为什么从WM_NCPAINT使用DrawImageUnscaled会导致闪烁
本文关键字:闪烁 DrawImageUnscaled 使用 WM NCPAINT 为什么 | 更新日期: 2023-09-27 17:58:39
我目前正在构建一个从System.Windows.Forms.ContainerControl
派生的控件,该控件有一个我需要自己绘制的边界区域。由于没有可重写的OnPaintNonClientArea
,我自己这样构建它(为了简洁起见,删除了对WM_NCCALCSIZE
、WM_NCHITTEST
等其他消息的处理):
protected override void WndProc(ref Message m)
{
switch (m.Msg)
{
case WM_NCPAINT:
IntPtr hDC = NativeApi.Methods.GetWindowDC(m.HWnd);
if (hDC != IntPtr.Zero)
{
using (Graphics canvas = Graphics.FromHdc(hDC))
{
if (Width > 0 && Height > 0)
using (PaintEventArgs e = new PaintEventArgs(canvas, new Rectangle(0, 0, Width, Height)))
{
OnPaintNonClientArea(e);
}
}
NativeApi.Methods.ReleaseDC(m.HWnd, hDC);
}
m.Result = IntPtr.Zero;
break;
}
base.WndProc(ref m);
}
在OnPaintNonClientArea
中,我做了:
private void OnPaintNonClientArea(PaintEventArgs e)
{
if (_ncBuffer == null)
{
_ncBuffer = new Bitmap(Width, Height);
}
using (Graphics g = Graphics.FromImage(_ncBuffer))
{
// painting occurs here ...
}
// this causes flickering
e.Graphics.DrawImageUnscaled(_ncBuffer, 0, 0, Width, Height);
}
保持OnPaintNonClientArea
不变,这将消除闪烁:
protected override void WndProc(ref Message m)
{
switch (m.Msg)
{
case WM_NCPAINT:
using(Bitmap ncBitmap = new Bitmap(Width, Height, System.Drawing.Imaging.PixelFormat.Format32bppArgb))
{
using(Graphics ncGraphics = Graphics.FromImage(ncBitmap))
{
using (PaintEventArgs e = new PaintEventArgs(ncGraphics, new Rectangle(0, 0, Width, Height)))
{
OnPaintNonClientArea(e);
IntPtr hDCWin = NativeApi.Methods.GetWindowDC(m.HWnd);
IntPtr hDCImg = ncGraphics.GetHdc();
IntPtr hBmp = ncBitmap.GetHbitmap();
IntPtr hBmpOld = NativeApi.Methods.SelectObject(hDCImg, hBmp);
Padding p = GetNonClientArea();
NativeApi.Methods.ExcludeClipRect(hDCWin, p.Left, p.Top,Width- p.Right, Height-p.Bottom);
NativeApi.Methods.BitBlt(hDCWin, 0, 0, Width, Height, hDCImg, 0, 0,NativeApi.TernaryRasterOperations.SRCCOPY);
NativeApi.Methods.SelectObject(hDCImg, hBmpOld);
NativeApi.Methods.DeleteObject(hBmp);
ncGraphics.ReleaseHdc(hDCImg);
NativeApi.Methods.ReleaseDC(m.HWnd, hDCWin);
}
}
}
m.Result = IntPtr.Zero;
break;
}
base.WndProc(ref m);
}
那么,为什么DrawImageUnscaled
会导致这种闪烁呢?在绘制缓冲区之前,它似乎要用白色画笔擦除它工作的区域。我没有在文件中找到任何澄清这个问题的东西。如果只是控件周围的一个小边界,那也没关系,但NC区域内会显示文本,因此该区域清晰可见,因此闪烁非常明显,令人讨厌。
相关问题:我做的原生GDI是对的吗,还是有我现在看不到的潜在问题?此外,在创建ncBitmap
时,我使用了控件的宽度和高度,但GDI+是独立于分辨率的,会有什么问题吗?
为了避免UserControl中的闪烁,我最好使用BufferedGraphics类。
MSDN
这是一种选择吗?