Read the section titled Common Color Pitfalls, explains there that this is a
known problem not a bug. Suggests workarounds, one way being to enclose the
dot product in parentheses, like so:  #declare RedFloat=(Shade.red)

Bob

Philippe Debar <phi### [at] hotmailcom> wrote in message
news:380d7086@news.povray.org...
> Hi everybody!
>
>
> It has been quite a long time since I last posted here - or used POV
> for that matter. Probably a year. For my defence I must say I had no
> occasion to do so - no time, no computer and/or no phone line (hence no
> Internet access). I now have my computer back, some more time and a
> good connection at work (ISDN).
>
> I have been browsing news.povray silently for two weeks. It is really
> good to read all of you again.
>
>
> SO
>
> As I am back to using POV, I am back to having problems with it. Can
> anybody tell me what's wrong here?
>
> I got a problem with colour component extraction. It seems that when
> you use colour component extraction and use the result immediately,
> what you got is a float. But if there is an intermediate step
> (#declare, #local or pass as a macro argument), it reverts to a colour.
>
> In other word:
> floatFunction(aColor.red) is OK, but
> #declare myFloat=aColor.red is not a float but a colour
>
> I suspect this is a bug. But of course I could be wrong (would not be
> the first time). Could you please check? I browsed p.bugreports but
> could find nothing related.
>
> Here is an illustration of the problem, along with some tests to narrow
> it:
> (All the lines that cause an error before 'no object in scene' are
> commented.) (All 'should work' or 'should fail' are based on what I
> expect POV to do.)
> */
>
>
>
> #declare LightBrown=color rgb <1,.5,.3>; // declare a color
> #declare BlueComponent=LightBrown.blue;  // extract blue component
>                                          // this should be a float
> /* Quote from doc :
> You may use the dot operator to extract a single component from a
> color. Suppose the identifier Shade was previously defined as a color.
> Then Shade.red is the float value of the red component of Shade.
> Similarly Shade.green, Shade.blue, Shade.filter and Shade.transmit
> extract the float value of the other color components.
> */
>
>
>
>
> // The simplest illustration
>
> #declare Test1=abs(LightBrown.blue);    // this works
> // #declare Test2=abs(BlueComponent);      // this fails
>
>
>
>
> // With macros:
>
> // Direct return without assignment
> #macro Test3Macro(cColor)
>   cColor.blue
> #end
> #declare Test3=abs(Test3Macro(LightBrown)); // this works
>
>
> /*
> // Return with #local
> #macro Test4Macro(cColor)
>   #local Test4Return=cColor.blue;
>   Test4Return
> #end
> #declare Test4=abs(Test4Macro(LightBrown)); // this fails
> */
>
> /*
> // Color component as an argument
> #macro Test5Macro(fFloat)
>   abs(fFloat);
> #end
> #declare Test5=Test5Macro(LightBrown.blue); // this fails
> */
>
>
>
>
> // Q: What type is BlueComponent?
> // A: color!
>
> // #declare BlueComponent=LightBrown;      // this works and should not
> // #declare BlueComponent=pi;              // this fails but should work
>
> #declare BlueBlueComponent=BlueComponent.blue;         // this works OK
> // #declare BlueBlueComponent=pi;          // this fails but should work
>
>
>
>
> // Q: If BlueComponent is a color, is it rgbft<0,0,blue,0,0>?
> // A: It seems BlueComponent = color blue, giving
> //    rgbft <blue,blue,blue,blue,blue> with operator promotion.
> //   read the #debug stream
>
> #debug "\n\n BlueComponent=rgbft < "
> #debug str(BlueComponent.red,2,2)
> #debug ", "
> #debug str(BlueComponent.green,2,2)
> #debug ", "
> #debug str(BlueComponent.blue,2,2)
> #debug ", "
> #debug str(BlueComponent.filter,2,2)
> #debug ", "
> #debug str(BlueComponent.transmit,2,2)
> #debug " >\n\n"
>
>
>
> // Q: What about the other components?
> // A: Same problem.
>
> #declare RedComponent=LightBrown.red;
> // #declare Test9=abs(RedComponent);       // this fails but should work
>
> #declare GreenComponent=LightBrown.green;
> // #declare Test10=abs(GreenComponent);    // this fails but should work
>
> #declare FilterComponent=LightBrown.filter;
> // #declare Test11=abs(FilterComponent);   // this fails but should work
>
> #declare TransmitComponent=LightBrown.transmit;
> // #declare Test12=abs(TransmitComponent); // this fails but should work
>
>
>
>
> // Testing myself for sanity
>
> // #declare test13=pi.blue;         // this fails OK - as it should
> // #declare test14=abs(LightBrown); // this fails OK
> #declare test15=<1,2,3>.x;
> #declare test15=pi;                // this works OK
> #declare test16=<1,2,3>.red;
> #declare test16=pi;                // this works OK
>
> #declare test17=rgb <1,2,3>;
> #declare test17=test17.blue;       // this works and should not
> // #declare test17=pi;              // this fails OK
>
> #declare test18=color rgb <1,2,3>;
> #declare test18=test18.blue;       // this works and should not
> #declare test18=test18.x;          // this works and should not
> // #declare test18=pi;              // this fails OK
>
> // #declare test19=color <1>;         // this fails OK
> #declare test20=color 1;           // this works
>
> #declare test21=abs(LightBrown.blue);// this works OK
> #declare test21=pi;                  // this works OK
>
>

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