Build your village into a town, trade with your neighbours,
raise an army, march to battle, and fight for your place in the Patchwork Empire!


  • View media
  • View media
  • View media
  • View media
  • View media
  • View media
RSS Articles

Modern OpenGL makes it easy to render simple 3D graphics: just put each model in a vertex buffer object (VBO) then throw them all at the graphics card, in any order. It's fast, it's fun, and it works. Unless the models include transparency, in which case it breaks horribly. Here is a video showing what we tried:

Our tree models have clusters of polygons textured with rough brushstrokes, to try and approximate a hand-painted look. The textures have areas around the edges that are fully or partially transparent, eg. they have an alpha channel with values less than 1.0. Without this the edges of the polygons would be too obvious, and the trees would look too geometrical. While we do like the low-poly style, we are trying to add more hand-made detail for Patchwork Empire.

Blending and Z-Buffering

If we just enable blending and render the tree, it doesn't work. The problem is polygons which are closer to the camera can be rendered before polygons which are further away, and blending interacts badly with z-buffering. The transparent areas of the polygon still update the z-buffer, so subsequent polygons will not be displayed in that area, even though they should be visible through the first polygon. This causes very strange gaps to open and close in the tree as it is viewed from different angles.

You can fix this problem by sorting the polygons from furthest to nearest before rendering them. However, you have to do this each frame, for every transparent polygon in the scene. It can make it impossible to batch models by texture ID, you can't just throw VBOs at the graphics card any more, and the sorting technique can't handle intersecting polygons. Far too much trouble!

Alpha Testing

OpenGL supports alpha testing, where fragments with alpha below a certain level can be discarded entirely, avoiding z-buffer writes and fixing the problem. Yay! But what level of alpha should we use? If we test that the alpha is greater than zero, we get strange color fringing gaps around the edge of the texture, where the alpha falls from one to zero. It's not as bad as straight blending, but it's definitely still noticeable.

If we test that the alpha is greater than 0.5, it looks better. We still get some blending, from 1.0 to 0.5, but we drop the fragments before they get too transparent, and start revealing too much of the background and creating gaps in the object. While this approach is definitely acceptable, there is an even better option!

Sample Alpha to Coverage

If you are using multisampling, you can enable sample alpha to coverage, and transparent objects will just work! (Up to a point). Multisampling collects multiple samples (surprise) per pixel, then combines them to smooth out hard edges on polygons. However, it can also perform a kind of blending by treating the alpha value of a fragment as the coverage for that pixel. It's not perfect, and if you have too many layers of overlapping transparent polygons it won't look right. But if you only have a couple of layers, which we do, then it's fantastic!

When skeletal animation goes wrong

When skeletal animation goes wrong

News

When skeletal animation goes wrong, the results are... awesome!

Polygon-based visibility for fog of war

Polygon-based visibility for fog of war

News

Check out these test videos of our new fog of war system. It is polygon-based, and terrain and other obstacles can block visibility. Maximum visibility...

Comments
Drone_Locker
Drone_Locker

Em i the only one who smells Populus...?
And thats actually a complement. I would love to play it!

Reply Good karma Bad karma+1 vote
firarain
firarain

looks colorfull and promising. just wat i like to see.

gonna follow

Reply Good karma Bad karma+1 vote
Breakc0re231
Breakc0re231

Great art style!

Reply Good karma Bad karma+4 votes
INtense! Staff
INtense!

i concur

Reply Good karma+1 vote
MohamedFS
MohamedFS

i like that type of games

Reply Good karma Bad karma+1 vote
ananasblau
ananasblau

I do like your concept art, hope this will be in the final game?

Reply Good karma Bad karma+1 vote
brocoio123
brocoio123

Looks promising.

Reply Good karma Bad karma+1 vote
Post a comment
Sign in or join with:

Only registered members can share their thoughts. So come on! Join the community today (totally free - or sign in with your social account on the right) and join in the conversation.

Follow Report Profile
Icon
Patchwork Empire
Platforms
Windows, Mac, Linux
Creator
mkdir
Engine
Unity
Contact
Send Message
Release date
Game watch
Follow
Share
Style
Genre
4X
Theme
Medieval
Players
MMO
Project
Indie
Twitter

Latest tweets from @patchworkempire

RT @DominoStones: First screenshot from our new puzzle game! #screenshotsaturday #madewithunity #gamedev #indiedev T.co

Nov 12 2016

RT @DominoStones: Athel reminds our American friends to remember to vote tomorrow! #indiedev #gamedev T.co

Nov 7 2016

First view of Athel from our new puzzle game! T.co

Nov 1 2016

Beautiful low-poly aesthetic, can't wait to see a demo! #indiedev #gamedev #lowpoly T.co

Jan 11 2016

Sweet! T.co

Dec 17 2015

RT @sketchfoo: Sketching the cats in my life :) T.co

Nov 4 2015

Embed Buttons
Link to Patchwork Empire by selecting a button and using the embed code provided more...
Patchwork Empire
Statistics
Last Update
Watchers
71 members
Articles
3