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

diff --git a/src/common/dcbase.cpp b/src/common/dcbase.cpp
index df11b95eeaca56d553859d9bb98040187ba4c844..fdb0a2f1b7f6729d4dd9db5591aa3a6e76f17690 100644 (file)
--- a/src/common/dcbase.cpp
+++ b/src/common/dcbase.cpp
@@ -1075,37 +1075,46 @@ void wxDCImpl::DoGradientFillConcentric(const wxRect& rect,
 
 
     //Radius
 
 
     //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)
     if (cx < cy)

-        nRadius = cx;
+        dRadius = cx;

     else
     else

-        nRadius = cy;
+        dRadius = cy;

 
     //Offset of circle
 
     //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
 
     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
 
             //normalize Gradient

-            if (nGradient < 0 )
-                nGradient = 0;
+            if (dGradient < 0)
+                dGradient = 0.0;

 
             //get dest colors
 
             //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));
 
             //set the pixel
             SetPen(wxColour(nR,nG,nB));