[roondar]

Originally Posted by litwr

@roondar Thank you. But your idea takes one color from the main screen. IMHO it is possible to use copper to change the value of color register 0 but it will require not very easy coding, we need to change the register two times for horizontal borders and one time for vertical.

Using the copper is indeed the better option if you need colour 0 to be different for the background and border part. Do note that in my idea you can still use colour 0 on the main screen, though it does indeed mean choosing a border colour that is 'useful' for the main screen as well.

To try and help you a bit more, the copper 'trick' you're referring to here really isn't hard. It's essentially the same thing as is done when you create a copper rainbow but instead of having one wait and one move command per scanline, there are two.

The copper list would look something like this for a PAL Amiga (I did this from memory, so there may be bugs ):

; ... whatever init stuff you have goes here ...

; Repeat this next part for every scanline up to VPOS=$fe
dc.w    <waiting_position_left_border>|1,$fffe
dc.w    $0180,$700        ; Set background colour to middle yellow
dc.w    <waiting_position_right_border>|1,$fffe
dc.w    $0180,$000        ; Set border colour to black

; However, for VPOS=$ff do
dc.w    <waiting_position_left_border>|1,$fffe
dc.w    $0180,$700        ; Set background colour to middle yellow
dc.w    <waiting_position_right_border>|1,$fffe
dc.w    $0180,$000        ; Set border colour to black
dc.w    $ffdf,$fffe       ; Wait for start of PAL area

; For the remaining lines continue as before
dc.w    <waiting_position_left_border>|1,$fffe
dc.w    $0180,$700        ; Set background colour to middle yellow
dc.w    <waiting_position_right_border>|1,$fffe
dc.w    $0180,$000        ; Set border colour to black

 ; ... whatever closing stuff you have goes here...
dc.w    $ffff,$fffe            ; End of copperlist

Note that the waiting positions do need to be correctly chosen. I haven't put any values in as the exact positions depend on how wide the screen is. Also note that this method requires the screen edges to be on multiples of 4 pixels due to limits in the Copper wait command.

Hope this helps, as I said - the copper is very nice and can be used for all sorts of tricks.