如何更改 canvas 区域的颜色

Question

我尝试在 TCanvas 上单击并拖动，然后在向下拖动时将背景颜色更改为 clHighlight，如果要反转拖动方向，则将其更改回 clWhite。如果你点击你正在阅读的这段文字并向下或向上拖动，几乎会发生什么，反正都是一样的想法。我已经从这个 link

中收集到了我能收集到的东西

自从我第一次发布此代码以来，我已经对下面的代码进行了大量编辑，下面的代码现在完成了我打算做的事情，除了如果你不按甚至速度，这是不可接受的。如果你真的快速上下移动鼠标，它肯定会搞砸。如果你移动鼠标以稳定的速度运行良好，这让我担心这个问题可能没有解决方案。我将继续关注这一点，如果有人有任何建议，那就太好了。我还遇到了一些 "Out of resources" 错误，还不确定这是怎么回事，我正在释放位图，没有涉及我所知道的其他资源。

下面的代码是在一个MouseMove event.srect是在TImage的Canvas中选中的矩形。 drect 与转换为 0,0 的 srect 相同。 bm1 包含使用 CopyRect 从 TImage 的 Canvas 复制的选定矩形。 bm2 包含 bm1，使用 BrushCopy 将 clWhite（背景）更改为 clHighlight（或相反）。然后使用 BitBlt 将 bm2 复制回原始 TImage 的选定矩形。

    // vp is derived from TImage
    if (Y > sel_data->_last_y)
    {
      TRect srect = Rect(sel_data->_rect.Left,sel_data->_last_y,sel_data->_rect.Right, Y);
      TRect drect = Rect(sel_data->_rect.Left,0,sel_data->_rect.Right, sel_data->_rect.Height() - 1);
      Graphics::TBitmap* bm1 = new Graphics::TBitmap;
      bm1->Width = srect.Width();
      bm1->Height = srect.Height();
      Graphics::TBitmap* bm2 = new Graphics::TBitmap;
      bm2->Width = srect.Width();
      bm2->Height = srect.Height();

      bm1->Canvas->CopyRect(drect, vp->Canvas, srect);

      bm2->Canvas->Brush->Color = clHighlight;
      bm2->Canvas->BrushCopy(drect, bm1, drect, clWindow);

      BitBlt(vp->Canvas->Handle, srect.Left, srect.Top, srect.Width(), srect.Height(),
         bm2->Canvas->Handle, 0, 0, SRCCOPY);  
      vp->Refresh();
      delete bm1;
      delete bm2;
    }
    else if (Y < sel_data->_last_y)
    {
      TRect srect = Rect(sel_data->_rect.Left, Y,sel_data->_rect.Right, sel_data->_last_y);
      TRect drect = Rect(sel_data->_rect.Left,0,sel_data->_rect.Right, sel_data->_rect.Height() - 1);
      Graphics::TBitmap* bm1 = new Graphics::TBitmap;
      bm1->Width = srect.Width();
      bm1->Height = srect.Height();
      Graphics::TBitmap* bm2 = new Graphics::TBitmap;
      bm2->Width = srect.Width();
      bm2->Height = srect.Height();

      bm1->Canvas->CopyRect(drect, vp->Canvas, srect);

      bm2->Canvas->Brush->Color = clWhite;
      bm2->Canvas->BrushCopy(drect, bm1, drect, clHighlight);

      int w = srect.Width();
      int h = srect.Height();
      BitBlt(vp->Canvas->Handle, srect.Left, srect.Top, w, h, bm2->Canvas->Handle, 0, 0, SRCCOPY);  
      vp->Refresh();
      delete bm1;
      delete bm2;
    }
    sel_data->_last_y = Y;
  }

Answer 1

这就是我的最终结果，据我所知，所有问题都已修复，我包括了整个 MouseMove 事件处理程序。上面提到的 link 提示我需要一个 CopyRect、一个 BrushCopy，然后是一个 BitBlt。

void __fastcall Tviewer_ui::viewerPageMouseMove(TObject *Sender, TShiftState Shift, int X, int Y)
{
  if (_selecting)
  {
    TColor to_color = 0;
    TColor from_color = 0; 
    Tviewer_page* vp = static_cast<Tviewer_page *>(Sender);
    Tsel_data* sel_data = &vp->_sel_datas[vp->_c_sel];

    // Scroll window if needed
    int sb_pos = _scrollBox->VertScrollBar->Position;
    if (Y > sb_pos - vp->_top + _scrollBox->Height - 10)
      _scrollBox->VertScrollBar->Position += 10;
    else 
      if (Y < sb_pos - vp->_top + 10)
        _scrollBox->VertScrollBar->Position -= 10;

    int y1 = 0;
    int y2 = 0;
    if (Y > sel_data->_start_y)
    {
      if (Y > sel_data->_last_y)
      {
        y1 = sel_data->_last_y;
        y2 = Y;
        from_color = clWhite;
        to_color = clHighlight;
      }
      else if (Y < sel_data->_last_y)
      {
        y1 = Y;
        y2 = sel_data->_last_y;
        from_color = clHighlight;
        to_color = clWhite;
      }
      sel_data->_rect.Bottom = Y;
    }
    else if (Y < sel_data->_start_y)
    {
      if (Y < sel_data->_last_y)
      {
        y1 = Y;
        y2 = sel_data->_last_y;
        from_color = clWhite;
        to_color = clHighlight;
      }
      else if (Y > sel_data->_last_y)
      {
        y1 = sel_data->_last_y;
        y2 = Y;
        from_color = clHighlight;
        to_color = clWhite;
      }
      sel_data->_rect.Top = Y;
    }
    int height = abs(y1 - y2);
    if (height > 0)
    {
      TRect srect = Rect(sel_data->_rect.Left, y1, sel_data->_rect.Right, y2);
      int width = srect.Width();
      TRect drect = Rect(sel_data->_rect.Left,0,sel_data->_rect.Right, height);
      Graphics::TBitmap* bm1 = new Graphics::TBitmap;
      bm1->Width = width;
      bm1->Height = height;
      Graphics::TBitmap* bm2 = new Graphics::TBitmap;
      bm2->Width = width;
      bm2->Height = height;

      bm1->Canvas->CopyRect(drect, vp->Canvas, srect);
      bm2->Canvas->Brush->Color = to_color;
      bm2->Canvas->BrushCopy(drect, bm1, drect, from_color);

      BitBlt(vp->Canvas->Handle, srect.Left, srect.Top, width, height, bm2->Canvas->Handle, 0, 0, SRCCOPY);  
      vp->Refresh();
      delete bm1;
      delete bm2;
    } 
    sel_data->_last_y = Y;
  }
}

如何更改 canvas 区域的颜色

How to change a color in an area of a canvas

delphi

graphics

vcl

canvas

c++builder