CODEWITHSUNDEEP
pythonpygtkgtk3cairopycairo
Adrian
Adrian

Reputation: 879

How can I get pixels from cairo.ImageSurface?

I made a Python program that draws a black rectangle with a white circle inside it when I click on a button. I use Gtk.DrawingArea and cairo.ImageSurface. The code is the following.

class App:

    def __init__(self, width, height):

        self.surface = cairo.ImageSurface(cairo.FORMAT_ARGB32, width, height)

        # Builder
        self.builder = Gtk.Builder()
        self.builder.add_from_file('ventana.glade')
        go = self.builder.get_object

        # Widgets
        self.window      = go('window')
        self.drawingarea = go('drawingarea')
        self.button      = go('button')

        signals = {
            'gtk_main_quit'    : Gtk.main_quit,
            'draw'             : self.draw
        }

        self.builder.connect_signals(signals)
        self.window.show_all()


    def draw(self, widget):
        context = self.drawingarea.get_window().cairo_create()
        context.set_source_surface(self.surface)

        context.set_source_rgba(0.0, 0.0, 0.0, 1.0)
        context.rectangle(0, 0, self.surface.get_width(), self.surface.get_height())
        context.fill()

        context.translate(10, 10)
        context.arc(0, 0, 10, 0, 2 * pi)
        context.set_source_rgba(1.0, 1.0, 1.0, 1.0)
        context.fill()

I get the following window.

enter image description here

It works fine, but I need to get the RGB values of the pixels of that picture, so I tried doing map(ord, self.surface.get_data()), but I get a list of zeros.

How can I get a list with the RGB of the pixels?

And I have another problem: when I minimize the window or change to another window, the drawing erases. Is it possible to avoid this?

Upvotes: 3

Views: 1768

Answers (2)

John C
John C

Reputation: 6527

You don't need to use a map, the MemoryView object has a tobytes() function. This will convert to a ByteArray, which can easily be converted to a list of ints:

# Set up pycairo
my_surface = cairo.ImageSurface(cairo.FORMAT_RGB24, 10, 10)
ctx = cairo.Context(my_surface)
ctx.set_source_rgb(0.8, 0.8, 0.8)
ctx.paint()

# Draw a small red rectangle
ctx.rectangle(1, 1, 5, 5)
ctx.set_source_rgb(1, 0, 0)
ctx.fill()

# Convert pixels to MemoryView object, then bytestring or list of ints
pixel_data_mv = my_surface.get_data()  # MemoryView object
pixels_as_bytes = pixel_data_mv.tobytes()  # ByteArray
pixels_as_list = list(pixels_as_bytes)

# Iterate through memoryview object
print(f"pixel_data_mv[{len(pixel_data_mv)}]:")
for one_data_bit in pixel_data_mv:
    print(f"{str(one_data_bit)}", end=', ')
print("")

# Print as ByteArray and list of ints
print(f"pixels_as_bytes[{len(pixels_as_bytes)}]:\n{pixels_as_bytes}")
print(f"pixels_as_list[{len(pixels_as_list)}]:\n{pixels_as_list}")

This will show both the ByteArray and list of ints:

pixels_as_bytes[400]:
b'\xcc\xcc\xcc\xff\xcc\xcc\xcc\xff\xcc\xcc\xcc\xff\xcc ...
pixels_as_list[400]:
[204, 204, 204, 255, 204, 204, 204, 255, 204, 204, 204, 255

Note that the pixels are "exploded" into four bytes, R/G/B/A.

Upvotes: 1

luciomrx
luciomrx

Reputation: 1195

i don't know about getting your color but about the drawing, connect your window with 'configure-event' (event being state of window changed) and then call drawingarea.queue_draw ()

Upvotes: 0

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