2018年12月02日

How to fill an irregular area with a pattern brush in VB Net

The Vb Net graphics class provides many methods for drawing shapes and filling area, The Vb Net currently has no support any method to fill an irregular area with solid brush,hatch brush or pattern brush. If you want to fill an irregular area with some brush, the easiest and fastest way is use Window Api ExtFloodFill function. In this article you will learn

(1)   how to use ExtFloodFill function

(2)   how to convert VB Net Bitmap class to Api int32 bitmap

(3)   how to use VB Net getHdc function

To use ExtFloodFill function, you shoud Declareit first.

[Private/㎝Public] Declare Function ExtFloodFill Lib "gdi32" Alias "ExtFloodFill" (ByVal hdc As Int32, ByVal x As Int32, ByVal y As Int32, ByVal crColor As Int32, ByVal wFillType As Int32) As Int32 

hdc

A handle of a device context to perform the flood fill on.

x

The x-coordinate of the point to begin the flood fill at.

y

The y-coordinate of the point to begin the flood fill at.

crColor

The RGB value of the color determining the extent of the flood fill operation. Its exact interpretation depends on the flag passed as wFillType .

wFillType

One of the following flags specifying how to determine the boundary of the flood fill operation:

FLOODFILLBORDER

Fill from the beginning point in all directions until a boundary of color crColor is reached. The flood fill will cover over any colors within the region which do not have the color of crColor.

FLOODFILLSURFACE

Fill from the beginning point in all directions as long as the fill-in color crColor is encountered. The boundary of the flood fill is made up of any color which is not identical to crColor.

The ExtFloodFill function is similar to FloodFill except it takes an extra parameter that determines the fill progresses.If wFillType set to Flloodfillborder(0),it fill stop as long as when it finds a pixel with same color crColor, If you set wFillType equal to Flloodfillsurface(1),the fill continues until the function finds the pixel have a different  color. Hereafter is the key snippet code of the program.

Private Sub FloodFillAPI(ByRef brushBmp As Bitmap, ByVal canvas_beFill As PictureBox, ByVal mFillType As Int16, ByVal colorFill As Int32, ByVal Pt As Point)

        If m_FillType = 2 Then

            Dim mbmpGetHbitmap As Int32

            Dim mBrush As Int32

            If mFillType = 2 And brushBmp Is Nothing Then Exit Sub

'convert VB net Bitmap class bitmap to api bitmap

            mbmpGetHbitmap = brushBmp.GetHbitmap           

            If mFillType = 2 Then mBrush = CreatePatternBrush(mbmpGetHbitmap)

            Dim picHdc As Int32 = canvas_beFill.CreateGraphics.GetHdc()

            Dim hmm As Int32 = SelectObject(picHdc, mBrush)

            ExtFloodFill(picHdc, Pt.X, Pt.Y, GetPixel(picHdc, Pt.X, Pt.Y), 1)

            'clearing memory

            DeleteDC(picHdc)

            DeleteObject(mBrush)

            DeleteObject(hmm)

            mbmpGetHbitmap = Nothing

            hmm = Nothing

        Else

            Dim mBrush As Int32

            Dim picHdc As Int32

            Dim hmm As Int32

            If mFillType = 0 Then mBrush = CreateSolidBrush(colorFill)

            If mFillType = 1 Then mBrush = CreateHatchBrush(m_HatchStyle, colorFill)

            picHdc = canvas_beFill.CreateGraphics.GetHdc()

            hmm = SelectObject(picHdc, mBrush)

            Dim ret As Int32 = ExtFloodFill(picHdc, Pt.X, Pt.Y, GetPixel(picHdc, Pt.X, Pt.Y), 1)

            DeleteDC(picHdc)

            DeleteObject(mBrush)

            DeleteObject(hmm)

            hmm = Nothing           

        End If

    End Sub

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