DynamicModule with constant image size

Question

I am new to this forum - I wonder if someone can help me improve this code.

1. I would like the angle $\theta$ to start in the middle of the slider i.e. $\theta = 0$ instead of starting at $\theta = -90$.

2. How do I keep the circle size constant as I slide the $\theta$?

Mohr[σxx_, σyy_, τxy_] := 
 DynamicModule[{g1, g2, g3}, OC = 1/2*(σxx + σyy); 
  R = Sqrt[((σxx - σyy)/2)^2 + τxy^2] ; 
  g1 = {Thickness[0.01], Circle[{OC, 0}, R]}; σxx1 := 
   1/2*(σxx + σyy) + 1/2*(σxx - σyy)*Cos[2*θ*Degree] + τxy*
     Sin[2*\[Theta]*Degree]; 
  σyy1 := 1/2*(σxx + σyy) + 1/2*(σyy - σxx)*Cos[2*θ*Degree] - τxy*Sin[2*θ*Degree];
  τxy1 := 1/2*(σyy - σxx)*Sin[2*θ*Degree] + τxy*Cos[2*θ*Degree];
  τxy1a := 1/2*(σyy - σxx)*Sin[(2*θ*Degree + π)] + τxy*Cos[(2*θ*Degree + π)]; 
  pts = {{σxx1, -τxy1}, {σyy1, -τxy1a}};
  g2 = {PointSize[0.05], Red, Point[pts] , 
    Inset[Row[{"\!\(\*SubscriptBox[\(σ\), \(xx\)]\) = ", NumberForm[σxx1, {6, 2}], ";", 
       "  \!\(\*SubscriptBox[\(τ\), \(xy\)]\) = ", NumberForm[-τxy1, {6, 2}]}], 
     Dynamic[{pts[[1, 1]], pts[[1, 2]]}]],
    Inset[
     Row[{"\!\(\*SubscriptBox[\(σ\), \(yy\)]\) = ", NumberForm[σyy1, {6, 2}], ";", 
     "  \!\(\*SubscriptBox[\(τ\), \(xy\)]\) = ", NumberForm[-τxy1a, {6, 2}]}], 
     Dynamic[{pts[[2, 1]], pts[[2, 2]]}]]
    }  ;
  g3 = {Thickness[0.01], Blue, Line[pts]};
  {Column[{Graphics[{g1, Dynamic[g2], Dynamic[g3], 
       Inset[Text[Style["Mohr's circle", 18, Purple, Italic]], {49.58, 68.99}]},
         ImageSize -> 300 ], 
     Row[{"θ = " Slider[Dynamic[θ], {-90, 90}], Dynamic@θ " degree"}]}]}]

Mohr[100, 0, 25]

Edit

barebones version

Mohr[x_, R_] :=
 DynamicModule[{g1, g2},
  g1 = Circle[{x, 0}, R];
  pts = Dynamic @{{R Cos@t + x, R Sin@t}, {R Cos[t + Pi] + x, R Sin[t + Pi]}};
  g2 = {PointSize[0.05], Red, Point[Dynamic@pts], 
        Inset["A very long text", Dynamic@(pts[[1, 1]])]};
  {Column[{Graphics[{g1, Dynamic[g2]}, Axes -> True], 
     Row[{"t = " Slider[Dynamic[t], {-Pi/2, Pi/2}], Dynamic@t }]}]}]

Mohr[100, 25]

Answer 1

Adding ImagePadding and ImageSize options and a few changes in the barebones version of your code:

Mohr2[x_, R_] := DynamicModule[{g1, g2, pts}, g1 = Circle[{x, 0}, R];
t = 0; 
pts = Dynamic@{{R Cos@t + x, R Sin@t}, {R Cos[t + Pi] + x, R Sin[t + Pi]}};
g2 = {PointSize[0.05], Red, Point[Dynamic@pts], Line[Dynamic@pts], 
Inset["A very long text", Dynamic@(pts[[1, 1]])]};
Column[{Graphics[{g1, Dynamic@g2}, Axes -> True, ImagePadding -> 30,
  ImageMargins -> 0, ImageSize -> 300], 
Row[{"t = " Slider[Dynamic[t], {-Pi, Pi}], Dynamic@t}]}, 
Alignment -> Center]]

 Mohr2[200, 15]

gives