HoughLinesP - java.lang.NullPointerException: Attempt to invoke virtual method 'org.bytedeco.javacpp.BytePointer org.bytedeco.javacpp.BytePointer.capacity(long)' on a null object reference

[nicemanis]

Hello,
I'm trying to use HoughLinesP method as follows:

Mat lines = new Mat();
HoughLinesP(mat_points, lines, 1, CV_PI / 180, 50);
IntRawIndexer linesIdx = lines.createIndexer();
for (long i = 0; i < linesIdx.rows(); i++) {
    int x0 = linesIdx.get(i, 0, 0);
    int y0 = linesIdx.get(i, 0, 1);
    int x1 = linesIdx.get(i, 0, 2);
    int y1 = linesIdx.get(i, 0, 3);
    line(roi, new Point(x0, y0), new Point(x1, y1), Scalar.GREEN);
}

However, it throws the following error on this (IntRawIndexer linesIdx = lines.createIndexer();) line:

java.lang.NullPointerException: Attempt to invoke virtual method 'org.bytedeco.javacpp.BytePointer org.bytedeco.javacpp.BytePointer.capacity(long)' on a null object reference
        at org.bytedeco.javacpp.helper.opencv_core$AbstractMat.createIndexer(opencv_core.java:1881)
        at org.bytedeco.javacpp.helper.opencv_core$AbstractArray.createIndexer(opencv_core.java:147)

Is it a bug in the library or am I using it wrong? I tried checking if lines object is null, but it is not.

[saudet]

It just looks like HoughLinesP() is failing. Make sure it succeeds before doing anything more.

[nicemanis]

How can I check if it succeeds? Lines object won't be null since I initialized it.
I managed to recreate it with cvHoughLines2 following this example. What are the differences between both of these and which method is preferred?

[saudet]

Actually, it looks like those functions don't accept a Mat for their outputs. I've fixed that in commit bytedeco/javacpp-presets@e1d516d. Please give it a try with 1.4.5-SNAPSHOT in a few hours when the builds are ready: http://bytedeco.org/builds/

[nicemanis]

How can I load the snapshot version with Gradle?
If I use:
implementation group: 'org.bytedeco.javacpp-presets', name: 'opencv-platform', version: '4.0.1-1.4.5-SNAPSHOT'
It returns
ERROR: Failed to resolve: org.bytedeco.javacpp-presets:opencv-platform:4.0.1-1.4.5-SNAPSHOT

[saudet]

The instructions for that are on the page:
http://bytedeco.org/builds/

[saudet]

The fixes are now included in JavaCV 1.5. Thanks for reporting and enjoy!