Array-like access to Spline

This patch was proposed by the Ingo in post posted on news.povray.org. The main idea is to allow asking about dimension_size of spline as well as for time parameter and vector result at control points. So the syntax with below patch can be now:

SPLINE_USAGE:
  SPLINE_EVALUATION | SPLINE_MEASUREMENT | SPLINE_ENTRY

SPLINE_EVALUATION:
  #declare Spline_Value = MySpline(Val);
  #declare Spline_Value = MySpline(Val, SPLINE_TYPE);

SPLINE_MEASUREMENT:
  #declare Number_Of_Entries = dimension_size( MySpline );

SPLINE_ENTRY:
  #declare Float_Time_Parameter = MySpline[ Counter ][ 0 ];
  #declare Vector_Value_Of_Entry = MySpline[ Counter ][ 1 ];

How it is implemented

All I need was to recognize some additional tokens and adjust number of terms returned in express.cpp file. First I turned on functionality of returning values for entries. There is function Parse_Spline_Call responsible for returning values when spline identifier is found in expression. There is only one expectation (LEFT_PAREN_TOKEN) in this function so I have to introduce whole expectation block. Validation for array subscript was copied from parsing 'real' array entry.

void Parse_Spline_Call(EXPRESS Express, int *Terms)
{
    SPLINE *spline = (SPLINE*)(Token.Data);
    DBL Val;
    int j,k;

    EXPECT
        CASE (LEFT_PAREN_TOKEN)
            Val=Parse_Float();
            Get_Token();

            if(Token.Token_Id == COMMA_TOKEN)
                {
                    /*If there is a second parameter, make a copy of the spline
                    with a new type and evaluate that.*/
                    spline = Copy_Spline(spline);
                    Get_Token();
                    switch(Token.Token_Id)
                    {
                        case LINEAR_SPLINE_TOKEN:
                            spline->Type = LINEAR_SPLINE;
                            break;
                        case QUADRATIC_SPLINE_TOKEN:
                            spline->Type = QUADRATIC_SPLINE;
                            break;
                        case CUBIC_SPLINE_TOKEN:
                            spline->Type = CATMULL_ROM_SPLINE;
                            break;
                        case NATURAL_SPLINE_TOKEN:
                            spline->Type = NATURAL_SPLINE;
                            break;
                        default:
                            Error("linear_spline, quadratic_spline, natural_spline, or cubic_spline expected.");
                            break;
                    }
                    GET(RIGHT_PAREN_TOKEN);
                    Get_Spline_Val(spline, Val, Express, Terms);
                    Destroy_Spline(spline);
                    spline = NULL;
                }
            else
                {
                    UNGET
                    GET(RIGHT_PAREN_TOKEN);
                    Get_Spline_Val(spline, Val, Express, Terms);
                }
            EXIT
        END_CASE
        CASE (LEFT_SQUARE_TOKEN)
            Val=Parse_Float();
            k=(int)(1.0e-08+Val);
            if ((k < 0) || (Val < -1.0e-08))
            {
                Error("Negative subscript");
            }
            if (k >= spline->Number_Of_Entries)
            {
                Error("Spline-Array subscript out of range");
            }
            GET(RIGHT_SQUARE_TOKEN);
            GET(LEFT_SQUARE_TOKEN);
            if ((int)Parse_Float())
            {
                *Terms = spline->Terms;
                for(j=0; j<spline->Terms; j++)
                {
                    Express[j]=spline->SplineEntries[k].vec[j];
                } 
            }
            else
            {
                *Terms = 1;
                Express[0]=spline->SplineEntries[k].par;
            }
            GET(RIGHT_SQUARE_TOKEN);
            EXIT
        END_CASE
        OTHERWISE
           Expectation_Error ("( or [");
        END_CASE
    END_EXPECT

}

The second part was asking about number of entries via dimension_size. This keyword is handled in Parse_Num_Factor function so again I added some additional tokens recognition:

void Parse_Num_Factor (EXPRESS Express,int *Terms)
{
  int i = 0;
  DBL Val,Val2;
  VECTOR Vect,Vect2,Vect3;
  OBJECT *Object;  
  TRANSFORM Trans;
  TURB Turb;
  UCS2 *Local_String, *Local_String2;
  char *Local_C_String;
  POV_ISTREAM *f;
  POV_ARRAY *a;
  int Old_Ok=Ok_To_Declare;
  DBL greater_val, less_val, equal_val ;
  SPLINE *spline;

  Ok_To_Declare=true;

  EXPECT
    CASE (FLOAT_FUNCT_TOKEN)
       /* All of these functions return a DBL result */
       switch(Token.Function_Id)
         {
          case ABS_TOKEN:
          :
          :
          :
          break;

          case DIMENSION_SIZE_TOKEN:
            GET(LEFT_PAREN_TOKEN)

            EXPECT
              CASE(ARRAY_ID_TOKEN)
                Parse_Comma();
                a = (POV_ARRAY *)(*(Token.DataPtr));
                i = (int)Parse_Float()-1.0;
                if ((i < 0) || (i > a->Dims))
                  Val = 0.0;
                else
                  Val = a->Sizes[i];
                EXIT
              END_CASE
              CASE(SPLINE_ID_TOKEN)
                spline = (SPLINE*)(Token.Data); 
                Val = spline->Number_Of_Entries;
                EXIT
              END_CASE
              OTHERWISE
                Expectation_Error ("spline or array");
              END_CASE
            END_EXPECT

            GET(RIGHT_PAREN_TOKEN)
            break;

         }
       :
       :
}

Notes

This patch was designed only for reading values. Returned vector should be adjusted with correct number of components according to components of spline.

Array-like access to Spline

Why it is introduced

How it is implemented

Notes

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