examples: backport exampleTransform.py

Example from the master branch, modified to work on 1.16

Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-python/-/merge_requests/38>

1 files changed, 63 insertions, 0 deletions

diff --git a/examples/plugins/python/exampleTransform.py b/examples/plugins/python/exampleTransform.py
new file mode 100644
index 0000000..f96dacf
--- /dev/null
+++ b/examples/plugins/python/exampleTransform.py
@@ -0,0 +1,63 @@
+#!/usr/bin/python3
+# exampleTransform.py
+# 2019 Daniel Klamt <graphics@pengutronix.de>
+
+# Inverts a grayscale image in place, requires numpy.
+#
+# gst-launch-1.0 videotestsrc ! ExampleTransform ! videoconvert ! xvimagesink
+
+import gi
+gi.require_version('Gst', '1.0')
+gi.require_version('GstBase', '1.0')
+gi.require_version('GstVideo', '1.0')
+
+from gi.repository import Gst, GObject, GstBase, GstVideo
+
+import numpy as np
+
+Gst.init(None)
+FIXED_CAPS = Gst.Caps.from_string('video/x-raw,format=GRAY8,width=[1,2147483647],height=[1,2147483647]')
+
+class ExampleTransform(GstBase.BaseTransform):
+    __gstmetadata__ = ('ExampleTransform Python','Transform',
+                      'example gst-python element that can modify the buffer gst-launch-1.0 videotestsrc ! ExampleTransform ! videoconvert ! xvimagesink', 'dkl')
+
+    __gsttemplates__ = (Gst.PadTemplate.new("src",
+                                           Gst.PadDirection.SRC,
+                                           Gst.PadPresence.ALWAYS,
+                                           FIXED_CAPS),
+                       Gst.PadTemplate.new("sink",
+                                           Gst.PadDirection.SINK,
+                                           Gst.PadPresence.ALWAYS,
+                                           FIXED_CAPS))
+
+    def do_set_caps(self, incaps, outcaps):
+        struct = incaps.get_structure(0)
+        self.width = struct.get_int("width").value
+        self.height = struct.get_int("height").value
+        return True
+
+    def do_transform(self, buf_in, buf_out):
+        try:
+            # Create a read-only memoryview
+            success, info = buf_in.map(Gst.MapFlags.READ)
+            if success == False:
+                raise RuntimeError("Could not map buffer to bytes object.")
+            
+            # Create a NumPy ndarray from the memoryview.
+            image_in = np.ndarray(shape = (self.height, self.width), dtype = np.uint8, buffer = info.data)
+            image_out = np.invert(image_in)
+
+            # Copy data in image_out to buf_out
+            buf_out.fill(0, image_out.tobytes())
+
+            # Unmap the memoryview
+            buf_in.unmap(info)
+
+            return Gst.FlowReturn.OK
+        except RuntimeError as e:
+            Gst.error("Runtime error: %s" % e)
+            return Gst.FlowReturn.ERROR
+
+GObject.type_register(ExampleTransform)
+__gstelementfactory__ = ("ExampleTransform", Gst.Rank.NONE, ExampleTransform)