use strictly background color for terrain

[kostmo]

Towards #1662

Prerequisite for #1672

To allow a robot-occupied cell to take on the underlying terrain color as the background color of its cell, the terrain color must be representable strictly as a "background". However, currently, the dirt, stone, and grass terrains are represented by a half-shaded foreground glyph upon black background.

Currently the "Medium Shade" unicode character (▒) is used to "blend" a somewhat bright color with a black background, resulting in a moderately dark color in the terminal for dirt, stone, and grass. However, these same dark colors are not reproducible in the 240-color scheme without this foreground+background blending trick; the closest approximations as a background-only or foreground-only color come out quite a bit lighter.

Visual comparison

Using:

scripts/play.sh -i creative --seed 2 --autoplay

Before	After

Possible approaches

So, we need to decide whether to:

1. Accept the new lighter colors
2. Choose new, alternative terrain colors that may be darker given the 240-color palette
3. Abandon support for 240 colors and assume "full" color terminals
4. Abandon efforts to passthrough terrain color as background of robot cells

[byorgey]

I don't think I like the new lighter colors, not just on aesthetic grounds but also functional grounds: if the goal is to pass through the background color behind entities and robots, having bright background colors is going to make it very difficult to see.

What would be the downside of abandoning 240-color support and assuming full color terminals?

[kostmo]

What would be the downside of abandoning 240-color support and assuming full color terminals?

Actually, this was simpler than I thought. We had been using the rgbColor function; I just swapped it for linearColor. I reverse-engineered the precise full-color RGB triples for the half-shade darkened terrain using the Gimp color picker.

The new colors look like so:

As a bonus, the PNG renderer is now more color-accurate (compare to previous version):

[byorgey]

Ah, that looks very nice indeed!

[byorgey]

Looks great!