Develop Reference

ERROR while trying to run my java game

Below is the code that i received in the console when trying to run my game download the code here.
Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: 64
at com.comli.blah.rainofwrath.graphics.Screen.<init>(Screen.java:22)
at com.comli.blah.rainofwrath.game.<init>(game.java:38)
at com.comli.blah.rainofwrath.game.main(game.java:123)
Code:
public class Screen {
private int width, height;
public int[] pixels;
public final int MAP_SIZE = 64;
public final int MAP_SIZE_MASK = MAP_SIZE - 1;
public int[] tiles = new int[8 * 8];
private Random random = new Random();
public Screen (int width, int height) {
this.width = width;
this.height = height;
pixels = new int[width * height]; // 50,400
for (int i = 0; i < MAP_SIZE * MAP_SIZE; i++) {
tiles[i] = random.nextInt(0xffffff);
}
}
public void clear() {
for (int i = 0; i < pixels.length; i++) {
pixels[i] = 0;
}
}
public void render(int xOffset, int yOffset) {
for (int y = 0; y < height; y++) {
int yy = y + yOffset;
// if (yy < 0 || yy >= height) break;
for (int x = 0; x < width; x++) {
int xx = x + xOffset;
// if (xx < 0 || xx >= width) break;
int tileIndex = ((xx >> 4) & MAP_SIZE_MASK) + ((yy >> 4) & MAP_SIZE_MASK) * MAP_SIZE;
pixels[x + y * width] = Sprite.grass.pixels[(x&15) + (y&15) * Sprite.grass.SIZE];
}
}
}
}

The problem here is in the tiles array. It has 64 (8 * 8) elements during initialization, whilst by specifying i < MAP_SIZE * MAP_SIZE (MAP_SIZE = 64) as stop-rule at you loop you are trying to go beyond this limit. I belive it should be:
public int[] tiles = new int[MAP_SIZE * MAP_SIZE]

How to make circle clickable

I am developing game using canvas. I have drawn grid of circles using loop. I want to get x,y coordinates of circles. For that I have to make those circles clickable so that whenever player click on a circle it should return its coordinates. I will pass those coordinates to lineDraw() method for drawing line between those circles.
This loop is defining grid of circles:
for (int y=0;y<rows;y++)
{
for (int x=0;x<cols;x++)
{
canvas.drawCircle((x + 1) * dw, (y + 1) *(3* dh), 20, pDot);
}
}
Here dw is (displayWidth) and dh is (displayHeight). Please suggest how I should make these circles clickable?

