Help: code not blending to complete black color

[thesolarcode]

I have this code and thought that with the _RGBA alpha setting (line 67) drawing over the whole screen the image should get darker and darker, but somehow the lines are stuck at some very dark grey color. Any idea how I can fix this?

Code: QB64: [Select]

1. $CHECKING:OFF
2. RANDOMIZE timer
3.  
4. dim shared screenx%, screeny%, tx1%, ty1%, tx2%, ty2%, x1%, y1%, x2%, y2%, d%
5. screenx%=800
6. screeny%=600
7.        
8. ' open new (full)screen
9. SCREEN _NEWIMAGE(screenx%,screeny%,32)
10. _FULLSCREEN
11.  
12. tx1%=screenx%*rnd
13. ty1%=screeny%*rnd
14. tx2%=screenx%*rnd
15. ty2%=screeny%*rnd
16. x1%=screenx%*rnd
17. y1%=screeny%*rnd
18. x2%=screenx%*rnd
19. y2%=screeny%*rnd
20. d%=3
21.  
22. _MOUSEHIDE
23. while INKEY$ = ""
24.         color _RGB(256*rnd, 256*rnd, 256*rnd)
25.         smearfx
26.        
27.         if x1% < tx1% then
28.                 x1% = x1% + d%
29.         ELSE
30.                 x1% = x1% - d%
31.         end if
32.         if ABS(x1%-tx1%) < d% then
33.                 tx1%=screenx%*rnd
34.         end if
35.  
36.         if y1% < ty1% then
37.                 y1% = y1% + d%
38.         ELSE
39.                 y1% = y1% - d%
40.         end if
41.         if abs(y1%-ty1%) < d% then
42.                 ty1%=screeny%*rnd
43.         end if
44.        
45.         if x2% < tx2% then
46.                 x2% = x2% + d%
47.         ELSE
48.                 x2% = x2% - d%
49.         end if
50.         if abs(x2%-tx2%) < d% then
51.                 tx2%=screenx%*rnd
52.         end if
53.  
54.         if y2% < ty2% then
55.                 y2% = y2% + d%
56.         ELSE
57.                 y2% = y2% - d%
58.         end if
59.         if abs(y2%-ty2%) < d% then
60.                 ty2%=screeny%*rnd
61.         end if
62. wend
63. _MOUSESHOW
64.  
65. sub smearfx()
66.     _LIMIT 50
67.     LINE (0, 0)-(screenx%, screeny%), _RGBA(0, 0, 0, 25), BF
68.         line (x1%, y1%)-(x2%, y2%)
69.     _DISPLAY
70. end sub
71.  

[bplus]

The screen is actually transparent until you cls, just cls will give default black background. That might help?

Hey nice effect!

[thesolarcode]

Thanks,

Not sure how to use CLS without destroying the line effect - I only draw one additional line per screen update, all the other lines are just made darker with one command :)
I'm probably doing the wrong thing - am I effectively just setting transparency to 25% and thus lines are still visible?

[bplus]

Oh just do it first thing before you start drawing, that sets the background to Black instead of transparent which looks black with no drawings on it.

I think you've got it right just CLS first thing, once, before drawing.

[FellippeHeitor]

thesolarcode: I've tried to understand the effect you're seeing with programs I'd written before, like fireworks and others. I never managed to understand why it doesn't eventually end up blacking the whole screen - those trails will remain there until you actually clear the screen with full alpha. I managed to observe the same outcome while playing with other programming languages too, it's still a mystery to me.

Here, try this one: https://openprocessing.org/sketch/1191793 (same technique of semi-transparent black rectangle to cover previous frame - same trail effect (defect)).

[johnno56]

I had a little problem when I ran this.... Cut and paste into IDE then F5. A small black window view appeared in the top left corner of the screen just for a moment. Pressed F5 again. The black window view appeared again and the whole display locked up. Rebooted. Re-ran. F5 black window again for a moment. F5 and the program ran normally. Escape to end. Tried again and the black window appeared again and locked up the system. Each time it locked up, the only two thing that worked was mouse movement and the system reset button....

I checked the listing. There doesn't seem to be anything there tat I have not used before (except for checking:off).

