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video/epic12.cpp: Apply clipping to Blitter calculations as well. (#11295)

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* Fixes excessive blitter delays when games do large over-draws.
* The fog in stage 1 of Mushihimesama Futari 1.5 is a good example of this.
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buffi 2023-06-01 08:04:08 +02:00 committed by GitHub
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commit ee569aa965
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src/devices/video/epic12.cpp
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@ -436,6 +436,18 @@ inline void epic12_device::gfx_draw_shadow_copy(address_space &space, offs_t *ad
return;
}
// Clip the blitter operations, to have the calculations only respect the area being written.
// It's not 100% clear this is how this is performed, but it is clear that there should be some amount of clipping
// applied here to match the hardware. This way seems most likely, and maps well to the delays seen on hardware.
// One example of this being utilized heavily is the transparent fog in Mushihimesama Futari Stage 1. This is drawn as
// 256x256 sprites, with large parts clipped away.
dst_x_start = std::max(dst_x_start, (u16)m_clip.min_x);
dst_y_start = std::max(dst_y_start, (u16)m_clip.min_y);
dst_x_end = std::min(dst_x_end, (u16)m_clip.max_x);
dst_y_end = std::min(dst_y_end, (u16)m_clip.max_y);
src_dimx = dst_x_end - dst_x_start + 1;
src_dimy = dst_y_end - dst_y_start + 1;
m_blit_idle_op_bytes = 0; // Blitter no longer idle.
// VRAM data is laid out in 32x32 pixel rows. Calculate amount of rows accessed.