Diagonal Line;
MoveTo(startx,starty);
LineTo(endx,endy);

// The dLargeAngle is whatever angle the line makes with the x axis.
// dAngle1 is the angle of the top surface of the arrowhead wrt the x axis.
dAngle1 = dLargeAngle +3.1415 -.255342;

// d1 is the length of the top surface of the arrow.
d1 = 3.0923*grid;

y1 = LengthTimesSine(d1,dAngle1);
x1 = LengthTimesCosine(d1,dAngle1);

pt0.x = endx;
pt0.y = endy;

pt1.x = endx +x1;
pt1.y = endy +y1;

// Here dAngle1 is the angle of the lower surface wrt the x axis.
dAngle1 = dLargeAngle -3.1415 +.255342;
d1 = 3.09232*grid;
y1 = LengthTimesSine(d1,dAngle1);
x1 = LengthTimesCosine(d1,dAngle1);

pt2.x = endx +x1;
pt2.y = endy +y1;

pt3.x = endx;
pt3.y = endy;

// Select a black brush
SolidBrush(RGB(0,0,0));

// 4 points
Polygon(4);
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