naps2/NAPS2.Lib.WinForms/Scan/Twain/Legacy/DibUtils.cs

using System.Drawing;
using System.Runtime.InteropServices;
using NAPS2.Images.Gdi;

namespace NAPS2.Scan.Twain.Legacy;

internal class DibUtils
{
    [DllImport("gdi32.dll", ExactSpelling = true)]
    internal static extern int SetDIBitsToDevice(IntPtr hdc, int xdst, int ydst,
        int width, int height, int xsrc, int ysrc, int start, int lines,
        IntPtr bitsptr, IntPtr bmiptr, int color);

    [DllImport("kernel32.dll", ExactSpelling = true)]
    internal static extern IntPtr GlobalLock(IntPtr handle);

    [DllImport("kernel32.dll", ExactSpelling = true)]
    internal static extern IntPtr GlobalFree(IntPtr handle);

    //THIS METHOD SAVES THE CONTENTS OF THE DIB POINTER INTO A BITMAP OBJECT
    public static Bitmap BitmapFromDib(IntPtr pDib, out int bitdepth)
    {
        IntPtr dibhand = pDib;
        IntPtr bmpptr = GlobalLock(dibhand);
        IntPtr pixptr = GetPixelInfo(bmpptr);
        BitmapInfoHeader binfo = GetDibInfo(bmpptr);
        float resx = binfo.biXPelsPerMeter * 0.0254f;
        float resy = binfo.biYPelsPerMeter * 0.0254f;
        var scannedImage = new Bitmap(binfo.biWidth, binfo.biHeight);
        Graphics scannedImageGraphics = Graphics.FromImage(scannedImage);
        IntPtr hdc = scannedImageGraphics.GetHdc();
        SetDIBitsToDevice(hdc, 0, 0, binfo.biWidth, binfo.biHeight, 0, 0, 0, binfo.biHeight, pixptr, bmpptr, 0);
        scannedImageGraphics.ReleaseHdc(hdc);
        GlobalFree(dibhand);
        scannedImageGraphics.Dispose();
        bitdepth = binfo.biBitCount;
        scannedImage.SafeSetResolution(resx, resy);
        return scannedImage;
    }

    //THIS METHOD GETS THE POINTER TO THE BITMAP HEADER INFO
    private static IntPtr GetPixelInfo(IntPtr bmpPtr)
    {
        var bmi = (BitmapInfoHeader)Marshal.PtrToStructure(bmpPtr, typeof(BitmapInfoHeader))!;

        if (bmi.biSizeImage == 0)
            bmi.biSizeImage = (uint)(((((bmi.biWidth * bmi.biBitCount) + 31) & ~31) >> 3) * bmi.biHeight);

        var p = (int)bmi.biClrUsed;
        if ((p == 0) && (bmi.biBitCount <= 8))
            p = 1 << bmi.biBitCount;
        p = (p * 4) + (int)bmi.biSize + (int)bmpPtr;
        return (IntPtr)p;
    }

    //THIS METHOD GETS THE POINTER TO THE BITMAP HEADER INFO
    private static BitmapInfoHeader GetDibInfo(IntPtr bmpPtr)
    {
        var bmi = (BitmapInfoHeader)Marshal.PtrToStructure(bmpPtr, typeof(BitmapInfoHeader))!;
        return bmi;
    }
}

[StructLayout(LayoutKind.Sequential, Pack = 1)]
internal struct BitmapInfoHeader
{
    public uint biSize;
    public int biWidth;
    public int biHeight;
    public ushort biPlanes;
    public ushort biBitCount;
    public uint biCompression;
    public uint biSizeImage;
    public int biXPelsPerMeter;
    public int biYPelsPerMeter;
    public uint biClrUsed;
    public uint biClrImportant;

    public void Init()
    {
        biSize = (uint)Marshal.SizeOf(this);
    }
}