private void ReleaseCanvas()
{
if (this.hdc != null)
{
NativeMethods.SetMapMode(this.hdc, this.oldMapMode);
NativeMethods.SetBkColor(this.hdc, this.oldBkColor);
this.hdc.Dispose();
this.hdc = null;
}
if (this.bitmap != null)
{
this.bitmap.Dispose();
this.bitmap = null;
}
if (this.hfont != null)
{
this.hfont.Dispose();
this.hfont = null;
}
}
/// <summary>
/// Initializes a new instance of the <see cref="Canvas"/> class.
/// </summary>
/// <param name="width">The canvas width.</param>
/// <param name="height">The canvas height.</param>
public Canvas(int width, int height)
{
try
{
// allocate enough to fit all characters
this.width = width <= 0 ? 2000 : width;
this.height = height;
// get handle to device context.
this.hdc = NativeMethods.CreateCompatibleDC(new SafeHdcHandle());
if (this.hdc.IsInvalid)
{
throw new InvalidOperationException(Properties.Resources.E_InvalidCanvasOperation);
}
// create destination bitmap
this.bitmap = NativeMethods.CreateCompatibleBitmap(this.hdc, this.width, this.height);
if (this.bitmap.IsInvalid)
{
throw new InvalidOperationException(Properties.Resources.E_InvalidCanvasOperation);
}
NativeMethods.SelectObject(this.hdc, this.bitmap);
// select color
this.oldMapMode = NativeMethods.SetBkMode(this.hdc, NativeMethods.TRANSPARENT);
this.oldBkColor = NativeMethods.SetTextColor(this.hdc, System.Drawing.ColorTranslator.ToWin32(System.Drawing.Color.Black));
// erase background
this.Clear();
}
catch
{
this.ReleaseCanvas();
throw;
}
}
public static extern bool ExtTextOut(SafeHdcHandle hdc, int x, int y, int options, ref Rect rect, string s, int count, int[] dx);
public static extern int DrawText(SafeHdcHandle hdc, string s, int count, ref Rect rect, int format);
public static extern int SetBkMode(SafeHdcHandle hdc, int mode);
public static extern int SetBkColor(SafeHdcHandle hdc, int color);
public static extern IntPtr SelectObject(SafeHdcHandle hdc, SafeHandle objectHandle);
public static extern SafeGdiObjectHandle CreateCompatibleBitmap(SafeHdcHandle hdc, int width, int height);
public static extern SafeHdcHandle CreateCompatibleDC(SafeHdcHandle hdc);
