# Forums - How to mosaic an rectangle area

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How to mosaic an rectangle area
371152061
Join Date: 13 May 22
Posts: 11
Posted: Tue, 2022-06-14 07:10

Hi,

I want to mosaic an area( such as an rectangle or  ellipse),  can anyone tell me how to implement it?

for rectangle(an RGB array set to gray), it doesnt work

int pos = x_pos+ y_pos;
fcvSetElementsc3u8(data+pos, dst_width, dst_height, stride, 128, 128, 128, NULL, 0);

371152061
Join Date: 13 May 22
Posts: 11
Posted: Wed, 2022-06-15 01:20

I use pure math to implement rectangle mosaic.

```static void mosaic_rectangle(uint8_t* src, int src_w,int startX, int startY, int w, int h)
{
uint8_t* line = (uint8_t*) fcvMemAlloc(w*3, 16);
memset(line, 128, w*3);
for(int i=0; i<h; i++){
int pos = startY*(src_w*3)+(src_w*3)*i  + startX*3;
memcpy(src+pos, line, w*3);
}
fcvMemFree(line);
}```

can give me some implementation advice for ellipse or circle?

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ss.pandiri
Join Date: 29 May 18
Posts: 58
Posted: Thu, 2022-07-28 07:03

hi,

Once you know the centre of the circle (coordinates)and its radius (coordinates) in your picture you can use the equation:

x^2 + y^2 = R^2 to determine whether a particular point (given by x, y) lies on a circle of radius (R).

You can use root of (x^2 + y^2) to know whether the point lies inside or outside the circle. if (root of (x^2 + y^2)) is greater than R then the point (x,y) lies outside the circle else inside.

thanks

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