base:20-pixel_sprite_interleave
Differences
This shows you the differences between two versions of the page.
| Both sides previous revisionPrevious revisionNext revision | Previous revisionNext revisionBoth sides next revision | ||
| base:20-pixel_sprite_interleave [2020-10-15 14:40] – raistlin | base:20-pixel_sprite_interleave [2020-10-15 14:44] – raistlin | ||
|---|---|---|---|
| Line 44: | Line 44: | ||
| === Updating Sprite Values === | === Updating Sprite Values === | ||
| - | Given all of that, you still need to update all 8 sprite values in as few cycles as possible. And you need to start the update from as close as possible to the right position. | + | Often, especially when dealing with a vertically scrolling screen, or the addition |
| For this, it's worth knowing about a neat little trick. | For this, it's worth knowing about a neat little trick. | ||
| - | The most basic way to update the sprite values would of course be: | + | The most basic and obvious |
| < | < | ||
| Line 55: | Line 55: | ||
| inx | inx | ||
| stx ScreenAddr + $3f8 + 1 | stx ScreenAddr + $3f8 + 1 | ||
| - | | + | |
| + | stx ScreenAddr + $3f8 + 2 | ||
| + | inx | ||
| + | stx ScreenAddr + $3f8 + 3 | ||
| + | inx | ||
| + | stx ScreenAddr + $3f8 + 4 | ||
| + | inx | ||
| + | stx ScreenAddr + $3f8 + 5 | ||
| + | inx | ||
| + | stx ScreenAddr + $3f8 + 6 | ||
| inx | inx | ||
| stx ScreenAddr + $3f8 + 7 | stx ScreenAddr + $3f8 + 7 | ||
| Line 64: | Line 73: | ||
| < | < | ||
| LDA #64 + 4 | LDA #64 + 4 | ||
| - | LDX #fb | + | LDX #$fb |
| - | SAX ScreenAddr + $3f8 + 0; <-- SAX will write A&X .. ie. 64 in this case (we mask out bit 2) | + | SAX ScreenAddr + $3f8 + 0; <-- SAX will write "A & X" |
| STA ScreenAddr + $3f8 + 4 | STA ScreenAddr + $3f8 + 4 | ||
| INX | INX | ||
| SAX ScreenAddr + $3f8 + 1 | SAX ScreenAddr + $3f8 + 1 | ||
| - | | + | |
| + | INX | ||
| + | SAX ScreenAddr + $3f8 + 2 | ||
| + | STA ScreenAddr + $3f8 + 6 | ||
| INX | INX | ||
| SAX ScreenAddr + $3f8 + 3 | SAX ScreenAddr + $3f8 + 3 | ||