Incompatible with matplotlib >=3.6: FigureCanvas.tostring_rgb() removed

[Xyc2016]

Description

Starting from matplotlib 3.6+, FigureCanvas.tostring_rgb() was removed (replaced by buffer_rgba()). This causes AttributeError when trying to render segmentation results in both fastsam/prompt.py and utils/tools.py.

Error

AttributeError: 'FigureCanvasAgg' object has no attribute 'tostring_rgb'. Did you mean: 'tostring_argb'?

Locations

1. fastsam/prompt.py line 172 (in plot_to_result())
2. utils/tools.py line 183 (in fast_process())

Both follow the same pattern:

try:
    buf = fig.canvas.tostring_rgb()
except AttributeError:
    fig.canvas.draw()
    buf = fig.canvas.tostring_rgb()

Note: The except block retries the same failing call, which will never succeed.

Suggested Fix

Replace tostring_rgb() with buffer_rgba() which is the modern matplotlib API:

try:
    buf = fig.canvas.buffer_rgba()
except AttributeError:
    fig.canvas.draw()
    buf = fig.canvas.buffer_rgba()

Also update the reshape from 3 channels (RGB) to 4 channels (RGBA), and switch color conversion accordingly.

Additional note

When running on a headless server (no display), matplotlib may also fail due to missing TkAgg backend. A robust fix would add matplotlib.use("Agg") or switch backend before plot calls.

[Xyc2016]

Fixed in PR #283. Replaced tostring_rgb() with buffer_rgba() in both prompt.py and tools.py. Also removed the broken try/except pattern.