在特定位置缩放图像 - 居中

Question

所以我想向地图添加纹理，但问题是我不太明白为什么在使用不同的缩放尺寸进行缩放时它没有到达正确的位置。

我通常尝试将背景上的纹理位置设置为我的位置，使自己保持在框架的中心：例如，我的纹理大小是 1500x1600，我位于该图片中的 X140，Y590（是的，坐标是当我检查控制台时正确检索），放大一些值并缩放纹理并将其位置设置为我所在的位置。

代码如下：

if (!areTexturesInit) {
        InitiateTextures();
        areTexturesInit = true;
    }

    wxBitmap bit(imageTest);
    wxPaintDC dc(this);

    double zoomSize = 0.9; // here I'm applying the zooming proportions ( 0.1 - bigger size of the texture, 0.9 - more zoomed in )

    this->SetSize(wxSize(386, 386)); // size of the main frame

    backgroundSize.x = GetSize().x; // get the size of the main frame
    backgroundSize.y = GetSize().y;

    middlePoint.x = (backgroundSize.x / 2); // calculate the middle point of the frame
    middlePoint.y = (backgroundSize.y / 2);


    mapSizeX = 25600 / -zoomSize; // scale vs zoom size
    mapSizeY = 25600 / zoomSize;

    Vector3 myPosition;

    GetPlayerPosition(&myPosition); // gets my location

    float TextureCoordinateX = middlePoint.x + (myPosition.x / mapSizeX) * backgroundSize.x;
    float TextureCoordinateY = middlePoint.y - (myPosition.y / mapSizeY) * backgroundSize.y;
    
    dc.DrawBitmap(bit, TextureCoordinateX, TextureCoordinateY);

    Vector3 myPosOnMap = PositionToMapPosition(myPosition, myPosition); // calculates my position on the map vs mapSizeX and Y & rotates vector
    dc.SetPen(wxPen(wxColor(255, 0, 0), 4));
    dc.DrawRectangle(wxRect(myPosOnMap.x, myPosOnMap.y, 2, 2)); // draws me on the map with a red square

问题是我认为我在某个地方弄乱了缩放部分。

我附上了一些演示，以便您可以看到我在说什么：

“zoomSize”为 0.9：

“zoomSize”为 0.67 - 哪种有效，但我需要将其更改为不同的 ZoomSizes，存在问题：

Answer 1

平移和缩放 DC 非常复杂。它需要使用 3 个独立的坐标系，并且很容易意外地在错误的坐标系中工作。

这是我不久前写的一个示例，它展示了如何进行允许 dc 平移和缩放的计算。

听起来您对平移部分不感兴趣，因此您可以忽略所有允许用户设置自己的平移的内容。但是，仍然需要仅使用平移向量进行缩放，以便将缩放居中在正确的位置。

    // For compilers that support precompilation, includes "wx/wx.h".
#include "wx/wxprec.h"

#ifdef __BORLANDC__
    #pragma hdrstop
#endif

// for all others, include the necessary headers (this file is usually all you
// need because it includes almost all "standard" wxWidgets headers)
#ifndef WX_PRECOMP
    #include "wx/wx.h"
#endif

#include <wx/graphics.h>
#include <wx/dcbuffer.h>

class PanAndZoomCanvas:public wxWindow
{
    public:
        PanAndZoomCanvas(wxWindow *parent,
                         wxWindowID id = wxID_ANY,
                         const wxPoint &pos=wxDefaultPosition,
                         const wxSize &size=wxDefaultSize,
                         long style=0,
                         const wxString &name="PanAndZoomCanvas");
        wxRect2DDouble GetUntransformedRect() const;

    protected:
        void DoDrawCanvas(wxGraphicsContext*);

    private:
        void OnPaint(wxPaintEvent&);

        void OnMouseWheel(wxMouseEvent&);

        void OnLeftDown(wxMouseEvent&);
        void OnMotion(wxMouseEvent&);
        void OnLeftUp(wxMouseEvent&);
        void OnCaptureLost(wxMouseCaptureLostEvent&);

        void ProcessPan(const wxPoint&,bool);
        void FinishPan(bool);

        int m_zoomFactor;

        wxPoint2DDouble m_panVector;
        wxPoint2DDouble m_inProgressPanVector;
        wxPoint m_inProgressPanStartPoint;
        bool m_panInProgress;
};

PanAndZoomCanvas::PanAndZoomCanvas(wxWindow *parent, wxWindowID id,
                                   const wxPoint &pos, const wxSize &size,
                                   long style, const wxString &name)
                 :wxWindow(parent,  id, pos, size,  style, name)
{
    Bind(wxEVT_PAINT,&PanAndZoomCanvas::OnPaint,this);
    Bind(wxEVT_MOUSEWHEEL,&PanAndZoomCanvas::OnMouseWheel,this);
    Bind(wxEVT_LEFT_DOWN,&PanAndZoomCanvas::OnLeftDown,this);

