您好，我现在正在用 C++ 编写一个 win32 应用程序，我真的很难放大我的窗口内容。这是我开始使用的伪代码来完成缩放:

// point One
int XPointOne = -200;
int YPointTwo = 0;

// point Two
int XPointTwo = 200;
int YPointTwo = 0;

// Draw point function.
DrawPoint(XCoordinate * ScalingFactor, YCoordinate * ScalingFactor) {
    ....
}

我的坐标系设置为原点在窗口的中心。我想在使用鼠标滚轮时进行缩放。上述解决方案的问题是缩放总是从窗口的中心发生。当您的鼠标不在窗口中央时，这看起来有点难看。我想放大鼠标所在的区域，但找不到合适的算法来计算 x 和 y 方向的偏移量。例如，如果鼠标的坐标为 (-200, 0)，那么点一的坐标应为 (-200, 0)，点二的坐标应为 (600, 0)，比例因子为 2。我已经尝试了很多东西，但没有让它起作用，尤其是当鼠标在缩放之间移动到其他位置时，一切都变得一团糟。任何人都知道如何解决这个问题？

这是我的应用程序的一些示例代码。第一个片段是我处理 WM_MOUSEWHEEL 消息的回调函数。

VOID OnMouseWheel(WPARAM const& WParam, LPARAM const& LParam) {
    if(GET_WHEEL_DELTA_WPARAM(WParam) > 0)
    {
        // Zoom in
        Draw.ScaleFactor += 0.1;
    }
    else
    {
         // Zoom out
    }
}

Draw 只是一个包装 GDI 函数的类。它有一个比例因子成员。下面的代码片段是我的 Draw 对象的 DrawCircle 成员函数，它使用比例因子在屏幕上正确显示圆。

VOID DrawCircle(DOUBLE const& XCoordinate, DOUBLE const& YCoordinate, DOUBLE const& Radius, COLORREF const& Color) {
    HBRUSH Brush = CreateSolidBrush(Color);
    HBRUSH OldBrush = (HBRUSH)SelectObject(this->MemoryDC, Brush);

    Ellipse(this->MemoryDC, (INT) ((XCoordinate - Radius) * this->ScaleFactor), 
        -(INT)((YCoordinate + Radius) * this->ScaleFactor), 
         (INT)((XCoordinate + Radius) * this->ScaleFactor), 
        -(INT)((YCoordinate - Radius) * this->ScaleFactor)); 
    SelectObject(this->MemoryDC, OldBrush);
    DeleteObject(Brush);
 }

如您所见，我的 DrawCircle 函数在应用当前比例因子时没有考虑鼠标位置。

编辑

好的，我更接近解决方案了，这里是我的鼠标回调函数的更新版本。

VOID OnMouseWheel(WPARAM const& WParam, LPARAM const& LParam) {
    // Get Mouse position in real coordinates and not window coordinates.
    INT XOffset = (Window.GetClientWidth() / -2) + XMousePos;
    INT YOffset = (Window.GetClientHeight() / 2) - YMousePos;


    if(GET_WHEEL_DELTA_WPARAM(WParam) > 0)
    {
        Draw.ScaleFactor += 0.1;
        Draw.XOffsetScale = -XOffset * (Draw.ScaleFactor - 1.0);
        Draw.YOffsetScale = YOffset * (Draw.ScaleFactor - 1.0);
    }
    else
    {
        // ...
    }
}

这里是画圆的函数。

VOID DrawCircle(DOUBLE const& XCoordinate, DOUBLE const& YCoordinate, DOUBLE const& Radius, COLORREF const& Color) {
        HBRUSH Brush = CreateSolidBrush(Color);
        HBRUSH OldBrush = (HBRUSH)SelectObject(this->MemoryDC, Brush);

        Ellipse(this->MemoryDC, (INT) ((XCoordinate - Radius) * this->ScaleFactor + XOffsetScale) , 
            -(INT)((YCoordinate + Radius) * this->ScaleFactor - YOffsetScale), 
            (INT)((XCoordinate + Radius) * this->ScaleFactor + XOffsetScale), 
            -(INT)((YCoordinate - Radius) * this->ScaleFactor - YOffsetScale)); 
        SelectObject(this->MemoryDC, OldBrush);
        DeleteObject(Brush);
 }

只要我将鼠标保持在同一位置，它就可以工作，但是当我移动到另一个位置时，它不会按预期缩放一次，之后它会再次正确缩放。也许这有点帮助。

提前致谢!

