C++ 使用中心点和比例因子变换垂直？

我的应用程序是一个矢量绘图应用程序。它与OpenGL一起工作。我将修改它，改为使用cairo2d图形库。问题在于缩放。使用openGL摄像头和比例因子，类似这样的工作：

 float scalediv = Current_Scene().camera.ScaleFactor / 2.0f;
 float cameraX = GetCameraX();
 float cameraY = GetCameraY();
 glMatrixMode(GL_PROJECTION);
 glLoadIdentity();

 float left = cameraX - ((float)controls.MainGlFrame.Dimensions.x) * scalediv;
 float right = cameraX + ((float)controls.MainGlFrame.Dimensions.x) * scalediv;
 float bottom = cameraY - ((float)controls.MainGlFrame.Dimensions.y) * scalediv;
 float top = cameraY + ((float)controls.MainGlFrame.Dimensions.y) * scalediv;

 glOrtho(left,
  right,
  bottom, 
  top,
  -0.01f,0.01f);

 // Set the model matrix as the current matrix
 glMatrixMode(GL_MODELVIEW);
 glLoadIdentity();

 hdc = BeginPaint(controls.MainGlContext.mhWnd,&ps);

 POINT _mouse = controls.MainGlFrame.GetMousePos();
vector2f mouse = functions.ScreenToWorld(_mouse.x,_mouse.y,GetCameraX(),GetCameraY(),
             Current_Scene().camera.ScaleFactor,
            controls.MainGlFrame.Dimensions.x,
            controls.MainGlFrame.Dimensions.y );

vector2f CGlEngineFunctions::ScreenToWorld(int x, int y, float camx, float camy, float scale, int width, int height)
{
 // Move the given point to the origin, multiply by the zoom factor and
 // add the model coordinates of the center point (camera position)
 vector2f p;


 p.x =  (float)(x - width / 2.0f) * scale +
  camx;

 p.y = -(float)(y - height / 2.0f) * scale +
  camy;

 return p;
}

鼠标位置如下所示：

 float scalediv = Current_Scene().camera.ScaleFactor / 2.0f;
 float cameraX = GetCameraX();
 float cameraY = GetCameraY();
 glMatrixMode(GL_PROJECTION);
 glLoadIdentity();

 float left = cameraX - ((float)controls.MainGlFrame.Dimensions.x) * scalediv;
 float right = cameraX + ((float)controls.MainGlFrame.Dimensions.x) * scalediv;
 float bottom = cameraY - ((float)controls.MainGlFrame.Dimensions.y) * scalediv;
 float top = cameraY + ((float)controls.MainGlFrame.Dimensions.y) * scalediv;

 glOrtho(left,
  right,
  bottom, 
  top,
  -0.01f,0.01f);

 // Set the model matrix as the current matrix
 glMatrixMode(GL_MODELVIEW);
 glLoadIdentity();

 hdc = BeginPaint(controls.MainGlContext.mhWnd,&ps);

 POINT _mouse = controls.MainGlFrame.GetMousePos();
vector2f mouse = functions.ScreenToWorld(_mouse.x,_mouse.y,GetCameraX(),GetCameraY(),
             Current_Scene().camera.ScaleFactor,
            controls.MainGlFrame.Dimensions.x,
            controls.MainGlFrame.Dimensions.y );

vector2f CGlEngineFunctions::ScreenToWorld(int x, int y, float camx, float camy, float scale, int width, int height)
{
 // Move the given point to the origin, multiply by the zoom factor and
 // add the model coordinates of the center point (camera position)
 vector2f p;


 p.x =  (float)(x - width / 2.0f) * scale +
  camx;

 p.y = -(float)(y - height / 2.0f) * scale +
  camy;

 return p;
}

从那里我画出了三角形的VBO。这使我可以平移和放大。鉴于Cairo只能基于坐标绘制，如何使顶点在不使用变换的情况下正确缩放和平移。基本上，GlOrtho通常会设置视口，但我不认为我可以用Cairo实现这一点

GlOrtho可以更改视口矩阵而不是修改垂直，但是我如何修改垂直以获得相同的结果呢

谢谢

---

*给定从ScreenToWorld获得的顶点p，我如何修改它，以便根据摄影机和比例因子对其进行缩放和平移？因为通常OpenGL基本上可以做到这一点

我认为Cairo可以做你想做的事情。。。看见这能解决你的问题吗？如果不能，为什么

基本上，我怎样才能让转换矩阵的行为和我在GL中所做的一样，告诉它最左上、最右和最底的坐标>好吧，你可以使用glgetfloatv来得到两个矩阵，乘以它们，给Cairo一个3x3的左上部分，并使用剩余最右边的列进行翻译（可能是cairoapi中的另一个函数？）