Improve drawing of highlight arrow

A diagonal arrow sometimes had a notch in the shaft because of
independent rounding of the starting and ending point coordinates.
Furthermore the width of the shaft was unnecessary variable(as a
function of direction) because half the width was rounded and then used
twice. Now rounding of end-points is always done towards a fixed grid
of square centers, which keeps diagonals purely diagonal, and one side
of the shaft is drawn relative to the other side, after the
position of the latter has been rounded, so any rounding error affects
the shaft width only once.

diff --git a/winboard/winboard.c b/winboard/winboard.c
index a0e2284..ccebf78 100644 (file)
--- a/winboard/winboard.c
+++ b/winboard/winboard.c
@@ -2952,7 +2952,7 @@ VOID RebuildTextureSquareInfo()
 \r
 /* [AS] Arrow highlighting support */\r
 \r
-static int A_WIDTH = 5; /* Width of arrow body */\r
+static double A_WIDTH = 5; /* Width of arrow body */\r
 \r
 #define A_HEIGHT_FACTOR 6   /* Length of arrow "point", relative to body width */\r
 #define A_WIDTH_FACTOR  3   /* Width of arrow "point", relative to body width */\r
@@ -2976,50 +2976,50 @@ VOID DrawArrowBetweenPoints( HDC hdc, int s_x, int s_y, int d_x, int d_y )
     if( d_x == s_x ) {\r
         int h = (d_y > s_y) ? +A_WIDTH*A_HEIGHT_FACTOR : -A_WIDTH*A_HEIGHT_FACTOR;\r
 \r
-        arrow[0].x = s_x + A_WIDTH;\r
+        arrow[0].x = s_x + A_WIDTH + 0.5;\r
         arrow[0].y = s_y;\r
 \r
-        arrow[1].x = s_x + A_WIDTH;\r
+        arrow[1].x = s_x + A_WIDTH + 0.5;\r
         arrow[1].y = d_y - h;\r
 \r
-        arrow[2].x = s_x + A_WIDTH*A_WIDTH_FACTOR;\r
+        arrow[2].x = arrow[1].x + A_WIDTH*(A_WIDTH_FACTOR-1) + 0.5;\r
         arrow[2].y = d_y - h;\r
 \r
         arrow[3].x = d_x;\r
         arrow[3].y = d_y;\r
 \r
-        arrow[4].x = s_x - A_WIDTH*A_WIDTH_FACTOR;\r
-        arrow[4].y = d_y - h;\r
-\r
-        arrow[5].x = s_x - A_WIDTH;\r
+        arrow[5].x = arrow[1].x - 2*A_WIDTH + 0.5;\r
         arrow[5].y = d_y - h;\r
 \r
-        arrow[6].x = s_x - A_WIDTH;\r
+        arrow[4].x = arrow[5].x - A_WIDTH*(A_WIDTH_FACTOR-1) + 0.5;\r
+        arrow[4].y = d_y - h;\r
+\r
+        arrow[6].x = arrow[1].x - 2*A_WIDTH + 0.5;\r
         arrow[6].y = s_y;\r
     }\r
     else if( d_y == s_y ) {\r
         int w = (d_x > s_x) ? +A_WIDTH*A_HEIGHT_FACTOR : -A_WIDTH*A_HEIGHT_FACTOR;\r
 \r
         arrow[0].x = s_x;\r
-        arrow[0].y = s_y + A_WIDTH;\r
+        arrow[0].y = s_y + A_WIDTH + 0.5;\r
 \r
         arrow[1].x = d_x - w;\r
-        arrow[1].y = s_y + A_WIDTH;\r
+        arrow[1].y = s_y + A_WIDTH + 0.5;\r
 \r
         arrow[2].x = d_x - w;\r
-        arrow[2].y = s_y + A_WIDTH*A_WIDTH_FACTOR;\r
+        arrow[2].y = arrow[1].y + A_WIDTH*(A_WIDTH_FACTOR-1) + 0.5;\r
 \r
         arrow[3].x = d_x;\r
         arrow[3].y = d_y;\r
 \r
-        arrow[4].x = d_x - w;\r
-        arrow[4].y = s_y - A_WIDTH*A_WIDTH_FACTOR;\r
-\r
         arrow[5].x = d_x - w;\r
-        arrow[5].y = s_y - A_WIDTH;\r
+        arrow[5].y = arrow[1].y - 2*A_WIDTH + 0.5;\r
+\r
+        arrow[4].x = d_x - w;\r
