Saturday, September 25, 2010

Nine Slice Scalling

Below is the public contract (constructor and methods) of my NineSliceImage component. It may be used to draw Buttons, Title bars and Frames.

import javax.microedition.lcdui.Graphics;
import javax.microedition.lcdui.Image;

public class NineSliceImage {

public NineSliceImage (Image img, int vMargin, int hMargin) { ... }

public void paintFrameAround (Graphics g, int x, int y, int width, int height) { ... }
public Image createFrameFor (int width, int height) { ... }

}

And below is a sample usage:

class MyClass extends Canvas {
MyClass () throws java.io.IOException {
Image i = Image.createImage("/pattern.PNG");
this.nsi = new NineSliceImage(i, 5, 5);
}
protected void paint(Graphics g) {
nsi.paintFrameAround(g, 20, 20, 20, 20);
}
}

Where patter is the following image:

And the resulting frame is:

Full component source code below:

import javax.microedition.lcdui.Graphics;
import javax.microedition.lcdui.Image;

public class NineSliceImage {

private Image originalImage;
private int verticalMargin;
private int horizontalMargin;
int middlePieceHeight;
int middlePieceWidth;

public NineSliceImage (Image img, int vMargin, int hMargin) {
validateConstructorParameters(img, vMargin, hMargin);
setAttributesValuesFor(img, vMargin, hMargin);
}

public Image createFrameFor (int width, int height) {
validateWidthAndHeight(width, height);

int middleHeight = getMiddleHeight(height);
int middleWidth = getMiddleWidth(width);
Image frame = Image.createImage(middleWidth + (2 * this.horizontalMargin),
middleHeight + (2 * this.verticalMargin));
Graphics g = frame.getGraphics();

this.paintFrameAround(g, horizontalMargin, verticalMargin, middleWidth, middleHeight);

return frame;
}

public void paintFrameAround (Graphics g, int x, int y, int width, int height) {
validateWidthAndHeight(width, height);

int middleWidth = getMiddleWidth(width);
int middleHeight = getMiddleWidth(height);
int totalWidth = middleWidth + (2 * this.horizontalMargin);
int totalHeight = middleHeight + (2 * this.verticalMargin);
x = x - ((middleWidth - width) / 2) - this.horizontalMargin;
y = y - ((middleHeight - height) / 2) - this.verticalMargin;

drawFrameCorners(g, x, y, middleWidth, middleHeight, totalWidth, totalHeight);
drawTopAndBottomLines(g, x, y, width, totalHeight);
drawLeftAndRightColumns(g, x, y, height, totalWidth);
}

private void validateConstructorParameters (Image img, int vMargin, int hMargin) {
if (img == null || vMargin <= 0 || hMargin <= 0) {
throw new IllegalArgumentException();
}
if (vMargin >= img.getHeight() / 2) {
throw new IllegalArgumentException();
}
if (hMargin >= img.getWidth() / 2) {
throw new IllegalArgumentException();
}
}

private void setAttributesValuesFor (Image img, int vMargin, int hMargin) {
this.originalImage = img;
this.verticalMargin = vMargin;
this.horizontalMargin = hMargin;
this.middlePieceHeight = this.originalImage.getHeight()
- (2 * this.verticalMargin);
this.middlePieceWidth = this.originalImage.getWidth()
- (2 * this.horizontalMargin);
}

private void validateWidthAndHeight (int width, int height) {
if (width <= 0 || height <= 0) {
throw new IllegalArgumentException();
}
}

private int getMiddleWidth (int width) {
return getHorizontalRepetitions(width) * middlePieceWidth;
}

private int getHorizontalRepetitions (int width) {
int horizontalRepetitions = width / middlePieceWidth;

if (width % middlePieceWidth > 0) {
horizontalRepetitions++;
}

return horizontalRepetitions;
}

private int getMiddleHeight (int height) {
return getVerticalRepetitions(height) * middlePieceHeight;
}

private int getVerticalRepetitions (int height) {
int verticalRepetitions = height / middlePieceHeight;

if (height % middlePieceHeight > 0) {
verticalRepetitions++;
}

return verticalRepetitions;
}

private void drawFrameCorners (Graphics g, int x, int y, int middleWidth,
int middleHeight, int totalWidth, int totalHeight) {
g.setClip(x, y,
this.horizontalMargin, this.verticalMargin);
g.drawImage(this.originalImage, x, y,
Graphics.LEFT | Graphics.TOP);
g.setClip(x, y + this.verticalMargin + middleHeight,
this.horizontalMargin, this.verticalMargin);
g.drawImage(this.originalImage, x, y + totalHeight,
Graphics.LEFT | Graphics.BOTTOM);
g.setClip(x + this.horizontalMargin + middleWidth, y,
this.horizontalMargin, this.verticalMargin);
g.drawImage(this.originalImage, x + totalWidth, y,
Graphics.RIGHT | Graphics.TOP);
g.setClip(x + this.horizontalMargin + middleWidth, y + this.verticalMargin + middleHeight,
this.horizontalMargin, this.verticalMargin);
g.drawImage(this.originalImage, x + totalWidth, y + totalHeight,
Graphics.RIGHT | Graphics.BOTTOM);
}

private void drawTopAndBottomLines (Graphics g, int x, int y, int width, int totalHeight) {
int horizontalRepetitions = getHorizontalRepetitions(width);
x += horizontalMargin;
for (int i = 0; i < horizontalRepetitions; i++) {
g.setClip(x, y, middlePieceWidth, this.verticalMargin);
g.drawImage(this.originalImage, x - this.horizontalMargin, y,
Graphics.LEFT | Graphics.TOP);
g.setClip(x, y + totalHeight - this.verticalMargin,
middlePieceWidth, this.verticalMargin);
g.drawImage(this.originalImage, x - this.horizontalMargin,
y + totalHeight - this.verticalMargin,
Graphics.LEFT | Graphics.TOP);
x += middlePieceWidth;
}
}

private void drawLeftAndRightColumns (Graphics g, int x, int y, int height, int totalWidth) {
int verticalRepetitions = getVerticalRepetitions(height);

y += this.verticalMargin;
for (int i = 0; i < verticalRepetitions; i++) {
g.setClip(x, y, this.horizontalMargin, middlePieceHeight);
g.drawImage(this.originalImage, x, y - this.verticalMargin,
Graphics.LEFT | Graphics.TOP);
g.setClip(x + totalWidth - this.horizontalMargin, y,
this.horizontalMargin, middlePieceHeight);
g.drawImage(this.originalImage, x + totalWidth - this.horizontalMargin,
y - this.verticalMargin,
Graphics.LEFT | Graphics.TOP);
y += middlePieceHeight;
}
}

}