The Warp method applies a warp transformation to this path. The Warp method also flattens (converts to a sequence of straight lines) the path.

Syntax

Status Warp(      
    const PointF *destPoints,
    INT count,
    const RectF &srcRect,
    const Matrix *matrix,
    WarpMode warpMode,
    REAL flatness
);

Parameters

destPoints

[in] Pointer to an array of points that, along with the srcRect parameter, defines the warp transformation.

count

[in] Integer that specifies the number of points in the destPoints array. The value of this parameter must be 3 or 4.

srcRect

[in] Reference to a rectangle that, along with the destPoints parameter, defines the warp transformation.

matrix

[in] Optional. Pointer to a Matrix object that represents a transformation to be applied along with the warp. If this parameter is NULL, no transformation is applied. The default value is NULL.

warpMode

[in] Optional. Element of the WarpMode enumeration that specifies the kind of warp to be applied. The default value is WarpModePerspective.

flatness

[in] Optional. Real number that influences the number of line segments that are used to approximate the original path. Small values specify that many line segments are used, and large values specify that few line segments are used. The default value is FlatnessDefault, which is a constant defined in Gdiplusenums.h.

Return Value

If the method succeeds, it returns Ok, which is an element of the Status enumeration.

If the method fails, it returns one of the other elements of the Status enumeration.

Remarks

A GraphicsPath object stores a collection of data points that represent lines and curves. The Warp method converts those data points so that they represent only lines. The flatness parameter influences the number of lines that are stored. The original data points that represented curves are lost.

If the count parameter has a value of 4, the warp transformation is defined as shown in the following table.

Source point	Destination point
Upper-left corner of srcRect	destPoints[0]
Upper-right corner of srcRect	destPoints[1]
Lower-left corner of srcRect	destPoints[2]
Lower-right corner of srcRect	destPoints[3]

A transformation specified by a source rectangle and four destination points is capable of mapping a rectangle to an arbitrary quadrilateral that is not necessarily a parallelogram.

If the count parameter has a value of 3, the warp transformation is defined as shown in the following table.

Source point	Destination point
Upper-left corner of srcRect	destPoints[0]
Upper-right corner of srcRect	destPoints[1]
Lower-left corner of srcRect	destPoints[2]

A transformation specified by a source rectangle and three destination points maps rectangles to parallelograms.

Example

The following example creates a GraphicsPath object and adds a closed figure to the path. The code defines a warp transformation by specifying a source rectangle and an array of four destination points. The source rectangle and destination points are passed to the Warp method. The code draws the path twice: once before it has been warped and once after it has been warped.

VOID WarpExample(HDC hdc)
{
   Graphics graphics(hdc);

   // Create a path.
   PointF points[] ={
      PointF(20.0f, 60.0f),
      PointF(30.0f, 90.0f),
      PointF(15.0f, 110.0f),
      PointF(15.0f, 145.0f),
      PointF(55.0f, 145.0f),
      PointF(55.0f, 110.0f),
      PointF(40.0f, 90.0f),
      PointF(50.0f, 60.0f)};

   GraphicsPath path;
   path.AddLines(points, 8);
   path.CloseFigure();

   // Draw the path before applying a warp transformation.
   Pen bluePen(Color(255, 0, 0, 255));
   graphics.DrawPath(&bluePen, &path);

   // Define a warp transformation, and warp the path.
   RectF srcRect(10.0f, 50.0f, 50.0f, 100.0f);

   PointF destPts[] = {
      PointF(220.0f, 10.0f),
      PointF(280.0f, 10.0f),
      PointF(100.0f, 150.0f),
      PointF(400.0f, 150.0f)};

   path.Warp(destPts, 4, srcRect);

   // Draw the warped path.
   graphics.DrawPath(&bluePen, &path);

   // Draw the source rectangle and the destination polygon.
   Pen blackPen(Color(255, 0, 0, 0));
   graphics.DrawRectangle(&blackPen, srcRect);
   graphics.DrawLine(&blackPen, destPts[0], destPts[1]);
   graphics.DrawLine(&blackPen, destPts[0], destPts[2]);
   graphics.DrawLine(&blackPen, destPts[1], destPts[3]);
   graphics.DrawLine(&blackPen, destPts[2], destPts[3]);
}

Method Information

Stock Implementation	gdiplus.dll
Header	Declared in Gdipluspath.h, include gdiplus.h
Import library	gdiplus.lib
Minimum availability	GDI+ 1.0
Minimum operating systems	Windows 98/Me, Windows XP, Windows 2000, Windows NT 4.0 SP6

See Also

GraphicsPath::Flatten, Matrix, GraphicsPath::Outline, GraphicsPath::Widen, WarpMode, Clipping with a Region, Constructing and Drawing Paths, Creating a Path Gradient, Flattening Paths, Paths