I had played with this project a little after your previous questions. I'm sure this isn't the most optimized way to do this, but without knowing how you plan to implement the game logic, I think this is flexible enough to adapt. The following is your custom View class, which I've renamed Board, in keeping with Java naming conventions.
public class Board extends View
{
Paint pBack = new Paint();
Paint pDot = new Paint();
Paint pLine = new Paint();
int cols = 5;
int rows = 6;
// Default initialization = false
boolean[][] dots = new boolean[cols][rows];
int canWidth = 0;
int canHeight = 0;
float xStep = 0;
float yStep = 0;
float[] xCoords = new float[cols];
float[] yCoords = new float[rows];
public Board(Context context)
{
super(context);
pBack.setARGB(255, 255, 102, 0);
pDot.setARGB(255, 255, 255, 255);
pLine.setStrokeWidth(5);
pLine.setARGB(255, 90, 10, 0);
}
public void setDots(boolean[][] dotSelected)
{
this.dots = dotSelected;
}
public boolean[][] getDots()
{
return dots;
}
protected void onSizeChanged(int w, int h, int oldw, int oldh)
{
canWidth = w;
canHeight = h;
xStep = canWidth / (cols + 1);
yStep = canHeight / (rows + 1);
for (int y = 0; y < rows; y++)
{
yCoords[y] = (y + 1) * yStep;
}
for (int x = 0; x < cols; x++)
{
xCoords[x] = (x + 1) * xStep;
}
}
protected void onDraw(Canvas canvas)
{
super.onDraw(canvas);
canvas.drawPaint(pBack);
// Grid, lines and box markings
for (int y = 0; y < rows; y++)
{
canvas.drawLine(xStep, yCoords[y], cols * xStep, yCoords[y], pDot);
for (int x = 0; x < cols; x++)
{
if (y == 0)
{
canvas.drawLine(xCoords[x], yStep, xCoords[x], rows * yStep, pDot);
}
if (dots[x][y])
{
boolean left = x > 0 && dots[x - 1][y];
boolean up = y > 0 && dots[x][y - 1];
if (left)
{
canvas.drawLine(xCoords[x], yCoords[y], xCoords[x - 1], yCoords[y], pLine);
}
if (up)
{
canvas.drawLine(xCoords[x], yCoords[y], xCoords[x], yCoords[y - 1], pLine);
}
if (left && up && dots[x - 1][y - 1])
{
canvas.drawCircle(xCoords[x] - xStep / 2, yCoords[y] - yStep / 2, 10, pLine);
}
}
}
}
// Dots
for (int y = 0; y < rows; y++)
{
for (int x = 0; x < cols; x++)
{
canvas.drawCircle(xCoords[x], yCoords[y], 20, pDot);
if (dots[x][y])
{
canvas.drawCircle(xCoords[x], yCoords[y], 15, pBack);
}
}
}
}
public boolean onTouchEvent(MotionEvent event)
{
super.onTouchEvent(event);
if (event.getAction() != MotionEvent.ACTION_DOWN)
return true;
int xNear = 0;
int yNear = 0;
float xMin = canWidth;
float yMin = canHeight;
for (int x = 0; x < cols; x++)
{
if (Math.abs(xCoords[x] - event.getX()) < xMin)
{
xMin = Math.abs(xCoords[x] - event.getX());
xNear = x;
}
}
for (int y = 0; y < rows; y++)
{
if (Math.abs(yCoords[y] - event.getY()) < yMin)
{
yMin = Math.abs(yCoords[y] - event.getY());
yNear = y;
}
}
dots[xNear][yNear] = !dots[xNear][yNear];
invalidate();
return true;
}
}

Store the data of your circles (for instance the position and the radius) in a list and check each of them for mouse collision(register a mouseeventlistener).
public class Circle
{
private int radius;
private int positionX;
private int positionY;
public Circle(int positionX, int positionY, int radius)
{
this.radius = radius;
this.positionX = positionX;
this.positionY = positionY;
}
public int getPositionX()
{
return this.positionX;
}
public int getPositionY()
{
return this.positionY;
}
public boolean contains(int posX, int posY)
{
int distanceX = this.positionX - posX;
int distanceY = this.positionY - posY;
return Math.sqrt((distanceX * distanceX) + (distanceY * distanceY)) <= this.radius;
}

