Javascript Bar Animation

I have this image above. I want to parts of the image to show depending on the RPM of the car. For example when the car starts only the bottom blue block is visible, as the speed increases more blocks become visible all the way to redline. Once the speed decreases the blocks disappear. I'm at a loss with this one i don't even know where to begin. Originally i was thinking of making each block a separate image but i was wondering if there was a better way of doing this. Any开发者_JS百科 ideas?

---

Check out the Raphael javascript library. Depending on your Javascript experience, you may have a bit of a learning curve, but I think you would have a much easier time recreating what you are showing above and attaching the desired behavior to each of the shapes, rather than trying to do it with images, particularly given the arrangement and orientation of the blocks.

UPDATE: I created this fiddle, as I thought this seemed like an interesting exercise. I just used rectangular blocks, but if you mouse over the green 'throttle' bar, you will see how the blocks are made to appear and disappear.