How to set new Color every time draw() loop is executed?

[john_god]

Just assign a qrand() to the r, g, b variables and perform a while cicle, until the randow values are diferent from the range values of the grey color.

In the case of Krish, and if you would have a maxim limit of curves to draw, like 100, another aproach would be to create a array/list of color's. That way you could give the user the change to personalize each curve color.

[Nadia]

Now, I just make simple check whether r, g an b values not equal (instead of while). But there are the colours that are not actually grey but very similar and lays bad on gray. And what does you mean "assign a qrand() to the r, g, b variables? I just do :

srand( time(0) );//somewhere in main
 
//and then in function then generate randoms
QColor crand = QColor(rand()%256, rand()%256, rand()%256);

srand( time(0) );//somewhere in main

//and then in function then generate randoms
QColor crand = QColor(rand()%256, rand()%256, rand()%256);

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But I think there are should be standard solutions (algorithms) for good colours combinations.

[john_god]

I mean something like:

int r;
int g;
int b;
 
//define the followin values for a range of grey defined by you
int r_upper_grey = ...;
int r_lower_grey = ...;
int g_upper_grey = ...;
int g_lower_grey = ...;
int b_upper_grey = ...;
int b_lower_grey = ...;
 
do 
{
    r= qrand() % 256;
    g= qrand() % 256;
    b= qrand() % 256;
 
}while (  (  r  < r_upper_grey && r > r_lower_grey)  && 
             (  g  < g_upper_grey && g > g_lower_grey)  &&
             (  b  < b_upper_grey && b > b_lower_grey)  );

int r;
int g;
int b;

//define the followin values for a range of grey defined by you
int r_upper_grey = ...;
int r_lower_grey = ...;
int g_upper_grey = ...;
int g_lower_grey = ...;
int b_upper_grey = ...;
int b_lower_grey = ...;

do 
{
    r= qrand() % 256;
    g= qrand() % 256;
    b= qrand() % 256;

}while (  (  r  < r_upper_grey && r > r_lower_grey)  && 
             (  g  < g_upper_grey && g > g_lower_grey)  &&
             (  b  < b_upper_grey && b > b_lower_grey)  );

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Get the picture ? Define a range of grey to avoid and keep random the numbers
until they out of the grey zone