Understanding hardware images

[Raven_Singularity]

I'm not able to see what your example does at the moment, but I started this thread because _SETALPHA does not respect an image's pre-existing partially translucent pixels.

[Petr]

Hi. So ... first I wrote a program that confirms what you say. SETALPHA adds a layer with transparency over the original colors. This shows the first part of the program. Then press Esc, please be patient and press + and - to set the alpha channel to rainbow.png for each pixel. I suppose this will be what you're looking for. Gradually extinguish and light up pixels based on their original values. I used slow commands, it can be speeded up if  MEM functions are used.

After pressing minus, the alpha is increased everywhere, not to the same value, but by the previous value of a particular pixel. Note that the blackness of the background around the circle also increases (the number in the upper left corner disappears). Plus shrinks transparency.

Code: QB64: [Select]

1. 'create transparent image
2. om = _NEWIMAGE(400, 300, 32)
3. _DEST om
4. FOR D = 100 TO 300 STEP 50
5.     LINE (D, 100)-(D + 49, 200), _RGBA32(255, 255, 255, D - 50), BF
6. NEXT D
7.  
8.  
9.  
10.  
11. nm = _COPYIMAGE(om, 32)
12. _SETALPHA 25, _RGBA32(0, 0, 0, 0) TO _RGBA32(255, 255, 255, 255), nm
13.  
14. SCREEN _NEWIMAGE(800, 600, 32)
15. _MOUSEMOVE 505, 104
16. _PUTIMAGE (1, 1), om
17. _PUTIMAGE (400, 1), nm
18.  
19. PCOPY _DISPLAY, 1
20. DO
21.     PCOPY 1, _DISPLAY
22.     WHILE _MOUSEINPUT: WEND
23.     _SOURCE 0
24.     alpha1 = _ALPHA32(POINT(_MOUSEX - 400, _MOUSEY))
25.     alpha2 = _ALPHA32(POINT(_MOUSEX, _MOUSEY))
26.  
27.     LOCATE 1, 1: PRINT "Left is original image. Right is image with applied SETALPHA 25 to original image."
28.     LOCATE 2, 1: PRINT "Original Alpha: "; alpha1; "New Alpha: "; alpha2
29.     LOCATE 3, 1: PRINT "Press ESC for quit."
30.     IF _MOUSEX > 0 AND _MOUSEY > 0 THEN
31.         IF _MOUSEX < 505 THEN _MOUSEMOVE 505, _MOUSEY
32.         IF _MOUSEY > 200 THEN _MOUSEMOVE _MOUSEX, 200
33.  
34.         IF _MOUSEY < 104 THEN _MOUSEMOVE _MOUSEX, 104
35.         IF _MOUSEX > 750 THEN _MOUSEMOVE 750, _MOUSEY
36.     END IF
37.     PSET (_MOUSEX - 400, _MOUSEY), _RGB32(255, 255, 255) - POINT(_MOUSEX - 400, _MOUSEY)
38.     _DISPLAY
39.  
40.     LINE (0, 0)-(800, 100), _RGB32(0, 0, 0), BF
41. LOOP UNTIL INKEY$ = CHR$(27)
42.  
43. _AUTODISPLAY
44. _FREEIMAGE om 'original alpha
45. _FREEIMAGE nm 'new alpha
46.  
47.  
48. CLS
49. im = _LOADIMAGE("rainbow.png", 32)
50. W = _WIDTH(im)
51. H = _HEIGHT(im)
52. DIM Alpha(W, H) AS _UNSIGNED _BYTE
53. 'DIM newAlpha AS _UNSIGNED _BYTE 'uncomment it for show how it works with owerflow QB64 solution
54. _SOURCE im
55. FOR y = 0 TO H - 1
56.     FOR x = 0 TO W - 1
57.         Alpha(x, y) = _ALPHA32(POINT(x, y))
58. NEXT x, y
59. _DEST 0
60. _PUTIMAGE (0, 0), im
61.  
62.  
63. DO UNTIL i$ = CHR$(27)
64.     CLS
65.     i$ = INKEY$
66.     SELECT CASE i$
67.         CASE "+": A = A + 1
68.         CASE "-": A = A - 1
69.  
70.     END SELECT
71.     LOCATE 1, 1: PRINT A
72.  
73.     FOR y = 0 TO H - 1
74.         FOR x = 0 TO W - 1
75.             newAlpha = Alpha(x, y) + A
76.             _SOURCE im
77.             CurrentColor~& = POINT(x, y)
78.             IF newAlpha < 0 THEN newAlpha = 0
79.             NewColor~& = _RGBA32(_RED32(CurrentColor~&), _GREEN32(CurrentColor~&), _BLUE32(CurrentColor~&), newAlpha)
80.             PSET (x, y), NewColor~&
81.     NEXT x, y
82.     i$ = ""
83.     _DISPLAY
84. LOOP
85.