Function sam3_sine_encode_box

sam3.cpp:7578–7601

Sinusoidal positional encoding for box coordinates. Matches Python PositionEmbeddingSine.encode_boxes(cx, cy, w, h). Output: [258] = [pos_y(128), pos_x(128), h, w]

// Matches Python PositionEmbeddingSine.encode_boxes(cx, cy, w, h).
// Output: [258] = [pos_y(128), pos_x(128), h, w]
static void sam3_sine_encode_box(float* out, float cx, float cy, float w, float h,
                                 int num_pos_feats, int temperature) {
    const float scale = 2.0f * (float)M_PI;
    float x_embed = cx * scale;
    float y_embed = cy * scale;

    // dim_t[i] = temperature^(2*(i//2)/num_pos_feats)
    for (int i = 0; i < num_pos_feats; ++i) {
        int div_idx = 2 * (i / 2);
        float dim_t = powf((float)temperature, (float)div_idx / (float)num_pos_feats);
        float px = x_embed / dim_t;
        float py = y_embed / dim_t;
        // Interleaved sin/cos: even indices get sin, odd get cos
        if (i % 2 == 0) {
            out[i] = sinf(py);                  // pos_y first
            out[num_pos_feats + i] = sinf(px);  // pos_x second
        } else {
            out[i] = cosf(py);
            out[num_pos_feats + i] = cosf(px);
        }
    }
    out[2 * num_pos_feats] = h;      // h
    out[2 * num_pos_feats + 1] = w;  // w
}

// CPU-side ROI Align matching torchvision.ops.roi_align behavior.
// Features in ggml [C, W, H] layout. Box in XYXY format scaled to feature grid coords.