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Added the four-cycle playfield output latency and ensured you can't get smaller-than-usual pixels by rapid register value changing.

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This commit is contained in:
Thomas Harte 2017-02-08 07:30:32 -05:00
parent a477499724
commit dcb7584060
1 changed files with 24 additions and 9 deletions
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33
Machines/Atari2600/TIA.cpp
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@ -391,6 +391,11 @@ void TIA::output_for_cycles(int number_of_cycles)
memset(collision_buffer_, 0, sizeof(collision_buffer_));
}
// accumulate an OR'dversion of the output into the collision buffer
draw_playfield(output_cursor, horizontal_counter_);
// convert to television signals
#define Period(function, target) \
if(output_cursor < target) \
{ \
@ -446,9 +451,6 @@ void TIA::output_for_cycles(int number_of_cycles)
pixel_target_ = crt_->allocate_write_area(160);
}
// accumulate an OR'dversion of the output into the collision buffer
draw_playfield(output_cursor, horizontal_counter_);
// convert that into pixels
if(pixel_target_) output_pixels(output_cursor, horizontal_counter_);
@ -527,15 +529,28 @@ void TIA::output_line()
}
}
#pragma mark - Background and playfield
#pragma mark - Playfield output
void TIA::draw_playfield(int start, int end)
{
int position = start;
while(position < end)
// don't do anything if this window ends too early
if(end < first_pixel_cycle - 4) return;
// look at what needs to be output four cycles into the future, to model playfield output latency
start += 4;
end += 4;
// clip to drawable bounds
start = std::max(start, first_pixel_cycle);
end = std::min(end, 228);
// proceed along four-pixel boundaries, plotting four pixels at a time
int aligned_position = (start + 3)&~3;
while(aligned_position < end)
{
int offset = (position - first_pixel_cycle) >> 2;
collision_buffer_[position - first_pixel_cycle] |= (background_[(offset/20)&background_half_mask_] >> (offset%20))&1;
position++;
int offset = (aligned_position - first_pixel_cycle) >> 2;
uint32_t value = ((background_[(offset/20)&background_half_mask_] >> (offset%20))&1) * 0x01010101;
*(uint32_t *)&collision_buffer_[aligned_position - first_pixel_cycle] |= value;
aligned_position += 4;
}
}