Java heightmap using lwjgl

I have coded a heightmap but it seems to lag the client. I just don't know how to increase the fps. I get about 3-6fps with the heightmap. Im using a quite large bmp for the heightmap, I think its 1024x1024. When i use a smaller on its fine, maybe im just not using the code effectively. Is there a better way to code this heightmap or did I just code it wrong. It is my first time I have worked on a heightmap. Thanks
public class HeightMap {
private final float xScale, yScale, zScale;
private float[][] heightMap;
private FloatBuffer vertices, normals, texCoords;
private IntBuffer indices;
private Vector3f[] verticesArray, normalsArray;
private int[] indicesArray;
private int width;
private int height;
public float getHeight(int x, int y) {
return heightMap[x][y] * yScale;
}
public HeightMap(String path, int resolution) {
heightMap = loadHeightmap("heightmap.bmp");
xScale = 1000f / resolution;
yScale = 8;
zScale = 1000f / resolution;
verticesArray = new Vector3f[width * height];
vertices = BufferUtils.createFloatBuffer(3 * width * height);
texCoords = BufferUtils.createFloatBuffer(2 * width * height);
for (int x = 0; x < width; x++) {
for (int y = 0; y < height; y++) {
final int pos = height * x + y;
final Vector3f vertex = new Vector3f(xScale * x, yScale * heightMap[x][y], zScale * y);
verticesArray[pos] = vertex;
vertex.store(vertices);
texCoords.put(x / (float) width);
texCoords.put(y / (float) height);
}
}
vertices.flip();
texCoords.flip();
normalsArray = new Vector3f[height * width];
normals = BufferUtils.createFloatBuffer(3 * width * height);
final float xzScale = xScale;
for (int x = 0; x < width; ++x) {
for (int y = 0; y < height; ++y) {
final int nextX = x < width - 1 ? x + 1 : x;
final int prevX = x > 0 ? x - 1 : x;
float sx = heightMap[nextX][y] - heightMap[prevX][y];
if (x == 0 || x == width - 1) {
sx *= 2;
}
final int nextY = y < height - 1 ? y + 1 : y;
final int prevY = y > 0 ? y - 1 : y;
float sy = heightMap[x][nextY] - heightMap[x][prevY];
if (y == 0 || y == height - 1) {
sy *= 2;
}
final Vector3f normal = new Vector3f(-sx * yScale, 2 * xzScale, sy * yScale).normalise(null);
normalsArray[height * x + y] = normal;
normal.store(normals);
}
}
normals.flip();
indicesArray = new int[6 * (height - 1) * (width - 1)];
indices = BufferUtils.createIntBuffer(6 * (width - 1) * (height - 1));
for (int i = 0; i < width - 1; i++) {
for (int j = 0; j < height - 1; j++) {
int pos = (height - 1) * i + j;
indices.put(height * i + j);
indices.put(height * (i + 1) + j);
indices.put(height * (i + 1) + (j + 1));
indicesArray[6 * pos] = height * i + j;
indicesArray[6 * pos + 1] = height * (i + 1) + j;
indicesArray[6 * pos + 2] = height * (i + 1) + (j + 1);
indices.put(height * i + j);
indices.put(height * i + (j + 1));
indices.put(height * (i + 1) + (j + 1));
indicesArray[6 * pos + 3] = height * i + j;
indicesArray[6 * pos + 4] = height * i + (j + 1);
indicesArray[6 * pos + 5] = height * (i + 1) + (j + 1);
}
}
indices.flip();
}
private float[][] loadHeightmap(String fileName) {
try {
BufferedImage img = ImageIO.read(ResourceLoader.getResourceAsStream(fileName));
width = img.getWidth();
height = img.getHeight();
float[][] heightMap = new float[width][height];
for (int x = 0; x < width; x++) {
for (int y = 0; y < height; y++) {
heightMap[x][y] = 0xFF & img.getRGB(x, y);
}
}
return heightMap;
} catch (IOException e) {
System.out.println("Nincs meg a heightmap!");
return null;
}
}
public void render() {
glEnableClientState(GL_NORMAL_ARRAY);
glEnableClientState(GL_VERTEX_ARRAY);
glEnableClientState(GL_TEXTURE_COORD_ARRAY);
glNormalPointer(0, normals);
glVertexPointer(3, 0, vertices);
glTexCoordPointer(2, 0, texCoords);
glDrawElements(GL_TRIANGLE_STRIP, indices);
glDisableClientState(GL_NORMAL_ARRAY);
glDisableClientState(GL_TEXTURE_COORD_ARRAY);
glDisableClientState(GL_VERTEX_ARRAY);
}
}

Sorry to bring up an old topic, however i see a lot of people ask this:
Use a display list, instead of re-making the heightmap every time.
TheCodingUniverse has a good tutorial on how to do this.

