using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Runtime.InteropServices;
using System.Text;
using System.Windows.Forms;

namespace WindowsFormsApplication2
{
    public partial class Form1 : Form
    {
        [DllImport("Msimg32.dll", EntryPoint = "GradientFill", ExactSpelling = true, SetLastError = true)]
        public static extern bool GradientFill(
            IntPtr hdc,           // handle to DC
            TRIVERTEX[] pVertex,    // array of vertices
            uint dwNumVertex,     // number of vertices
            GRADIENT_RECT[] pMesh,    // array of gradient rectangles, that each one keeps two indices in pVertex array, to determine its bounds
            uint dwNumMesh,       // number of gradient rectangles to draw
            GRADIENT_FILL dwMode);           // Use either GRADIENT_FILL.RECT_H or GRADIENT_FILL.RECT_V. Using the value GRADIENT_FILL.TRIANGLE is wrong in this overload!

        [DllImport("Msimg32.dll", EntryPoint = "GradientFill", ExactSpelling = true, SetLastError = true)]
        public static extern bool GradientFill(
            IntPtr hdc,           // handle to DC
            TRIVERTEX[] pVertex,    // array of vertices
            uint dwNumVertex,     // number of vertices
            GRADIENT_TRIANGLE[] pMesh, // array of gradient triangles, that each one keeps three indices in pVertex array, to determine its bounds
            uint dwNumMesh,       // number of gradient triangles to draw
            GRADIENT_FILL dwMode);           // Use only GRADIENT_FILL.TRIANGLE. Both values GRADIENT_FILL.RECT_H and GRADIENT_FILL.RECT_V are wrong in this overload!

        public delegate void MyDelegate(string parameter);
        public Form1()
        {
            InitializeComponent();
        }

        private void button1_Click(object sender, EventArgs e)
        {
            using (Graphics gr = Graphics.FromHwnd(this.Handle))
            {
                TRIVERTEX[] vertex = new TRIVERTEX[2]{
                    new TRIVERTEX(0,0,0x4000,0xf000,0x4000,0x0000)   ,
                    new TRIVERTEX(Width,Height,0x0000,0xd000,0xd000,0x8000)      
                };
                GRADIENT_RECT[] gRect = new GRADIENT_RECT[1] { new GRADIENT_RECT(0, 1) };
                IntPtr hdc = gr.GetHdc();
                bool rc = GradientFill(hdc, vertex, (uint)vertex.Length, gRect, (uint)gRect.Length, GRADIENT_FILL.RECT_H);                
                gr.ReleaseHdc(hdc);
            }
        }
        private void Form1_Paint(object sender, PaintEventArgs e)
        {
            using (Bitmap bm = new Bitmap(Width, Height, System.Drawing.Imaging.PixelFormat.Format32bppArgb))
            using (Graphics gr = System.Drawing.Graphics.FromImage(bm))
            {                
                TRIVERTEX[] vertex = new TRIVERTEX[2]{
                    new TRIVERTEX(0,0,0x0000,0x8000,0x8000,0x8000)   ,
                    new TRIVERTEX(Width,Height,0x0000,0xd000,0xd000,0x8000)      
                };
                GRADIENT_RECT[] gRect = new GRADIENT_RECT[1] { new GRADIENT_RECT(0, 1) };
                IntPtr hdc = gr.GetHdc();
                bool rc = GradientFill(hdc, vertex, (uint)vertex.Length, gRect, (uint)gRect.Length, GRADIENT_FILL.RECT_H);                
                gr.ReleaseHdc(hdc);
                e.Graphics.DrawImage(bm, 0, 0);
            }
        }
    }

    public enum GRADIENT_FILL : uint
    {
        RECT_H = 0,
        RECT_V = 1,
        TRIANGLE = 2,
        OP_FLAG = 0xff
    }

    [StructLayout(LayoutKind.Sequential)]
    public struct GRADIENT_TRIANGLE
    {
        public uint Vertex1;
        public uint Vertex2;
        public uint Vertex3;

        public GRADIENT_TRIANGLE(uint vertex1, uint vertex2, uint vertex3)
        {
            this.Vertex1 = vertex1;
            this.Vertex2 = vertex2;
            this.Vertex3 = vertex3;
        }
    }

    [StructLayout(LayoutKind.Sequential)]
    public struct GRADIENT_RECT
    {
        public uint UpperLeft;
        public uint LowerRight;

        public GRADIENT_RECT(uint upLeft, uint lowRight)
        {
            this.UpperLeft = upLeft;
            this.LowerRight = lowRight;
        }
    }
    [StructLayout(LayoutKind.Sequential)]
    public struct TRIVERTEX
    {
        public int x;
        public int y;
        public ushort Red;
        public ushort Green;
        public ushort Blue;
        public ushort Alpha;

        public TRIVERTEX(int x, int y, ushort red, ushort green, ushort blue, ushort alpha)
        {
            this.x = x;
            this.y = y;
            this.Red = red;
            this.Green = green;
            this.Blue = blue;
            this.Alpha = alpha;
        }
    }
}