Creating a smaller buffer for PolygonSelector when selection changes significantly?

@almarklein

I was taking a look at how the new mesh positions and indices buffers are set in the polygon selector, a new buffer is allocated if a larger one is required for the new selection. But if the selection is smaller, than a new buffer is not allocated. @almarklein just curious about the reason so I can understand it better. I'm working on the PolygonGraphic.

fastplotlib/fastplotlib/graphics/features/_selection_features.py

Lines 419 to 435 in 7b4c687

    
           # Need larger buffer? 
        
           if len(value) > geometry.positions.nitems: 
        
               arr = np.zeros((geometry.positions.nitems * 2, 3), np.float32) 
        
               geometry.positions = gfx.Buffer(arr) 
        
           if len(indices) > geometry.indices.nitems: 
        
               arr = np.zeros((geometry.indices.nitems * 2, 3), np.int32) 
        
               geometry.indices = gfx.Buffer(arr) 
        
           geometry.positions.data[: len(value)] = value 
        
           geometry.positions.data[len(value) :] = value[-1] if len(value) else (0, 0, 0) 
        
           geometry.positions.draw_range = 0, len(value) 
        
           geometry.positions.update_full() 
        
           geometry.indices.data[: len(indices)] = indices 
        
           geometry.indices.data[len(indices) :] = 0 
        
           geometry.indices.draw_range = 0, len(indices) 
        
           geometry.indices.update_full()

Mmm, that code could indeed be improved. It also fails if the new value is more than twice as large as previous.
I can make a pr to improve this, so we can use that in the polygongraphic too.

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Creating a smaller buffer for `PolygonSelector` when selection changes significantly? #955

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	# Need larger buffer?
	if len(value) > geometry.positions.nitems:
	arr = np.zeros((geometry.positions.nitems * 2, 3), np.float32)
	geometry.positions = gfx.Buffer(arr)
	if len(indices) > geometry.indices.nitems:
	arr = np.zeros((geometry.indices.nitems * 2, 3), np.int32)
	geometry.indices = gfx.Buffer(arr)

	geometry.positions.data[: len(value)] = value
	geometry.positions.data[len(value) :] = value[-1] if len(value) else (0, 0, 0)
	geometry.positions.draw_range = 0, len(value)
	geometry.positions.update_full()

	geometry.indices.data[: len(indices)] = indices
	geometry.indices.data[len(indices) :] = 0
	geometry.indices.draw_range = 0, len(indices)
	geometry.indices.update_full()

Creating a smaller buffer for PolygonSelector when selection changes significantly? #955

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almarklein commented on Dec 1, 2025

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Creating a smaller buffer for `PolygonSelector` when selection changes significantly? #955