Color Dialog

[bplus]

OK what did I forget?

Code: QB64: [Select]

1. OPTION _EXPLICIT
2. _TITLE "Color Dialog" 'started by B+ 2019-06-21
3.  
4. 'from :"Color CONST for _RGBA32(red, green, blue, alpha)" 'B+ 2019-05-19
5. '2019-05-26 update this for mouse inputs
6. '>>>>>>>>>>>> test your colors here
7. '>>>>>>>>>>>> then create and name Hex string CONSTs if you want to the Clipboard
8. 'sample clipping
9. CONST Purple = &HFFB400B4
10. ' 2019-06-21 start color dialog
11.  
12. SCREEN _NEWIMAGE(1200, 700, 32)
13. _SCREENMOVE 100, 20
14. DIM rc AS _UNSIGNED LONG, i
15. COLOR &HFF0000BB, &HFFAAAAAA
16. FOR i = 1 TO 150
17.     LINE (RND * 1200, RND * 700)-STEP(RND * 50, RND * 50), _RGB32(RND * 255, RND * 255, RND * 255), BF
18. NEXT
19. PRINT "in 4 secs Color Dialog comes up..."
20. _DISPLAY
21. _DELAY 4
22. colorDialog rc
23. PRINT "Color Dialog returned this:"; rc
24. IF rc <> 0 THEN LINE (100, 100)-STEP(1000, 500), rc, BF
25. PRINT: PRINT "End of Color Dialog test..."
26.  
27. SUB colorDialog (returnColor AS _UNSIGNED LONG)
28.  
29.     'first screen dimensions items to restore at exit
30.     DIM curRow AS INTEGER, curCol AS INTEGER, autoDisplay AS INTEGER
31.     DIM sw AS INTEGER, sh AS INTEGER, fg AS _UNSIGNED LONG, bg AS _UNSIGNED LONG
32.     DIM curScrn AS LONG, backScrn AS LONG 'some handles
33.  
34.     DIM cd AS LONG
35.     DIM r AS INTEGER, g AS INTEGER, b AS INTEGER, a AS INTEGER, mb AS INTEGER, mx AS INTEGER, my AS INTEGER
36.     DIM makeConst$, k$
37.  
38.     'save old settings to restore at end ofsub
39.     curRow = CSRLIN
40.     curCol = POS(0)
41.     autoDisplay = _AUTODISPLAY
42.     sw = _WIDTH
43.     sh = _HEIGHT
44.     fg = _DEFAULTCOLOR
45.     bg = _BACKGROUNDCOLOR
46.     _KEYCLEAR
47.     'screen snapshot
48.     curScrn = _DEST
49.     backScrn = _NEWIMAGE(sw, sh, 32)
50.     _PUTIMAGE , curScrn, backScrn
51.  
52.     cd = _NEWIMAGE(800, 600, 32)
53.     SCREEN cd
54.     r = 128: g = 128: b = 128: a = 128
55.     COLOR &HFFDDDDDD, 0
56.     DO
57.         CLS
58.         makeConst$ = "&H" + RIGHT$(STRING$(8, "0") + HEX$(_RGBA32(r, g, b, a)), 8)
59.         slider 16, 10, r, "Red"
60.         slider 16, 60, g, "Green"
61.         slider 16, 110, b, "Blue"
62.         slider 16, 160, a, "Alpha"
63.         _PRINTSTRING (150, 260), "Press enter or spacenbar, if you want to use the color: " + makeConst$
64.         _PRINTSTRING (210, 280), "Press escape or q, to not use any color, returns 0."
65.         LINE (90, 300)-(710, 590), , B
66.         LINE (100, 310)-(700, 580), VAL(makeConst$), BF
67.  
68.         WHILE _MOUSEINPUT: WEND
69.         mb = _MOUSEBUTTON(1)
70.         IF mb THEN 'clear it
71.             mx = _MOUSEX: my = _MOUSEY
72.             IF mx >= 16 AND mx <= 784 THEN
73.                 IF my >= 10 AND my <= 50 THEN
74.                     r = _ROUND((mx - 16) / 3)
75.                 ELSEIF my >= 60 AND my <= 100 THEN
76.                     g = _ROUND((mx - 16) / 3)
77.                 ELSEIF my >= 110 AND my <= 150 THEN
78.                     b = _ROUND((mx - 16) / 3)
79.                 ELSEIF my >= 160 AND my <= 200 THEN
80.                     a = _ROUND((mx - 16) / 3)
81.                 END IF
82.             END IF
83.         END IF
84.         k$ = INKEY$
85.         IF LEN(k$) THEN
86.             IF ASC(k$) = 27 OR k$ = "q" THEN returnColor = 0: EXIT DO
87.             IF ASC(k$) = 13 OR k$ = " " THEN returnColor = _RGBA32(r, g, b, a): EXIT DO
88.         END IF
89.         _DISPLAY
90.         _LIMIT 60
91.     LOOP
92.  
93.     'put things back
94.     SCREEN curScrn
95.     COLOR _RGB32(255, 255, 255), _RGB32(0, 0, 0): CLS
96.     _PUTIMAGE , backScrn
97.     _DISPLAY
98.     COLOR fg, bg
99.     _FREEIMAGE backScrn
100.     _FREEIMAGE cd
101.     IF autoDisplay THEN _AUTODISPLAY
102.     'clear key presses
103.     _KEYCLEAR
104.     'clear mouse clicks
105.     WHILE _MOUSEINPUT: WEND
106.     mb = _MOUSEBUTTON(1)
107.     IF mb THEN 'clear it
108.         WHILE mb 'OK!
109.             IF _MOUSEINPUT THEN mb = _MOUSEBUTTON(1)
110.             _LIMIT 10
111.         WEND
112.     END IF
113.     LOCATE curRow, curCol
114.  
115. END SUB
116.  
117. SUB slider (x, y, value, label$)
118.     DIM c~&, s$
119.     SELECT CASE label$
120.         CASE "Red": c~& = &HFFFF0000
121.         CASE "Green": c~& = &HFF008800
122.         CASE "Blue": c~& = &HFF0000FF
123.         CASE "Alpha": c~& = &H88FFFFFF
124.     END SELECT
125.     LINE (x, y)-STEP(768, 40), c~&, B
126.     LINE (x, y)-STEP(3 * value, 40), c~&, BF
127.     s$ = label$ + " = " + _TRIM$(STR$(value))
128.     _PRINTSTRING (x + 384 - 4 * LEN(s$), y + 12), s$
129. END SUB
130.  

