C++ win32项目双缓冲
我有一个 win32 应用程序，我想通过拖动鼠标来画一条线。我也使用双缓冲，但问题是它在鼠标路径中绘制多条线。这是我的绘图代码：
hdc = BeginPaint(hWnd, &ps);
hdcBack = CreateCompatibleDC(hdc);
GetClientRect(hWnd, &windowRect);
backBuffer = CreateCompatibleBitmap(hdc, windowRect.right, windowRect.bottom);
SelectObject(hdcBack, backBuffer);
FloodFill(hdcBack, 0, 0, RGB(255, 255, 255));
BitBlt(hdcBack,0,0,windowRect.right,windowRect.bottom,hdc,0,0,SRCCOPY);
color = RGB(rand() % 255, rand() % 255, rand() % 255);
hBrush = CreateSolidBrush(color);
SelectObject (hdcBack, hBrush);
MoveToEx(hdcBack,x1,y1,NULL); //x1,y1,x2,y2 are the initial click point and the current position of the mouse when keeping the left button down and dragging
LineTo(hdcBack,x2,y2);
BitBlt(hdc, 0, 0, windowRect.right, windowRect.bottom, hdcBack, 0, 0, SRCCOPY);
DeleteObject(hBrush);
DeleteDC(hdcBack);
DeleteObject(backBuffer);
EndPaint(hWnd, &ps);
我也尝试在绘制线条之前不将背景复制到缓冲区中，并且它会正确绘制线条，但是当我绘制新线条时，之前绘制的线条会消失。 那么如何使用双缓冲绘制多条线并保留之前绘制的线呢？
I have a win32 application and i want to draw a line by dragging the mouse. I use double buffering as well but the problem is it draws multiple lines in the path of the mouse. Here is my drawing code:
hdc = BeginPaint(hWnd, &ps);
hdcBack = CreateCompatibleDC(hdc);
GetClientRect(hWnd, &windowRect);
backBuffer = CreateCompatibleBitmap(hdc, windowRect.right, windowRect.bottom);
SelectObject(hdcBack, backBuffer);
FloodFill(hdcBack, 0, 0, RGB(255, 255, 255));
BitBlt(hdcBack,0,0,windowRect.right,windowRect.bottom,hdc,0,0,SRCCOPY);
color = RGB(rand() % 255, rand() % 255, rand() % 255);
hBrush = CreateSolidBrush(color);
SelectObject (hdcBack, hBrush);
MoveToEx(hdcBack,x1,y1,NULL); //x1,y1,x2,y2 are the initial click point and the current position of the mouse when keeping the left button down and dragging
LineTo(hdcBack,x2,y2);
BitBlt(hdc, 0, 0, windowRect.right, windowRect.bottom, hdcBack, 0, 0, SRCCOPY);
DeleteObject(hBrush);
DeleteDC(hdcBack);
DeleteObject(backBuffer);
EndPaint(hWnd, &ps);
I tried also not copying the background into the buffer before drawing the line and it draws the line correctly but when i draw a new line the previously drawn line disappears.
So how can i draw multiple lines with double buffering and keeping the previous drawn lines?
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如果我正确理解了需求，那么问题是设计中固有的。
第一个
BitBlt()将先前内容复制到缓冲区，然后绘制线条，然后将更改应用到屏幕，这会给出您想要的确切结果描述的。这样，您只是添加图形而不是替换图形，并且您会看到多行而不是一行。如果你想显示一条被鼠标拖动的线，你需要首先用你想要的任何背景填充后台缓冲区（称之为常量数据），然后在上面绘画每次鼠标移动时相关图形（称之为变化数据）。不管怎样，我相信评论第一个
BitBlt()应该可以解决问题。另外，您在调用使用笔的线条函数之前要选择画笔。该调用不应该在调用
FloodFill()之前进行吗？编辑：
按照我对您的评论中的建议，使用第三个缓冲区来保存最新数据。在“鼠标松开”处理程序中，最后在该缓冲区上绘制新线。
因此，当用户最终确定如何在鼠标移动处理程序和绘制处理程序中从该缓冲区中读取，并在鼠标释放处理程序中写入他想要画出自己的底线。
The problem's inherent in the design, if I understand the requirement correctly.
The first
BitBlt()copies the previous contents on to the buffer, then you draw the line, and then you apply the changes to the screen, which gives the exact results you described. This way you're only adding graphics rather than replacing, and you see several lines instead of one.If you want to display a line that's being dragged by the mouse, you need to first fill the back-buffer with whatever background you had in mind (call it the constant-data), and paint on it the relevant graphics (call it changing-data) every mouse move. Anyway, I believe that commenting that first
BitBlt()should do the trick.Also, you're selecting a brush before calling the line functions, which use a pen. Shouldn't that call come before calling
FloodFill()?EDIT:
Use a third buffer to hold the most recent data as suggested in my comment to yours. In your "mouse-up" handler, finally draw the new line on that buffer.
So you read from that buffer in your mouse-move handler and on-paint handler, and write to it in the mouse-up handler, when the user is finally sure how he wants his line drawn.
不使用后台缓冲区进行设计的一种方法是保留每次绘制的线条的动态列表。
您的消息过程可能如下所示：
在每次重绘时，您只需迭代列表并绘制每条线。
One way to design this without using a backbuffer is to keep a dynamic list of lines that you draw each time.
Your message proc could look something like this:
On each redraw you simply iterate through the list and draw each line.