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[MC6847] Fixed a bug from where video data was sampled that could cause too many samples to be loaded in low resolution video modes

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On the CoCo, this fixes some low resolution video modes (e.g. - G3R/PMODE2), used by Project Nebula and some other games
This commit is contained in:
Nathan Woods 2016-08-21 10:42:26 -04:00
parent 4765620175
commit f51eefb645
1 changed files with 7 additions and 1 deletions
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8
src/devices/video/mc6847.cpp
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@ -642,6 +642,11 @@ UINT8 mc6847_base_device::input(UINT16 address)
template<int sample_count, int yres>
void mc6847_base_device::record_scanline_res(int scanline, INT32 start_pos, INT32 end_pos)
{
// determine the "sample_modulo" (e.g. - for 32 samples per row, query the video RAM every
// position, for 16 samples per row, query every other position)
const int sample_modulo = 32 / sample_count;
static_assert((32 / sample_modulo) == sample_count, "Expected 32 to be divisible by sample_count");
UINT8 current_sample_count = (start_pos > 0) ? m_data[scanline].m_sample_count : 0;
// main loop
@ -651,7 +656,8 @@ void mc6847_base_device::record_scanline_res(int scanline, INT32 start_pos, INT3
if (pos == 0)
m_video_address = scanline / (192 / yres) * sample_count;
if ((sample_count == 32) || ((pos % 1) == 0))
// are we sampling this position?
if ((pos % sample_modulo) == 0)
{
// input data
UINT8 data = input(m_video_address++);