Canvas.Pixels 实例：判断一点是否在区域中

最新推荐文章于 2025-01-19 09:45:00 发布

转载最新推荐文章于 2025-01-19 09:45:00 发布 · 437 阅读

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原文链接：http://www.cnblogs.com/yzryc/p/6373560.html

The Windows 3.1 and Windows 95 GDI heap is limited in regards
to scan converting large and complex regions such as Ellipses,
Polygons, and PolyPolygons. One "Brute Force" technique is to
create an "in memory" monochrome bitmap and draw the
required shape in black. You can then test to see if a given point in
the bitmap is black or white. If the test pixel is black, then the given
point is "in" the given region.

Example:

procedure TForm1.Button1Click(Sender: TObject);
var
bm : TBitmap;
begin
bm := TBitmap.Create;
bm.Monochrome := true;
bm.Height := 100;
bm.Width := 100;
bm.Canvas.Brush.Color := clWhite;
bm.Canvas.FillRect(Rect(0, 0, 100, 100));
bm.Canvas.Brush.Color := clBlack;
bm.Canvas.Pen.Color := clBlack;
bm.Canvas.Ellipse(10, 10, 90, 90);
if bm.Canvas.Pixels[20, 20] = clBlack then
    ShowMessage('Point : (20, 20) is in region') else
    ShowMessage('Point : (20, 20) is not in region');
if bm.Canvas.Pixels[50, 50] = clBlack then
    ShowMessage('Point : (50, 50) is in region') else
    ShowMessage('Point : (50, 50) is not in region');
bm.Free;
end;