From 866f04e3776d4f1e2ec342b0abde7ea6494675aa Mon Sep 17 00:00:00 2001
From: Aleksandar Andrejevic <aandrejevic@reactos.org>
Date: Sun, 3 May 2015 22:02:41 +0000
Subject: [PATCH 1/1] [NTVDM] Implement VGA read mode 1.

svn path=/trunk/; revision=67541
---
 .../mvdm/ntvdm/hardware/video/vga.c           | 50 ++++++++++++++++---
 1 file changed, 43 insertions(+), 7 deletions(-)

diff --git a/reactos/subsystems/mvdm/ntvdm/hardware/video/vga.c b/reactos/subsystems/mvdm/ntvdm/hardware/video/vga.c
index 5e322b5cc1e..c3e0c1943fc 100644
--- a/reactos/subsystems/mvdm/ntvdm/hardware/video/vga.c
+++ b/reactos/subsystems/mvdm/ntvdm/hardware/video/vga.c
@@ -644,7 +644,9 @@ static inline DWORD VgaTranslateReadAddress(DWORD Address)
         Plane = VgaGcRegisters[VGA_GC_READ_MAP_SEL_REG] & 0x03;
     }
 
-    return Offset + Plane * VGA_BANK_SIZE;
+    /* Return the offset on plane 0 for read mode 1 */
+    if (VgaGcRegisters[VGA_GC_MODE_REG] & VGA_GC_MODE_READ) return Offset;
+    else return Offset + Plane * VGA_BANK_SIZE;
 }
 
 static inline DWORD VgaTranslateWriteAddress(DWORD Address)
@@ -1900,7 +1902,7 @@ VOID VgaRefreshDisplay(VOID)
 
 VOID NTAPI VgaReadMemory(ULONG Address, PVOID Buffer, ULONG Size)
 {
-    DWORD i;
+    DWORD i, j;
     DWORD VideoAddress;
     PUCHAR BufPtr = (PUCHAR)Buffer;
 
@@ -1909,13 +1911,47 @@ VOID NTAPI VgaReadMemory(ULONG Address, PVOID Buffer, ULONG Size)
     /* Ignore if video RAM access is disabled */
     if ((VgaMiscRegister & VGA_MISC_RAM_ENABLED) == 0) return;
 
-    /* Loop through each byte */
-    for (i = 0; i < Size; i++)
+    if (!(VgaGcRegisters[VGA_GC_MODE_REG] & VGA_GC_MODE_READ))
     {
-        VideoAddress = VgaTranslateReadAddress(Address + i);
+        /* Loop through each byte */
+        for (i = 0; i < Size; i++)
+        {
+            VideoAddress = VgaTranslateReadAddress(Address + i);
+    
+            /* Copy the value to the buffer */
+            BufPtr[i] = VgaMemory[VideoAddress];
+        }
+    }
+    else
+    {
+        /* Loop through each byte */
+        for (i = 0; i < Size; i++)
+        {
+            BYTE Result = 0xFF;
 
-        /* Copy the value to the buffer */
-        BufPtr[i] = VgaMemory[VideoAddress];
+            /* This should always return a plane 0 address for read mode 1 */
+            VideoAddress = VgaTranslateReadAddress(Address + i);
+
+            for (j = 0; j < VGA_NUM_BANKS; j++)
+            {
+                /* Don't consider ignored banks */
+                if (!(VgaGcRegisters[VGA_GC_COLOR_IGNORE_REG] & (1 << j))) continue;
+
+                if (VgaGcRegisters[VGA_GC_COLOR_COMPARE_REG] & (1 << j))
+                {
+                    /* Comparing with 11111111 */
+                    Result &= VgaMemory[j * VGA_BANK_SIZE + LOWORD(VideoAddress)];
+                }
+                else
+                {
+                    /* Comparing with 00000000 */
+                    Result &= ~(VgaMemory[j * VGA_BANK_SIZE + LOWORD(VideoAddress)]);
+                }
+            }
+
+            /* Copy the value to the buffer */
+            BufPtr[i] = Result;
+        }
     }
 
     /* Load the latch registers */
-- 
2.17.1