Fix T97796 EEVEE: Regression: Alpha clipped materials rendered as alpha hashed

This was because the alpha clip thresholding was previously done in the
material nodes codegen. Now it is the responsibility of the engine to
implement it.

This adds a loose uniform that is set by EEVEE itself to control the clip
behavior.

source/blender/draw/engines/eevee/eevee_lookdev.c

@@ -64,7 +64,7 @@ static void eevee_lookdev_hdri_preview_init(EEVEE_Data *vedata, EEVEE_ViewLayerD
 
     DRW_PASS_CREATE(psl->lookdev_diffuse_pass, state);
     grp = DRW_shgroup_create(sh, psl->lookdev_diffuse_pass);
-    EEVEE_material_bind_resources(grp, gpumat, sldata, vedata, NULL, NULL, false, false);
+    EEVEE_material_bind_resources(grp, gpumat, sldata, vedata, NULL, NULL, -1.0f, false, false);
     DRW_shgroup_add_material_resources(grp, gpumat);
     DRW_shgroup_call(grp, sphere, NULL);
   }
@@ -75,7 +75,7 @@ static void eevee_lookdev_hdri_preview_init(EEVEE_Data *vedata, EEVEE_ViewLayerD
 
     DRW_PASS_CREATE(psl->lookdev_glossy_pass, state);
     grp = DRW_shgroup_create(sh, psl->lookdev_glossy_pass);
-    EEVEE_material_bind_resources(grp, gpumat, sldata, vedata, NULL, NULL, false, false);
+    EEVEE_material_bind_resources(grp, gpumat, sldata, vedata, NULL, NULL, -1.0f, false, false);
     DRW_shgroup_add_material_resources(grp, gpumat);
     DRW_shgroup_call(grp, sphere, NULL);
   }

source/blender/draw/engines/eevee/eevee_materials.c

@@ -67,6 +67,7 @@ void EEVEE_material_bind_resources(DRWShadingGroup *shgrp,
                                    EEVEE_Data *vedata,
                                    const int *ssr_id,
                                    const float *refract_depth,
+                                   const float alpha_clip_threshold,
                                    bool use_ssrefraction,
                                    bool use_alpha_blend)
 {
@@ -91,6 +92,8 @@ void EEVEE_material_bind_resources(DRWShadingGroup *shgrp,
   DRW_shgroup_uniform_block(shgrp, "common_block", sldata->common_ubo);
   DRW_shgroup_uniform_block_ref(shgrp, "renderpass_block", &pd->renderpass_ubo);
 
+  DRW_shgroup_uniform_float_copy(shgrp, "alphaClipThreshold", alpha_clip_threshold);
+
   DRW_shgroup_uniform_int_copy(shgrp, "outputSssId", 1);
   DRW_shgroup_uniform_texture(shgrp, "utilTex", e_data.util_tex);
   if (use_diffuse || use_glossy || use_refract) {
@@ -480,6 +483,8 @@ BLI_INLINE void material_shadow(EEVEE_Data *vedata,
     /* Shadow Pass */
     const bool use_shadow_shader = ma->use_nodes && ma->nodetree &&
                                    ELEM(ma->blend_shadow, MA_BS_CLIP, MA_BS_HASHED);
+    float alpha_clip_threshold = (ma->blend_shadow == MA_BS_CLIP) ? ma->alpha_threshold : -1.0f;
+
     int mat_options = VAR_MAT_MESH | VAR_MAT_DEPTH;
     SET_FLAG_FROM_TEST(mat_options, use_shadow_shader, VAR_MAT_HASH);
     SET_FLAG_FROM_TEST(mat_options, is_hair, VAR_MAT_HAIR);
@@ -503,7 +508,8 @@ BLI_INLINE void material_shadow(EEVEE_Data *vedata,
     }
     else {
       *grp_p = grp = DRW_shgroup_create(sh, psl->shadow_pass);
-      EEVEE_material_bind_resources(grp, gpumat, sldata, vedata, NULL, NULL, false, false);
+      EEVEE_material_bind_resources(
+          grp, gpumat, sldata, vedata, NULL, NULL, alpha_clip_threshold, false, false);
     }
 
     DRW_shgroup_add_material_resources(grp, gpumat);
@@ -533,6 +539,7 @@ static EeveeMaterialCache material_opaque(EEVEE_Data *vedata,
   const bool use_ssrefract = use_gpumat && ((ma->blend_flag & MA_BL_SS_REFRACTION) != 0) &&
                              ((effects->enabled_effects & EFFECT_REFRACT) != 0);
   const bool use_depth_shader = use_gpumat && ELEM(ma->blend_method, MA_BM_CLIP, MA_BM_HASHED);
+  float alpha_clip_threshold = (ma->blend_method == MA_BM_CLIP) ? ma->alpha_threshold : -1.0f;
 
