>>417512061
Assuming card can be in 3 states:
1. Fully visible (dot > 0.9)
2. Partly transparent (0.8 > dot > 0.9)
3. Fully hidden (dot < 0.8)

1. If (dot > 0.9) draw normally.
2. If (0.8 > dot > 0.9), get the transparency value by normalizing with ((0.9-dot)/0.1).
3. If (dot < 0.8) replace with solid color of your choice. 

Play with numbers (0.9 and 0.8) until you get the desired result.