The time that it ran, it ran very well... I see what you mean about the 'dark grey' lines. Looks a lot like the qbasic screen saver, Mystify... Cool...

As the listing looks 'normal', I'm going to assume that the problem may be with my machine, and pass on running again until I try to figure out the problem.

I am running on Linux Mint 20, 64bit using QB64 1.5 stable from git 3043116

[johnno56]

Ok. First test... Removal of 'checking:off'. Successfully ran the program 7 times in succession... Locked up on the 8th try.... Oh well.... Worth a shot...

[thesolarcode]

I changed the code a bit - this time I copy an image over and over to achieve the fading effect, but I have the same problem with the faded lines being still visible.
I guess there is no other way in QB64 as to darken/fade each pixel individually, right?

Code: QB64: [Select]

1. RANDOMIZE timer
2.  
3. dim shared screenx%, screeny%, tx1%, ty1%, tx2%, ty2%, x1%, y1%, x2%, y2%, d%, handle2&
4. screenx%=800
5. screeny%=600
6.        
7. SCREEN _NEWIMAGE(screenx%,screeny%,32)
8. _FULLSCREEN
9. cls
10.  
11. ' create new black image with alpha channel
12. handle2& = _NEWIMAGE(screenx%,screeny%,32)
13. _DEST handle2&
14. LINE (0, 0)-(screenx%, screeny%), _RGBA(0, 0, 0, 3), BF
15. _dest 0
16.  
17. tx1%=screenx%*rnd
18. ty1%=screeny%*rnd
19. tx2%=screenx%*rnd
20. ty2%=screeny%*rnd
21. x1%=screenx%*rnd
22. y1%=screeny%*rnd
23. x2%=screenx%*rnd
24. y2%=screeny%*rnd
25. d%=3
26.  
27. _MOUSEHIDE
28. while INKEY$ = ""
29.         color _RGB(256*rnd, 256*rnd, 256*rnd)
30.         smearfx
31.        
32.         if x1% < tx1% then
33.                 x1% = x1% + d%
34.         ELSE
35.                 x1% = x1% - d%
36.         end if
37.         if ABS(x1%-tx1%) < d% then
38.                 tx1%=screenx%*rnd
39.         end if
40.  
41.         if y1% < ty1% then
42.                 y1% = y1% + d%
43.         ELSE
44.                 y1% = y1% - d%
45.         end if
46.         if abs(y1%-ty1%) < d% then
47.                 ty1%=screeny%*rnd
48.         end if
49.        
50.         if x2% < tx2% then
51.                 x2% = x2% + d%
52.         ELSE
53.                 x2% = x2% - d%
54.         end if
55.         if abs(x2%-tx2%) < d% then
56.                 tx2%=screenx%*rnd
57.         end if
58.  
59.         if y2% < ty2% then
60.                 y2% = y2% + d%
61.         ELSE
62.                 y2% = y2% - d%
63.         end if
64.         if abs(y2%-ty2%) < d% then
65.                 ty2%=screeny%*rnd
66.         end if
67. wend
68. _MOUSESHOW
69.  
70. sub smearfx()
71.     _LIMIT 50
72.     'LINE (0, 0)-(screenx%, screeny%), _RGBA(0, 0, 0, 25), BF
73.     _PUTIMAGE (0,0), handle2&, 0
74.     line (x1%, y1%)-(x2%, y2%)
75.     _DISPLAY
76. end sub
77.  

[johnno56]

It's not just QB64. Because of my "screen lock" issue, I tried to replicate the problem, using RCBasic. No screen lockup but the "dark line" issue was still there. Reducing the "alpha" to "30" reduced it a little... Too low and the display looks like only a few lines or too high and the "grey line" is more obvious. I will continue to research...

[johnno56]

Here is a rough conversion of a javascript example (

)

Even in the JS version, the remnants of the fading, was still present.

