如何在ListBoxDrawItem上绘制抗锯齿三角形?
ListBox.Canvas.Polygon
使用jags进行绘图。
谢谢!!!
如何在ListBoxDrawItem上绘制抗锯齿三角形?
ListBox.Canvas.Polygon
使用jags进行绘图。
谢谢!!!
使用GDI实现抗锯齿绘制的最简单方法是先绘制到一个较大的表面,然后缩放回原始尺寸并启用半色调拉伸模式。
下面的代码示例使用比列表框客户区域大16倍的位图(这是一个相当大的位图,绘制需要一定时间,但效果更容易观察)。
procedure TForm1.Button1Click(Sender: TObject);
const
ZOOM = 16;
var
Bmp: TBitmap;
StretchMode: Integer;
begin
// for comparison
ListBox2.Canvas.Polygon([Point(20, 10), Point(10, 50), Point(80, 30)]);
Bmp := TBitmap.Create;
// create a large bitmap and set coordinate extents accordingly
Bmp.SetSize(ListBox1.ClientWidth * ZOOM, ListBox1.ClientHeight * ZOOM);
SetMapMode(Bmp.Canvas.Handle, MM_ISOTROPIC);
SetWindowExtEx(Bmp.Canvas.Handle, 100, 100, nil);
SetViewportExtEx(Bmp.Canvas.Handle, 100 * ZOOM, 100 * ZOOM, nil);
// without halftone we won't gain anything
SetStretchBltMode(Bmp.Canvas.Handle, HALFTONE);
// transfer what's on the list box to bitmap canvas
BitBlt(Bmp.Canvas.Handle, 0, 0, Bmp.Width, Bmp.Height,
ListBox1.Canvas.Handle, 0, 0, SRCCOPY);
Bmp.Canvas.Polygon([Point(20, 10), Point(10, 50), Point(80, 30)]);
// transfer bitmap contents
StretchMode := SetStretchBltMode(ListBox1.Canvas.Handle, HALFTONE);
StretchBlt(ListBox1.Canvas.Handle, 0, 0,
ListBox1.ClientWidth * ZOOM, ListBox1.ClientHeight * ZOOM,
Bmp.Canvas.Handle, 0, 0, Bmp.Width, Bmp.Height, SRCCOPY);
SetStretchBltMode(ListBox1.Canvas.Handle, StretchMode);
Bmp.Free;
end;