C# Signature:

  [DllImport("gdi32.dll", EntryPoint="GdiGradientFill", ExactSpelling = 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 gradients
    uint dwNumMesh,       // size of gradient array
    uint dwMode           // gradient fill mode);

  [DllImport("gdi32.dll", EntryPoint="GdiGradientFill", ExactSpelling = true)]
  public static extern bool GradientFill(
    IntPtr hdc,           // handle to DC
    TRIVERTEX[] pVertex,    // array of vertices
    uint dwNumVertex,     // number of vertices
    GRADIENT_TRIANGE[] pMesh,           // array of gradients
    uint dwNumMesh,       // size of gradient array
    uint dwMode           // gradient fill mode);

VB Signature:

Declare Function GradientFill Lib "gdi32.dll" (TODO) As TODO

User-Defined Types:

GRADIENT_RECT

GRADIENT_TRIANGLE

TRIVERTEX

The dwMode is one of the constants from GRADIENT_.

Alternative Managed API:

Do you know one? Please contribute it!

Notes:

The GDI32.dll does not contain a GradientFill() function. The actual entry point is GdiGradientFill(). That's why the 'EntryPoint' attribute is present.

This method creates one entry each for rectangles and triangles. It's just a matter of convenience and error checking by the compiler.

Tips & Tricks:

Please add some!

Sample Code:

public class Gradient
{
    public const uint
      GRADIENT_FILL_RECT_H = 0x00000000,
      GRADIENT_FILL_RECT_V = 0x00000001,
      GRADIENT_FILL_TRIANGLE = 0x00000002,
      GRADIENT_FILL_OP_FLAG = 0x000000ff;

    [DllImport("gdi32.dll", EntryPoint="GdiGradientFill", ExactSpelling = 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 gradients
      uint dwNumMesh,       // size of gradient array
      uint dwMode           // gradient fill mode
    );

    public static void  DrawNiceRectangle(hDC graphPort, Rectangle Frame)
    {
      // Draw from whitish blue at the top, to a light blue at the bottom
      TRIVERTEX[] vert = new TRIVERTEX[]{
        new TRIVERTEX(Frame.Left,Frame.Top,0xff00,0xff00,0xffff,0x0),
        new TRIVERTEX(Frame.Right,Frame.Bottom,0x0000,0x0000,0xff00,0x0)};

      GRADIENT_RECT[] gRect = new GRADIENT_RECT[]{
        new GRADIENT_RECT(0,1)};

      Gradient.GradientFill(graphPort, vert, 2, gRect, 1, Gradient.GRADIENT_FILL_RECT_V);
    }
}