Code: QB64: [Select]

1. DIM SHARED canvWidth
2. DIM SHARED canvHeight
3.  
4. canvWidth = 800
5. canvHeight = 600
6. SCREEN _NEWIMAGE(canvWidth, canvHeight, 32)
7.  
8. DIM cyan AS _UNSIGNED LONG
9. DIM yellow AS _UNSIGNED LONG
10.  
11. DIM SHARED x1, y1, x2, y2
12. DIM SHARED xv1, yv1, xv2, yv2
13.  
14. DIM SHARED x1b, y1b, x2b, y2b
15. DIM SHARED xv1b, yv1b, xv2b, yv2b
16.  
17. DIM SHARED alpha
18.  
19. cyan = _RGB32(0, 255, 255)
20. yellow = _RGB32(255, 255, 0)
21.  
22. '   Init
23. x1 = INT(RND * canvWidth)
24. y1 = INT(RND * canvHeight)
25. x2 = INT(RND * canvWidth)
26. y2 = INT(RND * canvHeight)
27.  
28. x1b = INT(RND * canvWidth)
29. y1b = INT(RND * canvHeight)
30. x2b = INT(RND * canvWidth)
31. y2b = INT(RND * canvHeight)
32.  
33. xv1 = 5 - INT(RND * 10)
34. yv1 = 5 - INT(RND * 10)
35. xv2 = 5 - INT(RND * 10)
36. yv2 = 5 - INT(RND * 10)
37.  
38. xv1b = 5 - INT(RND * 10)
39. yv1b = 5 - INT(RND * 10)
40. xv2b = 5 - INT(RND * 10)
41. yv2b = 5 - INT(RND * 10)
42.  
43. alpha = 30
44.  
45. WHILE INKEY$ <> CHR$(27)
46.     update
47. WEND
48.  
49. SUB update
50.     _LIMIT 60
51.     LINE (0, 0)-(canvWidth - 1, canvHeight - 1), _RGBA(0, 0, 64, alpha), BF
52.     alpha = 15
53.  
54.     x1 = x1 + xv1
55.     y1 = y1 + yv1
56.     x2 = x2 + xv2
57.     y2 = y2 + yv2
58.     x1b = x1b + xv1b
59.     y1b = y1b + yv1b
60.     x2b = x2b + xv2b
61.     y2b = y2b + yv2b
62.  
63.     IF x1 < 0 OR x1 > canvWidth THEN
64.         xv1 = xv1 * -1
65.     END IF
66.     IF y1 < 0 OR y1 > canvHeight THEN
67.         yv1 = yv1 * -1
68.     END IF
69.     IF x2 < 0 OR x2 > canvWidth THEN
70.         xv2 = xv2 * -1
71.     END IF
72.     IF y2 < 0 OR y2 > canvHeight THEN
73.         yv2 = yv2 * -1
74.     END IF
75.  
76.     IF x1b < 0 OR x1b > canvWidth THEN
77.         xv1b = xv1b * -1
78.     END IF
79.     IF y1b < 0 OR y1b > canvHeight THEN
80.         yv1b = yv1b * -1
81.     END IF
82.     IF x2b < 0 OR x2b > canvWidth THEN
83.         xv2b = xv2b * -1
84.     END IF
85.     IF y2b < 0 OR y2b > canvHeight THEN
86.         yv2b = yv2b * -1
87.     END IF
88.  
89.     LINE (x1, y1)-(x2, y2), _RGB32(0, 255, 255)
90.     LINE (x1b, y1b)-(x2b, y2b), _RGB32(255, 255, 0)
91.     _DISPLAY
92. END SUB
93.  

[NOVARSEG]

I guess there is no other way in QB64 as to darken/fade each pixel individually, right?

MEMGET and MEMPUT to the rescue

Code: QB64: [Select]

