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Makes hasty attempt to shift 'NTSC' in the most natural direction.

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This commit is contained in:
Thomas Harte 2020-11-21 23:39:58 -05:00
parent dd816c5a0a
commit fca48e4b66
1 changed files with 42 additions and 34 deletions
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76
Machines/Apple/AppleIIgs/Video.cpp
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@ -58,19 +58,20 @@ VideoBase::VideoBase() :
crt_.set_visible_area(Outputs::Display::Rect(0.097f, 0.1f, 0.85f, 0.85f));
// Establish the shift lookup table for NTSC -> RGB output.
for(int c = 0; c < 256; c++) {
for(size_t c = 0; c < sizeof(ntsc_shift_lookup_) / sizeof(*ntsc_shift_lookup_); c++) {
const auto top_nibble = c >> 4;
// Otherwise, check for descending disagreements.
ntsc_shift_lookup_[c] = 4;
int mask = 0x10;
while(mask) {
ntsc_shift_lookup_[c] = 0;
decltype(c) mask = 0x01;
while(ntsc_shift_lookup_[c] < 4) {
if((top_nibble & mask) != (c & mask)) break;
mask >>= 1;
--ntsc_shift_lookup_[c];
mask <<= 1;
++ntsc_shift_lookup_[c];
}
ntsc_shift_lookup_[c] &= 3;
// If no incompatibilities were found then the low four bits are identical
// to the top four; can just leave the lookup at a shift of 0 as 0 == 4.
}
}
@ -207,11 +208,14 @@ void VideoBase::output_row(int row, int start, int end) {
if(start == end) return;
}
assert(end > start);
// Fetch and output such pixels as it is time for.
if(start >= start_of_pixels && start < start_of_right_border) {
const int end_of_period = std::min(start_of_right_border, end);
if(start == start_of_pixels) {
// printf("Begin\n");
// 640 is the absolute most number of pixels that might be generated
next_pixel_ = pixels_ = reinterpret_cast<uint16_t *>(crt_.begin_data(640, 2));
@ -265,6 +269,7 @@ void VideoBase::output_row(int row, int start, int end) {
}
if(end_of_period == start_of_right_border) {
// printf("End\n");
crt_.output_data((start_of_right_border - start_of_pixels) * CyclesPerTick, next_pixel_ ? size_t(next_pixel_ - pixels_) : 1);
next_pixel_ = pixels_ = nullptr;
}
@ -273,6 +278,8 @@ void VideoBase::output_row(int row, int start, int end) {
if(start == end) return;
}
assert(end > start);
// Output right border as far as currently known.
if(start >= start_of_right_border && start < start_of_sync) {
const int end_of_period = std::min(start_of_sync, end);
@ -432,10 +439,12 @@ uint16_t *VideoBase::output_low_resolution(uint16_t *target, int start, int end,
const int row_shift = row&4;
const uint16_t row_address = get_row_address(row);
for(int c = start; c < end; c++) {
ntsc_shift_ <<= 14;
ntsc_shift_ >>= 14;
const uint8_t source = ram_[row_address + c] >> row_shift;
// TODO: below is all wrong, now that I've corrected ntsc_shift_ direction.
// Convulve input as a function of odd/even row.
if((start + c)&1) {
ntsc_shift_ |= ((source & 4) >> 2) * 0x2222;
@ -459,15 +468,10 @@ uint16_t *VideoBase::output_low_resolution(uint16_t *target, int start, int end,
uint16_t *VideoBase::output_high_resolution(uint16_t *target, int start, int end, int row) {
const uint16_t row_address = get_row_address(row);
for(int c = start; c < end; c++) {
ntsc_shift_ <<= 14;
ntsc_shift_ >>= 14;
uint8_t source = ram_[row_address + c];
// HACK: bit reverse, for now.
// Because I'd forgotten which order the Apple II serialises bits in, and have predicated too much upon it.
// TODO: undo hack.
source = ((source >> 6) & 0x01) | ((source >> 4) & 0x02) | ((source >> 2) & 0x04) | ((source >> 0) & 0x08) | ((source << 2) & 0x10) | ((source << 4) & 0x20) | ((source << 6) & 0x40);
// TODO: can do this in two multiplies, I think.
const uint16_t doubled_source =
((source&0x01) * (0x0003 >> 0)) +
@ -479,12 +483,16 @@ uint16_t *VideoBase::output_high_resolution(uint16_t *target, int start, int end
((source&0x40) * (0x3000 >> 6));
// Just append new bits, doubled up (and possibly delayed).
// TODO: I can kill the conditional here.
if(source & high_resolution_mask_ & 0x80) {
ntsc_shift_ |= ((ntsc_shift_ >> 1) & 0x2000) | (doubled_source >> 1);
} else {
ntsc_shift_ |= doubled_source;
}
// TODO: I can kill the conditional here. Probably?
// if(source & high_resolution_mask_ & 0x80) {
// ntsc_shift_ |= doubled_source << 5;
// } else {
// ntsc_shift_ = (ntsc_shift_ & 0xf) | (doubled_source << 4) | ((doubled_source << 5) & 0x80000);
// }
// TODO: reintroduce delay bit. Delay bit should: (i) hold existing bit; and (ii) store top bit for potential
// delay into the next word.
ntsc_shift_ |= doubled_source << 4;
// TODO: initial state?
target = output_shift(target, (2 + (c * 14)) & 3);
@ -515,23 +523,23 @@ uint16_t *VideoBase::output_shift(uint16_t *target, int phase) const {
#define OutputPixel(offset) {\
const auto phase_offset = ntsc_shift_lookup_[(ntsc_shift_ >> offset) & 0xff]; \
const auto raw_bits = (ntsc_shift_ >> (offset + phase_offset)) & 0x0f; \
target[13 - offset] = appleii_palette[rolls[(phase + 13 - offset - phase_offset)&3][raw_bits]]; \
target[offset] = appleii_palette[rolls[(phase + offset + phase_offset)&3][raw_bits]]; \
}
OutputPixel(13);
OutputPixel(12);
OutputPixel(11);
OutputPixel(10);
OutputPixel(9);
OutputPixel(8);
OutputPixel(7);
OutputPixel(6);
OutputPixel(5);
OutputPixel(4);
OutputPixel(3);
OutputPixel(2);
OutputPixel(1);
OutputPixel(0);
OutputPixel(1);
OutputPixel(2);
OutputPixel(3);
OutputPixel(4);
OutputPixel(5);
OutputPixel(6);
OutputPixel(7);
OutputPixel(8);
OutputPixel(9);
OutputPixel(10);
OutputPixel(11);
OutputPixel(12);
OutputPixel(13);
#undef OutputPixel