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GPU: Use accurate VRAM display width rounding 

Modified version of Nocash algorithm, confirmed with hardware test.
Relies on proper horizontal display range rounding for correct results.
This commit is contained in:
Albert Liu 2020-09-27 07:35:55 -07:00
parent bbaebfd4c9
commit 1a0b1a3149
1 changed files with 10 additions and 5 deletions
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15
src/core/gpu.cpp
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@ -598,11 +598,16 @@ void GPU::UpdateCRTCDisplayParameters()
cs.display_width = (cs.horizontal_active_end - cs.horizontal_active_start) / cs.dot_clock_divider;
cs.display_height = (cs.vertical_active_end - cs.vertical_active_start) << height_shift;
// Determine number of pixels outputted from VRAM (align to 4-pixel boundary).
// TODO: Verify behavior if start > end and also if values are outside of the active video portion of scanline.
const u16 horizontal_display_ticks = horizontal_display_end - horizontal_display_start;
cs.display_vram_width =
(static_cast<u16>(std::round(horizontal_display_ticks / static_cast<float>(cs.dot_clock_divider))) + 2u) & ~3u;
// Determine number of pixels outputted from VRAM (in general, round to 4-pixel multiple).
// TODO: Verify behavior if values are outside of the active video portion of scanline.
const u16 horizontal_display_ticks =
(horizontal_display_end < horizontal_display_start) ? 0 : (horizontal_display_end - horizontal_display_start);
const u16 horizontal_display_pixels = horizontal_display_ticks / cs.dot_clock_divider;
if (horizontal_display_pixels == 1u)
cs.display_vram_width = 4u;
else
cs.display_vram_width = (horizontal_display_pixels + 2u) & ~3u;
// Determine if we need to adjust the VRAM rectangle (because the display is starting outside the visible area) or add
// padding.