smiley.60p

// smiley.60p - SixtyPical translation of smiley.oph (2018),
//   which is itself a stripped-down version of atari-2600-example.oph

// SPDX-FileCopyrightText:  Chris Pressey, the author of this work, has dedicated it to the public domain.
// For more information, please refer to <https://unlicense.org/>
// SPDX-License-Identifier: Unlicense

byte VSYNC         @ $00
byte VBLANK        @ $01
byte WSYNC         @ $02
byte NUSIZ0        @ $04
byte NUSIZ1        @ $05
byte COLUPF        @ $08
byte COLUBK        @ $09
byte PF0           @ $0D
byte PF1           @ $0E
byte PF2           @ $0F
byte SWCHA         @ $280
byte INTIM         @ $284
byte TIM64T        @ $296
byte CTRLPF        @ $0A
byte COLUP0        @ $06
byte COLUP1        @ $07
byte GP0           @ $1B
byte GP1           @ $1C
byte HMOVE         @ $2a
byte RESP0         @ $10
byte RESP1         @ $11

byte colour @ $80
byte luminosity @ $81
byte joystick_delay @ $82

byte table[8] image_data : 126, 129, 153, 165, 129, 165, 129, 126
        // %01111110 
        // %10000001
        // %10011001
        // %10100101
        // %10000001
        // %10100101
        // %10000001
        // %01111110


define vertical_blank routine
  outputs VSYNC, WSYNC, TIM64T
  trashes a, x, z, n
{
    ld x, $00
    ld a, $02
    st a, WSYNC
    st a, WSYNC
    st a, WSYNC
    st a, VSYNC
    st a, WSYNC
    st a, WSYNC
    ld a, $2C
    st a, TIM64T
    ld a, $00
    st a, WSYNC
    st a, VSYNC
}

define display_frame routine
  inputs INTIM, image_data
  outputs WSYNC, HMOVE, VBLANK, RESP0, GP0, PF0, PF1, PF2, COLUPF, COLUBK
  trashes a, x, y, z, n
{
    repeat {
        ld a, INTIM
    } until z

    //; (After that loop finishes, we know the accumulator must contain 0.)

    st a, WSYNC
    st a, HMOVE
    st a, VBLANK

    //;
    //; Wait for $3f (plus one?) scan lines to pass, by waiting for
    //; WSYNC that many times.
    //;

    ld x, $3F
    repeat {
        st a, WSYNC
        dec x
    } until n
    st a, WSYNC

    //;
    //; Delay while the raster scans across the screen.  The more
    //; we delay here, the more to the right the player will be when
    //; we draw it.
    //;

    nop
    nop
    nop
    nop
    nop
    nop
    nop
    nop
    nop
    nop
    nop
    nop
    nop
    nop
    nop

    //;
    //; OK, *now* display the player.
    //;
        
    st a, RESP0

    //;
    //; Loop over the rows of the sprite data, drawing each to the screen
    //; over four scan lines.
    //;
    //; TODO understand this better and describe it!
    //;

    ld y, $07
    for y down to 0 {
        ld a, image_data + y
        st a, GP0

        st a, WSYNC
        st a, WSYNC
        st a, WSYNC
        st a, WSYNC
    }                  // FIXME original was "dec y; bpl _image_loop"

    ld a, $00
    st a, GP0

    //;
    //; Turn off screen display and clear display registers.
    //;

    ld a, $02
    st a, WSYNC
    st a, VBLANK
    ld a, $00
    st a, PF0
    st a, PF1
    st a, PF2
    st a, COLUPF
    st a, COLUBK
}

define colourize_player routine
  inputs colour, luminosity
  outputs COLUP0
  trashes a, z, c, n
{
    ld a, colour
    st off, c
    shl a
    shl a
    shl a
    shl a
    or a, luminosity
    st a, COLUP0
}

define main routine
  inputs image_data, INTIM
  outputs CTRLPF, colour, luminosity, NUSIZ0, VSYNC, WSYNC, TIM64T, HMOVE, VBLANK, RESP0, GP0, PF0, PF1, PF2, COLUPF, COLUBK, COLUP0
  trashes a, x, y, z, c, n
{
    ld a, $00
    st a, CTRLPF
    ld a, $0c
    st a, colour
    ld a, $0a
    st a, luminosity
    ld a, $00
    st a, NUSIZ0
    repeat {
        call vertical_blank
        call display_frame
        call colourize_player
    } forever
}