1. RANDOMIZE TIMER
2.  
3. DIM SHARED screenx%, screeny%, tx1%, ty1%, tx2%, ty2%, x1%, y1%, x2%, y2%, d%, handle2&
4. DIM R AS _UNSIGNED _BYTE
5. DIM G AS _UNSIGNED _BYTE
6. DIM B AS _UNSIGNED _BYTE
7.  
8. DIM T AS _UNSIGNED LONG
9. DIM m AS _MEM
10. DIM handle AS LONG
11. screenx% = 800
12. screeny% = 600
13.  
14. handle = _NEWIMAGE(screenx%, screeny%, 32)
15.  
16. m = _MEMIMAGE(handle)
17.  
18. SCREEN handle
19.  
20. _FULLSCREEN
21.  
22. ' create new black image with alpha channel
23. 'handle2& = _NEWIMAGE(screenx%, screeny%, 32)
24. '_DEST handle2&
25. 'LINE (0, 0)-(screenx%, screeny%), _RGBA(0, 0, 0, 255), BF
26. '_DEST 0
27.  
28. tx1% = screenx% * RND
29. ty1% = screeny% * RND
30. tx2% = screenx% * RND
31. ty2% = screeny% * RND
32. x1% = screenx% * RND
33. y1% = screeny% * RND
34. x2% = screenx% * RND
35. y2% = screeny% * RND
36. d% = 3
37.  
38. _MOUSEHIDE
39. WHILE INKEY$ = ""
40.     COLOR _RGB(256 * RND, 256 * RND, 256 * RND)
41.     ' smearfx
42.  
43.  
44.     FOR T = 0 TO (800 * 600 - 1) * 4 STEP 4
45.         B = _MEMGET(m, m.OFFSET + T, _UNSIGNED _BYTE)
46.         G = _MEMGET(m, m.OFFSET + T + 1, _UNSIGNED _BYTE)
47.         R = _MEMGET(m, m.OFFSET + T + 2, _UNSIGNED _BYTE)
48.         IF B > 1 THEN B = B - 2
49.         IF B = 1 THEN B = 0
50.         IF G > 1 THEN G = G - 2
51.         IF G = 1 THEN G = 0
52.         IF R > 1 THEN R = R - 2
53.         IF R = 1 THEN R = 0
54.         _MEMPUT m, m.OFFSET + T, B
55.         _MEMPUT m, m.OFFSET + T + 1, G
56.         _MEMPUT m, m.OFFSET + T + 2, R
57.     NEXT T
58.  
59.     IF x1% < tx1% THEN
60.         x1% = x1% + d%
61.     ELSE
62.         x1% = x1% - d%
63.     END IF
64.     IF ABS(x1% - tx1%) < d% THEN
65.         tx1% = screenx% * RND
66.     END IF
67.  
68.     IF y1% < ty1% THEN
69.         y1% = y1% + d%
70.     ELSE
71.         y1% = y1% - d%
72.     END IF
73.     IF ABS(y1% - ty1%) < d% THEN
74.         ty1% = screeny% * RND
75.     END IF
76.  
77.     IF x2% < tx2% THEN
78.         x2% = x2% + d%
79.     ELSE
80.         x2% = x2% - d%
81.     END IF
82.     IF ABS(x2% - tx2%) < d% THEN
83.         tx2% = screenx% * RND
84.     END IF
85.  
86.     IF y2% < ty2% THEN
87.         y2% = y2% + d%
88.     ELSE
89.         y2% = y2% - d%
90.     END IF
91.     IF ABS(y2% - ty2%) < d% THEN
92.         ty2% = screeny% * RND
93.     END IF
94.  
95.     LINE (x1%, y1%)-(x2%, y2%)
96. WEND
97.  
98. _MOUSESHOW
99. END
100. SUB smearfx ()
101.     _LIMIT 50
102.     LINE (0, 0)-(screenx%, screeny%), _RGBA(0, 0, 0, 10), BF
103.     '_PUTIMAGE (0, 0), handle2&, 0
104.     LINE (x1%, y1%)-(x2%, y2%)
105.     _DISPLAY
106. END SUB

[thesolarcode]

Yes, that is it - the effect looks really great now (even better if you decrease by 1 - then it fades really slowly towards black color).
Today I learned something new (how to use MEMGET/PUT for gfx).
Thanks :)

[NOVARSEG]

Decrease by 1 does look better.

