Add optional helix pitch constraint.

src/group.cpp

@@ -813,6 +813,12 @@ void Group::GenerateEquations(IdList<Equation,hEquation> *l) {
         AddEq(l, (EC(axis.z))->Minus(EP(6)), 5);
 #undef EC
 #undef EP
+        if(type == Type::HELIX) {
+            if(valB != 0.0) {
+                AddEq(l, Expr::From(h.param(7))->Times(Expr::From(PI))->
+                Minus(Expr::From(h.param(3))->Times(Expr::From(valB))), 6);
+            }
+        }
     } else if(type == Type::EXTRUDE) {
         if(predef.entityB != Entity::FREE_IN_3D) {
             // The extrusion path is locked along a line, normal to the

src/textscreens.cpp

@@ -299,6 +299,23 @@ void TextWindow::ScreenChangeGroupScale(int link, uint32_t v) {
     SS.TW.edit.meaning = Edit::GROUP_SCALE;
     SS.TW.edit.group.v = v;
 }
+void TextWindow::ScreenChangeHelixPitch(int link, uint32_t v) {
+    Group *g = SK.GetGroup(SS.TW.shown.group);
+    double pitch = g->valB/SS.MmPerUnit();
+    SS.TW.ShowEditControl(3, ssprintf("%.8f", pitch));
+    SS.TW.edit.meaning = Edit::HELIX_PITCH;
+    SS.TW.edit.group.v = v;
+}
+void TextWindow::ScreenChangePitchOption(int link, uint32_t v) {
+    Group *g = SK.GetGroup(SS.TW.shown.group);
+    if(g->valB == 0.0) {
+        g->valB = SK.GetParam(g->h.param(7))->val * PI /
+              (SK.GetParam(g->h.param(3))->val);
+    } else {
+        g->valB = 0.0;
+    }
+    SS.GW.Invalidate();
+}
 void TextWindow::ScreenDeleteGroup(int link, uint32_t v) {
     SS.UndoRemember();
 
@@ -398,6 +415,26 @@ void TextWindow::ShowGroupInfo() {
     }
     Printf(false, "");
 
+    if(g->type == Group::Type::HELIX) {
+        Printf(false, "%Ft pitch - length per turn%E");
+
+        if (fabs(g->valB) != 0.0) {
+            Printf(false, "  %Ba %# %Fl%Ll%f%D[change]%E",
+            g->valB / SS.MmPerUnit(),
+            &TextWindow::ScreenChangeHelixPitch, g->h.v);
+        } else {
+            Printf(false, "  %Ba %# %E",
+              SK.GetParam(g->h.param(7))->val * PI /
+              ( (SK.GetParam(g->h.param(3))->val) * SS.MmPerUnit() ),
+              &TextWindow::ScreenChangeHelixPitch, g->h.v);
+        }
+        Printf(false, "   %Fd%f%LP%s  fixed",
+            &TextWindow::ScreenChangePitchOption,
+            g->valB != 0 ? CHECK_TRUE : CHECK_FALSE);
+
+        Printf(false, ""); // blank line    
+    }
+
     if(g->type == Group::Type::EXTRUDE || g->type == Group::Type::LATHE ||
        g->type == Group::Type::REVOLVE || g->type == Group::Type::LINKED ||
        g->type == Group::Type::HELIX) {
@@ -789,6 +826,15 @@ void TextWindow::EditControlDone(std::string s) {
             }
             break;
 
+        case Edit::HELIX_PITCH:  // stored in valB
+            if(Expr *e = Expr::From(s, /*popUpError=*/true)) {
+                double ev = e->Eval();
+                Group *g = SK.GetGroup(edit.group);
+                g->valB = ev * SS.MmPerUnit();
+                SS.MarkGroupDirty(g->h);
+            }
+            break;
+
         case Edit::GROUP_COLOR: {
             Vector rgb;
             if(sscanf(s.c_str(), "%lf, %lf, %lf", &rgb.x, &rgb.y, &rgb.z)==3) {

src/ui.h

@@ -342,7 +342,9 @@ public:
         VIEW_PROJ_RIGHT       = 702,
         VIEW_PROJ_UP          = 703,
         // For tangent arc
-        TANGENT_ARC_RADIUS    = 800
+        TANGENT_ARC_RADIUS    = 800,
+        // For helix pitch
+        HELIX_PITCH           = 802
     };
     struct {
         bool        showAgain;
@@ -473,6 +475,8 @@ public:
     static void ScreenChangeExprA(int link, uint32_t v);
     static void ScreenChangeGroupName(int link, uint32_t v);
     static void ScreenChangeGroupScale(int link, uint32_t v);
+    static void ScreenChangeHelixPitch(int link, uint32_t v);
+    static void ScreenChangePitchOption(int link, uint32_t v);
     static void ScreenChangeLightDirection(int link, uint32_t v);
     static void ScreenChangeLightIntensity(int link, uint32_t v);
     static void ScreenChangeLightAmbient(int link, uint32_t v);