Android Box Blur Algorithm

I have been trying to implement a box blur algorithm in android.
The code seems to be fine but when trying to apply it, some areas in the blurred image have big yellow and white smudges all over the blurred photo.
Can anyone help me find out what i'm doing wrong?
Thanks:
Here is what i have:
public static Bitmap boxBlur(Bitmap bmp, int range) {
assert (range & 1) == 0 : "Range must be odd.";
Bitmap blurred = Bitmap.createBitmap(bmp.getWidth(), bmp.getHeight(),
Config.ARGB_8888);
Canvas c = new Canvas(blurred);
int w = bmp.getWidth();
int h = bmp.getHeight();
int[] pixels = new int[bmp.getWidth() * bmp.getHeight()];
bmp.getPixels(pixels, 0, w, 0, 0, w, h);
boxBlurHorizontal(pixels, w, h, range / 2);
boxBlurVertical(pixels, w, h, range / 2);
c.drawBitmap(pixels, 0, w, 0.0F, 0.0F, w, h, true, null);
return blurred;
}
private static void boxBlurHorizontal(int[] pixels, int w, int h,
int halfRange) {
int index = 0;
int[] newColors = new int[w];
for (int y = 0; y < h; y++) {
int hits = 0;
long r = 0;
long g = 0;
long b = 0;
for (int x = -halfRange; x < w; x++) {
int oldPixel = x - halfRange - 1;
if (oldPixel >= 0) {
int color = pixels[index + oldPixel];
if (color != 0) {
r -= Color.red(color);
g -= Color.green(color);
b -= Color.blue(color);
}
hits--;
}
int newPixel = x + halfRange;
if (newPixel < w) {
int color = pixels[index + newPixel];
if (color != 0) {
r += Color.red(color);
g += Color.green(color);
b += Color.blue(color);
}
hits++;
}
if (x >= 0) {
newColors[x] = Color.argb(0xFF, (byte) (r / hits),
(byte) (g / hits), (byte) (b / hits));
}
}
for (int x = 0; x < w; x++) {
pixels[index + x] = newColors[x];
}
index += w;
}
}
private static void boxBlurVertical(int[] pixels, int w, int h,
int halfRange) {
int[] newColors = new int[h];
int oldPixelOffset = -(halfRange + 1) * w;
int newPixelOffset = (halfRange) * w;
for (int x = 0; x < w; x++) {
int hits = 0;
long r = 0;
long g = 0;
long b = 0;
int index = -halfRange * w + x;
for (int y = -halfRange; y < h; y++) {
int oldPixel = y - halfRange - 1;
if (oldPixel >= 0) {
int color = pixels[index + oldPixelOffset];
if (color != 0) {
r -= Color.red(color);
g -= Color.green(color);
b -= Color.blue(color);
}
hits--;
}
int newPixel = y + halfRange;
if (newPixel < h) {
int color = pixels[index + newPixelOffset];
if (color != 0) {
r += Color.red(color);
g += Color.green(color);
b += Color.blue(color);
}
hits++;
}
if (y >= 0) {
newColors[y] = Color.argb(0xFF, (byte) (r / hits),
(byte) (g / hits), (byte) (b / hits));
}
index += w;
}
for (int y = 0; y < h; y++) {
pixels[y * w + x] = newColors[y];
}
}
}

Found the problem!
The line:
newColors[x] = Color.argb(0xFF, (byte) (r / hits), (byte) (g / hits), (byte) (b / hits));
I converted the averages to bytes, where they should have been ints.
Changed it to:
newColors[x] = Color.argb(0xFF, (int) (r / hits), (int) (g / hits), (int) (b / hits));

Canny Edge Detection using Processing

I am looking for a copy paste implementation of Canny Edge Detection in the processing language. I have zero idea about Image processing and very little clue about Processing, though I understand java pretty well.
Can some processing expert tell me if there is a way of implementing this http://www.tomgibara.com/computer-vision/CannyEdgeDetector.java in processing?

