When working with Python, there are multiple ways to solve a problem. In this article, we will explore different approaches to filling a polygon with a transparent line using the Cairo library. We will present three options and evaluate which one is the best.
Option 1: Using Cairo’s set_line_width() method
import cairo
surface = cairo.ImageSurface(cairo.FORMAT_ARGB32, 400, 400)
context = cairo.Context(surface)
# Set the line width to 0.0 to make it transparent
context.set_line_width(0.0)
# Draw the polygon
context.move_to(100, 100)
context.line_to(200, 200)
context.line_to(300, 100)
context.close_path()
# Fill the polygon with a transparent line
context.fill_preserve()
# Stroke the polygon to make the line visible
context.stroke()
# Save the result to a PNG file
surface.write_to_png("polygon.png")
In this option, we use Cairo’s set_line_width() method to set the line width to 0.0, effectively making it transparent. We then draw the polygon using the move_to(), line_to(), and close_path() methods. After filling the polygon with a transparent line using the fill_preserve() method, we stroke the polygon to make the line visible. Finally, we save the result to a PNG file.
Option 2: Using Cairo’s set_source_rgba() method
import cairo
surface = cairo.ImageSurface(cairo.FORMAT_ARGB32, 400, 400)
context = cairo.Context(surface)
# Set the source color to transparent black
context.set_source_rgba(0, 0, 0, 0)
# Draw the polygon
context.move_to(100, 100)
context.line_to(200, 200)
context.line_to(300, 100)
context.close_path()
# Fill the polygon with a transparent line
context.fill_preserve()
# Stroke the polygon to make the line visible
context.stroke()
# Save the result to a PNG file
surface.write_to_png("polygon.png")
In this option, we use Cairo’s set_source_rgba() method to set the source color to transparent black. This effectively makes the line transparent. The rest of the code is similar to option 1, where we draw the polygon, fill it with a transparent line, stroke it, and save the result to a PNG file.
Option 3: Using Cairo’s set_operator() method
import cairo
surface = cairo.ImageSurface(cairo.FORMAT_ARGB32, 400, 400)
context = cairo.Context(surface)
# Set the operator to SOURCE
context.set_operator(cairo.OPERATOR_SOURCE)
# Draw the polygon
context.move_to(100, 100)
context.line_to(200, 200)
context.line_to(300, 100)
context.close_path()
# Fill the polygon with a transparent line
context.fill_preserve()
# Stroke the polygon to make the line visible
context.stroke()
# Save the result to a PNG file
surface.write_to_png("polygon.png")
In this option, we use Cairo’s set_operator() method to set the operator to SOURCE. This means that the source color will be used as is, without any blending with the destination color. By default, the source color is opaque black, so setting the operator to SOURCE effectively makes the line transparent. The rest of the code is similar to the previous options.
After evaluating the three options, it is clear that option 1, using Cairo’s set_line_width() method, is the most straightforward and intuitive solution. It explicitly sets the line width to 0.0, making it transparent. Option 2 and option 3 require setting the source color or operator, which may be less intuitive for some developers. Therefore, option 1 is the recommended approach for filling a polygon with a transparent line using Cairo in Python.
