Add new CV2 screen recording example

arcade/experimental/video_record_cv2.py

@@ -0,0 +1,79 @@
+"""
+Simple video recorder with cv2.
+Records Arcade screen to a video file, with minimal
+I/O operations and minimal memory usage.
+
+We read pixels directly from OpenGL framebuffer, then into
+a NumPy array that we can hand to OpenCV for the video writing.
+
+The other ways of doing this with built-in arcade.get_image()
+function would require either a lot of re-processing of images
+on CPU for no real reason, saving/reloading each frame as an image file,
+or having rampant memory usage problems.
+
+This attempts to have optimal performance while not increasing memory usage
+by having as few steps in between the pixel data in VRAM and the final video
+file as possible.
+
+Dependencies:
+    pip install opencv-python numpy
+"""
+
+import cv2  # type: ignore
+import numpy  # type: ignore
+import pyglet.gl as gl
+
+import arcade
+
+SCREEN_WIDTH = 800
+SCREEN_HEIGHT = 600
+SCREEN_TITLE = "Starting Template"
+
+
+class VideoRecorderCV2(arcade.Window):
+    def __init__(self, width, height, title):
+        super().__init__(width, height, title)
+        arcade.set_background_color(arcade.color.BLACK)
+
+        # The video files produced by this are un-compressed and will be massive. Think 1GB+
+        # for even like 15 seconds+ of 1920x1080. If you want compressed video, you can replace the
+        # below line with something like this to use H.264 encoding(this probably needs ffmpeg available):
+        # fourcc = cv2.VideoWriter_fourcc(*'mp4v')
+        # self.video = cv2.VideoWriter("my_video.mp4", fourcc, 60, (self.width, self.height))
+        self.video = cv2.VideoWriter("my_video.avi", 0, 60, (self.width, self.height))
+
+        # This is just used to count frames so we can cut it off at some point
+        self.frames = 0
+
+    def on_draw(self):
+        self.clear()
+
+    def on_update(self, delta_time):
+        self.frames += 1
+        img = self.get_image()
+        self.video.write(img)
+        if self.frames >= 1000:
+            self.video.release()
+            cv2.destroyAllWindows()
+            arcade.exit()
+
+        # make something happen for our video
+        arcade.set_background_color(arcade.types.Color(self.frames % 255, 0, 0))
+
+    # This is sort of a re-implementation of arcade.get_image(). Really the only difference
+    # is in the last line, where we create a numpy array with the buffer instead of
+    # creating a PIL image, and the fact that we are just capturing the whole screen instead
+    # of allowing to capture a specific sub-section.
+    def get_image(self):
+        image_buffer = (gl.GLubyte * (3 * self.width * self.height))(0)
+        gl.glReadPixels(0, 0, self.width, self.height, gl.GL_BGR, gl.GL_UNSIGNED_BYTE, image_buffer)
+        return numpy.frombuffer(image_buffer, dtype='uint8').reshape(self.height, self.width, 3)  # type: ignore
+
+
+def main():
+    VideoRecorderCV2(SCREEN_WIDTH, SCREEN_HEIGHT, SCREEN_TITLE)
+    arcade.run()
+
+
+if __name__ == "__main__":
+    main()