void draw(unsigned char *image)
{
for (int y = 0; y < HEIGHT; y++)
{
for (int x = 0; x < WIDTH; x++)
{
if (someCondition)
{
int red = x * 256 / WIDTH;
int green = 255;
int blue = y * 256 / HEIGHT;
image[0] = (unsigned char)blue;
image[1] = (unsigned char)green;
image[2] = (unsigned char)red;
}
else
{
image[0] = 0;
image[1] = 0;
image[2] = 0;
}
image += 3;
}
}
}
What does incrementing image+=3; actually do here. I’m trying to convert the same c++ code to C#, but unable to achieve this. I’m using byte[] image in C#, now how should I do image+=3 in C#. Is it scaling the image?
>Solution :
From the code it is evident that the pointer points to an element of an array of unsigned char:
[ ][ ][ ][ ] ........... [ ]
^
|
image
Next consider that image[i] is equivalent (really equivalent, that is how it is defined) to *(image + i), ie it increments the pointer by i and dereferences it. You can write image[0] to get the element image points to. You can type image[1] to get the next element in the array.
Lets call the actual array x then you can access its elements via incrementing image like this:
x[0] x[1] x[2] x[3] x[4] x[5]
image[0] image[1] image[2]
(image+3)[0] (image+3)[1] (image+3)[2]
In other words, the author could have used some offset in the outer loop which increments by 3 in each iteration and then instead of image[ i ] they would have used image[ i + offset ]. Instead they choose to increment image which has the same effect.