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video/pc_vga.cpp: fix Read Mode 1 target color for comparison

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* fixes at least transparent pen sprite-like in ibm5150:lombrall & ibm5150:intsocch and missing text in ibm5150:pcglobe sets
This commit is contained in:
angelosa 2022-12-03 22:37:44 +01:00
parent 5903b7d269
commit f5fb38acf1
1 changed files with 9 additions and 7 deletions
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16
src/devices/video/pc_vga.cpp
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@ -2072,20 +2072,22 @@ uint8_t vga_device::mem_r(offs_t offset)
if (vga.gc.read_mode)
{
uint8_t byte,layer;
uint8_t fill_latch;
data=0;
// In Read Mode 1 latch is checked against this
// cfr. lombrall & intsocch where they RMW sprite-like objects
// and anything outside this formula goes transparent.
const u8 target_color = (vga.gc.color_compare & vga.gc.color_dont_care);
data = 0;
for(byte=0;byte<8;byte++)
for(u8 byte = 0; byte < 8; byte++)
{
fill_latch = 0;
for(layer=0;layer<4;layer++)
u8 fill_latch = 0;
for(u8 layer = 0; layer < 4; layer++)
{
if(vga.gc.latch[layer] & 1 << byte)
fill_latch |= 1 << layer;
}
fill_latch &= vga.gc.color_dont_care;
if(fill_latch == vga.gc.color_compare)
if(fill_latch == target_color)
data |= 1 << byte;
}
}