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Do well enough at other colour depths.

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This commit is contained in:
Thomas Harte 2024-03-25 22:09:55 -04:00
parent fc880ac130
commit b112987556
1 changed files with 86 additions and 9 deletions
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95
Machines/Acorn/Archimedes/Video.hpp
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@ -88,6 +88,9 @@ struct Video {
case 0b10: set_clock_divider(3); break; // 16Mhz.
case 0b11: set_clock_divider(2); break; // 24Mhz.
}
// Set colour depth.
colour_depth_ = Depth((value >> 2) & 0b11);
break;
//
@ -116,6 +119,7 @@ struct Video {
if(horizontal_state_.position == horizontal_timing_.period) {
horizontal_state_.position = 0;
vertical_state_.increment_position(vertical_timing_);
pixel_count_ = 0;
if(vertical_state_.position == vertical_timing_.period) {
vertical_state_.position = 0;
@ -150,6 +154,13 @@ struct Video {
pixels_ = reinterpret_cast<uint16_t *>(crt_.begin_data(PixelBufferSize));
}
const auto next_byte = [&]() -> uint8_t {
const auto next = ram_[address_];
++address_;
if(address_ == buffer_end_) address_ = buffer_start_;
return next;
};
if(pixels_) {
// Each tick in here is two ticks of the pixel clock, so:
//
@ -157,20 +168,78 @@ struct Video {
// 4bpp mode: output one byte;
// 2bpp mode: output one byte every second tick;
// 1bpp mode: output one byte every fourth tick.
switch(colour_depth_) {
case Depth::EightBPP: {
// TODO: real 8bpp mapping here.
uint8_t next = next_byte();
pixels_[0] = colours_[next & 0xf];
// TODO: don't assume 4bpp.
const uint8_t next = ram_[address_];
++address_;
if(address_ == buffer_end_) address_ = buffer_start_;
next = next_byte();
pixels_[1] = colours_[next & 0xf];
pixels_[0] = colours_[next & 0xf];
pixels_[1] = colours_[next >> 4];
pixels_ += 2;
pixels_ += 2;
} break;
case Depth::FourBPP: {
const uint8_t next = next_byte();
pixels_[0] = colours_[next & 0xf];
pixels_[1] = colours_[next >> 4];
pixels_ += 2;
} break;
case Depth::TwoBPP: {
if(!(pixel_count_&1)) {
const uint8_t next = next_byte();
pixels_[0] = colours_[next & 3];
pixels_[1] = colours_[(next >> 2) & 3];
pixels_[2] = colours_[(next >> 4) & 3];
pixels_[3] = colours_[next >> 6];
pixels_ += 4;
}
} break;
case Depth::OneBPP: {
if(!(pixel_count_&3)) {
const uint8_t next = next_byte();
pixels_[0] = colours_[next & 1];
pixels_[1] = colours_[(next >> 1) & 1];
pixels_[2] = colours_[(next >> 2) & 1];
pixels_[3] = colours_[(next >> 3) & 1];
pixels_[4] = colours_[(next >> 4) & 1];
pixels_[5] = colours_[(next >> 5) & 1];
pixels_[6] = colours_[(next >> 6) & 1];
pixels_[7] = colours_[next >> 7];
pixels_ += 8;
}
} break;
}
} else {
// TODO: don't assume 4bpp here either.
++address_;
if(address_ == buffer_end_) address_ = buffer_start_;
switch(colour_depth_) {
case Depth::EightBPP:
next_byte();
next_byte();
break;
case Depth::FourBPP:
next_byte();
break;
case Depth::TwoBPP:
if(!(pixel_count_&1)) {
next_byte();
}
break;
case Depth::OneBPP:
if(!(pixel_count_&3)) {
next_byte();
}
break;
}
}
++pixel_count_;
}
// Determine current output phase.
@ -290,6 +359,7 @@ private:
State horizontal_state_, vertical_state_;
Phase phase_ = Phase::Sync;
uint32_t time_in_phase_ = 0;
uint32_t pixel_count_ = 0;
uint16_t *pixels_ = nullptr;
static constexpr size_t PixelBufferSize = 320;
@ -317,6 +387,13 @@ private:
// places horizontal events — display start, end, sync period, etc.
uint32_t clock_divider_ = 0;
enum class Depth {
OneBPP = 0b00,
TwoBPP = 0b01,
FourBPP = 0b10,
EightBPP = 0b11,
} colour_depth_;
void set_clock_divider(uint32_t divider) {
if(divider == clock_divider_) {
return;