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Emulate window pixel insertion glitch, fixes Star Trek - 25th Anniversary, closes #278

This commit is contained in:
Lior Halphon 2022-07-22 00:27:21 +03:00
parent 3a86b868fe
commit 1fedb81ab7
1 changed files with 29 additions and 4 deletions
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31
Core/display.c
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@ -1294,9 +1294,18 @@ static inline uint16_t mode3_batching_length(GB_gameboy_t *gb)
if (gb->hdma_on) return 0;
if (gb->stopped) return 0;
if (GB_is_dma_active(gb)) return 0;
if (gb->wy_triggered && (gb->io_registers[GB_IO_LCDC] & 0x20) && (gb->io_registers[GB_IO_WX] < 8 || gb->io_registers[GB_IO_WX] == 166)) {
if (gb->wy_triggered) {
if (gb->io_registers[GB_IO_LCDC] & 0x20) {
if ((gb->io_registers[GB_IO_WX] < 8 || gb->io_registers[GB_IO_WX] == 166)) {
return 0;
}
}
else {
if (gb->io_registers[GB_IO_WX] < 167 && !GB_is_cgb(gb)) {
return 0;
}
}
}
// No objects or window, timing is trivial
if (gb->n_visible_objs == 0 && !(gb->wy_triggered && (gb->io_registers[GB_IO_LCDC] & 0x20))) return 167 + (gb->io_registers[GB_IO_SCX] & 7);
@ -1683,16 +1692,32 @@ void GB_display_run(GB_gameboy_t *gb, unsigned cycles, bool force)
}
}
/* TODO: What happens when WX=0? */
/* TODO: What happens when WX=0? When the fifo is full? */
if (!GB_is_cgb(gb) && gb->wx_triggered && !gb->window_is_being_fetched &&
gb->fetcher_state == 0 && gb->io_registers[GB_IO_WX] == (uint8_t) (gb->position_in_line + 7) ) {
gb->fetcher_state == 0 && gb->io_registers[GB_IO_WX] == (uint8_t) (gb->position_in_line + 7) && gb->bg_fifo.size == 8) {
// Insert a pixel right at the FIFO's end
gb->bg_fifo.read_end--;
gb->bg_fifo.read_end &= GB_FIFO_LENGTH - 1;
gb->bg_fifo.fifo[gb->bg_fifo.read_end] = (GB_fifo_item_t){0,};
gb->bg_fifo.size++;
gb->window_is_being_fetched = false;
}
/* TODO: WX=0 behaves wrong, but WX=0 behaves wrong regardless in DMG mode */
if (!GB_is_cgb(gb) && gb->wy_triggered && !(gb->io_registers[GB_IO_LCDC] & 0x20) && gb->bg_fifo.size == 1) {
/* See https://github.com/LIJI32/SameBoy/issues/278 for documentation */
uint8_t logical_position = gb->position_in_line + 8;
if (logical_position >= (uint8_t)(-8)) {
logical_position += 8;
}
if (gb->io_registers[GB_IO_WX] == logical_position) {
gb->bg_fifo.read_end--;
gb->bg_fifo.read_end &= GB_FIFO_LENGTH - 1;
gb->bg_fifo.fifo[gb->bg_fifo.read_end] = (GB_fifo_item_t){0,};
gb->bg_fifo.size = 2;
}
}
/* Handle objects */
/* When the object enabled bit is off, this proccess is skipped entirely on the DMG, but not on the CGB.
On the CGB, this bit is checked only when the pixel is actually popped from the FIFO. */