extract reusable prepass_alpha_discard

This renames the old prepase_alpha_discard to
prepass_sample_color_and_alpha_discard to indicate
that it accessing PBR-specific texture bindings.

crates/bevy_pbr/src/render/pbr_prepass.wgsl

@@ -32,21 +32,10 @@ struct FragmentInput {
 // Cutoff used for the premultiplied alpha modes BLEND and ADD.
 const PREMULTIPLIED_ALPHA_CUTOFF = 0.05;
 
-// We can use a simplified version of alpha_discard() here since we only need to handle the alpha_cutoff
-fn prepass_alpha_discard(in: FragmentInput) {
-
-#ifdef MAY_DISCARD
-    var output_color: vec4<f32> = bevy_pbr::pbr_bindings::material.base_color;
-
-#ifdef VERTEX_UVS
-    if (bevy_pbr::pbr_bindings::material.flags & bevy_pbr::pbr_types::STANDARD_MATERIAL_FLAGS_BASE_COLOR_TEXTURE_BIT) != 0u {
-        output_color = output_color * textureSampleBias(bevy_pbr::pbr_bindings::base_color_texture, bevy_pbr::pbr_bindings::base_color_sampler, in.uv, bevy_pbr::prepass_bindings::view.mip_bias);
-    }
-#endif // VERTEX_UVS
-
-    let alpha_mode = bevy_pbr::pbr_bindings::material.flags & bevy_pbr::pbr_types::STANDARD_MATERIAL_FLAGS_ALPHA_MODE_RESERVED_BITS;
+fn prepass_alpha_discard(material_flags: u32, alpha_cutoff: f32, output_color: vec4<f32>) {
+    let alpha_mode = material_flags & bevy_pbr::pbr_types::STANDARD_MATERIAL_FLAGS_ALPHA_MODE_RESERVED_BITS;
     if alpha_mode == bevy_pbr::pbr_types::STANDARD_MATERIAL_FLAGS_ALPHA_MODE_MASK {
-        if output_color.a < bevy_pbr::pbr_bindings::material.alpha_cutoff {
+        if output_color.a < alpha_cutoff {
             discard;
         }
     } else if (alpha_mode == bevy_pbr::pbr_types::STANDARD_MATERIAL_FLAGS_ALPHA_MODE_BLEND || alpha_mode == bevy_pbr::pbr_types::STANDARD_MATERIAL_FLAGS_ALPHA_MODE_ADD) {
@@ -58,6 +47,25 @@ fn prepass_alpha_discard(in: FragmentInput) {
             discard;
         }
     }
+}
+
+// We can use a simplified version of alpha_discard() here since we only need to handle the alpha_cutoff
+fn prepass_sample_color_and_alpha_discard(in: FragmentInput) {
+
+#ifdef MAY_DISCARD
+    var output_color: vec4<f32> = bevy_pbr::pbr_bindings::material.base_color;
+
+#ifdef VERTEX_UVS
+    if (bevy_pbr::pbr_bindings::material.flags & bevy_pbr::pbr_types::STANDARD_MATERIAL_FLAGS_BASE_COLOR_TEXTURE_BIT) != 0u {
+        output_color = output_color * textureSampleBias(bevy_pbr::pbr_bindings::base_color_texture, bevy_pbr::pbr_bindings::base_color_sampler, in.uv, bevy_pbr::prepass_bindings::view.mip_bias);
+    }
+#endif // VERTEX_UVS
+
+    prepass_alpha_discard(
+        bevy_pbr::pbr_bindings::material.flags,
+        bevy_pbr::pbr_bindings::material.alpha_cutoff,
+        output_color
+    );
 
 #endif // MAY_DISCARD
 }
@@ -79,7 +87,7 @@ struct FragmentOutput {
 
 @fragment
 fn fragment(in: FragmentInput) -> FragmentOutput {
-    prepass_alpha_discard(in);
+    prepass_sample_color_and_alpha_discard(in);
 
     var out: FragmentOutput;
 
@@ -135,6 +143,6 @@ fn fragment(in: FragmentInput) -> FragmentOutput {
 #else
 @fragment
 fn fragment(in: FragmentInput) {
-    prepass_alpha_discard(in);
+    prepass_sample_color_and_alpha_discard(in);
 }
 #endif // PREPASS_FRAGMENT