已解决

好的， 我现在解决了我的问题。我只是根据鼠标位置乘以比例因子移动坐标系的原点。感谢您的回答。

最佳答案

最“通用”的解决方案使用矩阵变换，但这里有一个简化的解释。以下伪代码可能对您有所帮助:

/*
    VARIABLES (all in space coordinates, not pixel coordinates):

      input:
        viewRect = rectangle of the viewed area
        zoomFactor = factor of zoom relative to viewRect, ex 1.1
        mousePos = position of the mouse

      output:
        zoomedRect = viexRect after zoom
*/

/*
    A little schema:

      viewRect
    *-----------------------------------------------------------------------*
    |                       ^                                               |
    |                       | d_up                                          |
    |        zoomedRect     v                                               |
    |      *-----------------------------------------*                      |
    |d_left|                                         |       d_right        |
    |<---->|                mousePos                 |<-------------------->|
    |      |                    +                    |                      |
    |      |                                         |                      |
    |      |                                         |                      |
    |      *-----------------------------------------*                      |
    |                       ^                                               |
    |                       |                                               |
    |                       |                                               |
    |                       | d_down                                        |
    |                       |                                               |
    |                       v                                               |
    *-----------------------------------------------------------------------*

    dX = d_left + d_right
    dY = d_up + d_down
    The origin of rects is the upper left corner.
*/

/*
    First, find differences of size between zoomed rect and original rect
    Here, 1 / zoomFactor is used, because computations are made relative to the
    original view area, not the final rect):
*/
dX = viewRect.width * (1 - 1 / zoomFactor)
dY = viewRect.height * (1 - 1 / zoomFactor)

/*
    Second, find d_* using the position of the mouse.
    pX = position of the mouse along X axis, relative to viewRect (percentage)
    pY = position of the mouse along Y axis, relative to viewRect (percentage)
    The value of d_right and d_down is not computed because is not directly needed
    in the final result.
*/
pX = (mousePos.X - viewRect.X) / viewRect.width
pY = (mousePos.Y - viewRect.Y) / viewRect.height

d_left = pX * dX
d_up = pY * dY

/*
    Third and last, compute the output rect
*/
zoomedRect = viewRect
zoomedRect.X += d_left
zoomedRect.Y += d_up
zoomedRect.width -= dX
zoomedRect.height -= dY

// That's it!

对于您的问题，您需要将 View (您的窗口)与场景(绘制的对象)分开。您应该有一个绘制部分(或全部)场景的函数:

void drawScene(Rect viewArea);

和一个缩放区域的函数(使用之前介绍的算法):

Rect zoomArea(Rect rectToZoom, Point zoomCenter, double factor);

现在，您的回调要简单得多:

VOID OnMouseWheel(WPARAM const& WParam, LPARAM const& LParam)
{
    // Get the position of the mouse relative to the window (in percent)
    double XMouseRel = XMousePos / double(Window.GetClientWidth());
    double YMouseRel = YMousePos / double(Window.GetClientHeight());

    // Get Mouse position in scene coordinates and not window coordinates.
    // viewArea is in scene coordinates
    // window = your window or your draw information on the scene
    // The following assumes that you're using a scene with X left-to-right and
    // Y top-to-bottom.
    double XMouse = window.viewArea.width * XMouseRel + window.viewArea.upperleft.X;
    double YMouse = window.viewArea.height * YMouseRel + window.viewArea.upperleft.Y;

    // Zoom parameters
    double zFactor = 0.1 * GET_WHEEL_DELTA_WPARAM(WParam);
    Rect viewArea = getViewArea(); // or something like this
    Point zCenter(XMouse,YMouse);

    // Zoom
    Rect zoomedRect = zoomArea(viewArea,zCenter,zFactor);
    drawScene(zoomedRect);
}

关于c++ - 根据鼠标位置放大窗口，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/13316481/