Parametrize MAX_STEPS, fix iteration count

crates/bevy_pbr/src/parallax.rs

@@ -1,6 +1,6 @@
 use bevy_reflect::{FromReflect, Reflect};
 
-/// The parallax mapping method to use to compute a displacement based on the
+/// The parallax mapping method to use to compute depth based on the
 /// material's [`depth_map`].
 ///
 /// See the `parallax_mapping.wgsl` shader code for implementation details
@@ -12,9 +12,25 @@ pub enum ParallaxMappingMethod {
     /// A simple linear interpolation, using a single texture sample.
     #[default]
     ParallaxOcclusionMapping,
-    /// A discovery of 5 iterations of the best displacement
-    /// value. Each iteration incurs a texture sample.
+    /// Discovers the best depth value based on binary search.
     ///
+    /// Each iteration incurs a texture sample.
     /// The result has fewer visual artifacts than `ParallaxOcclusionMapping`.
-    ReliefMapping { n_steps: u32 },
+    ReliefMapping {
+        /// How many additional steps to use at most to find the depth value.
+        max_steps: u32,
+    },
+}
+impl ParallaxMappingMethod {
+    /// [`ReliefMapping`] with a 5 steps, a reasonable default.
+    ///
+    /// [`ReliefMapping`]: Self::ReliefMapping
+    pub const DEFAULT_RELIEF_MAPPING: Self = ParallaxMappingMethod::ReliefMapping { max_steps: 5 };
+
+    pub(crate) fn max_steps(&self) -> u32 {
+        match self {
+            ParallaxMappingMethod::ParallaxOcclusionMapping => 0,
+            ParallaxMappingMethod::ReliefMapping { max_steps } => *max_steps,
+        }
+    }
 }

crates/bevy_pbr/src/pbr_material.rs

@@ -431,6 +431,9 @@ pub struct StandardMaterialUniform {
     /// If your `parallax_depth` is >0.1 and you are seeing jaggy edges,
     /// increase this value. However, this incurs a performance cost.
     pub max_parallax_layer_count: f32,
+    /// Using [`ParallaxMappingMethod::ReliefMapping`], how many additional
+    /// steps to use at most to find the depth value.
+    pub max_relief_mapping_search_steps: u32,
 }
 
 impl AsBindGroupShaderType<StandardMaterialUniform> for StandardMaterial {
@@ -502,6 +505,7 @@ impl AsBindGroupShaderType<StandardMaterialUniform> for StandardMaterial {
             alpha_cutoff,
             parallax_depth: self.parallax_depth,
             max_parallax_layer_count: self.max_parallax_layer_count,
+            max_relief_mapping_search_steps: self.parallax_mapping_method.max_steps(),
         }
     }
 }

crates/bevy_pbr/src/render/parallax_mapping.wgsl

@@ -9,6 +9,7 @@ fn sample_depth_map(uv: vec2<f32>) -> f32 {
 fn parallaxed_uv(
     depth: f32,
     max_layer_count: f32,
+    max_steps: u32,
     // The original uv
     uv: vec2<f32>,
     // The vector from camera to the surface of material
@@ -42,7 +43,7 @@ fn parallaxed_uv(
     var current_height = sample_depth_map(uv);
 
     // This at most runs layer_count times
-    for (var i: i32 = 0; current_height > current_layer_height && i < i32(layer_count); i++) {
+    for (var i: i32 = 0; current_height > current_layer_height && i <= i32(layer_count); i++) {
         current_layer_height += layer_height;
         uv -= delta_uv;
         current_height = sample_depth_map(uv);
@@ -55,13 +56,12 @@ fn parallaxed_uv(
     // with a binary search between the layer selected by steep parallax
     // and the next one to find a point closer to the depth map surface.
     // This reduces the jaggy step artifacts from steep parallax mapping.
-    let MAX_STEPS: i32 = 5;
 
     delta_uv *= 0.5;
     var delta_height = 0.5 * layer_height;
     uv += delta_uv;
     current_layer_height -= delta_height;
-    for (var i: i32 = 0; i < MAX_STEPS; i++) {
+    for (var i: u32 = 0u; i < max_steps; i++) {
         // Sample depth at current offset
         current_height = sample_depth_map(uv);
 

crates/bevy_pbr/src/render/pbr.wgsl

@@ -32,7 +32,13 @@ fn fragment(in: FragmentInput) -> @location(0) vec4<f32> {
             dot(V, -cross(in.world_normal, in.world_tangent.xyz) * sign(in.world_tangent.w)),
             dot(V, in.world_normal),
         );
-        uv = parallaxed_uv(material.parallax_depth, material.max_parallax_layer_count, uv, tangent_V);
+        uv = parallaxed_uv(
+            material.parallax_depth,
+            material.max_parallax_layer_count,
+            material.max_relief_mapping_search_steps,
+            uv,
+            tangent_V,
+        );
     }
 #endif
 #endif

crates/bevy_pbr/src/render/pbr_types.wgsl

@@ -11,6 +11,7 @@ struct StandardMaterial {
     alpha_cutoff: f32,
     parallax_depth: f32,
     max_parallax_layer_count: f32,
+    max_relief_mapping_search_steps: u32,
 };
 
 const STANDARD_MATERIAL_FLAGS_BASE_COLOR_TEXTURE_BIT: u32         = 1u;
@@ -47,6 +48,7 @@ fn standard_material_new() -> StandardMaterial {
     material.alpha_cutoff = 0.5;
     material.parallax_depth = 0.1;
     material.max_parallax_layer_count = 16.0;
+    material.max_relief_mapping_search_steps = 5u;
 
     return material;
 }

examples/3d/parallax_mapping.rs

@@ -90,7 +90,7 @@ fn switch_algo(
     if input.just_pressed(KeyCode::Space) {
         *current = match *current {
             ReliefMapping { .. } => ParallaxOcclusionMapping,
-            ParallaxOcclusionMapping => ReliefMapping { n_steps: 5 },
+            ParallaxOcclusionMapping => ReliefMapping { max_steps: 5 },
         }
     } else {
         return;
@@ -258,7 +258,7 @@ fn setup(
         // white the lowest.
         depth_map: Some(asset_server.load("textures/parallax_example/cube_depth.jpg")),
         parallax_depth,
-        parallax_mapping_method: ParallaxMappingMethod::ReliefMapping { n_steps: 5 },
+        parallax_mapping_method: ParallaxMappingMethod::DEFAULT_RELIEF_MAPPING,
         max_parallax_layer_count,
         ..default()
     });