I've spent about a week just making "not completely grim" horizontal sprites, only to realise I have no clue how to add shadows and also that a bunch of them don't line up properly. And I've not even started on the vertical sprites yet.
Brief summary:
During construction...
![Image](https://forums.factorio.com/images/ext/614a88321442051b61c0db944e752fe0.png)
Each end of the bridge consists of a platform and a ramp. Between the two platforms, there is a repeating foundation. What you're looking at is a customised "pipe-to-ground"
![Wink ;)](./images/smilies/icon_e_wink.gif)
Once built...
![Image](https://forums.factorio.com/images/ext/81877873833c992f55ed0a1a0670ba1f.png)
The middle section is "filled" with segments, replacing the foundations. There are 6 segments in the image above.
Detailed info
Sprite orientations:
* Ramp: north, east, south, west
* Platform: north, east, south, west
* Foundation: as far as I can tell, the same sprite is used for all orientations
* Segments: vertical, horizontal
Ramps and platforms:
If two bridges are built end to end, the ramps (pipe covers) will disappear, giving the impression of a continuous bridge. This means the platform sprites must line up with their 180º rotated counterpart (eg. west + east side by side should look like one solid platform).
Due to the way the bridge is placed, the first platform will always be waters-edge, like an offshore-pump (as that's what's actually placed initially, then it gets instantly replaced with a pipe-to-ground for remainder of construction). The second platform, however, can either be waters edge or on land (anywhere you could place a pipe-to-ground).
Foundation:
It's the left-side of __core__/graphics/arrows/underground-lines.png -- I can give each type of bridge (wood, stone, steel) it's own foundations image, and it looks like I can change the dimensions used. Main issue here is that the same image is used for all rotations, so any shadows would get rotated with the image = looks weird.
Segments:
These use simple-entity object, which can be given multiple pictures - each time the entity is placed, a random picture from the list is chosen.
Shadows:
I can determine when platforms and segments are directly over ground, water edge or water; potentially I could alter the shadows accordingly. If possible, having shadow layer separate from rest of sprite will allow some experimentation in that area.
Sizing & Bridge Types
If possible double-sized images are preferred (64x64px per tile instead of usual 32x32).
Wood bridge:
* Platform, segments and ramp are 1x1 tile.
* Foundations are 1x2 tile but can be bigger/smaller if desired. Max length of bridge is 30 tiles.
Stone bridge: Similar to wood, but 2 or 3 tiles wide. Max length of bridge is 40 tiles.
Steel bridge: Similar to wood, but 4 or 5 tiles wide, enough to accommodate tanks. Max length of bridge is 60 tiles.
Any help greatly appreciated
![Smile :)](./images/smilies/icon_e_smile.gif)