These days I'm working on few games which I'm writing in Java. I needed functions to draw lines and circles etc. Instead of using the Java libraries, I wrote my own functions. Thinking may be some day, some body else use them too I'm putting the source code to these functions here, in my blog.

//////////////////////////////////////////////////////////////////////////// // NibblesFunctions.java // // Written by, Sohail Qayum Malik // // Last modified on, Monday, 7th of March, 2010 @7:12AM // //////////////////////////////////////////////////////////////////////////// package Nibbles; import java.lang.Math; import java.awt.Graphics; public class NibblesFunctions { //Bresenham circle //Read the following book at page 29... //http://books.google.com.pk/books?id=7gT1MhI1SbIC&pg=PP3&dq=+"Computer+Graphics++"SCHAUM's+outline+series"&cd=1#v=onepage&q= "Computer Graphics "SCHAUM's outline series"&f=false // a and b is an origin ordinate pair(a,b) // r is the radius public static void drawCircle(Graphics graphics, int a, int b, int r) { //We'll start at the right hand side of the circle //First point is always on the circle so error is zero and we know that x is r and y is 0 //There are only two valid moves... //Up = x^2 + (y + 1)^2 - r^2 and Left = (x - 1)^2 + (y + 1)^2 - r^2 //Our d = Up + Left int x = r, y = 0, d = 3 - 2*r; // x is initially r, x will be same as y at 45(degree) angle while(y <= x) { // Eight way symmetry of circle graphics.drawString(".", x + b, y + a); graphics.drawString(".", y + b, x + a); graphics.drawString(".", (-1)*y + b, x + a); graphics.drawString(".", (-1)*x + b, y + a); graphics.drawString(".", (-1)*x + b, (-1)*y + a); graphics.drawString(".", (-1)*y + b, (-1)*x + a); graphics.drawString(".", y + b, (-1)*x + a); graphics.drawString(".", x + b, (-1)*y + a); if(d < 0) // move Up = d + Up + 2 d = d + 4*y + 6; else { // move Left = d + Left + 2 d = d - 4*(x - y) + 10; //Since we've started at the right hand side of the circle x = x - 1; } // Since we have started at top of the circle y = y + 1; } } /* //Bresenham circle //Read the following book at page 29... //http://books.google.com.pk/books?id=7gT1MhI1SbIC&pg=PP3&dq=+"Computer+Graphics++"SCHAUM's+outline+series"&cd=1#v=onepage&q= "Computer Graphics "SCHAUM's outline series"&f=false // a and b is an origin ordinate pair(a,b) // r is the radius public static void drawCircle(Graphics graphics, int a, int b, int r) { //We'll start at the top of the circle //First point is always on the circle so error is zero and we know that x is zero and y is r int x = 0, y = r, d = 3 - 2*r; // x is initially zero, x will be same as y at 45(degree) angle while(x <= y) { // Eight way symmetry of circle graphics.drawString(".", x + b, y + a); graphics.drawString(".", y + b, x + a); graphics.drawString(".", (-1)*y + b, x + a); graphics.drawString(".", (-1)*x + b, y + a); graphics.drawString(".", (-1)*x + b, (-1)*y + a); graphics.drawString(".", (-1)*y + b, (-1)*x + a); graphics.drawString(".", y + b, (-1)*x + a); graphics.drawString(".", x + b, (-1)*y + a); if(d < 0) // move right d = d + 4*x + 6; else { // move down d = d + 4*(x - y) + 10; //Since we've started at the top of the circle y = y - 1; } // Since we have started at top of the circle x = x + 1; } } */ //Bresenham line //Read chapter 3 at page 28 of the following book //http://books.google.com.pk/books?id=7gT1MhI1SbIC&pg=PP3&dq=+"Computer+Graphics++"SCHAUM's+outline+series"&cd=1#v=onepage&q= "Computer Graphics "SCHAUM's outline series"&f=false //I also went through following two documents //http://cs.fit.edu/~wds/classes/graphics/Rasterize/rasterize/rasterize.html //http://en.wikipedia.org/wiki/Bresenham's_line_algorithm public static void drawLine(Graphics graphics, int x1, int y1, int x2, int y2) { int x, y, dx, dy, d, ystep, tmp; //This algorithm only deals with lines having shallow slopes. When a line has steep slope then we take the advantage of the fact that steep line can be reflected across the line y = x boolean steep = Math.abs(y2 - y1) > Math.abs(x2 - x1); //Yes line has steep slope make it shallow if(steep) { //swap(x1, y1) //Because Java for scalar types is pass by value tmp = y1; y1 = x1; x1 = tmp; //swap(x2, y2) //Because Java for scalar types is pass by value tmp = y2; y2 = x2; x2 = tmp; } //We always move from left to right(that is x is always incremented) if(x1 > x2) { //swap(x1, x2); //Because Java for scalar types is pass by value tmp = x2; x2 = x1; x1 = tmp; //swap(y1, y2) //Because Java for scalar types is pass by value tmp = y2; y2 = y1; y1 = tmp; } dx = x2 - x1; dy = Math.abs(y2 - y1); //Initial value, the first and the last points are always on the line, so error is zero(2e=2(0)=0) //e = dyX - dxY + c //eR = dy(X + 1) - dxY + c = e + dy //eD = dy(X + 1) - dx(Y + 1) + c = e + dy - dx //d = eR + eD d = 2*dy - dx; //Find out if we'll increment or decrement y if(y1 < y2) ystep = 1; else ystep = -1; //Initial values(initial ordinate pair) x = x1; y = y1; while(x <= x2) { //x is reflected as y(transitive) if(steep) graphics.drawString(".", y, x); else graphics.drawString(".", x, y); //We only allow two moves, move to the right, or move diagonally. when we move to the right we only increment x otherwise we increment both(sign of ystep) if(d < 0) d = d + 2*dy; else { d = d + 2*dy - 2*dx; y = y + ystep; } x = x + 1; } } // Trigonometric method // a = length of major axis, b = length of minor axis // h,k ordinate pair for the center of the ellipse // x = a * cos(0 to PI/2 radians) + h // y = b * sin(0 to PI/2 radians) + k // Inorder to rotate on axis, make minor greater than major public static void drawEllipse(Graphics graphics, int h, int k, int a, int b) { int x = 0, y = 0; //i is the magnitude of increment to radian at each step, this should not be fixed as it is now double radian = 0, i = 0.01; while(radian <= Math.PI/2) { x = (int)(a*(Math.cos(radian))); y = (int)(b*(Math.sin(radian))); //Ellipses have 4 way symmetry graphics.drawString(".", x + h, y + k); graphics.drawString(".", (-1)*x + h, y + k); graphics.drawString(".", (-1)*x + h, (-1)*y + k); graphics.drawString(".", x + h, (-1)*y + k); radian = radian + i; } } // It is easy, no special algorithm there, just draw four lines public static void drawRectangle(Graphics graphics, int x1, int y1, int width, int height) { drawLine(graphics, x1, y1, x1 + width, y1); drawLine(graphics, x1, y1 + height, x1 + width, y1 + height); drawLine(graphics, x1, y1, x1, y1 + height); drawLine(graphics, x1 + width, y1, x1 + width, y1 + height); } public static void fillRectangle(Graphics graphics, int x1, int y1, int width, int height) { int x, y; if(width < 2 || height < 2) { drawRectangle(graphics, x1, y1, width, height); return; } for(y = 0; y < height + 1; y++) for(x = 0; x < width + 1; x++) graphics.drawString(".", x1 + x, y1 + y); } public static void fillCircle(Graphics graphics, int a, int b, int r) { int r1; for(r1 = r; r1 > 0; r1--) drawCircle(graphics, a, b, r1); } };