Progress update

[+SpiceWare]

After a long break, I'm finally getting back into 2600 development.  Been working on Part 9 - Arena.  It shows off how to use the incremental data streams as well as a jump data stream for program flow control.

 

 

 

 

 

 

 

You may have noticed the playfield data is using 5 bytes per row instead of the usual 6. I'm showing how to convert that to the 6 bytes needed for the playfield registers. I used a slightly more advanced version of this in Stay Frosty 2, which allowed for scrolling levels of arbitrary widths.

 

void PrepArenaBuffers()
{
    // The 40 bits for each row of arena data are stored in 5 bytes arranged like this:
    // byte 0    byte 1    byte 2    byte 3    byte 4
    // 33333333  33222222  22221111  11111100  00000000
    // 98765432  10987654  32109876  54321098  76543210
    //
    // They need to be converted to this arrangement for the playfield datastreams:
    // LEFT                          RIGHT
    // PF0       PF1       PF2       PF0       PF1       PF2
    // 3333----  33333322  22222222  1111----  11111100  00000000
    // 6789----  54321098  01234567  6789----  54321098  01234567
    
    int r;
    unsigned char *arena = ROM + arena_graphics[mm_arena];
    unsigned char *arena_pf0_left   = RAM + _BUF_PF0_LEFT;
    unsigned char *arena_pf1_left   = RAM + _BUF_PF1_LEFT;
    unsigned char *arena_pf2_left   = RAM + _BUF_PF2_LEFT;
    unsigned char *arena_pf0_right  = RAM + _BUF_PF0_RIGHT;
    unsigned char *arena_pf1_right  = RAM + _BUF_PF1_RIGHT;
    unsigned char *arena_pf2_right  = RAM + _BUF_PF2_RIGHT;

    
    for(r=0; r<arena_heights[mm_arena]; r++)
    {
        arena_pf0_left[r] = BitReversal(arena[r*5 + 0]) << 4;
        arena_pf1_left[r] = (arena[r*5 + 0] << 4) + (arena[r*5 + 1] >> 4);
        arena_pf2_left[r] = BitReversal((arena[r*5 + 1] << 4) + (arena[r*5 + 2] >> 4));
        arena_pf0_right[r] = BitReversal(arena[r*5 + 2]);
        arena_pf1_right[r] = arena[r*5 + 3];
        arena_pf2_right[r] = BitReversal(arena[r*5 + 4]);
    }
}

 

 

[+SpiceWare]

Program logic for the next update is finished.  I'm now doing a review of the code to revise the comments, such as this:

Mode:           ds 1    ; $00 = splash, $01 = menu, $80 = game

 

became this:

 

Mode:           ds 1    ; $00 = splash, $01 = menu, $80 = game
                        ; these values allow for easy testing of Mode:
                        ;   LDA Mode
                        ;   BMI GAME_ROUTINE
                        ;   BNE MENU_ROUTINE
                        ;   BEQ SPLASH_routine 

 

 

and revise variable names such as:

 

_ARENA_HEIGHT       = 182

 

 

became this:

 

_ARENA_SCANLINES    = 180   ; number of scanlines for the arena

 

 

because the original name could easily be confused with the new heights table for the arenas:

 

_ARENA_HEIGHTS:
        .byte Arena1_Height
        .byte Arena2_Height
        .byte Arena3_Height
        .byte Arena4_Height

 

 

The 6507 review is finished, and am about half way done with the C review.  I hope to get the next entry posted this weekend.