gdi32: Fix ArcTo to use proper starting and ending points.

dlls/gdi32/painting.c

@@ -118,19 +118,26 @@ BOOL WINAPI ArcTo( HDC hdc,
     if(!dc) return FALSE;
 
     if(dc->funcs->pArcTo)
-    {
         result = dc->funcs->pArcTo( dc->physDev, left, top, right, bottom,
 				  xstart, ystart, xend, yend );
-        GDI_ReleaseObj( hdc );
-        return result;
-    }
-    GDI_ReleaseObj( hdc );
+    else
+    {
+        double width = fabs(right-left),
+            height = fabs(bottom-top),
+            xradius = width/2,
+            yradius = height/2,
+            xcenter = right > left ? left+xradius : right+xradius,
+            ycenter = bottom > top ? top+yradius : bottom+yradius;
         /*
          * Else emulate it.
          * According to the documentation, a line is drawn from the current
          * position to the starting point of the arc.
          */
-    LineTo(hdc, xstart, ystart);
+        double angle = atan2(
+            ((ystart-ycenter)/height),
+            ((xstart-xcenter)/width));
+        LineTo(hdc, GDI_ROUND(xcenter+(cos(angle)*xradius)),
+               GDI_ROUND(ycenter+(sin(angle)*yradius)));
         /*
          * Then the arc is drawn.
          */
@@ -139,7 +146,16 @@ BOOL WINAPI ArcTo( HDC hdc,
          * If no error occurred, the current position is moved to the ending
          * point of the arc.
          */
-    if (result) MoveToEx(hdc, xend, yend, NULL);
+        if (result)
+        {
+            angle = atan2(
+                ((yend-ycenter)/height),
+                ((xend-xcenter)/width));
+            MoveToEx(hdc, GDI_ROUND(xcenter+(cos(angle)*xradius)),
+                     GDI_ROUND(ycenter+(sin(angle)*yradius)), NULL);
+        }
+    }
+    GDI_ReleaseObj( hdc );
     return result;
 }
 

dlls/gdi32/tests/path.c

@@ -193,7 +193,7 @@ static void ok_path(HDC hdc, const path_test_t *expected, int expected_size, BOO
 
 static const path_test_t arcto_path[] = {
     {0, 0, PT_MOVETO, 0, 0}, /* 0 */
-    {229, 215, PT_LINETO, 0, 1}, /* 1 */
+    {229, 215, PT_LINETO, 0, 0}, /* 1 */
     {248, 205, PT_BEZIERTO, 1, 0}, /* 2 */
     {273, 200, PT_BEZIERTO, 0, 0}, /* 3 */
     {300, 200, PT_BEZIERTO, 0, 0}, /* 4 */
@@ -203,7 +203,7 @@ static const path_test_t arcto_path[] = {
     {399, 263, PT_BEZIERTO, 0, 0}, /* 8 */
     {389, 275, PT_BEZIERTO, 0, 0}, /* 9 */
     {370, 285, PT_BEZIERTO, 0, 0}, /* 10 */
-    {363, 277, PT_LINETO, 1, 1}, /* 11 */
+    {363, 277, PT_LINETO, 1, 0}, /* 11 */
     {380, 270, PT_BEZIERTO, 1, 0}, /* 12 */
     {389, 260, PT_BEZIERTO, 0, 0}, /* 13 */
     {389, 250, PT_BEZIERTO, 0, 0}, /* 14 */