Add stereo preview example

Add an example demonstrating the use of stride, where the stride is set
to twice the image width to allow an image from a second camera to be
copied into the empty space, creating a stereo image

Signed-off-by: William Vinnicombe <[email protected]>

examples/stereo_preview.py

@@ -0,0 +1,73 @@
+#!/usr/bin/python3
+
+import time
+from threading import Lock
+
+from picamera2 import MappedArray, Picamera2, libcamera
+
+cam2_request = None
+lock = Lock()
+
+
+def pre_callback(request):
+    # Set the size, to make preview window and MappedArray remapping work
+    request.config["main"]["size"] = full_size
+    request.stream_map["main"].configuration.size = libcamera.Size(*full_size)
+
+
+def copy_image(request):
+    global cam2_request
+    with lock:
+        request_2 = cam2_request
+        if request_2 is None:
+            return
+        request_2.acquire()
+    # Copy second image into right hand side of main image
+    with MappedArray(request, "main") as m1, MappedArray(request_2, "main") as m2:
+        a1 = m1.array
+        a2 = m2.array
+        a1[:, -a2.shape[1]:] = a2
+    request_2.release()
+
+
+def save_request(request):
+    # Store most recent request for use by other camera
+    global cam2_request
+    with lock:
+        if cam2_request is not None:
+            cam2_request.release()
+        request.acquire()
+        cam2_request = request
+
+
+picam2a = Picamera2(0)
+
+full_size = (1920, 1080)
+half_size = (full_size[0] // 2, full_size[1])
+# Calculate stride for full frame
+full_config = picam2a.create_preview_configuration({"size": full_size})
+picam2a.configure(full_config)
+stride = picam2a.camera_config["main"]["stride"]
+
+# Configure as half frame, with full frame stride so right side is blank
+picam2a.pre_callback = pre_callback
+picam2a.post_callback = copy_image
+main_config = picam2a.create_preview_configuration(
+    main={"size": half_size, "stride": stride},
+    controls={"ScalerCrop": (0, 0, picam2a.sensor_resolution[0], picam2a.sensor_resolution[1])}
+)
+picam2a.configure(main_config)
+picam2a.start_preview(True)
+
+# Configure as half frame normally
+picam2b = Picamera2(1)
+picam2b.pre_callback = save_request
+half_config = picam2a.create_preview_configuration(
+    main={"size": half_size},
+    controls={"ScalerCrop": (0, 0, picam2a.sensor_resolution[0], picam2a.sensor_resolution[1])}
+)
+picam2b.configure(half_config)
+
+picam2a.start()
+picam2b.start()
+time.sleep(10)