lightweight variant (#1)

Reviewed-on: #1
Co-authored-by: Aleksandr Neychev <alexnejchev73@gmail.com>

CursorLang.Agent/Interop/GdiNative.cs

@@ -0,0 +1,161 @@
+using System.Drawing;
+using System.Runtime.InteropServices;
+using CursorLang.Core.Interop;
+
+namespace CursorLang.Agent.Interop;
+
+/// <summary>
+/// Plain GDI: a font, text, and an off-screen bitmap to draw them into.
+/// </summary>
+/// <remarks>
+/// GDI rather than GDI+ on purpose. <c>System.Drawing.Common</c> would make the drawing
+/// code shorter, but it is a separate assembly with a native GDI+ library behind it, and
+/// how little this process weighs is the entire reason it exists apart from the window.
+/// Everything the popup needs — one rounded rectangle and one line of text — GDI can do
+/// on its own, and it draws the text with ClearType, exactly as Windows does everywhere else.
+/// </remarks>
+internal static class GdiNative
+{
+    internal const int TRANSPARENT = 1;
+
+    internal const uint DT_SINGLELINE = 0x00000020;
+    internal const uint DT_CENTER = 0x00000001;
+    internal const uint DT_VCENTER = 0x00000004;
+    internal const uint DT_CALCRECT = 0x00000400;
+    internal const uint DT_NOPREFIX = 0x00000800;
+    internal const uint DT_NOCLIP = 0x00000100;
+
+    private const int DEFAULT_CHARSET = 1;
+    private const int OUT_TT_PRECIS = 4;
+    private const int CLIP_DEFAULT_PRECIS = 0;
+    private const int CLEARTYPE_QUALITY = 5;
+    private const int DEFAULT_PITCH = 0;
+
+    /// <summary>
+    /// The face the popup is written in.
+    /// </summary>
+    /// <remarks>
+    /// WPF is asked for "Segoe UI" at FontWeight SemiBold and resolves that to the
+    /// seguisb.ttf face. To GDI that face is a family of its own — "Segoe UI Semibold" —
+    /// and asking for the "Segoe UI" family at weight 600 lands on Bold instead, which
+    /// is visibly heavier. So the family is named outright and the weight is left to the
+    /// mapper: the family has one member and no synthetic emboldening happens.
+    /// </remarks>
+    private const string SemiBoldFace = "Segoe UI Semibold";
+
+    private const int FW_DONTCARE = 0;
+
+    /// <summary>
+    /// A font of the given size in physical pixels.
+    /// </summary>
+    /// <remarks>
+    /// The size in the settings is in WPF units, that is 1/96 inch, while GDI counts
+    /// pixels — hence the multiplication by the monitor scale. The height is negative:
+    /// that asks for the em size rather than the cell height, which is what a font size
+    /// means everywhere else.
+    /// </remarks>
+    internal static IntPtr CreateFont(double wpfFontSize, double scale)
+    {
+        var height = (int)Math.Round(wpfFontSize * scale);
+
+        return CreateFontW(
+            -height, 0, 0, 0, FW_DONTCARE,
+            false, false, false,
+            DEFAULT_CHARSET, OUT_TT_PRECIS, CLIP_DEFAULT_PRECIS, CLEARTYPE_QUALITY, DEFAULT_PITCH,
+            SemiBoldFace);
+    }
+
+    /// <summary>The size of a single line of text with the font selected into the context.</summary>
+    internal static Size MeasureText(IntPtr deviceContext, string text)
+    {
+        var bounds = default(PopupWindowNative.Rect);
+        DrawText(deviceContext, text, text.Length, ref bounds,
+            DT_CALCRECT | DT_SINGLELINE | DT_NOPREFIX);
+
+        return new Size(bounds.Right - bounds.Left, bounds.Bottom - bounds.Top);
+    }
+
+    /// <summary>A colour as GDI wants it: 0x00BBGGRR, the alpha carried elsewhere.</summary>
+    internal static uint ToColorRef(Color color) =>
+        (uint)(color.R | (color.G << 8) | (color.B << 16));
+
+    [DllImport("gdi32.dll", CharSet = CharSet.Unicode, EntryPoint = "CreateFontW")]
+    private static extern IntPtr CreateFontW(int cHeight, int cWidth, int cEscapement, int cOrientation,
+        int cWeight, bool bItalic, bool bUnderline, bool bStrikeOut,
+        int iCharSet, int iOutPrecision, int iClipPrecision, int iQuality, int iPitchAndFamily,
+        string pszFaceName);
+
+    /// <summary>
+    /// A 32-bit surface to draw the popup into before anyone can see it.
+    /// </summary>
+    /// <remarks>
+    /// Top-down — a negative height — so that the first row of <paramref name="bits"/>
+    /// is the top row of the picture and the alpha fixing up afterwards can walk the
+    /// memory straight through.
+    /// </remarks>
+    internal static IntPtr CreateSurface(IntPtr deviceContext, int width, int height, out IntPtr bits)
+    {
+        var header = new BitmapInfoHeader
+        {
+            biSize = Marshal.SizeOf<BitmapInfoHeader>(),
+            biWidth = width,
+            biHeight = -height,
+            biPlanes = 1,
+            biBitCount = 32,
+            biCompression = BI_RGB,
+        };
+
+        return CreateDIBSection(deviceContext, ref header, DIB_RGB_COLORS, out bits, IntPtr.Zero, 0);
+    }
+
+    private const uint BI_RGB = 0;
+    private const uint DIB_RGB_COLORS = 0;
+
+    [DllImport("gdi32.dll")]
+    internal static extern IntPtr CreateCompatibleDC(IntPtr hdc);
+
+    [DllImport("gdi32.dll")]
+    internal static extern bool DeleteDC(IntPtr hdc);
+
+    [DllImport("gdi32.dll")]
+    private static extern IntPtr CreateDIBSection(IntPtr hdc, ref BitmapInfoHeader header, uint usage,
+        out IntPtr bits, IntPtr section, uint offset);
+
+    [DllImport("gdi32.dll")]
+    internal static extern IntPtr SelectObject(IntPtr hdc, IntPtr h);
+
+    [DllImport("gdi32.dll")]
+    internal static extern bool DeleteObject(IntPtr ho);
+
+    [DllImport("gdi32.dll")]
+    internal static extern int SetBkMode(IntPtr hdc, int mode);
+
+    [DllImport("gdi32.dll")]
+    internal static extern uint SetTextColor(IntPtr hdc, uint color);
+
+    [DllImport("user32.dll", CharSet = CharSet.Unicode, EntryPoint = "DrawTextW")]
+    internal static extern int DrawText(IntPtr hdc, string lpchText, int cchText,
+        ref PopupWindowNative.Rect lprc, uint format);
+
+    [DllImport("user32.dll")]
+    internal static extern IntPtr GetDC(IntPtr hWnd);
+
+    [DllImport("user32.dll")]
+    internal static extern int ReleaseDC(IntPtr hWnd, IntPtr hDC);
+
+    [StructLayout(LayoutKind.Sequential)]
+    private struct BitmapInfoHeader
+    {
+        public int biSize;
+        public int biWidth;
+        public int biHeight;
+        public short biPlanes;
+        public short biBitCount;
+        public uint biCompression;
+        public uint biSizeImage;
+        public int biXPelsPerMeter;
+        public int biYPelsPerMeter;
+        public uint biClrUsed;
+        public uint biClrImportant;
+    }
+}