[英]C++ MFC How to Draw Alpha transparent Rectangle
in a C++ MFC application. 在C ++ MFC应用程序中。 using the dc of (
CPaintDC dc(this);
) 使用dc (
CPaintDC dc(this);
)
How do i draw a rectangle ( LPRECT
) with an alpha transparency that i can adjust.? 如何绘制一个可以调整的Alpha透明度矩形(
LPRECT
)。
Following is an example c# code which i need to convert into C++ 以下是我需要转换为C ++的示例c#代码
private void pictureBox1_Paint(object sender, PaintEventArgs e)
{
Graphics g = e.Graphics;
Color color = Color.FromArgb(75,Color.Red); //sets color Red with 75% alpha transparency
Rectangle rectangle = new Rectangle(100,100,400,400);
g.FillRectangle(new SolidBrush(color), rectangle); //draws the rectangle with the color set.
}
You need to look into GDI+. 你需要研究GDI +。 Its a bit of a faff but you can create a "Graphics" object as follows:
它有点像faff但你可以创建一个“Graphics”对象,如下所示:
Gdiplus::Graphics g( dc.GetSafeHdc() );
Gdiplus::Color color( 192, 255, 0, 0 );
Gdiplus::Rect rectangle( 100, 100, 400, 400 );
Gdiplus::SolidBrush solidBrush( color );
g.FillRectangle( &solidBrush, rectangle );
Don't forget to do 别忘了做
#include <gdiplus.h>
and to call 和打电话
GdiplusStartup(...);
somewhere :) 某处:)
You'll notice it's pretty damned similar to your C# code ;) 你会发现它非常类似于你的C#代码;)
Its worth noting that the 75 you put in your FromArgb
code doesn't set 75% alpha it actually sets 75/255 alpha or ~29% alpha. 值得注意的是,你在
FromArgb
代码中放入的75并没有设置75%的alpha值,它实际上设置了75/255 alpha或~29%alpha。
GDI (and thus MFC) has no decent support for drawing with an alpha. GDI(以及MFC)对使用alpha绘图没有得体。 But GDI+ is available in C++ code as well.
但是GDI +也可以在C ++代码中使用。 Use
#include <gdiplus.h>
and initialize it with GdiplusStartup(). 使用
#include <gdiplus.h>
并使用GdiplusStartup()初始化它。 You can use the Graphics class, create one with its Graphics(HDC) constructor from your CPaintDC. 您可以使用Graphics类,使用CPaintDC中的Graphics(HDC)构造函数创建一个。 And use its FillRectangle() method.
并使用其FillRectangle()方法。 The SDK docs are here .
SDK文档在这里 。
int StartHoriz,StartVert,BarWidth,BarHeight; // rect start, width and height
StartHoriz=0;
StartVert=100;
width = 100;
height=120;
CDC* pCDC = GetDC(); // Get CDC pointer
CRect Rect(StartHoriz,StartVert,BarWidth,BarHeight); //create rectangle dimensions
pCDC->Rectangle(Rect); //draw rectangle
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