Eevee: Improve Hashed Alpha transparency by reducing noise size

This only affect renders and static viewport accumulation.
It reduces helps reduce noise when lots of half transparent surfaces
overlaps.

2 files changed, 7 insertions, 3 deletions

diff --git a/source/blender/draw/engines/eevee/eevee_materials.c b/source/blender/draw/engines/eevee/eevee_materials.c
index eee1e716da1..212f89e7216 100644
--- a/source/blender/draw/engines/eevee/eevee_materials.c
+++ b/source/blender/draw/engines/eevee/eevee_materials.c
@@ -71,6 +71,7 @@ static struct {
 	uint sss_count;
 
 	float alpha_hash_offset;
+	float alpha_hash_scale;
 	float noise_offsets[3];
 } e_data = {NULL}; /* Engine data */
 
@@ -635,11 +636,13 @@ void EEVEE_materials_init(EEVEE_ViewLayerData *sldata, EEVEE_StorageList *stl, E
 	    ((stl->effects->enabled_effects & EFFECT_TAA) == 0))
 	{
 		e_data.alpha_hash_offset = 0.0f;
+		e_data.alpha_hash_scale = 1.0f;
 	}
 	else {
 		double r;
 		BLI_halton_1D(5, 0.0, stl->effects->taa_current_sample - 1, &r);
 		e_data.alpha_hash_offset = (float)r;
+		e_data.alpha_hash_scale = 0.01f;
 	}
 
 	{
@@ -1206,6 +1209,8 @@ static void material_opaque(
 				else if (ma->blend_method == MA_BM_HASHED) {
 					DRW_shgroup_uniform_float(*shgrp_depth, "hashAlphaOffset", &e_data.alpha_hash_offset, 1);
 					DRW_shgroup_uniform_float(*shgrp_depth_clip, "hashAlphaOffset", &e_data.alpha_hash_offset, 1);
+					DRW_shgroup_uniform_float_copy(*shgrp_depth, "hashAlphaScale", e_data.alpha_hash_scale);
+					DRW_shgroup_uniform_float_copy(*shgrp_depth_clip, "hashAlphaScale", e_data.alpha_hash_scale);
 				}
 			}
 		}
diff --git a/source/blender/draw/engines/eevee/shaders/prepass_frag.glsl b/source/blender/draw/engines/eevee/shaders/prepass_frag.glsl
index 1c0e65f0613..6b6ab0c0bcc 100644
--- a/source/blender/draw/engines/eevee/shaders/prepass_frag.glsl
+++ b/source/blender/draw/engines/eevee/shaders/prepass_frag.glsl
@@ -11,14 +11,13 @@ float hash3d(vec3 a) {
 }
 
 uniform float hashAlphaOffset;
+uniform float hashAlphaScale = 1.0; /* Roughly in pixel */
 
 float hashed_alpha_threshold(vec3 co)
 {
-	const float hash_scale = 1.0; /* Roughly in pixel */
-
 	/* Find the discretized derivatives of our coordinates. */
 	float max_deriv = max(length(dFdx(co)), length(dFdy(co)));
-	float pix_scale = 1.0 / (hash_scale * max_deriv);
+	float pix_scale = 1.0 / (hashAlphaScale * max_deriv);
 
 	/* Find two nearest log-discretized noise scales. */
 	float pix_scale_log = log2(pix_scale);