A monochrome screen is stored as a single array of bytes, allowing eight consecutive pixels to be stored in one byte. The screen has width w, where w is divisible by 8 (that is, no byte will be split across rows). The height of the screen, of course, can be derived from the length of the array and the width. Implement a function drawHorizontalLi…

CC150-5.8.java

package POJ;

import java.util.ArrayList;

public class Main{
 
	/**
	 * 
	 * 5.8 A monochrome screen is stored as a single array of bytes, allowing eight consecutive pixels to be stored
	 * in one byte. The screen has width w, where w is divisible by 8 (that is, no byte will be split across rows).
	 * The height of the screen, of course, can be derived from the length of the array and the width. Implement a 
	 * function drawHorizontalLine(byte[] screen, int width, int x1, int x2, int y) which draws a horizontal line from
	 * (x 1, y) to (x2, y).
	 * 
	 */
//	public static void main(String[] args) {
//		Main so = new Main();
//	}
	public void drawLine(byte[] screen, int width, int x1, int x2, int y) {
		int start_offset = x1 % 8;
		int first_full_byte = x1 / 8;
		if (start_offset != 0) {
			first_full_byte++;
		}
		int end_offset = x2 % 8;
		int last_full_byte = x2 / 8;
		if (end_offset != 7)
			last_full_byte--;
		// set full bytes
		for (int i = first_full_byte; i <= last_full_byte; i++)
			screen[y * (width / 8) + i] = (byte) 0xFF;
		// create masks for start and end of line;
		byte startMask = (byte) (0xFF >> start_offset);
		byte endMask = (byte) ~(0xFF >> (end_offset + 1));
		// set start and end of line
		if ((x1 / 8) == (x2 / 8)) {
			// x1 and x2 are in the same byte
			byte mask = (byte) (startMask & endMask);
			screen[y * (width / 8) + x1 / 8] |= mask;
		} else {
			if (start_offset != 0) {
				screen[y * (width / 8) + first_full_byte - 1] |= startMask;
			}
			if (end_offset != 7) {
				screen[y * (width / 8) + last_full_byte + 1] |= endMask;
			}
		}
	}
}