Set values of a 2D array using specific coordinates-CodePudding

Disclaimer: This could apply to any programming langage but I am using C , so I'm using the C tag.

I have an array of an xyz structure:

struct xyz {
    float x, y, z;
};

In the array I create, at first I only initialize the x and y as I know the z value only later in the code like this:

size = Width * Height;    
Cloud = new xyz[size];

// Remplissage des indices de Pixels
for (int i = 0; i < size; i  )
{
    Cloud[i].x = i % Width;

    Cloud[i].y = i / Width;
}

};

This results in an array that looks like that:

x; y; z
0; 0; 0
1; 0; 0
2; 0; 0
3; 0; 0
0; 1; 0
1; 1; 0
2; 1; 0
3; 1; 0
0; 2; 0
1; 2; 0
2; 2; 0
3; 2; 0

So after that, I want to set a z value for such x and y values but I don't know how to do that in an effective way (I don't want to use a loop that goes through my whole array until I find the right x and y set).

My problem I guess is how to do the inverse math of Cloud[i].x = i % Width and Cloud[i].y = i / Width into something to do Cloud[??].z = someValue.

Thank you in advance!

CodePudding user response：

That is simple mathematics. If you have x and y and want to know the index to address the z-value later, then you may calculate "y * width x".

So:

Cloud[y * Width   x].z = zValue;