Question

我正在使用Win32 GDI本机API绘制线条。现在，我想画一条透明的线。我已经在颜色中设置了alpha通道属性。但是，将Alpha通道设置为彩色不会将线绘制为透明。我读到有关Alpha Blend Api的信息，但找不到解决方案。

var hdc = g.GdiDeviceContext;
var srcHdc = CreateCompatibleDC(hdc);

var clipRegion = CreateRectRgn(x, y, x + width, y + height);

SelectClipRgn(hdc, clipRegion);

var pen = CreatePen(PenStyle.Solid, LineWidth, (uint)ColorTranslator.ToWin32(colour));



if (pen != IntPtr.Zero)
{
     var oldPen = SelectObject(hdc, pen);
     Polyline(hdc, points, points.Length);
     SelectObject(hdc, oldPen);
     DeleteObject(pen);
}

SelectClipRgn(hdc, IntPtr.Zero);
AlphaBlend(hdc, x, y, width, height, srcHdc, x, y, width, height, new BlendFunction(0x00, 0, 0x7f, 0x00));
DeleteObject(clipRegion);

我正试图将线条画得透明。

Answer 1

var srcHdc = CreateCompatibleDC(hdc);

这将创建一个存储设备上下文。这是正确的第一步。但是内存dc尚未准备好。它也需要一个内存位图。

SelectObject(hdc, pen);
Polyline(hdc, points, points.Length);

这将在Windows设备上下文中进行绘制。但是我们想利用内存设备上下文，然后使用HDC

将内存吸引到AlphaBlend

请参见以下示例：

int w = 100;
int h = 100;

//create memory device context
var memdc = CreateCompatibleDC(hdc); 

//create bitmap
var hbitmap = CreateCompatibleBitmap(hdc, w, h);

//select bitmap in to memory device context
var holdbmp = SelectObject(memdc, hbitmap);

//begine drawing:
var hpen = CreatePen(0, 4, 255);
var holdpen = SelectObject(memdc, hpen);
Rectangle(memdc, 10, 10, 90, 90);

//draw memory device (memdc) context on to windows device context (hdc)
AlphaBlend(hdc, 0, 0, w, h, memdc, 0, 0, w, h, new BLENDFUNCTION(0, 0, 128, 0));

//clean up:
SelectObject(memdc, holdbmp);
SelectObject(memdc, holdpen);
DeleteObject(hbitmap);
DeleteObject(hpen);
DeleteDC(memdc);

使用本地Win32 GDI绘制透明线

1 个答案: