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Maintain an actual pixel buffer.

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This commit is contained in:
Thomas Harte 2023-11-22 13:40:50 -05:00
parent 12179e486f
commit f249e4ada6
1 changed files with 46 additions and 13 deletions
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59
Machines/PCCompatible/PCCompatible.cpp
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@ -90,30 +90,59 @@ class MDA {
}
void perform_bus_cycle_phase1(const Motorola::CRTC::BusState &state) {
// Determine new output state.
const OutputState new_state =
(state.hsync | state.vsync) ? OutputState::Sync :
(state.display_enable ? OutputState::Pixels : OutputState::Border);
if(new_state != output_state) {
switch(output_state) {
case OutputState::Sync:
crt.output_sync(count);
break;
case OutputState::Border:
case OutputState::Pixels: {
uint8_t *const target = crt.begin_data(1);
if(target) {
target[0] = (output_state == OutputState::Border) ? 0x00 : 0xff;
}
crt.output_level(count);
} break;
// Upon either a state change or just having accumulated too much local time...
if(new_state != output_state || count > 882) {
// (1) flush preexisting state.
if(count) {
switch(output_state) {
case OutputState::Sync: crt.output_sync(count); break;
case OutputState::Border: crt.output_blank(count); break;
case OutputState::Pixels:
crt.output_data(count);
pixels = pixel_pointer = nullptr;
break;
}
}
// (2) adopt new state.
output_state = new_state;
count = 0;
}
// Collect pixels if applicable.
if(output_state == OutputState::Pixels) {
if(!pixels) {
pixel_pointer = pixels = crt.begin_data(DefaultAllocationSize);
// Flush any period where pixels weren't recorded due to back pressure.
if(pixels && count) {
crt.output_blank(count);
count = 0;
}
}
if(pixels) {
pixel_pointer[0] = pixel_pointer[2] = pixel_pointer[4] = pixel_pointer[6] = 0;
pixel_pointer[1] = pixel_pointer[3] = pixel_pointer[5] = pixel_pointer[7] = pixel_pointer[8] = 1;
pixel_pointer += 9;
}
}
// Advance.
count += 9;
// Output pixel row prematurely if storage is exhausted.
if(output_state == OutputState::Pixels && pixel_pointer == pixels + DefaultAllocationSize) {
crt.output_data(count);
count = 0;
pixels = pixel_pointer = nullptr;
}
}
void perform_bus_cycle_phase2(const Motorola::CRTC::BusState &) {}
@ -123,6 +152,10 @@ class MDA {
Sync, Pixels, Border
} output_state = OutputState::Sync;
int count = 0;
uint8_t *pixels = nullptr;
uint8_t *pixel_pointer = nullptr;
static constexpr size_t DefaultAllocationSize = 720;
} outputter_;
Motorola::CRTC::CRTC6845<CRTCOutputter> crtc_;