Java: how to do fast copy of a BufferedImage's pixels? (include unit test)
- by WizardOfOdds
I want to do a copy (of a rectangle area) of the ARGB values from a source BufferedImage into a destination BufferedImage. No compositing should be done: if I copy a pixel with an ARGB value of 0x8000BE50 (alpha value at 128), then the destination pixel must be exactly 0x8000BE50, totally overriding the destination pixel.
I've got a very precise question and I made a unit test to show what I need. The unit test is fully functional and self-contained and is passing fine and is doing precisely what I want.
However, I want a faster and more memory efficient method to replace copySrcIntoDstAt(...).
That's the whole point of my question: I'm not after how to "fill" the image in a faster way (what I did is just an example to have a unit test). All I want is to know what would be a fast and memory efficient way to do it (ie fast and not creating needless objects).
The proof-of-concept implementation I've made is obviously very memory efficient, but it is slow (doing one getRGB and one setRGB for every pixel).
Schematically, I've got this: (where A indicates corresponding pixels from the destination image before the copy)
AAAAAAAAAAAAAAAAAAAA
AAAAAAAAAAAAAAAAAAAA
AAAAAAAAAAAAAAAAAAAA
AAAAAAAAAAAAAAAAAAAA
AAAAAAAAAAAAAAAAAAAA
AAAAAAAAAAAAAAAAAAAA
And I want to have this:
AAAAAAAAAAAAAAAAAAAA
AAAAAAAAAAAAAAAAAAAA
AAAAAAAAAAAAAAAAAAAA
AAAAAAAAAAAAABBBBAAA
AAAAAAAAAAAAABBBBAAA
AAAAAAAAAAAAAAAAAAAA
where 'B' represents the pixels from the src image.
I'm looking for an exact replacement of the method, not for an API link/quote.
import org.junit.Test;
import java.awt.image.BufferedImage;
import static org.junit.Assert.*;
public class TestCopy {
private static final int COL1 = 0x8000BE50; // alpha at 128
private static final int COL2 = 0x1732FE87; // alpha at 23
@Test
public void testPixelsCopy() {
final BufferedImage src = new BufferedImage( 5, 5, BufferedImage.TYPE_INT_ARGB );
final BufferedImage dst = new BufferedImage( 20, 20, BufferedImage.TYPE_INT_ARGB );
convenienceFill( src, COL1 );
convenienceFill( dst, COL2 );
copySrcIntoDstAt( src, dst, 3, 4 );
for (int x = 0; x < dst.getWidth(); x++) {
for (int y = 0; y < dst.getHeight(); y++) {
if ( x >= 3 && x <= 7 && y >= 4 && y <= 8 ) {
assertEquals( COL1, dst.getRGB(x,y) );
} else {
assertEquals( COL2, dst.getRGB(x,y) );
}
}
}
}
// clipping is unnecessary
private static void copySrcIntoDstAt(
final BufferedImage src,
final BufferedImage dst,
final int dx,
final int dy
) {
// TODO: replace this by a much more efficient method
for (int x = 0; x < src.getWidth(); x++) {
for (int y = 0; y < src.getHeight(); y++) {
dst.setRGB( dx + x, dy + y, src.getRGB(x,y) );
}
}
}
// This method is just a convenience method, there's
// no point in optimizing this method, this is not what
// this question is about
private static void convenienceFill(
final BufferedImage bi,
final int color
) {
for (int x = 0; x < bi.getWidth(); x++) {
for (int y = 0; y < bi.getHeight(); y++) {
bi.setRGB( x, y, color );
}
}
}
}