I think if you treat processing in lights of Java then some of the problems could be solved very easily. What it means is that you can use Java classes as such.
For the demo I am using the implementation which you have shared.
>>Original Image
>>Changed Image
>>Code
import java.awt.image.BufferedImage;
import java.util.Arrays;
PImage orig;
PImage changed;
void setup() {
orig = loadImage("c:/temp/image.png");
size(250, 166);
CannyEdgeDetector detector = new CannyEdgeDetector();
detector.setLowThreshold(0.5f);
detector.setHighThreshold(1f);
detector.setSourceImage((java.awt.image.BufferedImage)orig.getImage());
detector.process();
BufferedImage edges = detector.getEdgesImage();
changed = new PImage(edges);
noLoop();
}
void draw()
{
//image(orig, 0,0, width, height);
image(changed, 0,0, width, height);
}
// The code below is taken from "http://www.tomgibara.com/computer-vision/CannyEdgeDetector.java"
// I have stripped the comments for conciseness
public class CannyEdgeDetector {
// statics
private final static float GAUSSIAN_CUT_OFF = 0.005f;
private final static float MAGNITUDE_SCALE = 100F;
private final static float MAGNITUDE_LIMIT = 1000F;
private final static int MAGNITUDE_MAX = (int) (MAGNITUDE_SCALE * MAGNITUDE_LIMIT);
// fields
private int height;
private int width;
private int picsize;
private int[] data;
private int[] magnitude;
private BufferedImage sourceImage;
private BufferedImage edgesImage;
private float gaussianKernelRadius;
private float lowThreshold;
private float highThreshold;
private int gaussianKernelWidth;
private boolean contrastNormalized;
private float[] xConv;
private float[] yConv;
private float[] xGradient;
private float[] yGradient;
// constructors
/**
* Constructs a new detector with default parameters.
*/
public CannyEdgeDetector() {
lowThreshold = 2.5f;
highThreshold = 7.5f;
gaussianKernelRadius = 2f;
gaussianKernelWidth = 16;
contrastNormalized = false;
}
public BufferedImage getSourceImage() {
return sourceImage;
}
public void setSourceImage(BufferedImage image) {
sourceImage = image;
}
public BufferedImage getEdgesImage() {
return edgesImage;
}
public void setEdgesImage(BufferedImage edgesImage) {
this.edgesImage = edgesImage;
}
public float getLowThreshold() {
return lowThreshold;
}
public void setLowThreshold(float threshold) {
if (threshold < 0) throw new IllegalArgumentException();
lowThreshold = threshold;
}
public float getHighThreshold() {
return highThreshold;
}
public void setHighThreshold(float threshold) {
if (threshold < 0) throw new IllegalArgumentException();
highThreshold = threshold;
}
public int getGaussianKernelWidth() {
return gaussianKernelWidth;
}
public void setGaussianKernelWidth(int gaussianKernelWidth) {
if (gaussianKernelWidth < 2) throw new IllegalArgumentException();
this.gaussianKernelWidth = gaussianKernelWidth;
}
public float getGaussianKernelRadius() {
return gaussianKernelRadius;
}
public void setGaussianKernelRadius(float gaussianKernelRadius) {
if (gaussianKernelRadius < 0.1f) throw new IllegalArgumentException();
this.gaussianKernelRadius = gaussianKernelRadius;
}
public boolean isContrastNormalized() {
return contrastNormalized;
}
public void setContrastNormalized(boolean contrastNormalized) {
this.contrastNormalized = contrastNormalized;
}
// methods
public void process() {
width = sourceImage.getWidth();
height = sourceImage.getHeight();
picsize = width * height;
initArrays();
readLuminance();
if (contrastNormalized) normalizeContrast();
computeGradients(gaussianKernelRadius, gaussianKernelWidth);
int low = Math.round(lowThreshold * MAGNITUDE_SCALE);
int high = Math.round( highThreshold * MAGNITUDE_SCALE);
performHysteresis(low, high);
thresholdEdges();
writeEdges(data);
}
// private utility methods
private void initArrays() {
if (data == null || picsize != data.length) {
data = new int[picsize];
magnitude = new int[picsize];
xConv = new float[picsize];
yConv = new float[picsize];
xGradient = new float[picsize];
yGradient = new float[picsize];
}
}
private void computeGradients(float kernelRadius, int kernelWidth) {
//generate the gaussian convolution masks
float kernel[] = new float[kernelWidth];
float diffKernel[] = new float[kernelWidth];
int kwidth;
for (kwidth = 0; kwidth < kernelWidth; kwidth++) {
float g1 = gaussian(kwidth, kernelRadius);
if (g1 <= GAUSSIAN_CUT_OFF && kwidth >= 2) break;
float g2 = gaussian(kwidth - 0.5f, kernelRadius);
float g3 = gaussian(kwidth + 0.5f, kernelRadius);
kernel[kwidth] = (g1 + g2 + g3) / 3f / (2f * (float) Math.PI * kernelRadius * kernelRadius);
diffKernel[kwidth] = g3 - g2;
}
int initX = kwidth - 1;
int maxX = width - (kwidth - 1);
int initY = width * (kwidth - 1);
int maxY = width * (height - (kwidth - 1));
//perform convolution in x and y directions
for (int x = initX; x < maxX; x++) {
for (int y = initY; y < maxY; y += width) {
int index = x + y;
float sumX = data[index] * kernel[0];
float sumY = sumX;
int xOffset = 1;
int yOffset = width;
for(; xOffset < kwidth ;) {
sumY += kernel[xOffset] * (data[index - yOffset] + data[index + yOffset]);
sumX += kernel[xOffset] * (data[index - xOffset] + data[index + xOffset]);
yOffset += width;
xOffset++;
}
yConv[index] = sumY;
xConv[index] = sumX;
}
}
for (int x = initX; x < maxX; x++) {
for (int y = initY; y < maxY; y += width) {
float sum = 0f;
int index = x + y;
for (int i = 1; i < kwidth; i++)
sum += diffKernel[i] * (yConv[index - i] - yConv[index + i]);
