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int Y_AXIS = 1;
int X_AXIS = 2;

void setup(){
size(400,400);
//create some gradients
//background
color b1 = color(190,190,190);
color b2 = color(20,20,20);
setGradient(0,0,width,height,b1,b2,Y_AXIS);
//center squares
color c1 = color(255,120,0);
color c2 = color(10,45,255);
color c3 = color(10,255,15);
color c4 = color(125,2,140);
color c5 = color(255,255,0);
color c6 = color(25,255,200);
setGradient(50,50,150,150,c1,c2,Y_AXIS);
setGradient(200,50,150,150,c3,c4,X_AXIS);
setGradient(50,200,150,150,c2,c5,X_AXIS);
setGradient(200,200,150,150,c4,c6,Y_AXIS);
}

void setGradient(int x, int y, float w, float h, color c1, color c2, int axis){
float deltaR = red(c2)-red(c1);
float deltaG = green(c2)-green(c1);
float deltaB = green(c2)-green(c1);


// choose axis
if(axis == Y_AXIS){
for(int i = x; i <= (x + w); i++){
for(int j =y; j <= (y+h); j++){
color c = color(
(red(c1)+(j-y)*(deltaR/h)),(green(c1)+(j-y)*(deltaG/h)),(blue(c1)+(j-y)*(deltaB/h)) );
set(i,j,c);
}
}
}
else if(axis == X_AXIS){
for(int i =y; i <= (y+h); i++){
for(int j = x; j <= (x+w); j++){
color c = color(
(red(c1)+(j-x)*(deltaR/h)),(green(c1)+(j-x)*(deltaG/h)),(blue(c1)+(j-x)*(deltaB/h)) );
set(j,i,c);
}
}
}
}