I'm working on a sketch, using Processing 2.0b6 and P3D mode, that consists of a flat background where images are displayed (and 3D objects on top). The background image is made of two pictures randomly loaded and mixed using different blending modes also chosen randomly. Everything works fine except that I'm trying to blend the pictures gradually using tint(). For some blending modes this works but for others the pictures don't blend gradually but are shown suddenly. I'm assuming this is due to some of the blending modes not using alpha for blending (?). I was wondering if there's another way of achieving this gradual crossfade with all blending modes.

These are the relevant lines of the sketch:

2. int[] blending = {BLEND,ADD,SUBTRACT,LIGHTEST,DARKEST,DIFFERENCE,EXCLUSION,MULTIPLY,
3. SCREEN,REPLACE};
4. 
   
5. void draw() {
6.   background(0);
7. 
   
8.   tint(255, 255);
9.   image(img[rndimg1], 0, 0); // img[] is a PImage[] array containing loaded images (PNG)
10. 
    
11.   blendMode(blending[blending1]);  
12.   tint(255, picAlpha);
13.   image(img[rndimg2], 0, 0);
14. 
    
15.   picAlpha = picAlpha + (1*alphaMult);
16.   if (picAlpha < 0) {
17.     alphaMult = 1;
18.     rndimg2 = (int) random(1,10);
19.     txture = (int) random(1,10);
20.     texmap = img[txture];
21.     blending1 = (int) random(0,10);
22.   } 
23.  // go to 1000 so the image remains without changing alpha for some time
24.   else if (picAlpha > 1000) { 
25.     alphaMult = -1;
26.     rndimg1 = (int) random(1,10);
27.     blending2 = (int) random(0,10);
28.   }
29. }

Any ideas will be very appreciated!

Thanks,

Hector