xGradient[index] = sum;
}
}
for (int x = kwidth; x < width - kwidth; x++) {
for (int y = initY; y < maxY; y += width) {
float sum = 0.0f;
int index = x + y;
int yOffset = width;
for (int i = 1; i < kwidth; i++) {
sum += diffKernel[i] * (xConv[index - yOffset] - xConv[index + yOffset]);
yOffset += width;
}
yGradient[index] = sum;
}
}
initX = kwidth;
maxX = width - kwidth;
initY = width * kwidth;
maxY = width * (height - kwidth);
for (int x = initX; x < maxX; x++) {
for (int y = initY; y < maxY; y += width) {
int index = x + y;
int indexN = index - width;
int indexS = index + width;
int indexW = index - 1;
int indexE = index + 1;
int indexNW = indexN - 1;
int indexNE = indexN + 1;
int indexSW = indexS - 1;
int indexSE = indexS + 1;
float xGrad = xGradient[index];
float yGrad = yGradient[index];
float gradMag = hypot(xGrad, yGrad);
//perform non-maximal supression
float nMag = hypot(xGradient[indexN], yGradient[indexN]);
float sMag = hypot(xGradient[indexS], yGradient[indexS]);
float wMag = hypot(xGradient[indexW], yGradient[indexW]);
float eMag = hypot(xGradient[indexE], yGradient[indexE]);
float neMag = hypot(xGradient[indexNE], yGradient[indexNE]);
float seMag = hypot(xGradient[indexSE], yGradient[indexSE]);
float swMag = hypot(xGradient[indexSW], yGradient[indexSW]);
float nwMag = hypot(xGradient[indexNW], yGradient[indexNW]);
float tmp;
if (xGrad * yGrad <= (float) 0 /*(1)*/
? Math.abs(xGrad) >= Math.abs(yGrad) /*(2)*/
? (tmp = Math.abs(xGrad * gradMag)) >= Math.abs(yGrad * neMag - (xGrad + yGrad) * eMag) /*(3)*/
&& tmp > Math.abs(yGrad * swMag - (xGrad + yGrad) * wMag) /*(4)*/
: (tmp = Math.abs(yGrad * gradMag)) >= Math.abs(xGrad * neMag - (yGrad + xGrad) * nMag) /*(3)*/
&& tmp > Math.abs(xGrad * swMag - (yGrad + xGrad) * sMag) /*(4)*/
: Math.abs(xGrad) >= Math.abs(yGrad) /*(2)*/
? (tmp = Math.abs(xGrad * gradMag)) >= Math.abs(yGrad * seMag + (xGrad - yGrad) * eMag) /*(3)*/
&& tmp > Math.abs(yGrad * nwMag + (xGrad - yGrad) * wMag) /*(4)*/
: (tmp = Math.abs(yGrad * gradMag)) >= Math.abs(xGrad * seMag + (yGrad - xGrad) * sMag) /*(3)*/
&& tmp > Math.abs(xGrad * nwMag + (yGrad - xGrad) * nMag) /*(4)*/
) {
magnitude[index] = gradMag >= MAGNITUDE_LIMIT ? MAGNITUDE_MAX : (int) (MAGNITUDE_SCALE * gradMag);
//NOTE: The orientation of the edge is not employed by this
//implementation. It is a simple matter to compute it at
//this point as: Math.atan2(yGrad, xGrad);
} else {
magnitude[index] = 0;
}
}
}
}
private float hypot(float x, float y) {
return (float) Math.hypot(x, y);
}
private float gaussian(float x, float sigma) {
return (float) Math.exp(-(x * x) / (2f * sigma * sigma));
}
private void performHysteresis(int low, int high) {
Arrays.fill(data, 0);
int offset = 0;
for (int y = 0; y < height; y++) {
for (int x = 0; x < width; x++) {
if (data[offset] == 0 && magnitude[offset] >= high) {
follow(x, y, offset, low);
}
offset++;
}
}
}
private void follow(int x1, int y1, int i1, int threshold) {
int x0 = x1 == 0 ? x1 : x1 - 1;
int x2 = x1 == width - 1 ? x1 : x1 + 1;
int y0 = y1 == 0 ? y1 : y1 - 1;
int y2 = y1 == height -1 ? y1 : y1 + 1;
data[i1] = magnitude[i1];
for (int x = x0; x <= x2; x++) {
for (int y = y0; y <= y2; y++) {
int i2 = x + y * width;
if ((y != y1 || x != x1)
&& data[i2] == 0
&& magnitude[i2] >= threshold) {
follow(x, y, i2, threshold);
return;
}
}
}
}
private void thresholdEdges() {
for (int i = 0; i < picsize; i++) {
data[i] = data[i] > 0 ? -1 : 0xff000000;
}
}
private int luminance(float r, float g, float b) {
return Math.round(0.299f * r + 0.587f * g + 0.114f * b);
}
private void readLuminance() {
int type = sourceImage.getType();
if (type == BufferedImage.TYPE_INT_RGB || type == BufferedImage.TYPE_INT_ARGB) {
int[] pixels = (int[]) sourceImage.getData().getDataElements(0, 0, width, height, null);
for (int i = 0; i < picsize; i++) {
int p = pixels[i];
int r = (p & 0xff0000) >> 16;
int g = (p & 0xff00) >> 8;
int b = p & 0xff;
data[i] = luminance(r, g, b);
}
} else if (type == BufferedImage.TYPE_BYTE_GRAY) {
byte[] pixels = (byte[]) sourceImage.getData().getDataElements(0, 0, width, height, null);
for (int i = 0; i < picsize; i++) {
data[i] = (pixels[i] & 0xff);
}
} else if (type == BufferedImage.TYPE_USHORT_GRAY) {
short[] pixels = (short[]) sourceImage.getData().getDataElements(0, 0, width, height, null);
for (int i = 0; i < picsize; i++) {
data[i] = (pixels[i] & 0xffff) / 256;
}
} else if (type == BufferedImage.TYPE_3BYTE_BGR) {
byte[] pixels = (byte[]) sourceImage.getData().getDataElements(0, 0, width, height, null);
int offset = 0;
for (int i = 0; i < picsize; i++) {
int b = pixels[offset++] & 0xff;
int g = pixels[offset++] & 0xff;
int r = pixels[offset++] & 0xff;
data[i] = luminance(r, g, b);
}
} else {
throw new IllegalArgumentException("Unsupported image type: " + type);
}
}
private void normalizeContrast() {
int[] histogram = new int[256];
for (int i = 0; i < data.length; i++) {
histogram[data[i]]++;
}
int[] remap = new int[256];
int sum = 0;
int j = 0;
for (int i = 0; i < histogram.length; i++) {
sum += histogram[i];
int target = sum*255/picsize;
for (int k = j+1; k <=target; k++) {
remap[k] = i;
}
j = target;
}
for (int i = 0; i < data.length; i++) {
data[i] = remap[data[i]];
}
}
private void writeEdges(int pixels[]) {
if (edgesImage == null) {
edgesImage = new BufferedImage(width, height, BufferedImage.TYPE_INT_ARGB);
}
edgesImage.getWritableTile(0, 0).setDataElements(0, 0, width, height, pixels);
}
}

