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Fix atmosphere particles clustering on left side of screen

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When wind is zero or near-zero, dust particles were always spawning at
the left viewport edge (the "upwind" edge for wind >= 0). Without wind
force to carry them across, they accumulated on the left side. Now
particles spawn across the full viewport when wind is calm (< 5 px/s²),
with random drift directions for even distribution.

Closes #2

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
This commit is contained in:
root
2026-03-14 14:14:52 +00:00
parent 5793af4896
commit c57ac68a04
1 changed files with 58 additions and 27 deletions
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85
src/engine/particle.c
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@@ -556,38 +556,69 @@ void particle_emit_atmosphere_dust(Vec2 cam_pos, Vec2 vp) {
* Two sub-layers for depth: large slow "far" motes and small quick
* "near" specks. Wind carries them; gravity_scale controls how much
* environmental forces (wind + gravity) affect each particle.
* Particles spawn along the upwind viewport edge and drift inward;
* occasional interior spawns prevent a visible edge seam. */
float wind = physics_get_wind();
float margin = 32.0f;
float dir = (wind >= 0.0f) ? 1.0f : -1.0f; /* velocity sign */
* When wind is strong, particles spawn along the upwind viewport edge
* and drift inward. When wind is calm, particles spawn across the
* full viewport to avoid clustering on one side. */
float wind = physics_get_wind();
float margin = 32.0f;
float abs_wind = (wind >= 0.0f) ? wind : -wind;
int has_wind = abs_wind > 5.0f; /* threshold for edge-spawning */
/* Upwind edge X for the two edge-spawned layers */
float edge_far = (wind >= 0.0f) ? cam_pos.x - margin
: cam_pos.x + vp.x + margin;
float edge_near = (wind >= 0.0f) ? cam_pos.x - margin * 0.5f
: cam_pos.x + vp.x + margin * 0.5f;
if (has_wind) {
float dir = (wind >= 0.0f) ? 1.0f : -1.0f;
/* Far dust motes — large, slow, translucent (1/frame) */
spawn_dust_mote(
vec2(edge_far, cam_pos.y + randf() * vp.y),
vec2(dir * randf_range(8.0f, 25.0f), randf_range(-6.0f, 6.0f)),
4.0f, 7.0f, 1.5f, 3.0f, 0.3f, 0.08f,
180, 140, 100, 25);
/* Upwind edge X for the two edge-spawned layers */
float edge_far = (wind >= 0.0f) ? cam_pos.x - margin
: cam_pos.x + vp.x + margin;
float edge_near = (wind >= 0.0f) ? cam_pos.x - margin * 0.5f
: cam_pos.x + vp.x + margin * 0.5f;
/* Near dust specks — small, quicker, brighter (1/frame) */
spawn_dust_mote(
vec2(edge_near, cam_pos.y + randf() * vp.y),
vec2(dir * randf_range(15.0f, 40.0f), randf_range(-10.0f, 10.0f)),
2.5f, 5.0f, 0.8f, 1.5f, 0.2f, 0.12f,
200, 160, 120, 20);
/* Far dust motes — large, slow, translucent (1/frame) */
spawn_dust_mote(
vec2(edge_far, cam_pos.y + randf() * vp.y),
vec2(dir * randf_range(8.0f, 25.0f), randf_range(-6.0f, 6.0f)),
4.0f, 7.0f, 1.5f, 3.0f, 0.3f, 0.08f,
180, 140, 100, 25);
/* Occasional interior spawn — prevents edge seam on calm wind */
if (rand() % 3 == 0) {
/* Near dust specks — small, quicker, brighter (1/frame) */
spawn_dust_mote(
vec2(edge_near, cam_pos.y + randf() * vp.y),
vec2(dir * randf_range(15.0f, 40.0f), randf_range(-10.0f, 10.0f)),
2.5f, 5.0f, 0.8f, 1.5f, 0.2f, 0.12f,
200, 160, 120, 20);
/* Occasional interior spawn — prevents edge seam */
if (rand() % 3 == 0) {
spawn_dust_mote(
vec2(cam_pos.x + randf() * vp.x, cam_pos.y + randf() * vp.y),
vec2(randf_range(-5.0f, 5.0f), randf_range(-8.0f, 3.0f)),
3.0f, 6.0f, 1.0f, 2.5f, 0.4f, 0.06f,
160, 130, 95, 25);
}
} else {
/* Calm wind — spawn across the full viewport to distribute evenly */
/* Far dust motes — large, slow, translucent (1/frame) */
spawn_dust_mote(
vec2(cam_pos.x + randf() * vp.x, cam_pos.y + randf() * vp.y),
vec2(randf_range(-5.0f, 5.0f), randf_range(-8.0f, 3.0f)),
3.0f, 6.0f, 1.0f, 2.5f, 0.4f, 0.06f,
160, 130, 95, 25);
vec2(randf_range(-10.0f, 10.0f), randf_range(-6.0f, 6.0f)),
4.0f, 7.0f, 1.5f, 3.0f, 0.3f, 0.08f,
180, 140, 100, 25);
/* Near dust specks — small, quicker, brighter (1/frame) */
spawn_dust_mote(
vec2(cam_pos.x + randf() * vp.x, cam_pos.y + randf() * vp.y),
vec2(randf_range(-15.0f, 15.0f), randf_range(-10.0f, 10.0f)),
2.5f, 5.0f, 0.8f, 1.5f, 0.2f, 0.12f,
200, 160, 120, 20);
/* Extra interior mote for density parity with windy path */
if (rand() % 3 == 0) {
spawn_dust_mote(
vec2(cam_pos.x + randf() * vp.x, cam_pos.y + randf() * vp.y),
vec2(randf_range(-5.0f, 5.0f), randf_range(-8.0f, 3.0f)),
3.0f, 6.0f, 1.0f, 2.5f, 0.4f, 0.06f,
160, 130, 95, 25);
}
}
}