Imagine that there is a beer can on a table in a room that is brightly lit from an overhead source. Light from the source will reflect off the beer can (some directly from the overhead source, some that has already been reflected off other surfaces in the room). At any point in the room to which there is an uninterrupted path from the beer can, there will be light that has reflected off the beer can. Because of the natural laws governing the reflection of light off surfaces of particular textures, colors, and chemical makeup, the light at any such point will be structured in a very particular way by its having reflected off the beer can. In situation s1, the light at point p has structure a of type A. Given the laws just mentioned, there is a constraint connecting the situations with light-structure type A to the beer-can-present situations of type B. So the light structure at point p contains information about token beer-can-presence b (of type B). Notice too that, because of conventional constraints governing the relationship between cans and their contents, beer-can-presence b being of type B carries information about beer-presence c of type C. Furthermore, the light at some point in the room from which the beer can is visible will contain information about the beer can's affordances. Take some point p, which is at my eye height. The light structure available at this point will contain not just information about the beer can and the beer, but also about the distance the point is from the ground, the relationship between that distance and the distance the beer can is from the ground, and hence the reach ability of the beer can and drinkability of the beer for a person with eyes at that height. (Chemero, 2009, pp. 118-9)Ok. So, the stuff up until "Notice too that ..." is essentially the Gibsonian line (of Gibson, 1979, p.127) about surfaces structuring light. That sound right. The trick, then, is to somehow connect the structuring of light by surfaces to affordances. Gibson, 1979, p. 127, tried to make the connection by way of the hypothesis that the composition and layout of surfaces constitutes affordances. Chemero has a different idea: There are constraints between surfaces and their innards. In the case of beer cans, society puts beer in beer cans. That's the constraint. From there, Chemero glides willy-nilly (i.e. without telling us how) to having constraints go all the way to drinkability.
But, this is not going to work. Take two beer cans that are physically identical on the outside. Have one with beer and the other with something non-potable, say, bleach. Subjects will, presumably, have the same visual perceptions of the two cans, but the two cans afford different things, so visual perception is not of affordances. I take it as evident how to run this with the exploding boxes, piles of white stuff, panes of glass, etc.
This goes back to the cartoonish formulation of the problems. Visual perception is typically based on outers; affordances are typically based on innards.
Chemero could rightly point out that in this imagined scenario, we do not have the requisite conventions regarding the contents of beer cans. Correct, but we still have perception, right? Which suggests that social conventions regarding the physical configurations of things do not have that much to do with perception.
Maybe there is some trick Chemero has up his sleeve later, but we shall see ...