[Petr]

Hi BPlus, do you remember that Alpha changes color depending on the background color? This means that the resulting color will always be of a different appearance but of the same value if you add a different screen clearing color than black to the CLS command on row 57?

This assumes that you apply the obtained value as a color number to different commands. Then there will be color mixing (for alpha < 255) depending on the background. The only way in which background color mixing does not occur is to insert colors into the image directly with the MEM command.

[Dimster]

What a handy little Color Mix Decoder for want of something more descriptive. I don't exactly follow what Petr is pointing out. I do see where, if I set the Alpha to zero there is no color whatever the RBG settings, and with Alpha at it's highest level, color mixes seem more vibrant. I normally work with adding color on a black background, is Petr saying the color mix this program provides ONLY works on a black background?

Thanks bplus - was handy hexidecimeter.

[Petr]

Here I solved it. Fellippe explained it to me. https://www.qb64.org/forum/index.php?topic=1325.0

[bplus]

Hi,

I think what Petr is concerned about is that if I lay a transparent color over another color and then take a POINT reading of that color value, the POINT will return Neither the transparent color value Nor the original color value that it overlaid. POINT will return some blend of those two numbers.

Petr's point gives me the idea to show a range of colors for background, so that one can see how the transparent or even the solid colors being tested compare to other colors side by side.

Correct me please if I am wrong.

[bplus]

Oh, also which would be better to return: the Hexidecimal$ which a FUNCTION can return or the _UNSIGNED LONG value that _RGBA() function gives us which, I think, we can't return with FUNCTIONs (hence my use of a SUB)?

[Petr]

I don't understand exactly your question. Both the SUB and the FUNCTION can return an unsigned long value. Just use ~& in function name, something as FUNCTION GETCOLOR~& to return these values, for SUB, follow these steps:

DIM c AS _UNSIGNED LONG
GetColor c~&
PRINT _ALPHA32(c~&), _RED32(c~&), _GREEN32(c~&), _BLUE32(c~&)


SUB GetColor (OutColor AS _UNSIGNED LONG)
    OutColor~& = &HFFFF0000
END SUB

Petr's point gives me the idea to show a range of colors for background, so that one can see how the transparent or even the solid colors being tested compare to other colors side by side.

I am curious to the way you want to do it. Perhaps it would be if the user set a background color where he apply a new color... but how do you do this in case, for example, a partially transparent rectangle will paint over many different colors?

