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Elucidate a magic constant, add an extra constexpr.

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This commit is contained in:
Thomas Harte 2023-01-07 09:10:41 -05:00
parent 4875148617
commit de45536b5c
2 changed files with 32 additions and 31 deletions
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7
Components/9918/Implementation/9918.cpp
View File

@ -756,13 +756,12 @@ bool TMS9918<personality>::get_interrupt_line() const {
}
// TODO: [potentially] remove Master System timing assumptions in latch and get_latched below.
template <Personality personality>
uint8_t TMS9918<personality>::get_latched_horizontal_counter() const {
template <Personality personality>uint8_t TMS9918<personality>::get_latched_horizontal_counter() const {
// Translate from internal numbering, which puts pixel output
// in the final 256 pixels of 342, to the public numbering,
// which makes the 256 pixels the first 256 spots, but starts
// which counts the 256 pixels as items 0–255, starts
// counting at -48, and returns only the top 8 bits of the number.
int public_counter = this->latched_column_ - 86;
int public_counter = this->latched_column_ - (342 - 256);
if(public_counter < -46) public_counter += 342;
return uint8_t(public_counter >> 1);
}

56
Components/9918/Implementation/9918Base.hpp
View File

@ -349,37 +349,39 @@ template <Personality personality> struct Base {
default: return;
case MemoryAccess::Write:
if(master_system_.cram_is_selected) {
// Adjust the palette. In a Master System blue has a slightly different
// scale; cf. https://www.retrorgb.com/sega-master-system-non-linear-blue-channel-findings.html
constexpr uint8_t rg_scale[] = {0, 85, 170, 255};
constexpr uint8_t b_scale[] = {0, 104, 170, 255};
master_system_.colour_ram[ram_pointer_ & 0x1f] = palette_pack(
rg_scale[(read_ahead_buffer_ >> 0) & 3],
rg_scale[(read_ahead_buffer_ >> 2) & 3],
b_scale[(read_ahead_buffer_ >> 4) & 3]
);
if constexpr (is_sega_vdp(personality)) {
if(master_system_.cram_is_selected) {
// Adjust the palette. In a Master System blue has a slightly different
// scale; cf. https://www.retrorgb.com/sega-master-system-non-linear-blue-channel-findings.html
constexpr uint8_t rg_scale[] = {0, 85, 170, 255};
constexpr uint8_t b_scale[] = {0, 104, 170, 255};
master_system_.colour_ram[ram_pointer_ & 0x1f] = palette_pack(
rg_scale[(read_ahead_buffer_ >> 0) & 3],
rg_scale[(read_ahead_buffer_ >> 2) & 3],
b_scale[(read_ahead_buffer_ >> 4) & 3]
);
// Schedule a CRAM dot; this is scheduled for wherever it should appear
// on screen. So it's wherever the output stream would be now. Which
// is output_lag cycles ago from the point of view of the input stream.
CRAMDot &dot = upcoming_cram_dots_.emplace_back();
dot.location.column = write_pointer_.column - output_lag;
dot.location.row = write_pointer_.row;
// Schedule a CRAM dot; this is scheduled for wherever it should appear
// on screen. So it's wherever the output stream would be now. Which
// is output_lag cycles ago from the point of view of the input stream.
CRAMDot &dot = upcoming_cram_dots_.emplace_back();
dot.location.column = write_pointer_.column - output_lag;
dot.location.row = write_pointer_.row;
// Handle before this row conditionally; then handle after (or, more realistically,
// exactly at the end of) naturally.
if(dot.location.column < 0) {
--dot.location.row;
dot.location.column += 342;
// Handle before this row conditionally; then handle after (or, more realistically,
// exactly at the end of) naturally.
if(dot.location.column < 0) {
--dot.location.row;
dot.location.column += 342;
}
dot.location.row += dot.location.column / 342;
dot.location.column %= 342;
dot.value = master_system_.colour_ram[ram_pointer_ & 0x1f];
break;
}
dot.location.row += dot.location.column / 342;
dot.location.column %= 342;
dot.value = master_system_.colour_ram[ram_pointer_ & 0x1f];
} else {
ram_[ram_pointer_ & 16383] = read_ahead_buffer_;
}
ram_[ram_pointer_ & 16383] = read_ahead_buffer_;
break;
case MemoryAccess::Read:
read_ahead_buffer_ = ram_[ram_pointer_ & 16383];