# Graphics Problems

Graphics problems typically focus on your ability to implement primitive graphics functions rather than using a high-level API as you would in most programming projects.

## Eighth of a Circle

**PROBLEM**Write a function that draws the upper-eighth of a circle centered at (0, 0) with a given radius, where the upper-eighth is defined as the portion starting at 12 and going to 1:30 on a clock face. Use the following prototype:

`void drawEighthOfCircle( int radius );`

`void setPixel( int xCoord, int yCoord );`

This problem is not as contrived as it seems. If you were trying to implement a full-circle drawing routine, you would want to do as little calculation as possible to maintain optimum performance. Given the pixels for one-eighth of a circle, you can easily determine the pixels for the remainder of the circle from symmetry.

**NOTE**If a point (x, y) is on a circle, so are the points (–x, y), (x, –y), (–x, –y), (y, x), (–y, x), (y, –x), and (–y, –x).

This problem is an example of a scan conversion, converting a geometric drawing to a pixel-based raster image. You need an equation for a circle before you can calculate anything. The common mathematical function that produces a circle is:

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