[bplus]

Both the SUB and the FUNCTION can return an unsigned long value. Just use ~& in function name, something as FUNCTION GETCOLOR~& to return these values, for SUB, follow these steps:

Right, there was some reason I did not like or did not want ~& at the end of a function name...

Here is mod that returns the Hex$ and shows what the color looks like laid over a host of color!
To use the hex$ value just apply VAL(hex$):

Code: QB64: [Select]

1. OPTION _EXPLICIT
2. _TITLE "Color Dialog" 'started by B+ 2019-06-21
3.  
4. 'from :"Color CONST for _RGBA32(red, green, blue, alpha)" 'B+ 2019-05-19
5. '2019-05-26 update this for mouse inputs
6. '>>>>>>>>>>>> test your colors here
7. '>>>>>>>>>>>> then create and name Hex string CONSTs if you want to the Clipboard
8. 'sample clipping
9. CONST Purple = &HFFB400B4
10. ' 2019-06-21 start Color Dialog
11.  
12. SCREEN _NEWIMAGE(1200, 700, 32)
13. _SCREENMOVE 100, 20
14. DIM rc$, i
15. COLOR &HFF0000BB, &HFFAAAAAA
16. FOR i = 1 TO 150
17.     LINE (RND * 1200, RND * 700)-STEP(RND * 150, RND * 150), _RGBA32(RND * 256, RND * 256, RND * 256, RND * 256), BF
18. NEXT
19. PRINT "in 4 secs Color Dialog comes up..."
20. _DISPLAY
21. _DELAY 4
22. rc$ = colorDialog$
23. PRINT "Color Dialog returned this:"; rc$
24. IF rc$ <> "" THEN LINE (100, 100)-STEP(1000, 500), VAL(rc$), BF
25. PRINT: PRINT "End of Color Dialog test..."
26.  
27. FUNCTION colorDialog$
28.  
29.     'first screen dimensions items to restore at exit
30.     DIM curRow AS INTEGER, curCol AS INTEGER, autoDisplay AS INTEGER
31.     DIM sw AS INTEGER, sh AS INTEGER, fg AS _UNSIGNED LONG, bg AS _UNSIGNED LONG
32.     DIM curScrn AS LONG, backScrn AS LONG 'some handles
33.  
34.     DIM cd AS LONG
35.     DIM r AS INTEGER, g AS INTEGER, b AS INTEGER, a AS INTEGER, mb AS INTEGER, mx AS INTEGER, my AS INTEGER, i AS INTEGER
36.     DIM makeConst$, k$
37.     DIM f AS SINGLE
38.  
39.     'save old settings to restore at end ofsub
40.     curRow = CSRLIN
41.     curCol = POS(0)
42.     autoDisplay = _AUTODISPLAY
43.     sw = _WIDTH
44.     sh = _HEIGHT
45.     fg = _DEFAULTCOLOR
46.     bg = _BACKGROUNDCOLOR
47.     _KEYCLEAR
48.     'screen snapshot
49.     curScrn = _DEST
50.     backScrn = _NEWIMAGE(sw, sh, 32)
51.     _PUTIMAGE , curScrn, backScrn
52.  
53.     cd = _NEWIMAGE(800, 600, 32)
54.     SCREEN cd
55.     r = 128: g = 128: b = 128: a = 128
56.     COLOR &HFFDDDDDD, 0
57.     DO
58.         CLS
59.         makeConst$ = "&H" + RIGHT$(STRING$(8, "0") + HEX$(_RGBA32(r, g, b, a)), 8)
60.         slider 16, 10, r, "Red"
61.         slider 16, 60, g, "Green"
62.         slider 16, 110, b, "Blue"
63.         slider 16, 160, a, "Alpha"
64.         _PRINTSTRING (150, 260), "Press enter or spacenbar, if you want to use the color: " + makeConst$
65.         _PRINTSTRING (210, 280), "Press escape or q, to not use any color, returns 0."
66.         LINE (90, 300)-(710, 590), , B
67.         FOR i = 100 TO 700
68.             f = 255 * (i - 100) / 600
69.             LINE (i, 310)-STEP(0, 30), _RGB32(f, 0, 0)
70.             LINE (i, 340)-STEP(0, 30), _RGB32(0, f, 0)
71.             LINE (i, 370)-STEP(0, 30), _RGB32(0, 0, f)
72.             LINE (i, 400)-STEP(0, 30), _RGB32(f, f, 0)
73.             LINE (i, 430)-STEP(0, 30), _RGB32(0, f, f)
74.             LINE (i, 460)-STEP(0, 30), _RGB32(f, 0, f)
75.             LINE (i, 490)-STEP(0, 30), _RGB32(f, f, f)
76.             LINE (i, 520)-STEP(0, 30), _RGB32(0, 0, 0)
77.             LINE (i, 550)-STEP(0, 30), _RGB32(255, 255, 255)
78.         NEXT
79.         LINE (100, 310)-(700, 580), VAL(makeConst$), BF
80.         WHILE _MOUSEINPUT: WEND
81.         mb = _MOUSEBUTTON(1)
82.         IF mb THEN 'clear it
83.             mx = _MOUSEX: my = _MOUSEY
84.             IF mx >= 16 AND mx <= 781 THEN
85.                 IF my >= 10 AND my <= 50 THEN
86.                     r = INT((mx - 16) / 3)
87.                 ELSEIF my >= 60 AND my <= 100 THEN
88.                     g = INT((mx - 16) / 3)
89.                 ELSEIF my >= 110 AND my <= 150 THEN
90.                     b = INT((mx - 16) / 3)
91.                 ELSEIF my >= 160 AND my <= 200 THEN
92.                     a = INT((mx - 16) / 3)
93.                 END IF
94.             END IF
95.         END IF
96.         k$ = INKEY$
97.         IF LEN(k$) THEN
98.             IF ASC(k$) = 27 OR k$ = "q" THEN EXIT DO
99.             IF ASC(k$) = 13 OR k$ = " " THEN colorDialog$ = makeConst$: EXIT DO
100.         END IF
101.         _DISPLAY
102.         _LIMIT 60
103.     LOOP
104.  
105.     'put things back
106.     SCREEN curScrn
107.     COLOR _RGB32(255, 255, 255), _RGB32(0, 0, 0): CLS
108.     _PUTIMAGE , backScrn
109.     _DISPLAY
110.     COLOR fg, bg
111.     _FREEIMAGE backScrn
112.     _FREEIMAGE cd
113.     IF autoDisplay THEN _AUTODISPLAY
114.     'clear key presses
115.     _KEYCLEAR
116.     'clear mouse clicks
117.     WHILE _MOUSEINPUT: WEND
118.     mb = _MOUSEBUTTON(1)
119.     IF mb THEN 'clear it
120.         WHILE mb 'OK!
121.             IF _MOUSEINPUT THEN mb = _MOUSEBUTTON(1)
122.             _LIMIT 10
123.         WEND
124.     END IF
125.     LOCATE curRow, curCol
126.  
127. END FUNCTION
128.  
129. SUB slider (x, y, value, label$)
130.     DIM c~&, s$
131.     SELECT CASE label$
132.         CASE "Red": c~& = &HFFFF0000
133.         CASE "Green": c~& = &HFF008800
134.         CASE "Blue": c~& = &HFF0000FF
135.         CASE "Alpha": c~& = &H88FFFFFF
136.     END SELECT
137.     LINE (x, y)-STEP(765, 40), c~&, B
138.     LINE (x, y)-STEP(3 * value, 40), c~&, BF
139.     s$ = label$ + " = " + _TRIM$(STR$(value))
140.     _PRINTSTRING (x + 384 - 4 * LEN(s$), y + 12), s$
141. END SUB
142.  

