如何绘制图像的一部分？ [英] How to draw part of a image?

问题描述

我有一个普通的Bitmap加载了一个PNGImage。以下代码显示整个图像;但我正在寻找的是像下面的示例显示为例。我想基本上减少虚拟的地方，它将被绘。注意，我不能只是调整大小的PaintBox的原因，我可以枚举，如果有人问。我想我必须使用Rects和一些复制功能，但我不知道自己。有人知道如何做吗？

I have an ordinary Bitmap loaded with a PNGImage. The following code shows the whole image; but what I am looking for is to show like the sample below for example. I want basically to reduce the virtual "place" where it would be painted. Note that I can't just resize the PaintBox by reasons I can enumerate if someone asks. I guess I have to use Rects and or some Copy function, but I could not figure out by myself. Does anyone know how to do?

procedure TForm1.PaintBox1Paint(Sender: TObject);
begin
    PaintBox1.Canvas.Brush.Color := clBlack;
    PaintBox1.Brush.Style := bsSolid;
    PaintBox1.Canvas.FillRect(GameWindow.Screen.ClientRect);
    PaintBox1.Canvas.Draw(0, 0, FBitmap, FOpacity);
end;

推荐答案

一种方法是修改paintbox画布的剪裁区域：

One way is to modify the clipping region of your paintbox's canvas:

...
IntersectClipRect(PaintBox1.Canvas.Handle, 20, 20,
    PaintBox1.Width - 20, PaintBox1.Height - 20);
PaintBox1.Canvas.Draw(0, 0, FBitmap, FOpacity);

当然，我确定你知道<$ c $您的 Canvas.Draw 调用中的c>（0，0 ）是坐标，您可以根据自己的喜好绘制：

Of course, I'm sure you're aware that the (0, 0 in your Canvas.Draw call are coordinates. You can draw to whereever you like:

...
FBitmap.Canvas.CopyRect(Rect(0, 0, 80, 80), FBitmap.Canvas,
    Rect(20, 20, 100, 100));
FBitmap.SetSize(80, 80);
PaintBox1.Canvas.Draw(20, 20, FBitmap, FOpacity);

如果您不想剪辑绘图区域，不要修改源位图（FBitmap ），并且不想制作它的临时副本，则可以直接调用 AlphaBlend ，而不是通过 Canvas.Draw ：

var
  BlendFn: TBlendFunction;
begin
  BlendFn.BlendOp := AC_SRC_OVER;
  BlendFn.BlendFlags := 0;
  BlendFn.SourceConstantAlpha := FOpacity;
  BlendFn.AlphaFormat := AC_SRC_ALPHA;

  winapi.windows.AlphaBlend(PaintBox1.Canvas.Handle,
      20, 20, PaintBox1.Width - 20, PaintBox1.Height - 20,
      FBitmap.Canvas.Handle, 20, 20, PaintBox1.Width - 20, PaintBox1.Height - 20,
      BlendFn);

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