While I’m thinking about it…
Yesterday’s devlog showed the new ground cover on Savannah One. Three things made the difference between grass that reads as grass and grass that reads as a field of paper cards.
1. Optimization is 90% about the alpha.
Grass cards are mostly empty space. Each card is a rectangle with a few blades painted in, and the GPU pays for every pixel of that rectangle, including the transparent ones it throws away. Stack hundreds of cards behind each other and you pay that cost many times over for the same spot on screen. That’s called overdraw, and it’s the real bill. When we measured, roughly 60% of the pixels the grass shader worked on were transparent corners that got discarded. So most of the work went there: a simpler material, fewer cards as distance grows, and thinning the field wherever the eye won’t notice. On a laptop’s integrated graphics that is the difference between grass you can afford and grass you can’t. The next big step is trimming the cards to the shape of the grass inside them, so the GPU stops shading empty air.
2. Stagger the bottoms of the cards.
If every blade on a card runs straight off the bottom edge of the texture, you get a hard horizontal line wherever the card meets the ground, and the eye finds those lines instantly. Instead, the blade bases sit at different heights inside the card, as if you were looking back through rows of grass in depth. The bottom edge goes soft and the grass seems to come out of the ground instead of standing on it. Darkening the roots toward the soil color helps too: it hides the seam and reads as shadow down among the blades.
3. Shear the cards to fit the slope.
Terrain is almost never flat, and a flat card on a slope has two bad options:
- Keep it upright, and it cuts into the hill on the uphill side, so the bottom is chopped off at an angle.
- Tilt it to match the ground, and the grass leans sideways. Plants don’t grow that way, and you notice.
The fix is a shear rather than a rotation. Each bottom corner of the card drops to the ground height under it, and the top moves by the same amount. The card becomes a parallelogram that hugs the slope, and because points only move straight up or down, every blade still points straight up. It’s like squishing putty instead of tipping a board. It’s a small piece of math, and it made the ledges and sideways grass disappear.
Bonus: break the grid.
Every card gets its own random rotation, size, color variation and a slightly different phase in the wind. The eye is very good at spotting repetition, and that randomness is what keeps it from noticing the cards.
Next up: brushes, so sim owners can paint where grass grows.
I’m still kind of figuring it out myself - but i’m very excited about the upcoming combat quest sprints.