 

Well the solid colors will just be one solid block... :)
Oh wait... got another idea :)

[bplus]

Side by side and overlay:

Code: QB64: [Select]

1. OPTION _EXPLICIT
2. _TITLE "Color Dialog" 'started by B+ 2019-06-21
3.  
4. 'from :"Color CONST for _RGBA32(red, green, blue, alpha)" 'B+ 2019-05-19
5. '2019-05-26 update this for mouse inputs
6. '>>>>>>>>>>>> test your colors here
7. '>>>>>>>>>>>> then create and name Hex string CONSTs if you want to the Clipboard
8. 'sample clipping
9. CONST Purple = &HFFB400B4
10. ' 2019-06-21 start Color Dialog
11.  
12. SCREEN _NEWIMAGE(1200, 700, 32)
13. _SCREENMOVE 100, 20
14. DIM rc$, i
15. COLOR &HFF0000BB, &HFFAAAAAA
16. FOR i = 1 TO 150
17.     LINE (RND * 1200, RND * 700)-STEP(RND * 150, RND * 150), _RGBA32(RND * 256, RND * 256, RND * 256, RND * 256), BF
18. NEXT
19. PRINT "in 4 secs Color Dialog comes up..."
20. _DISPLAY
21. _DELAY 4
22. rc$ = colorDialog$
23. PRINT "Color Dialog returned this:"; rc$
24. IF rc$ <> "" THEN LINE (100, 100)-STEP(1000, 500), VAL(rc$), BF
25. PRINT: PRINT "End of Color Dialog test..."
26.  
27. FUNCTION colorDialog$
28.  
29.     'first screen dimensions items to restore at exit
30.     DIM curRow AS INTEGER, curCol AS INTEGER, autoDisplay AS INTEGER
31.     DIM sw AS INTEGER, sh AS INTEGER, fg AS _UNSIGNED LONG, bg AS _UNSIGNED LONG
32.     DIM curScrn AS LONG, backScrn AS LONG 'some handles
33.  
34.     DIM cd AS LONG
35.     DIM r AS INTEGER, g AS INTEGER, b AS INTEGER, a AS INTEGER, mb AS INTEGER, mx AS INTEGER, my AS INTEGER, i AS INTEGER
36.     DIM makeConst$, k$
37.     DIM f AS SINGLE
38.  
39.     'save old settings to restore at end ofsub
40.     curRow = CSRLIN
41.     curCol = POS(0)
42.     autoDisplay = _AUTODISPLAY
43.     sw = _WIDTH
44.     sh = _HEIGHT
45.     fg = _DEFAULTCOLOR
46.     bg = _BACKGROUNDCOLOR
47.     _KEYCLEAR
48.     'screen snapshot
49.     curScrn = _DEST
50.     backScrn = _NEWIMAGE(sw, sh, 32)
51.     _PUTIMAGE , curScrn, backScrn
52.  
53.     cd = _NEWIMAGE(800, 600, 32)
54.     SCREEN cd
55.     r = 128: g = 128: b = 128: a = 128
56.     COLOR &HFFDDDDDD, 0
57.     DO
58.         CLS
59.         makeConst$ = "&H" + RIGHT$(STRING$(8, "0") + HEX$(_RGBA32(r, g, b, a)), 8)
60.         slider 16, 10, r, "Red"
61.         slider 16, 60, g, "Green"
62.         slider 16, 110, b, "Blue"
63.         slider 16, 160, a, "Alpha"
64.         _PRINTSTRING (150, 260), "Press enter or spacenbar, if you want to use the color: " + makeConst$
65.         _PRINTSTRING (210, 280), "Press escape or q, to not use any color, returns 0."
66.         LINE (90, 300)-(710, 590), , B
67.         FOR i = 100 TO 700
68.             f = 255 * (i - 100) / 600
69.             LINE (i, 310)-STEP(0, 30), _RGB32(f, 0, 0): LINE (i, 310)-STEP(0, 20), VAL(makeConst$)
70.             LINE (i, 340)-STEP(0, 30), _RGB32(0, f, 0): LINE (i, 340)-STEP(0, 20), VAL(makeConst$)
