Help on bounding box not properly drawn

General
1

Hello! I’m ack again, my account was deleted :sweat_smile:.
I recently developed a C++ app integrated into LVGL to have my own graphic interface and show prediction on video input, actually i’m testing on walkin people “example_640.mp4” using yolov6n.hef.
It works, i see prediction but i’m not able to draw bounding boxes correctly on the source video

WhatsApp Image 2025-06-17 at 15.35.59
WhatsApp Image 2025-06-17 at 15.35.591200×1600 175 KB

What could be the problem? I use GStreamer pipeline and for drawing boxes

#define FRAME_WIDTH 640
#define FRAME_HEIGHT 640

void draw_detection_overlay(uint8_t *rgb888, int width, int height) {
    for (int i = 0; i < g_num_detections; ++i) {
        Detection det = g_detections[i];

        // Coordinate normalizzate su immagine intera
        int x0 = (int)((det.x - det.w / 2.0f) * width);
        int y0 = (int)((det.y - det.h / 2.0f) * height);
        int x1 = (int)((det.x + det.w / 2.0f) * width);
        int y1 = (int)((det.y + det.h / 2.0f) * height);

        // Clamp
        x0 = MY_CLAMP(x0); y0 = MY_CLAMP(y0);
        if (x1 > width) x1 = width;
        if (y1 > height) y1 = height;

        // Colore in base alla classe
        uint8_t r = 255, g = 0, b = 0;
        if (det.class_id < num_class_colors) {
            r = class_colors[det.class_id][0];
            g = class_colors[det.class_id][1];
            b = class_colors[det.class_id][2];
        }

        for (int y = y0; y < y1; ++y) {
            for (int x = x0; x < x1; ++x) {
                if (x == x0 || x == x1 - 1 || y == y0 || y == y1 - 1) {
                    int idx = (y * width + x) * 3;
                    rgb888[idx + 0] = r;
                    rgb888[idx + 1] = g;
                    rgb888[idx + 2] = b;
                }
            }
        }

        printf("Detection: class=%d box=(%.2f %.2f %.2f %.2f)\n",
       det.class_id, det.x, det.y, det.w, det.h);

    }
}

int gstreamer_grab_frame(lv_color_t *dst_buffer) {
    GstSample *sample = gst_app_sink_pull_sample(GST_APP_SINK(appsink));
    if (!sample) return -1;

    GstBuffer *buffer = gst_sample_get_buffer(sample);
    GstMapInfo map;
    if (!gst_buffer_map(buffer, &map, GST_MAP_READ)) {
        gst_sample_unref(sample);
        return -1;
    }

    const uint8_t *rgb_data = map.data;
    uint8_t rgb_copy[FRAME_WIDTH * FRAME_HEIGHT * 3];
    memcpy(rgb_copy, rgb_data, FRAME_WIDTH * FRAME_HEIGHT * 3);

    draw_detection_overlay(rgb_copy, FRAME_WIDTH, FRAME_HEIGHT);
    rgb888_to_rgb565(rgb_copy, dst_buffer, FRAME_WIDTH * FRAME_HEIGHT);

    gst_buffer_unmap(buffer, &map);
    gst_sample_unref(sample);
    return 0;
}


int main(int argc, char **argv) {
    (void)argc;
    (void)argv;

    lv_init();
    hal_init();

    if (gstreamer_init() < 0) {
        return 1;
    }

    ui_init();
    lv_img_set_src(ui_VideoFrame, &webcam_img);

    while (1) {
        pthread_mutex_lock(&buffer_mutex);
        lv_color_t *dst_buffer = (current_buffer == webcam_buffer_a) ? webcam_buffer_b : webcam_buffer_a;

        if (gstreamer_grab_frame(dst_buffer) == 0) {
            current_buffer = dst_buffer;
            webcam_img.data = (const uint8_t *)current_buffer;
            lv_img_cache_invalidate_src(&webcam_img);
            lv_obj_invalidate(ui_VideoFrame);
        }

        pthread_mutex_unlock(&buffer_mutex);

        lv_timer_handler();
        if (gstreamer_grab_frame_and_infer() != 0) {
            break;
        }
        usleep(1000);
    }

    return 0;
}

Yes something strange in the code could be in! This is just a try, and for next step and finalizing prototype, i need to have correctly drawn bounding boxes…someone could help?