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fix(rendering): reduce terrain chunk edge seams (#56)

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Two sources of visible chunk-boundary squares:

1. Derivative-based bump mapping (bumpStrength=9) used dFdx/dFdy which
   are invalid across draw-call boundaries, producing strong normal
   discontinuities at every chunk edge.  Fade bump to zero near chunk
   edges using LayerUV as the chunk-space distance metric.

2. sampleAlpha used an abrupt step() to switch between point-sampled
   and 4-tap-blurred alpha, creating a visible ring 2 texels from each
   chunk edge.  Replace with smoothstep transition and a 5-tap average
   that includes the center sample.
This commit is contained in:
Kelsi 2026-04-06 18:18:14 -07:00
parent 7b746a3045
commit faf1d70c34
1 changed files with 16 additions and 11 deletions
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27
assets/shaders/terrain.frag.glsl
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@ -50,19 +50,21 @@ float sampleShadowPCF(sampler2DShadow smap, vec3 coords) {
}
float sampleAlpha(sampler2D tex, vec2 uv) {
// Smooth 5-tap box near chunk edges to hide alpha-map seams;
// blends gradually to avoid a visible ring at the transition.
vec2 edge = min(uv, 1.0 - uv);
float border = min(edge.x, edge.y);
float doBlur = step(border, 2.0 / 64.0);
if (doBlur < 0.5) {
return texture(tex, uv).r;
}
float blurWeight = 1.0 - smoothstep(0.5 / 64.0, 3.0 / 64.0, border);
float center = texture(tex, uv).r;
if (blurWeight < 0.001) return center;
vec2 texel = vec2(1.0 / 64.0);
float a = 0.0;
a += texture(tex, uv + vec2(-texel.x, 0.0)).r;
a += texture(tex, uv + vec2(texel.x, 0.0)).r;
a += texture(tex, uv + vec2(0.0, -texel.y)).r;
a += texture(tex, uv + vec2(0.0, texel.y)).r;
return a * 0.25;
float avg = center;
avg += texture(tex, uv + vec2(-texel.x, 0.0)).r;
avg += texture(tex, uv + vec2( texel.x, 0.0)).r;
avg += texture(tex, uv + vec2(0.0, -texel.y)).r;
avg += texture(tex, uv + vec2(0.0, texel.y)).r;
avg *= 0.2;
return mix(center, avg, blurWeight);
}
void main() {
@ -87,9 +89,12 @@ void main() {
vec3 norm = normalize(Normal);
// Derivative-based normal mapping: perturb vertex normal using texture detail.
// Fade out with distance — looks noisy/harsh beyond ~100 units.
// Fade out with distance and near chunk edges (dFdx/dFdy are invalid across
// chunk draw-call boundaries, producing visible seams if not faded).
float fragDist = length(viewPos.xyz - FragPos);
float bumpFade = 1.0 - smoothstep(50.0, 125.0, fragDist);
float edgeDist = min(min(LayerUV.x, 1.0 - LayerUV.x), min(LayerUV.y, 1.0 - LayerUV.y));
bumpFade *= smoothstep(0.0, 0.06, edgeDist);
if (bumpFade > 0.001) {
float lum = dot(finalColor.rgb, vec3(0.299, 0.587, 0.114));
float dLdx = dFdx(lum);