71.             LINE (i, 370)-STEP(0, 30), _RGB32(0, 0, f): LINE (i, 370)-STEP(0, 20), VAL(makeConst$)
72.             LINE (i, 400)-STEP(0, 30), _RGB32(f, f, 0): LINE (i, 400)-STEP(0, 20), VAL(makeConst$)
73.             LINE (i, 430)-STEP(0, 30), _RGB32(0, f, f): LINE (i, 430)-STEP(0, 20), VAL(makeConst$)
74.             LINE (i, 460)-STEP(0, 30), _RGB32(f, 0, f): LINE (i, 460)-STEP(0, 20), VAL(makeConst$)
75.             LINE (i, 490)-STEP(0, 30), _RGB32(f, f, f): LINE (i, 490)-STEP(0, 20), VAL(makeConst$)
76.             LINE (i, 520)-STEP(0, 30), _RGB32(0, 0, 0): LINE (i, 520)-STEP(0, 20), VAL(makeConst$)
77.             LINE (i, 550)-STEP(0, 30), _RGB32(255, 255, 255): LINE (i, 550)-STEP(0, 20), VAL(makeConst$)
78.         NEXT
79.         WHILE _MOUSEINPUT: WEND
80.         mb = _MOUSEBUTTON(1)
81.         IF mb THEN 'clear it
82.             mx = _MOUSEX: my = _MOUSEY
83.             IF mx >= 16 AND mx <= 781 THEN
84.                 IF my >= 10 AND my <= 50 THEN
85.                     r = INT((mx - 16) / 3)
86.                 ELSEIF my >= 60 AND my <= 100 THEN
87.                     g = INT((mx - 16) / 3)
88.                 ELSEIF my >= 110 AND my <= 150 THEN
89.                     b = INT((mx - 16) / 3)
90.                 ELSEIF my >= 160 AND my <= 200 THEN
91.                     a = INT((mx - 16) / 3)
92.                 END IF
93.             END IF
94.         END IF
95.         k$ = INKEY$
96.         IF LEN(k$) THEN
97.             IF ASC(k$) = 27 OR k$ = "q" THEN EXIT DO
98.             IF ASC(k$) = 13 OR k$ = " " THEN colorDialog$ = makeConst$: EXIT DO
99.         END IF
100.         _DISPLAY
101.         _LIMIT 60
102.     LOOP
103.  
104.     'put things back
105.     SCREEN curScrn
106.     COLOR _RGB32(255, 255, 255), _RGB32(0, 0, 0): CLS
107.     _PUTIMAGE , backScrn
108.     _DISPLAY
109.     COLOR fg, bg
110.     _FREEIMAGE backScrn
111.     _FREEIMAGE cd
112.     IF autoDisplay THEN _AUTODISPLAY
113.     'clear key presses
114.     _KEYCLEAR
115.     'clear mouse clicks
116.     WHILE _MOUSEINPUT: WEND
117.     mb = _MOUSEBUTTON(1)
118.     IF mb THEN 'clear it
119.         WHILE mb 'OK!
120.             IF _MOUSEINPUT THEN mb = _MOUSEBUTTON(1)
121.             _LIMIT 10
122.         WEND
123.     END IF
124.     LOCATE curRow, curCol
125.  
126. END FUNCTION
127.  
128. SUB slider (x, y, value, label$)
129.     DIM c~&, s$
130.     SELECT CASE label$
131.         CASE "Red": c~& = &HFFFF0000
132.         CASE "Green": c~& = &HFF008800
133.         CASE "Blue": c~& = &HFF0000FF
134.         CASE "Alpha": c~& = &H88FFFFFF
135.     END SELECT
136.     LINE (x, y)-STEP(765, 40), c~&, B
137.     LINE (x, y)-STEP(3 * value, 40), c~&, BF
138.     s$ = label$ + " = " + _TRIM$(STR$(value))
139.     _PRINTSTRING (x + 384 - 4 * LEN(s$), y + 12), s$
140. END SUB
141.  