[NOVARSEG]

small bug . changed
 FOR T = 0 TO (800 * 600 - 1) * 4 STEP 4
to
FOR T = 0 TO 800 * 600 * 4 - 1 STEP 4

Code: QB64: [Select]

1. RANDOMIZE TIMER
2.  
3. DIM SHARED screenx%, screeny%, tx1%, ty1%, tx2%, ty2%, x1%, y1%, x2%, y2%, d%, handle2&
4. DIM R AS _UNSIGNED _BYTE
5. DIM G AS _UNSIGNED _BYTE
6. DIM B AS _UNSIGNED _BYTE
7.  
8. DIM T AS _UNSIGNED LONG
9. DIM m AS _MEM
10. DIM handle AS LONG
11. screenx% = 800
12. screeny% = 600
13.  
14. handle = _NEWIMAGE(screenx%, screeny%, 32)
15.  
16. m = _MEMIMAGE(handle)
17.  
18. SCREEN handle
19.  
20. _FULLSCREEN
21.  
22. ' create new black image with alpha channel
23. 'handle2& = _NEWIMAGE(screenx%, screeny%, 32)
24. '_DEST handle2&
25. 'LINE (0, 0)-(screenx%, screeny%), _RGBA(0, 0, 0, 255), BF
26. '_DEST 0
27.  
28. tx1% = screenx% * RND
29. ty1% = screeny% * RND
30. tx2% = screenx% * RND
31. ty2% = screeny% * RND
32. x1% = screenx% * RND
33. y1% = screeny% * RND
34. x2% = screenx% * RND
35. y2% = screeny% * RND
36. d% = 3
37.  
38. _MOUSEHIDE
39. WHILE INKEY$ = ""
40.     COLOR _RGB(256 * RND, 256 * RND, 256 * RND)
41.     ' smearfx
42.  
43.     FOR T = 0 TO 800 * 600 * 4 - 1 STEP 4
44.         B = _MEMGET(m, m.OFFSET + T, _UNSIGNED _BYTE)
45.         G = _MEMGET(m, m.OFFSET + T + 1, _UNSIGNED _BYTE)
46.         R = _MEMGET(m, m.OFFSET + T + 2, _UNSIGNED _BYTE)
47.         IF B > 1 THEN B = B - 1
48.         'IF B = 1 THEN B = 0
49.         IF G > 1 THEN G = G - 1
50.         ' IF G = 1 THEN G = 0
51.         IF R > 1 THEN R = R - 1
52.         'IF R = 1 THEN R = 0
53.         _MEMPUT m, m.OFFSET + T, B
54.         _MEMPUT m, m.OFFSET + T + 1, G
55.         _MEMPUT m, m.OFFSET + T + 2, R
56.     NEXT T
57.  
58.     IF x1% < tx1% THEN
59.         x1% = x1% + d%
60.     ELSE
61.         x1% = x1% - d%
62.     END IF
63.     IF ABS(x1% - tx1%) < d% THEN
64.         tx1% = screenx% * RND
65.     END IF
66.  
67.     IF y1% < ty1% THEN
68.         y1% = y1% + d%
69.     ELSE
70.         y1% = y1% - d%
71.     END IF
72.     IF ABS(y1% - ty1%) < d% THEN
73.         ty1% = screeny% * RND
74.     END IF
75.  
76.     IF x2% < tx2% THEN
77.         x2% = x2% + d%
78.     ELSE
79.         x2% = x2% - d%
80.     END IF
81.     IF ABS(x2% - tx2%) < d% THEN
82.         tx2% = screenx% * RND
83.     END IF
84.  
85.     IF y2% < ty2% THEN
86.         y2% = y2% + d%
87.     ELSE
88.         y2% = y2% - d%
89.     END IF
90.     IF ABS(y2% - ty2%) < d% THEN
91.         ty2% = screeny% * RND
92.     END IF
93.  
94.     LINE (x1%, y1%)-(x2%, y2%)
95. WEND
96.  
97. _MOUSESHOW
98. END
99. SUB smearfx ()
100.     _LIMIT 50
101.     LINE (0, 0)-(screenx%, screeny%), _RGBA(0, 0, 0, 1), BF
102.     _PUTIMAGE (0, 0), handle2&, 0
103.     LINE (x1%, y1%)-(x2%, y2%)
104.     _DISPLAY
105. END SUB
106.  

[johnno56]

I still have difficulty executing. Eventually it started and the fade effect is much better... Well done!