GradientFill function (wingdi.h)

Article
10/13/2021

The GradientFill function fills rectangle and triangle structures.

Syntax

BOOL GradientFill(
  [in] HDC        hdc,
  [in] PTRIVERTEX pVertex,
  [in] ULONG      nVertex,
  [in] PVOID      pMesh,
  [in] ULONG      nMesh,
  [in] ULONG      ulMode
);

Parameters

[in] hdc

A handle to the destination device context.

[in] pVertex

A pointer to an array of TRIVERTEX structures that each define a vertex.

[in] nVertex

The number of vertices in pVertex.

[in] pMesh

An array of GRADIENT_TRIANGLE structures in triangle mode, or an array of GRADIENT_RECT structures in rectangle mode.

[in] nMesh

The number of elements (triangles or rectangles) in pMesh.

[in] ulMode

The gradient fill mode. This parameter can be one of the following values.

Value	Meaning
GRADIENT_FILL_RECT_H	In this mode, two endpoints describe a rectangle. The rectangle is defined to have a constant color (specified by the TRIVERTEX structure) for the left and right edges. GDI interpolates the color from the left to right edge and fills the interior.
GRADIENT_FILL_RECT_V	In this mode, two endpoints describe a rectangle. The rectangle is defined to have a constant color (specified by the TRIVERTEX structure) for the top and bottom edges. GDI interpolates the color from the top to bottom edge and fills the interior.
GRADIENT_FILL_TRIANGLE	In this mode, an array of TRIVERTEX structures is passed to GDI along with a list of array indexes that describe separate triangles. GDI performs linear interpolation between triangle vertices and fills the interior. Drawing is done directly in 24- and 32-bpp modes. Dithering is performed in 16-, 8-, 4-, and 1-bpp mode.

Return value

If the function succeeds, the return value is TRUE.

If the function fails, the return value is FALSE.

Remarks

To add smooth shading to a triangle, call the GradientFill function with the three triangle endpoints. GDI will linearly interpolate and fill the triangle. Here is the drawing output of a shaded triangle.

Illustration of a triangle that fills from orange at the top point to magenta on the bottom line

To add smooth shading to a rectangle, call GradientFill with the upper-left and lower-right coordinates of the rectangle. There are two shading modes used when drawing a rectangle. In horizontal mode, the rectangle is shaded from left-to-right. In vertical mode, the rectangle is shaded from top-to-bottom. Here is the drawing output of two shaded rectangles - one in horizontal mode, the other in vertical mode: Illustration of a rectangle that shades from dark on the left side to light on the right side

Illustration of a rectangle that shades from dark on the left side to light on the right side

Illustration of a rectangle that shades from dark on the top to light on the bottom

The GradientFill function uses a mesh method to specify the endpoints of the object to draw. All vertices are passed to GradientFill in the pVertex array. The pMesh parameter specifies how these vertices are connected to form an object. When filling a rectangle, pMesh points to an array of GRADIENT_RECT structures. Each GRADIENT_RECT structure specifies the index of two vertices in the pVertex array. These two vertices form the upper-left and lower-right boundary of one rectangle.

In the case of filling a triangle, pMesh points to an array of GRADIENT_TRIANGLE structures. Each GRADIENT_TRIANGLE structure specifies the index of three vertices in the pVertex array. These three vertices form one triangle.

To simplify hardware acceleration, this routine is not required to be pixel-perfect in the triangle interior.

Note that GradientFill does not use the Alpha member of the TRIVERTEX structure. To use GradientFill with transparency, call GradientFill and then call AlphaBlend with the desired values for the alpha channel of each vertex.

For more information, see Smooth Shading, Drawing a Shaded Triangle, and Drawing a Shaded Rectangle.

Requirements

Requirement	Value
Minimum supported client	Windows 2000 Professional [desktop apps only]
Minimum supported server	Windows 2000 Server [desktop apps only]
Target Platform	Windows
Header	wingdi.h (include Windows.h)
Library	Msimg32.lib
DLL	Msimg32.dll