In Baroque music, textures were often very dense with intricate layers of multiple melodies stacked on top of one another to create a sense of style and sophistication.
This example by Corelli illustrates this point well. Like Bach's piece, this is also a concerto grosso featuring a concertino of 2 violins.
From 0'31 we hear a slow and solemn melody from the lower strings, characterised by a rising octave.
At 0'38, another melody starts from the solo violin and viola. Two seconds later a third melody is heard (0'40) from the second solo violin.
Once every melody has been introduced they continue to play with independence, interweaving with each other very elegantly and angelically until 1'38 where the parts become homophonic for the final perfect cadence. Melodically and harmonically, the use of suspensions are very striking in their dissonance.
The polyphonic texture heard here is very typical of Baroque music!
Overall, the texture contributes a lot towards the energetic nature of the music which sounds highly vibrant with a sense of style that is undoubtedly Baroque.
The fugal structure is, by nature, polyphonic as it involves the introduction and layering up of different melodies simultaneously playing a subject alongside countersubjects. Technically, the texture is monophonic at the very beginning as the first fugal entry plays on its own.
Stretto is when the entry points of different melodies are closer together, to the extent that they overlap. This happens from bar 64 (0'59) when the ripieno instruments play the opening melody in quick succession.
When the harpsichord plays solo from bar 163 (2'33) it plays a canon. Its right hand plays the main subject before the left hand repeats it an octave lower before the first phrase has finished. This is another specific example of a polyphonic texture.
The flute and violin often have imitation between their parts. The passage from bar 193 (3'02) is a good example where snippets of the main subject are heard from the flute and imitated by the violin.
Though the texture is often polyphonic, there are lots of moments where parts are heard in parallel (as discussed in Harmony). This is often the case between the left and right hands in the harpsichord part.
At other times they are even in unison, an example being bar 157 (2'28) where the four upper parts play the subject, all at the same pitch. This emphasises the distinctive subject and brings out the ritornello.