fix(core): correct opacity in interleaved mode

[felixpalmer]

Background

When using PostProcessEffect with interleaved: true, due to clearing of the canvas the result is the basemap is completely cleared with a solid grey color:

With this change, the clearing is applied only when needed, and the blending in ScreenPass is fixed to give correct results. Here is a layer, drawn with opacity with a ink postprocess applied, in interleaved mode.

Screen.Recording.2025-05-22.at.09.44.57.mov

In order to test, the layer browser has been enhanced to include a toggle for interleaved rendering

Change List

• Do not clear canvas in deck-renderer when clearCanvas is explicitly set to false
• Correct blending in ScreenPass (only used in PostProcessEffect)
• Tidy up RasterLayer
• Enhance layer browser to support interleaved

[felixpalmer]

interleaved and the view prop do not play nicely together with postprocessing as the MapboxOverlay does a double render, thus applying the postprocess twice to the mapbox canvas.

Details: hasNonMapboxViews ends up being true due to the custom views: https://github.com/visgl/deck.gl/blob/master/modules/mapbox/src/deck-utils.ts#L340-L357