Here is the math to compute the new bitmap size before rotating

// pre-compute cosine and sine
// radians = (2*PI*Degrees)/360)
cosine := cos(radians);
sine := sin(radians);

// Take 3 corners (not origin) and rotate them
x1 := round(-OldHeight * sine);   //note minus sign
y1 := round(OldHeight * cosine);
x2 := round(OldWidth * cosine - OldHeight * sine);
y2 := round(OldHeight * cosine + OldWidth * sine);
x3 := round(OldWidth * cosine);
y3 := round(OldWidth * sine);

// The rotated corners tell us how big
// to make the new bitmap.
// this code uses the D3 Math Unit!
minx := MinIntValue([0,MinIntValue([x1, MinIntValue([x2,x3])])]);
miny := MinIntValue([0,MinIntValue([y1, MinIntValue([y2,y3])])]);
maxx := MaxIntValue([x1, MaxIntValue([x2,x3])]);
maxy := MaxIntValue([y1, MaxIntValue([y2,y3])]);

// Compute the new bitmap dimensions
NewWidth := maxx - minx;
NewHeight := maxy - miny;

This could be improved further by adding Bilinear Interpolation (smoothing) during the rotation.

I will gladly send code to any requests sent to Brien@tassoft.com