Q140848: How to Convert Object Color Values to RGB Equivalents
Article: Q140848
Product(s): Microsoft FoxPro
Version(s): WINDOWS:3.0
Operating System(s):
Keyword(s): kbcode
Last Modified: 11-DEC-1999
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The information in this article applies to:
- Microsoft Visual FoxPro for Windows, version 3.0
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SUMMARY
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This article lists a function (Dec2RGB) that you can use to determine which
color values have been chosen in an application that allows custom color
settings.
MORE INFORMATION
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When colors are assigned through the Property Sheet, they are displayed in the
sheet as individual red, green, and blue (RGB) values -- separated by commas.
However, the actual value assigned to the object internally is the decimal
equivalent of a hexadecimal number that has the individual red, green, and blue
values encoded positionally.
Evaluating a color property does not display the RGB values; instead it displays
the decimal number. An example of this number can be seen by typing the
following statement in the Command window:
? _SCREEN.BACKCOLOR
Each color can be set within a range of 0 to 255, so it is difficult to determine
from a single decimal value the color the user chose. With the exception of
black (0), it is hard to distinguish all the potential colors ranging up to
white (16777215). The individual colors can be parsed to compare with other
color settings to avoid potential problems due to extremes in contrast, and
reset other colors in the interface to accommodate the custom settings.
The function in this article converts the number to hexadecimal, extracts the
individual RGB values, then converts the results for each value to decimal and
returns the result as a string in the expected RGB format.
The value that FoxPro assigns to an object's color property consists of a double
word in hexadecimal notation. The first byte of the first word is ignored. The
remaining three bytes indicate the individual red, green, and blue values in the
following format:
[XX][BB][GG][RR]
Note that the blue and red values are reversed when encoded, and must be
manipulated to be presented in the expected RGB format.
The first section of the function converts the decimal value to hexadecimal by
factoring the next highest exponent of 2 contained within the decimal value, and
so on until the remaining factor is 1.
Once converted, the resulting string is parsed and the first and third bytes are
swapped so that they are in Red-Green-Blue order.
The final section reverts the hexadecimal value of each pair back to a decimal
value between 0 and 255, representing the intensity of the color that it
indicates. The colors values are then concatenated and returned to the calling
program in the RGB format.
The code may be used as a method within a class or form, or as a function within
a .prg or procedure file.
Dec2RGB Function Code
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***********************************************************************
*
* Dec2RGB function: returns separate RGB values from object color value
*
* Usage:
* RGB = Dec2RGB(<Decimal Color>) && such as _SCREEN.BACKCOLOR
* ? RGB = "192, 192, 192" && color is light gray if true
*
* FUNCTION dec2rgb
LPARAMETERS tnDec
IF tnDec < 0
WAIT WINDOW 'Must be a positive value'
RETURN ""
ENDIF
lTalk=IIF(SET('TALK')='ON',.T.,.F.)
SET TALK OFF
* Determine the hexadecimal equivalent of the decimal parameter passed
lcHex = ""
lnFactor = 24 && set up factor value one exponent greater than
used
FOR lnPos = 6 TO 1 STEP -1
lnFactor = lnFactor - 4 && decrement factorial
lnExp = 2 ^ lnFactor && extrapolate next least power of two
FOR lnOrd = 15 TO 1 STEP -1
IF tnDec < lnExp && no value greater than current one,
lcHex = lcHex + "0" && so store a zero in this position
EXIT && go back for the next value
ENDIF
IF tnDec >= lnExp * lnOrd && is value greater than or equal to?
* find the matching hex value from its ordinal position
lcHex = lcHex + SUBSTR('123456789ABCDEF', lnOrd, 1)
EXIT
ENDIF
ENDFOR
tnDec = tnDec % lnExp && leave remainder of exponential division
ENDFOR
* reverse the order of the individual color indicators
lcHex = RIGHT(lcHex, 2) + SUBSTR(lcHex, 3, 2) + LEFT(lcHex, 2)
* convert the pairs into decimal values
lnPick = 2 && offset to determine which pair to convert
lcRGB = ["] && start of string delineator
* parse each color indicator and convert to decimal
FOR lnColor = 1 TO 3
lcHue = SUBSTR(lcHex, (lnPick * lnColor) - 1, 2) && pull out color
lnMSB = ASC(LEFT(lcHue, 1)) && "Most Significant Bit"
lnLSB = ASC(RIGHT(lcHue, 1)) && "Least Significant Bit"
* subtract appropriate value from each to get decimal equivalent
lnMSB = lnMSB - IIF(lnMSB > 57, 55, 48)
lnLSB = lnLSB - IIF(lnLSB > 57, 55, 48)
* then add decimals together
lcRGB = lcRGB + TRANSFORM( lnMSB * 16 + lnLSB, '999') + ", "
ENDFOR
lcRGB = LEFT(lcRGB, LEN(lcRGB) - 2) + ["] && replace last comma with quote
RETURN lcRGB
Additional query words: HLS HBS vfp hex VFoxWin
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Keywords : kbcode
Technology : kbVFPsearch kbAudDeveloper kbVFP300
Version : WINDOWS:3.0
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