 # Reaction Diffusion : add an image

Hi Everybody, I hope someone can help :
I have the reaction diffusion code based on points, what I’m trying to do is to add a black and white image inside the code and say in the condition loop that I want to apply the reaction diffusion only where the color is black.
I tried several times but no results yet, hope someone that is more expert can help to figure out, I’ll leave the code where I’m working in, is in processing 3, and I’m leaving an image to show you what I’m looking for ``````import java.awt.Color;

Cell[][] grid;
Cell[][] prev;

void setup() {
size(300, 300);
grid = new Cell[width][height];
prev = new Cell[width][height];

for (int i = 0; i < width; i++) {
for (int j = 0; j < height; j ++) {
float a = 1;
float b = 0;
grid[i][j] = new Cell(a, b);
prev[i][j] = new Cell(a, b);
}
}

for (int n = 0; n < 50; n++) {
int startx = int(random(20, width-20));
int starty = int(random(20, height-20));

for (int i = startx; i < startx+10; i++) {
for (int j = starty; j < starty+10; j ++) {
float a = 5;
float b = 5;
grid[i][j] = new Cell(a, b);
prev[i][j] = new Cell(a, b);
}
}
}
}

float dA = 1.0;
float dB = 0.5;
float feed = 0.08;
float k = 0.06;

class Cell {
float a;
float b;

Cell(float a_, float b_) {
a = a_;
b = b_;
}
}

void update() {
for (int i = 1; i < width-1; i++) {
for (int j = 1; j < height-1; j ++) {

Cell spot = prev[i][j];
Cell newspot = grid[i][j];

float a = spot.a;
float b = spot.b;

float laplaceA = 0;
laplaceA += a*-1;
laplaceA += prev[i+1][j].a*0.2;
laplaceA += prev[i-1][j].a*0.2;
laplaceA += prev[i][j+1].a*0.2;
laplaceA += prev[i][j-1].a*0.2;
laplaceA += prev[i-1][j-1].a*0.05;
laplaceA += prev[i+1][j-1].a*0.05;
laplaceA += prev[i-1][j+1].a*0.05;
laplaceA += prev[i+1][j+1].a*0.05;

float laplaceB = 0;
laplaceB += b*-1;
laplaceB += prev[i+1][j].b*0.2;
laplaceB += prev[i-1][j].b*0.2;
laplaceB += prev[i][j+1].b*0.2;
laplaceB += prev[i][j-1].b*0.2;
laplaceB += prev[i-1][j-1].b*0.05;
laplaceB += prev[i+1][j-1].b*0.05;
laplaceB += prev[i-1][j+1].b*0.05;
laplaceB += prev[i+1][j+1].b*0.05;

newspot.a = a + (dA*laplaceA - a*b*b + feed*(1-a))*1;
newspot.b = b + (dB*laplaceB + a*b*b - (k+feed)*b)*1;

newspot.a = constrain(newspot.a, 0, 1);
newspot.b = constrain(newspot.b, 0, 1);
}
}
}

void swap() {
Cell[][] temp = prev;
prev = grid;
grid = temp;
}

void draw() {
//println(frameRate);

for (int i = 0; i < 1; i++) {
update();
swap();
}

for (int i = 1; i < width-1; i++) {
for (int j = 1; j < height-1; j ++) {
Cell spot = grid[i][j];
float a = spot.a;
float b = spot.b;
int pos = i + j * width;
//pixels[pos] = color((a-b)*255);

color aColor = color (0, 0, 0);
color bColor = color (255, 255, 255);
pixels[pos] = lerpColor(aColor, bColor, (a-b));
}
}
updatePixels();

}

``````

https://github.com/StanLepunK/Shader you can find the shader in the folder `fx_post`and the code in the tab `Z_R_FX_post_rendering.pde` line 1596… I don’t if that’s help you…
Thanks again 