What I find quite irritating is that in most Invaders versions the aliens get increasingle faster the fewer there are.
The last one can be a PITA and I often lost a life because I couldn't shoot him in time.
I'm not sure if the reason is a design choice or the result of system constraints (more capable modern systems may have intentionally adapted to this).
I can't speak for the arcade hardware but simpler systems like the early Apple II's for example have to
a) draw each enemy indivually (keyword: "block shapes")
and
b) don't synchronize their CPU calculations with the screen, which would make precise timing possible (keyword: "VSYNC")
This leads to the CPU having a huge load of work when there are many enemies to draw on screen. This results in a low speed.
When more and more enemies are shot down there is less to do per time span, as there are fewer enemies to draw. The result is that the speed gets bumped up automatically when it isn't artificially slowed down by synchronizing it with a fixed clock (VSYNC).
From what I've read the Atari 400/800 version is even more clever:
It doesn't move the enemies indivually but simply modifies the screen address pointer of the respective row (the Ataris use a thing called display list which controls the screens layout) which is lightningly fast, of course!
Because of this and the capability to synchronize the action with the screen's timing the movement is smooth and every speed bump you see in this version is intentional.
The missiles of the player's ship and the enemies and most importantly the big alien mother ship on the left screen side are "player/missile graphics" (sprites) which exist and move individually from the playfield area - making the illusion perfect.
What I find quite irritating is that in most Invaders versions the aliens get increasingle faster the fewer there are.
The last one can be a PITA and I often lost a life because I couldn't shoot him in time.
I'm not sure if the reason is a design choice or the result of system constraints (more capable modern systems may have intentionally adapted to this).
I can't speak for the arcade hardware but simpler systems like the early Apple II's for example have to
a) draw each enemy indivually (keyword: "block shapes")
and
b) don't synchronize their CPU calculations with the screen, which would make precise timing possible (keyword: "VSYNC")
This leads to the CPU having a huge load of work when there are many enemies to draw on screen. This results in a low speed.
When more and more enemies are shot down there is less to do per time span, as there are fewer enemies to draw. The result is that the speed gets bumped up automatically when it isn't artificially slowed down by synchronizing it with a fixed clock (VSYNC).
From what I've read the Atari 400/800 version is even more clever:
It doesn't move the enemies indivually but simply modifies the screen address pointer of the respective row (the Ataris use a thing called display list which controls the screens layout) which is lightningly fast, of course!
Because of this and the capability to synchronize the action with the screen's timing the movement is smooth and every speed bump you see in this version is intentional.
The missiles of the player's ship and the enemies and most importantly the big alien mother ship on the left screen side are "player/missile graphics" (sprites) which exist and move individually from the playfield area - making the illusion perfect.
take care,
Calibrator
take care,
Calibrator