I've been spending some time with the Gibara Canny implementation and I'm inclined to agree with Settembrini's comment above; further to this one needs to change the implementation of the Gaussian Kernel generation.
The Gibara Canny uses:
(g1 + g2 + g3) / 3f / (2f * (float) Math.PI * kernelRadius * kernelRadius)
The averaging across a pixel (+-0.5 pixels) in (g1 + g2 + g3) / 3f is great, but the correct variance calculation on the bottom half of the equation for single dimensions is:
(g1 + g2 + g3) / 3f / (Math.sqrt(2f * (float) Math.PI) * kernelRadius)
The standard deviation kernelRadius is sigma in the following equation:
Single direction gaussian
I'm assuming that Gibara is attempting to implement the two dimensional gaussian from the following equation: Two dimensional gaussian where the convolution is a direct product of each gaussian. Whilst this is probably possible and more concise, the following code will correctly convolve in two directions with the above variance calculation:
// First Convolution
for (int x = initX; x < maxX; x++) {
for (int y = initY; y < maxY; y += sourceImage.width) {
int index = x + y;
float sumX = data[index] * kernel[0];
int xOffset = 1;
int yOffset = sourceImage.width;
for(; xOffset < k ;) {;
sumX += kernel[xOffset] * (data[index - xOffset] + data[index + xOffset]);
yOffset += sourceImage.width;
xOffset++;
}
xConv[index] = sumX;
}
}
// Second Convolution
for (int x = initX; x < maxX; x++) {
for (int y = initY; y < maxY; y += sourceImage.width) {
int index = x + y;
float sumY = xConv[index] * kernel[0];
int xOffset = 1;
int yOffset = sourceImage.width;
for(; xOffset < k ;) {;
sumY += xConv[xOffset] * (xConv[index - xOffset] + xConv[index + xOffset]);
yOffset += sourceImage.width;
xOffset++;
}
yConv[index] = sumY;
}
}
NB the yConv[] is now the bidirectional convolution, so the following gradient Sobel calculations are as follows:
for (int x = initX; x < maxX; x++) {
for (int y = initY; y < maxY; y += sourceImage.width) {
float sum = 0f;
int index = x + y;
for (int i = 1; i < k; i++)
sum += diffKernel[i] * (yConv[index - i] - yConv[index + i]);
xGradient[index] = sum;
}
}
for (int x = k; x < sourceImage.width - k; x++) {
for (int y = initY; y < maxY; y += sourceImage.width) {
float sum = 0.0f;
int index = x + y;
int yOffset = sourceImage.width;
for (int i = 1; i < k; i++) {
sum += diffKernel[i] * (yConv[index - yOffset] - yConv[index + yOffset]);
yOffset += sourceImage.width;
}
yGradient[index] = sum;
}
}
Gibara's very neat implementation of non-maximum suppression requires that these gradients be calculated seperately, however if you want to output an image with these gradients one can sum them using either Euclidean or Manhattan distances, the Euclidean would look like so:
// Calculate the Euclidean distance between x & y gradients prior to suppression
int [] gradients = new int [picsize];
for (int i = 0; i < xGradient.length; i++) {
gradients[i] = Math.sqrt(Math.sq(xGradient[i]) + Math.sq(yGradient[i]));
}
Hope this helps, is all in order and apologies for my code! Critique most welcome