Solid:
 

50% transparent overlay:
 

[SMcNeill]

Hi BPlus, do you remember that Alpha changes color depending on the background color? This means that the resulting color will always be of a different appearance but of the same value if you add a different screen clearing color than black to the CLS command on row 57?

This assumes that you apply the obtained value as a color number to different commands. Then there will be color mixing (for alpha < 255) depending on the background. The only way in which background color mixing does not occur is to insert colors into the image directly with the MEM command.

Or set _DONTBLEND.

https://www.qb64.org/wiki/BLEND
https://www.qb64.org/wiki/DONTBLEND

[SMcNeill]

A quick demo to highlight the difference of blended and unblended colors.:

Code: [Select]

SCREEN _NEWIMAGE(640, 480, 32)

CLS , &HFF000000~&
_BLEND
LINE (0, 0)-(640, 480), &H99FFFFFF~&, BF 'faded white background box
PRINT "Black color: "; HEX$(&HFF000000~&)
PRINT "Box color: "; HEX$(&H99FFFFFF~&)
PRINT "Mixed color: "; HEX$(POINT(300, 300))
PRINT "(These are values of blended colors.)"

SLEEP 'Pause for user input


CLS , &HFF000000~&
_DONTBLEND
LINE (0, 0)-(640, 480), &H99FFFFFF~&, BF 'faded white background box
PRINT "Black color: "; HEX$(&HFF000000~&)
PRINT "Box color: "; HEX$(&H99FFFFFF~&)
PRINT "Mixed color: "; HEX$(POINT(300, 300))
PRINT "(These are values of unblended colors.)"

If the color mixer is going to have alpha settings, you'll probably want to run your program in a _DONTBLEND state so that the background doesn't affect the true appearance of the chosen color.  (Or else add a toggle button to swap between Blend and Not Blend, so the user could see how the alpha value would end up actually looking in real conditions with their backgrounds.)

[Petr]

Yes. If the user exactly specifies the area where the color will be applied, then the resulting color with the alpha channel application can be shown to the user and set. Without background knowledge, there is no way to determine how the color see, if the alpha channel will be less than 255.