VB6 GDI+で軸指定の画像回転をするには？ (ID:86553)

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本文 VB6の環境で、GDI+を使用した画像の回転に挑戦しています。 現状、画像の回転までは成功したんですが、任意の回転軸の座標を指定 し、そこを中心に回転させる場合、GdipDrawImageRectI関数に渡す 描画始点の座標が解からずにいます。 その解決策についてアドバイスをお願いします。 回転軸の座標を引き数にしたGDI+のGraphics関数があればベストなんですが MSDNを調べても該当する関数の解説が見つかりません。 以下は、現状のテストコードです。 Option Explicit Private Type GdiplusStartupInput GdiplusVersion As Long DebugEventCallback As Long SuppressBackgroundThread As Long SuppressExternalCodecs As Long End Type Private Declare Function GdiplusStartup Lib "gdiplus" (token As Long, inputbuf As GdiplusStartupInput, Optional ByVal outputbuf As Long = 0) As Long Private Declare Function GdiplusShutdown Lib "gdiplus" (ByVal token As Long) As Long Private Declare Function GdipLoadImageFromFile Lib "gdiplus" (ByVal FileName As Long, image As Long) As Long Private Declare Function GdipDisposeImage Lib "gdiplus" (ByVal image As Long) As Long Private Declare Function GdipCreateFromHDC Lib "gdiplus" (ByVal hdc As Long, Graphics As Long) As Long Private Declare Function GdipDeleteGraphics Lib "gdiplus" (ByVal Graphics As Long) As Long Enum MatrixOrder MatrixOrderPrepend = 0 MatrixOrderAppend = 1 End Enum Private Declare Function GdipRotateWorldTransform Lib "GDIPlus" (ByVal Graphics As Long, ByVal Angle As Single, ByVal Order As MatrixOrder) As Long Private Declare Function GdipGetImageWidth Lib "gdiplus" (ByVal image As Long, Width As Long) As Long Private Declare Function GdipGetImageHeight Lib "gdiplus" (ByVal image As Long, Height As Long) As Long Private Declare Function GdipDrawImageRectI Lib "gdiplus" (ByVal Graphics As Long, ByVal image As Long, ByVal X As Long, ByVal Y As Long, ByVal Width As Long, ByVal Height As Long) As Long Private Sub Command1_Click() Dim sfilename As String sfilename = App.Path & "\test.bmp" With Picture1 .AutoRedraw = True .Picture = LoadPicture() ' とりあえず、４５度で回転してみる。 Call RotatedImageFromFile(sfilename, Picture1.hdc, 45) .Picture = .image End With End Sub Private Sub RotatedImageFromFile(ByVal sfilename As String, _ ByVal hdc As Long, ByVal angle As Single) ' sfilename - bmp, jpg, gif, emf, wmf, tif, png, ico ファイルのパス名 ' hdc - Form1.hdc または Picture1.hdc ' angle - 回転角度(degrees) Dim pstat As GdiplusStartupInput Dim ltoken As Long, lstatus As Long Dim lgraphics As Long, limage As Long Dim x As Long, y As Long Dim lwidth As Long, lheight As Long pstat.GdiplusVersion = 1 If (GdiplusStartup(ltoken, pstat) <> 0) Then Exit Sub lstatus = GdipLoadImageFromFile(StrPtr(sfilename), limage) If (lstatus = 0) Then lstatus = GdipCreateFromHDC(hdc, lgraphics) If (lstatus = 0) Then Call GdipRotateWorldTransform(lgraphics, angle, MatrixOrderAppend) Call GdipGetImageWidth(limage, lwidth) Call GdipGetImageHeight(limage, lheight) '------------------------------- ' 回転軸の座標(x0, y0)を指定した場合、GdipDrawImageRectI関数 ' に渡す正しい描画始点(x, y)座標を求めることができていません。 Const pi = 3.14159 Dim r As Single Dim x0 As Single, y0 As Single ' 回転軸のx, y座標 Dim theta As Single x0 = CSng(lwidth) / 2 y0 = CSng(lheight) / 2 r = Sqr(x0 * x0 + y0 * y0) theta = Atn(y0 / x0) theta = theta + (angle * pi / 180) x = x0 - r * Cos(theta) y = y0 - r * Sin(theta) '------------------------------- Call GdipDrawImageRectI(lgraphics, limage, x, y, lwidth, lheight) Call GdipDeleteGraphics(lgraphics) End If Call GdipDisposeImage(limage) End If Call GdiplusShutdown(ltoken) End Sub