Energy bars - were probably all done using a sprite overlay in the original game. As you know I'm using all 8 sprites for the parallax. To make the energy bars:
* blit them onto the current screen (slowest method - consider all the player and enemy are blitted)
* block paste them into an unused area
* 'virtual' sprites set above the others
A mock up as to how they could work using 'virtual' sprites:
As you can see, the parallax layer has to be lower than the health bars. This would also be the case when displaying an enemy health bar below the players, so the parallax layer would have to go even lower! Instead of buildings in the background we could put in a little garden fence...
As a workaraound for this there could be 3 health bars, 1 either side for the players and one in the middle for the enemy. We don't need the timer as this isn't an arcade (neither do we really need the flashing 'go'. We can use the timer in sections that we need it such as the bonus stages (when there are no baddies).
A limitation of using sprites could end up being the number of colours used. If you imagine there are a few changing elements in the HUD; lives counter, the health bar. There are a number of methods to display these - a sliding bar that moves offscreen as the player loses health/ using different frames of animation for chunk of health lost. If several sprites are needed then they will have to be 3 colour. I'm going with black & whitish for now.
Doing this I think it's still possible to multiplex the parallax layer horizontally later - if the skill becomes acquired or I can ever be bothered to learn to program properly. I looked into this a couple of months ago. There are I think, no working examples of it in Blitz. The way to access the copper is pretty much the ASM route, bar some blitzized commands which can help facilitate it. Understanding would be one thing, but integrating it is another. Between the two it is a tricky exercise figuring out where you're going wrong. I might post the results of this if I get into it again.
The score panel is another thing, but that may just sit above everything else, out of the way.