+        arrow[4].y = arrow[5].y - A_WIDTH*(A_WIDTH_FACTOR-1) + 0.5;\r
 \r
         arrow[6].x = s_x;\r
-        arrow[6].y = s_y - A_WIDTH;\r
+        arrow[6].y = arrow[1].y - 2*A_WIDTH + 0.5;\r
     }\r
     else {\r
         /* [AS] Needed a lot of paper for this! :-) */\r
@@ -3036,8 +3036,8 @@ VOID DrawArrowBetweenPoints( HDC hdc, int s_x, int s_y, int d_x, int d_y )
         arrow[0].x = Round(x - j);\r
         arrow[0].y = Round(y + j*dx);\r
 \r
-        arrow[1].x = Round(x + j);\r
-        arrow[1].y = Round(y - j*dx);\r
+        arrow[1].x = Round(arrow[0].x + 2*j);   // [HGM] prevent width to be affected by rounding twice\r
+        arrow[1].y = Round(arrow[0].y - 2*j*dx);\r
 \r
         if( d_x > s_x ) {\r
             x = (double) d_x - k;\r
@@ -3048,20 +3048,22 @@ VOID DrawArrowBetweenPoints( HDC hdc, int s_x, int s_y, int d_x, int d_y )
             y = (double) d_y + k*dy;\r
         }\r
 \r
-        arrow[2].x = Round(x + j);\r
-        arrow[2].y = Round(y - j*dx);\r
+        x = Round(x); y = Round(y); // [HGM] make sure width of shaft is rounded the same way on both ends\r
 \r
-        arrow[3].x = Round(x + j*A_WIDTH_FACTOR);\r
-        arrow[3].y = Round(y - j*A_WIDTH_FACTOR*dx);\r
+        arrow[6].x = Round(x - j);\r
+        arrow[6].y = Round(y + j*dx);\r
+\r
+        arrow[2].x = Round(arrow[6].x + 2*j);\r
+        arrow[2].y = Round(arrow[6].y - 2*j*dx);\r
+\r
+        arrow[3].x = Round(arrow[2].x + j*(A_WIDTH_FACTOR-1));\r
+        arrow[3].y = Round(arrow[2].y - j*(A_WIDTH_FACTOR-1)*dx);\r
 \r
         arrow[4].x = d_x;\r
         arrow[4].y = d_y;\r
 \r
-        arrow[5].x = Round(x - j*A_WIDTH_FACTOR);\r
-        arrow[5].y = Round(y + j*A_WIDTH_FACTOR*dx);\r
-\r
-        arrow[6].x = Round(x - j);\r
-        arrow[6].y = Round(y + j*dx);\r
+        arrow[5].x = Round(arrow[6].x - j*(A_WIDTH_FACTOR-1));\r
+        arrow[5].y = Round(arrow[6].y + j*(A_WIDTH_FACTOR-1)*dx);\r
     }\r
 \r
     Polygon( hdc, arrow, 7 );\r
@@ -3086,20 +3088,20 @@ VOID DrawArrowBetweenSquares( HDC hdc, int s_col, int s_row, int d_col, int d_ro
     SquareToPos( d_row, d_col, &d_x, &d_y);\r
 \r
     if( d_y > s_y ) {\r
-        d_y += squareSize / 4;\r
+        d_y += squareSize / 2 - squareSize / 4; // [HGM] round towards same centers on all sides!\r
     }\r
     else if( d_y < s_y ) {\r
-        d_y += 3 * squareSize / 4;\r
+        d_y += squareSize / 2 + squareSize / 4;\r
     }\r
     else {\r
         d_y += squareSize / 2;\r
     }\r
 \r
     if( d_x > s_x ) {\r
-        d_x += squareSize / 4;\r
+        d_x += squareSize / 2 - squareSize / 4;\r
     }\r
     else if( d_x < s_x ) {\r
-        d_x += 3 * squareSize / 4;\r
+        d_x += squareSize / 2 + squareSize / 4;\r
     }\r
     else {\r
         d_x += squareSize / 2;\r
@@ -3109,7 +3111,7 @@ VOID DrawArrowBetweenSquares( HDC hdc, int s_col, int s_row, int d_col, int d_ro
     s_y += squareSize / 2;\r
 \r
     /* Adjust width */\r
-    A_WIDTH = squareSize / 14;\r
+    A_WIDTH = squareSize / 14.; //[HGM] make float\r
 \r
     /* Draw */\r
     stLB.lbStyle = BS_SOLID;\r