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  • Joined: 06 Sep 2015
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Plotting tiles
Post Posted: Thu Jan 10, 2019 4:39 pm
So what I want to do is make a wall using tile $001E down the length of the screen in my Game Gear game I decided to make. But I'm having trouble. I can get one tile where I want the start of the wall to be vertically, but that's it. Here is my code so far:

SCREEN_2:
       ld hl,$38EE
       call vrampr
       ld hl,screen2tile
       ld bc,1*32         
       call vramwr   

draw_on_screen:
       ld a,(wallbuild)
       add a,1
       ld (wallbuild),a

       ld a,(wallbuild)
       cp 16
       jp z,Screen_2_end

       jp draw_on_screen

Screen_2_end:
       ret

screen2tile      .dw $001E

Any attempts to add 32 to $38EE leave me with no result I want. The wallbuild variable is a timer to make sure it ends the wall where I want it to end (at the bottom of the screen) So, how do I do this?
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Post Posted: Thu Jan 10, 2019 5:39 pm
You appear to only be calling vramwr once. You need to add 32 to move down one row.
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Post Posted: Thu Jan 10, 2019 6:06 pm
That's what I was having the problem with. I couldn't add 64 to $38EE. The next block I want at $392E, and $392e-$38ee=64. So I need to add 64 to $38EE, but I can't for some reason.
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Post Posted: Thu Jan 10, 2019 6:11 pm
Found out my problem.
Remove call vrampr from the loop.
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Post Posted: Thu Jan 10, 2019 6:25 pm
But now I need to figure out how to make it not make the tile afterwards for the first one. I have a sky and a ground, and it puts the sky tiles in front of the blocks on the ground.
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Post Posted: Thu Jan 10, 2019 8:32 pm
Your descriptions are confusing.
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Post Posted: Thu Jan 10, 2019 9:00 pm
Sorry. What I need is a better way to do this:

SCREEN_2:
       ld hl,$38EE
       call this_is_tedious
       ld hl,$392E
       call this_is_tedious
       ld hl,$396E
       call this_is_tedious
       ld hl,$39AE
       call this_is_tedious
       ld hl,$39EE
       call this_is_tedious
       ld hl,$3A2E
       call this_is_tedious
       ld hl,$3A6E
       call this_is_tedious
       ld hl,$3AAE
       call this_is_tedious
       ld hl,$3AEE
       call this_is_tedious
       ld hl,$3B2E
       call this_is_tedious
       ld hl,$3B6E
       call this_is_tedious
       ld hl,$3BAE
       call this_is_tedious
       ld hl,$3BEE
       call this_is_tedious
       ld hl,$3C2E
       call this_is_tedious
       ld hl,$3C6E
       call this_is_tedious
       ld hl,$3CAE
       call this_is_tedious
       ld hl,$3CEE
       call this_is_tedious
       ld hl,$3D2E
       call this_is_tedious
       ret

this_is_tedious:
       call vrampr
       ld hl,screen2tile
       ld bc,1*2
       call vramwr
       ret

screen2tile      .dw $001E
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Post Posted: Fri Jan 11, 2019 3:01 am
There are two solutions: get your assembler to write the code statically, if it can, or write a quick loop.

I've no idea which assembler you're using so can't help with the former. Look in its manual for its macros section.

Otherwise, suboptimally:


    ld hl, $38ee
    ld a, 18
your_loop:
    push af
    push hl
    call this_is_tedious
    pop hl
    ld bc, 64
    add hl, bc
    pop af
    dec a
    jr nz, your_loop

this_is_tedious:
       call vrampr
       ld hl,screen2tile
       ld bc,1*2
       call vramwr
       ret


... and possibly improve on that by finding a smarter way to preserve HL and A than constantly pushing and popping them. In fact, whether you need to push and pop AF at all depends on what you do in vrampr and vramwr, but it's a safe guess.
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Post Posted: Fri Jan 11, 2019 9:14 am
all you need is a 16-bit variable in RAM to hold the VRAM address you want to write to, then you do:

[a] initialize that var to $38EE
[b] load the value to HL
[c] out HL to VDP control so that it sets the address
[d] set DE to 64
[e] add DE to HL
[f] save HL to that var we created
[g] now load screen2tile to HL
[h] out HL to VDP data so that it sets the tile
[i] if you're not done (you may keep a counter in B register), go back to [b]
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Plotting tiles
Post Posted: Fri Jan 11, 2019 2:45 pm
My thinking is similar to TomHarte above.

SCREEN_2:
       ld b,18
       ld hl,$38EE
       ld de,64
TEDIOUS_LOOP:
       call this_is_tedious
       add hl,de
       djnz TEDIOUS_LOOP
       ret

this_is_tedious:
       push af
       push bc
       push hl
       call vrampr
       ld hl,screen2tile
       ld bc,1*2
       call vramwr
       pop hl
       pop bc
       pop af
       ret

screen2tile      .dw $001E
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Post Posted: Fri Jan 11, 2019 5:33 pm
Thank you so much! I'm using TomHarte's version and it works great.
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