This is very old code of mine that I've recently found after backing up stuff off my old computer. Added some comments to it; thought I'd post it here.
#define D_RIGHT 0
#define D_UP 1
#define D_LEFT 2
#define D_DOWN 3
typedef int DIRECTION;
void WindowSpiral(HWND hWnd, int jumpdiv)
/* Declarations */
int centerX, centerY, jumps = 1, i, curX, curY, xjumpamt, yjumpamt;
DIRECTION direction = D_RIGHT;
/* Get the rect for dimension and jump configuration */
/* Integer division but at most we'd be off by one pixel; gets the center of the window */
centerX = dimensions.left+((dimensions.right-dimensions.left)/2);
centerY = dimensions.top+((dimensions.bottom-dimensions.top)/2);
/* These will be the amount jumped each iteration; integer division but good enough */
xjumpamt = (dimensions.right-dimensions.left)/jumpdiv;
yjumpamt = (dimensions.bottom-dimensions.top)/jumpdiv;
/* Get into the middle of the window before we start */
curX = centerX; curY = centerY;
//if(direction < 3) direction = D_RIGHT;
for(i = 0; i < jumps; i++)
// The above two lines are NOT necessary; they are only so you can see the current location of the spiral loop.
jumps++; direction++; // increment jumps and direction each time around so that the spiral will grow outward
/* Check if we're out of the window rect; if so, no more*/
if(p.x >= dimensions.right) break;
if(p.y >= dimensions.bottom) break;
if(p.x <= dimensions.left) break;
if(p.y <= dimensions.top) break;
From here, you can add GetPixel and change the return type to make a color clicker.
The SetCursorPos/GetCursorPos and Sleep lines shouldn't be in a finished application; those are there so the cursor can be used to indicate the path of the spiral. To check if you're finished in an application without those lines, compare curX/curY with the dimension.top/bottom/left/right values.