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feat(render3d): an aspen quakes, and a tree is no longer bent like a bow

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layer_flutter(l, v) gives a scatter layer a per-leaf tremble. The vertex stage offsets
each leaf by a phase taken from its own place on the card, so neighbouring leaves are
never in step, and writes the result out as a varying the fragment stage uses to flash
the leaf's pale underside as it turns - which is the part that reads, since a still
frame of a tremble is a still frame of nothing. One uniform, one varying, no extra pass.

And the sway itself was measured in METRES: hgt * hgt * 0.35 is right for a 40 cm
flower and puts ten metres of sideways into a 14 m trunk, so every tall tree in the
valley stood bent over like a fishing rod. It is a fraction of the model's own height
now - the tip moves a few per cent of the tree whatever the tree is, and the base does
not move at all.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
This commit is contained in:
Orkun ÇAKILKAYA 2026-09-19 21:13:42 +03:00
parent 4975c60ac1
commit ab6f310013
47 changed files with 99 additions and 19 deletions
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31
packages/ludic.render3d/shaders/model.vert
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@ -54,8 +54,15 @@ out vec2 v_rot;
// have been shaded since SpeedTree; without it a card crown reads as frosted.
uniform float u_model_h; // the model's height (m), 0 = not a crown
out float v_hull; // 0 at the crown's axis .. 1 at its rim
// An aspen leaf hangs on a flattened stalk, so it twists in air a conifer does not feel at
// all. u_flutter is per layer: 0 for everything else, and the quake is written out as a
// varying so the fragment stage can flash the leaf's pale underside as it turns - which is
// the part you actually SEE. A still frame of a tremble is a still frame of nothing.
uniform float u_flutter;
out float v_quake;
void main() {
float s = i_rot.x, c = i_rot.y;
v_quake = 0.0;
vec3 p = a_pos * i_pos.w;
#ifdef CARD
p = vec3(p.x * u_card_w, p.y * u_card_h, p.z * u_card_w);
@ -81,8 +88,28 @@ void main() {
// read at the tree's own place in the world, so a gust crosses the grass and goes on into
// the trees. `stiff` is 0.35 because a bole resists what a blade cannot.
float sway = windSway(i_pos.xz, u_time, ph, 0.35) * u_wind * i_rot.w;
p.x += sway * hgt * hgt * 0.35;
p.z += sway * hgt * hgt * 0.15 * cos(ph * 0.7);
// The bend is a FRACTION OF THE TREE, not a number of metres. `hgt * hgt` in metres is
// fine for a 40 cm flower and ruinous for a 14 m aspen - it put ten metres of sideways
// into a trunk and bent it over like a fishing rod, which is what standing under one and
// looking up finally showed. Normalised, the tip moves a few per cent of the tree's own
// height whatever the tree is, and the base does not move at all.
float th = max(u_model_h * i_pos.w, 0.001);
float hn = (u_model_h > 2.0) ? clamp(hgt / th, 0.0, 1.0) : min(hgt, 1.0);
float reach = (u_model_h > 2.0) ? th * 0.22 : 0.35;
p.x += sway * hn * hn * reach;
p.z += sway * hn * hn * reach * 0.43 * cos(ph * 0.7);
if (u_flutter > 0.0) {
// per-leaf, not per-tree: the phase comes from the vertex's own place on the card, so
// neighbouring leaves are never in step - a crown that trembles as one block reads as
// the whole tree shivering.
float qp = u_time * 8.5 + a_pos.x * 11.3 + a_pos.z * 9.7 + a_pos.y * 4.1 + i_rot.z * 6.2831;
float q = sin(qp) * 0.65 + sin(qp * 1.73 + 1.1) * 0.35;
float amp = u_flutter * (0.40 + 0.60 * windGust(i_pos.xz, u_time)) * smoothstep(0.0, 1.2, hgt);
p.x += q * amp * 0.10;
p.y += q * amp * 0.05;
p.z += cos(qp * 0.9) * amp * 0.10;
v_quake = q * amp;
}
#endif
v_hull = 1.0;
if (u_model_h > 2.0) {