In addition to Favonius' answer, you might want to try Greg's OpenCV Processing library which you can now easily install via Sketch > Import Library... > Add Library... and select OpenCV for Processing
After you install the library, you can have a play with the FindEdges example:
import gab.opencv.*;
OpenCV opencv;
PImage src, canny, scharr, sobel;
void setup() {
src = loadImage("test.jpg");
size(src.width, src.height);
opencv = new OpenCV(this, src);
opencv.findCannyEdges(20,75);
canny = opencv.getSnapshot();
opencv.loadImage(src);
opencv.findScharrEdges(OpenCV.HORIZONTAL);
scharr = opencv.getSnapshot();
opencv.loadImage(src);
opencv.findSobelEdges(1,0);
sobel = opencv.getSnapshot();
}
void draw() {
pushMatrix();
scale(0.5);
image(src, 0, 0);
image(canny, src.width, 0);
image(scharr, 0, src.height);
image(sobel, src.width, src.height);
popMatrix();
text("Source", 10, 25);
text("Canny", src.width/2 + 10, 25);
text("Scharr", 10, src.height/2 + 25);
text("Sobel", src.width/2 + 10, src.height/2 + 25);
}

Just as I side note. I studied the Gibara Canny implementation some time ago and found some flaws. E.g. he separates the Gauss-Filtering in 1d filters in x and y direction (which is ok and efficient as such), but then he doesn't apply two passes of those filters (one after another) but just applies SobelX to the x-first-pass-Gauss and SobelY to the y-first-pass-Gauss, which of course leads to low quality gradients. Thus be careful just by copy-past such code.