Why does my offscreen image rendering doesn't work?
I have to create a little tool in Java. I have a task to render a text (single letter) to an ofscreen i开发者_开发百科mage and the count all the white and black pixels within a specified rectangle.
/***************************************************************************
* Calculate black to white ratio for a given font and letters
**************************************************************************/
private static double calculateFactor(final Font font,
final Map<Character, Double> charWeights) {
final char[] chars = new char[1];
double factor = 0.0;
for (final Map.Entry<Character, Double> entry : charWeights.entrySet()) {
final BufferedImage image = new BufferedImage(height, width,
BufferedImage.TYPE_INT_ARGB);
chars[0] = entry.getKey();
final Graphics graphics = image.getGraphics();
graphics.setFont(font);
graphics.setColor(Color.black);
graphics.drawChars(chars, 0, 1, 0, 0);
final double ratio = calculateBlackRatio(image.getRaster());
factor += (ratio * entry.getValue());
}
return factor / charWeights.size();
}
/***************************************************************************
* Count ration raster
**************************************************************************/
private static double calculateBlackRatio(final Raster raster) {
final int maxX = raster.getMinX() + raster.getWidth();
final int maxY = raster.getMinY() + raster.getHeight();
int blackCounter = 0;
int whiteCounter = 0;
for (int indexY = raster.getMinY(); indexY < maxY; ++indexY) {
for (int indexX = raster.getMinX(); indexX < maxX; ++indexX) {
final int color = raster.getSample(indexX, indexY, 0);
if (color == 0) {
++blackCounter;
} else {
++whiteCounter;
}
}
}
return blackCounter / (double) whiteCounter;
}
the probllem is that raster.getSample always returns 0.
What did I do wrong ?
If I am not mistaken, you draw chars at x=0, y=0 where x, y are "The baseline of the first character [...] in this graphics context's coordinate system."
Since the baseline is at the bottom of the chars, you draw them above the image.
Use x=0, y=height.
Also, the correct constructor is: BufferedImage(int width, int height, int imageType)
: you inverted width and height.
Perhaps the char isn't draw to the image at all. If I recall correctly the .drawChars() method draws to the Y-baseline. So you I think you must add the font height to the Y value.
OK PhiLho's nas Waverick's answers were right. Additionally I had to clear the background and change font color to black :)
final Graphics graphics = image.getGraphics();
graphics.setFont(font);
graphics.setColor(Color.white);
graphics.fillRect(0, 0, width, height);
graphics.setColor(Color.black);
graphics.drawChars(chars, 0, 1, 0, height);
精彩评论