   /* HACK: Assume the struct will never be smaller than our variations.
    * This allow us to only keep one ghash and avoid bigger keys comparisons/hashing. */
@@ -581,7 +588,8 @@ static EeveeMaterialCache material_opaque(EEVEE_Data *vedata,
     }
     else {
       *grp_p = grp = DRW_shgroup_create(sh, depth_ps);
-      EEVEE_material_bind_resources(grp, gpumat, sldata, vedata, NULL, NULL, false, false);
+      EEVEE_material_bind_resources(
+          grp, gpumat, sldata, vedata, NULL, NULL, alpha_clip_threshold, false, false);
     }
 
     DRW_shgroup_add_material_resources(grp, gpumat);
@@ -630,8 +638,15 @@ static EeveeMaterialCache material_opaque(EEVEE_Data *vedata,
     }
     else {
       *grp_p = grp = DRW_shgroup_create(sh, shading_pass);
-      EEVEE_material_bind_resources(
-          grp, gpumat, sldata, vedata, &ssr_id, &ma->refract_depth, use_ssrefract, false);
+      EEVEE_material_bind_resources(grp,
+                                    gpumat,
+                                    sldata,
+                                    vedata,
+                                    &ssr_id,
+                                    &ma->refract_depth,
+                                    alpha_clip_threshold,
+                                    use_ssrefract,
+                                    false);
     }
     DRW_shgroup_add_material_resources(grp, gpumat);
 
@@ -677,7 +692,7 @@ static EeveeMaterialCache material_transparent(EEVEE_Data *vedata,
 
     DRWShadingGroup *grp = DRW_shgroup_create(sh, psl->transparent_pass);
 
-    EEVEE_material_bind_resources(grp, gpumat, sldata, vedata, NULL, NULL, false, true);
+    EEVEE_material_bind_resources(grp, gpumat, sldata, vedata, NULL, NULL, -1.0f, false, true);
     DRW_shgroup_add_material_resources(grp, gpumat);
 
     cur_state = DRW_STATE_WRITE_DEPTH | DRW_STATE_DEPTH_LESS_EQUAL;
@@ -699,7 +714,7 @@ static EeveeMaterialCache material_transparent(EEVEE_Data *vedata,
                                               psl->transparent_pass);
 
     EEVEE_material_bind_resources(
-        grp, gpumat, sldata, vedata, &ssr_id, &ma->refract_depth, use_ssrefract, true);
+        grp, gpumat, sldata, vedata, &ssr_id, &ma->refract_depth, -1.0f, use_ssrefract, true);
     DRW_shgroup_add_material_resources(grp, gpumat);
 
     cur_state = DRW_STATE_WRITE_COLOR | DRW_STATE_BLEND_CUSTOM;

source/blender/draw/engines/eevee/eevee_private.h

@@ -1141,6 +1141,7 @@ void EEVEE_material_bind_resources(DRWShadingGroup *shgrp,
                                    EEVEE_Data *vedata,
                                    const int *ssr_id,
                                    const float *refract_depth,
+                                   const float alpha_clip_threshold,
                                    bool use_ssrefraction,
                                    bool use_alpha_blend);
 /* eevee_lights.c */

source/blender/draw/engines/eevee/shaders/prepass_frag.glsl

@@ -11,6 +11,8 @@
 #pragma BLENDER_REQUIRE(surface_lib.glsl)
 
 #ifdef USE_ALPHA_HASH
+/* A value of -1.0 will disable alpha clip and use alpha hash. */
+uniform float alphaClipThreshold;
 
 /* From the paper "Hashed Alpha Testing" by Chris Wyman and Morgan McGuire */
 float hash(vec2 a)
@@ -76,9 +78,16 @@ void main()
 
   float opacity = saturate(1.0 - avg(cl.transmittance));
 
-  /* Hashed Alpha Testing */
-  if (opacity < hashed_alpha_threshold(worldPosition)) {
-    discard;
+  if (alphaClipThreshold == -1.0) {
+    /* NOTE: uniform control flow required for dFdx(). */
+    if (opacity < hashed_alpha_threshold(worldPosition)) {
+      discard;
+    }
+  }
+  else {
+    if (opacity <= alphaClipThreshold) {
+      discard;
+    }
   }
 #endif
 }