I am implementing dragging 3D object by mouse in my engine.

I have the following formulas:

1. I get length of the vector from camera to object

2. Calculate angles like FOV/width (for X axis) * mouseDelta.X

3. Find triangle side length like var x = Math.Tan(angleX)*distance;

4. multiply X *= frame time;

So, I receive the length in the 3D world space on which I must move the model.

Then I multiply my camera relative X and Y axis on those final values (X and Y) and add to the current position.

And it seems working for fps 300.

But when I set 60 fps, my gametime increases and object become moving much faster.

My goal is to make my dragging algorithm fps independent and move all objects with constant speed.

Does anyone know how to reach that?

Maybe the frametime is incorrect, Can you post your original code, and also tell us what frametime values you get from the debugger at both high and normal FPS?

My frame time is correct. I am sure. for 220 fps its - 0.004, for 60 fps - 0.016. Si, its logic that multiply the same value on different frametime will give me different results and in the second case result will be bigger.

Here is my calculations:

//Distance - distance to object (length of the vector (offset - absolute position))
               var distance = SelectedEntity.GetDistanceToCamera(cameraController.UserControlledCamera.Offset).Length();
               //angle of the triangle = (FOVx / width of the screen) * mouse offset for X axis
               var angleX = (cameraController.UserControlledCamera.Fov/cameraController.UserControlledCamera.Width)*
                           (totalDelta.X* (float)GameTime.FrameTime);
               //angle of the triangle = (FOVy / width of the screen) * mouse offset for Y axis
               var angleY = (cameraController.UserControlledCamera.Fov / cameraController.UserControlledCamera.Height) *
                           (totalDelta.Y * (float)GameTime.FrameTime);
               //find shift for X axis
               var x = Math.Tan(angleX)*distance;
               //find shift for Y axis
               var y = Math.Tan(angleY)*distance;
               
               SelectedEntity.MoveRelX(right, (decimal)x  );
               SelectedEntity.MoveRelY(up, (decimal)-y);

My question is how to keep object exactly under the cursor? Because In my case they have big shift.

Maybe my calculations incorrect?

But result of intersection is in the screen coordinates. How I will translate them to my 3d world coordinates?

Ok, seems I implement this, but I see a serious issue regarding intersection point.

I dont know why, but in some places (mostly near the edges of directX window) plane intersection check gives floating results for the same coordinates.

And this causing objects jump from one position to another.

Maybe My implementation is not correct. Could you just take a look on it?

var ray2 = CalculateRay(MouseManager.RelativeCoordinates, cameraController.UserControlledCamera,
                   SelectedEntity.GetActualMatrix());
               Plane p = new Plane(cameraController.UserControlledCamera.ViewMatrix.Backward, Vector3.UnitZ);
               Vector3 position;
               var res = ray2.Intersects(ref p, out position);
               RenderSystem.D2DText += "Distance to plane = " + SelectedEntity.GetRelativePosition() + "\n";
               RenderSystem.D2DText += "Intersection with plane = " +res+"\n";
               RenderSystem.D2DText += "Point = " + position + "\n";
               if (res)
               {
                  startPoint.X += (decimal)position.X;
                  startPoint.Y += (decimal)position.Y;
                  SelectedEntity.SetPosition(startPoint);

               }

I not set plane to the distance to the object bacuse in that case object not synced with the mouse cursor. And jump are much more bigger at that case.

When plane at the same distance as the object, it also give me diferent (in most cases opposite) results from frame to frame. For ex, X = 4000 and at the next frame it will be -4000. This leads to visual effect when seems that object is in 2 different places at the same time.

I suspect that I do something wrong with plane.