From 90424967b7bf6792dad437fe9f3cec65d811f0fa Mon Sep 17 00:00:00 2001
From: Tiberiu Chibici <chibicitiberiu@gmail.com>
Date: Tue, 14 Sep 2021 19:03:47 +0300
Subject: [PATCH] video.cpp

---
 exp/video.cpp | 166 ++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 166 insertions(+)
 create mode 100644 exp/video.cpp

diff --git a/exp/video.cpp b/exp/video.cpp
new file mode 100644
index 0000000..d5655f2
--- /dev/null
+++ b/exp/video.cpp
@@ -0,0 +1,166 @@
+#include <stdio.h>
+#include <conio.h>
+#include <dos.h>
+#include <string.h>
+#include <stdlib.h>
+
+typedef unsigned char uint8;
+typedef unsigned uint16;
+typedef unsigned long uint32;
+
+struct vbeInfo {
+	char Signature[4];
+	uint16 Version;
+	uint32 OemString;
+	uint8 Capabilities[4];
+	uint32 VideoModes;
+	uint16 TotalMem;
+};
+
+struct modeInfo {
+	uint16 attributes;
+	uint8 winA,winB;
+	uint16 granularity;
+	uint16 winsize;
+	uint16 segmentA, segmentB;
+	uint32 realFctPtr;
+	uint16 pitch; // uint8s per scanline
+
+	uint16 Xres, Yres;
+	uint8 Wchar, Ychar, planes, bpp, banks;
+	uint8 memory_model, bank_size, image_pages;
+	uint8 reserved0;
+
+	uint8 red_mask, red_position;
+	uint8 green_mask, green_position;
+	uint8 blue_mask, blue_position;
+	uint8 rsv_mask, rsv_position;
+	uint8 directcolor_attributes;
+
+	uint32 physbase;  // your LFB address ;)
+	uint32 reserved1;
+	uint16 reserved2;
+};
+
+uint16 GetInfo (vbeInfo far* info)
+{
+	REGS regs;
+	SREGS segregs;
+	
+	regs.x.ax = 0x4f00;
+	regs.x.di = FP_OFF(info);
+	segregs.es = FP_SEG(info);
+	int86x(0x10, &regs, &regs, &segregs);
+	
+	return regs.x.ax;
+}
+
+uint16 GetModeInfo (modeInfo far* info, uint16 mode)
+{
+	REGS regs;
+	SREGS segregs;
+	
+	regs.x.ax = 0x4f01;
+	regs.x.cx = mode;
+	regs.x.di = FP_OFF(info);
+	segregs.es = FP_SEG(info);
+	int86x(0x10, &regs, &regs, &segregs);
+	
+	return regs.x.ax;
+}
+
+void SetMode (uint16 mode)
+{
+	REGS regs;
+	
+	regs.x.ax = 0x4F02;
+	regs.x.bx = mode;
+	int86(0x10, &regs, &regs);
+}
+
+uint16 bank_current = 0xffff;
+void SwitchBank (uint16 bank)
+{
+	if (bank == bank_current) return;
+	
+	REGS regs;
+	regs.x.ax = 0x4F05;
+	regs.x.bx = 0;
+	regs.x.dx = bank;
+	int86(0x10, &regs, &regs);
+	
+	bank_current = bank;
+}
+
+modeInfo* CurrentMode;
+
+void PutPixel (int x, int y, uint16 color)
+{
+	unsigned address = (y * CurrentMode->Xres) + x;
+	unsigned bank_size = CurrentMode->granularity * 1024;
+	unsigned bank_number = address / bank_size;
+	unsigned bank_offset = address % bank_size;
+	
+	SwitchBank (bank_number);
+	
+	uint16 far* ptr = (uint16 far*) (bank_offset + 0xA0000l);
+	*ptr = color;
+}
+
+void SetBestMode (uint16 X, uint16 Y, uint8 bpp)
+{
+	vbeInfo* info = (vbeInfo*) malloc (sizeof(vbeInfo) * 2);
+	modeInfo* modeinf = (modeInfo*) malloc (sizeof(modeInfo) * 4);
+	
+	strncpy(info->Signature, "VBE2", 4);
+	
+	if (GetInfo(info) != 0x4F) {
+		printf("Error\n"); return;
+	}
+		
+	uint16 far* modes = (uint16 far*) info->VideoModes;
+	uint16 best = 0x13;
+	uint16 bestpixdiff = (320 * 200) - (X * Y);
+	uint16 bestdppdiff = 8 >= bpp ? 8 - bpp : (bpp - 8) * 2;
+	
+	for (int i = 0; modes[i] != 0xFFFF; i++)
+	{
+		if (GetModeInfo(modeinf, modes[i]) != 0x4F) continue;	
+		if ((modeinf->attributes & 0x90) != 0x90) continue;
+		if (modeinf->memory_model != 4 && modeinf->memory_model != 6) continue;
+		
+		if (X == modeinf->Xres && Y == modeinf->Yres && bpp == modeinf->bpp) {
+			best = modes[i]; break;
+		}
+		
+		uint16 pixdiff = (modeinf->Xres * modeinf->Yres) - (X*Y);
+		uint16 dppdiff = (modeinf->bpp >= bpp) ? (modeinf->bpp - bpp) : (bpp - modeinf->bpp);
+		if ( bestpixdiff > pixdiff || (bestpixdiff == pixdiff && bestdppdiff > dppdiff) )
+		{
+			best = modes[i];
+			bestpixdiff = pixdiff;
+			bestdppdiff = dppdiff;
+		}
+	}
+	
+	CurrentMode = modeinf;
+	GetModeInfo(CurrentMode, best);
+	printf("Best mode found: %ux%u %ubpp\n", CurrentMode->Xres, CurrentMode->Yres, CurrentMode->bpp);
+
+	// Set mode
+	SetMode (best);
+	
+	free (info);
+}
+
+int main()
+{
+	SetBestMode(800, 600, 15);
+	
+	for (int i = 0; i < 700; i++)
+		for (int j = 0; j < 500; j++)
+			PutPixel (i, j, 0x7FFF - i - j);
+	
+	free (CurrentMode);
+	return 0;
+}
\ No newline at end of file