    SetBackgroundStyle(wxBG_STYLE_PAINT);

    m_zoomFactor = 100;

    m_panVector = wxPoint2DDouble(0,0);
    m_inProgressPanStartPoint = wxPoint(0,0);
    m_inProgressPanVector = wxPoint2DDouble(0,0);
    m_panInProgress = false;
}

void PanAndZoomCanvas::DoDrawCanvas(wxGraphicsContext* gc)
{
    gc->SetPen(*wxBLACK_PEN);

    wxGraphicsPath path = gc->CreatePath();
    path.MoveToPoint(100,100);
    path.AddLineToPoint(300,100);
    path.AddLineToPoint(300,300);
    path.CloseSubpath();
    gc->StrokePath(path);
}

void PanAndZoomCanvas::OnPaint(wxPaintEvent& WXUNUSED(event))
{
    wxAutoBufferedPaintDC dc(this);
    dc.Clear();

    wxGraphicsContext* gc = wxGraphicsContext::Create(dc);

    if ( gc )
    {
        double a = m_zoomFactor / 100.0;
        wxPoint2DDouble totalPan = m_panVector + m_inProgressPanVector;

        gc->Translate(-totalPan.m_x, -totalPan.m_y);
        gc->Scale(a, a);

        DoDrawCanvas(gc);

        delete gc;
    }
}

void PanAndZoomCanvas::OnMouseWheel(wxMouseEvent& event)
{
    if ( m_panInProgress )
    {
        FinishPan(false);
    }

    int rot = event.GetWheelRotation();
    int delta = event.GetWheelDelta();

    int oldZoom = m_zoomFactor;
    m_zoomFactor += 10*(rot/delta);

    if ( m_zoomFactor<10 )
    {
        m_zoomFactor = 10;
    }

    if ( m_zoomFactor>800)
    {
        m_zoomFactor = 800;
    }

    double a = oldZoom / 100.0;
    double b = m_zoomFactor / 100.0;

    // Set the panVector so that the point below the cursor in the new
    // scaled/panned cooresponds to the same point that is currently below it.
    wxPoint2DDouble uvPoint = event.GetPosition();
    wxPoint2DDouble stPoint = uvPoint + m_panVector;
    wxPoint2DDouble xypoint  = stPoint/a;
    wxPoint2DDouble newSTPoint  = b * xypoint;
    m_panVector = newSTPoint - uvPoint;

    Refresh();
}

void PanAndZoomCanvas::ProcessPan(const wxPoint& pt, bool refresh)
{
    m_inProgressPanVector = m_inProgressPanStartPoint - pt;

    if ( refresh )
    {
        Refresh();
    }
}

void PanAndZoomCanvas::FinishPan(bool refresh)
{
    if ( m_panInProgress )
    {
        SetCursor(wxNullCursor);

        if ( HasCapture() )
        {
            ReleaseMouse();
        }

        Unbind(wxEVT_LEFT_UP, &PanAndZoomCanvas::OnLeftUp, this);
        Unbind(wxEVT_MOTION, &PanAndZoomCanvas::OnMotion, this);
        Unbind(wxEVT_MOUSE_CAPTURE_LOST, &PanAndZoomCanvas::OnCaptureLost, this);

        m_panVector += m_inProgressPanVector;
        m_inProgressPanVector = wxPoint2DDouble(0,0);
        m_panInProgress = false;

        if ( refresh )
        {
            Refresh();
        }
    }
}

wxRect2DDouble PanAndZoomCanvas::GetUntransformedRect() const
{
    double a = m_zoomFactor / 100.0;

    wxSize sz = GetSize();
    wxPoint2DDouble zero  = m_panVector/a;

    return wxRect2DDouble(zero.m_x, zero.m_y, sz.GetWidth()/a, sz.GetHeight()/a);
}

void PanAndZoomCanvas::OnLeftDown(wxMouseEvent& event)
{
    wxCursor cursor(wxCURSOR_HAND);
    SetCursor(cursor);

    m_inProgressPanStartPoint = event.GetPosition();
    m_inProgressPanVector = wxPoint2DDouble(0,0);
    m_panInProgress = true;

    Bind(wxEVT_LEFT_UP, &PanAndZoomCanvas::OnLeftUp, this);
    Bind(wxEVT_MOTION, &PanAndZoomCanvas::OnMotion, this);
    Bind(wxEVT_MOUSE_CAPTURE_LOST, &PanAndZoomCanvas::OnCaptureLost, this);

    CaptureMouse();
}

void PanAndZoomCanvas::OnMotion(wxMouseEvent& event)
{
    ProcessPan(event.GetPosition(), true);
}

void PanAndZoomCanvas::OnLeftUp(wxMouseEvent& event)
{
    ProcessPan(event.GetPosition(), false);
    FinishPan(true);
}

void PanAndZoomCanvas::OnCaptureLost(wxMouseCaptureLostEvent&)
{
    FinishPan(true);
}

class MyFrame : public wxFrame
{
    public:
        MyFrame(wxWindow* parent, int id = wxID_ANY, wxString title = "Demo",
                wxPoint pos = wxDefaultPosition, wxSize size = wxDefaultSize,
                int style = wxDEFAULT_FRAME_STYLE );
};

MyFrame::MyFrame( wxWindow* parent, int id, wxString title, wxPoint pos
                 , wxSize size, int style )
        :wxFrame( parent, id, title, pos, size, style )
{
    PanAndZoomCanvas* canvas = new PanAndZoomCanvas(this);
}

class myApp : public wxApp
{
    public:
        virtual bool OnInit()
        {
            MyFrame* frame = new MyFrame(NULL);
            frame->Show();
            return true;
        }
};

wxIMPLEMENT_APP(myApp);

在 Windows 上，这看起来像这样：