README.md

Create RGBA Image with Python on Ubuntu Touch

[статья на русском] Let's create a new project in Clickable, enter the command in the terminal:

clickable create

Select the Python project type and fill in: Title [App Title]: Rendering RGBA
App Name [appname]: example-RGBA

Delete the Python object in the Main.qml file, and convert the Page object to the form:

Page {
        anchors.fill: parent
        header: PageHeader {
            id: header
            title: i18n.tr('Rendering RGBA')
        }

        Image {
        id: image
        fillMode: Image.PreserveAspectFit
        anchors {
            top: header.bottom
            left: parent.left
            right: parent.right
            bottom: parent.bottom
        }

            Python {
                Component.onCompleted: {
                addImportPath(Qt.resolvedUrl('../src/'));
                importModule('example', function () {
                    image.source = 'image://python/image-id-passed-from-qml';
                });
                }

                onError: console.log('Python error: ' + traceback)
            }
        }
    }

Thus, on the Page we created the Image object. To Image a Python code processing object ** was created, which will fire when initialized and return the render image.

Now select the project, find the src directory and change example.py.

import pyotherside
import math

def render(image_id, requested_size):
    print('image_id: "{image_id}", size: {requested_size}'.format(**locals()))

    # width and height will be -1 if not set in QML
    if requested_size == (-1, -1):
        requested_size = (300, 300)

    width, height = requested_size

    # center for circle
    cx, cy = width/2, 10

    pixels = []
    for y in range(height):
        for x in range(width):
            pixels.extend(reversed([
                255, # alpha
                int(10 + 10 * ((x - y * 0.5) % 20)), # red
                20 + 10 * (y % 20), # green
                int(255 * abs(math.sin(0.3*math.sqrt((cx-x)**2 + (cy-y)**2)))) # blue
            ]))
    return bytearray(pixels), (width, height), pyotherside.format_argb32

pyotherside.set_image_provider(render)

pyothersid allows our code to create and return QML objects. So render will return us a byte image in format_argb32 format. During function, we create a two-dimensional array of pixels-bytes. Each element contains 4 bits - Alpha transparency (0-255), the value of red (0-255), green (0-255) and blue (0 -255). Use mathematical calculations, we can generate textures and edit images.

All that remains for us is to open a terminal in the project folder, connect the phone and start compilation with the command:

clickable

P.S. another gradient generation function:

def render(image_id, requested_size):
    print('image_id: "{image_id}", size: {requested_size}'.format(**locals()))

    # width and height will be -1 if not set in QML
    if requested_size == (-1, -1):
        requested_size = (300, 300)

    width, height = requested_size

    pixels = []
    for y in range(height):
        for x in range(width):
            pixels.extend(reversed([
                255, # alpha
                int(round(255/width*x)), # red
                int(round((255-255/width*x)*(1-y/width))), # green
                int(round(255/height*y)) # blue
            ]))
    return bytearray(pixels), (width, height), pyotherside.format_argb32