircleOffY)
+                                         )
+                         ) * 100
+                        ) / dRadius;
 
             //normalize Gradient
-            if (nGradient < 0 )
-                nGradient = 0;
+            if (dGradient < 0)
+                dGradient = 0.0;
 
             //get dest colors
-            nR = (wxUint8)(nR1 + ((nR2 - nR1) * nGradient / 100));
-            nG = (wxUint8)(nG1 + ((nG2 - nG1) * nGradient / 100));
-            nB = (wxUint8)(nB1 + ((nB2 - nB1) * nGradient / 100));
+            nR = (wxUint8)(nR1 + ((nR2 - nR1) * dGradient / 100));
+            nG = (wxUint8)(nG1 + ((nG2 - nG1) * dGradient / 100));
+            nB = (wxUint8)(nB1 + ((nB2 - nB1) * dGradient / 100));
 
             //set the pixel
             SetPen(wxColour(nR,nG,nB));