Add support for setting blending mode

src/asset.rs

@@ -103,7 +103,7 @@ pub enum SimulationCondition {
 /// rendered during the [`Transparent2d`] render phase.
 ///
 /// [`Transparent2d`]: bevy::core_pipeline::core_2d::Transparent2d
-#[derive(Debug, Default, Clone, Copy, PartialEq, Reflect, Serialize, Deserialize)]
+#[derive(Debug, Default, Clone, Copy, Eq, PartialEq, Reflect, Serialize, Deserialize, Hash)]
 #[non_exhaustive]
 pub enum AlphaMode {
     /// Render the effect with alpha blending.
@@ -127,6 +127,33 @@ pub enum AlphaMode {
     #[default]
     Blend,
 
+    /// Similar to [`AlphaMode::Blend`], however assumes RGB channel values are
+    /// [premultiplied](https://en.wikipedia.org/wiki/Alpha_compositing#Straight_versus_premultiplied).
+    ///
+    /// For otherwise constant RGB values, behaves more like [`AlphaMode::Blend`] for
+    /// alpha values closer to 1.0, and more like [`AlphaMode::Add`] for
+    /// alpha values closer to 0.0.
+    ///
+    /// Can be used to avoid “border” or “outline” artifacts that can occur
+    /// when using plain alpha-blended textures.
+    Premultiply,
+
+    /// Combines the color of the fragments with the colors behind them in an
+    /// additive process, (i.e. like light) producing lighter results.
+    ///
+    /// Black produces no effect. Alpha values can be used to modulate the result.
+    ///
+    /// Useful for effects like holograms, ghosts, lasers and other energy beams.
+    Add,
+
+    /// Combines the color of the fragments with the colors behind them in a
+    /// multiplicative process, (i.e. like pigments) producing darker results.
+    ///
+    /// White produces no effect. Alpha values can be used to modulate the result.
+    ///
+    /// Useful for effects like stained glass, window tint film and some colored liquids.
+    Multiply,
+
     /// Render the effect with alpha masking.
     ///
     /// With this mode, the final alpha value computed per particle fragment is

src/lib.rs

@@ -1109,6 +1109,8 @@ pub struct CompiledParticleEffect {
     z_layer_2d: FloatOrd,
     /// Layout flags.
     layout_flags: LayoutFlags,
+    /// Alpha mode.
+    alpha_mode: AlphaMode,
 }
 
 impl Default for CompiledParticleEffect {
@@ -1121,6 +1123,7 @@ impl Default for CompiledParticleEffect {
             #[cfg(feature = "2d")]
             z_layer_2d: FloatOrd(0.0),
             layout_flags: LayoutFlags::NONE,
+            alpha_mode: default(),
         }
     }
 }
@@ -1196,6 +1199,7 @@ impl CompiledParticleEffect {
         };
 
         self.layout_flags = shader_source.layout_flags;
+        self.alpha_mode = asset.alpha_mode;
 
         let init_shader = shader_cache.get_or_insert(&asset.name, &shader_source.init, shaders);
         let update_shaders: Vec<_> = shader_source

src/render/batch.rs

@@ -11,7 +11,7 @@ use super::{
     effect_cache::{DispatchBufferIndices, EffectSlices},
     EffectCacheId, GpuCompressedTransform, LayoutFlags,
 };
-use crate::{EffectAsset, EffectShader, ParticleLayout, PropertyLayout};
+use crate::{AlphaMode, EffectAsset, EffectShader, ParticleLayout, PropertyLayout};
 
 /// Data needed to render all batches pertaining to a specific effect.
 #[derive(Debug, Component)]
@@ -39,6 +39,8 @@ pub(crate) struct EffectBatches {
     pub particle_layout: ParticleLayout,
     /// Flags describing the render layout.
     pub layout_flags: LayoutFlags,
+    /// Alpha mode.
+    pub alpha_mode: AlphaMode,
     /// Entities holding the source [`ParticleEffect`] instances which were
     /// batched into this single batch. Used to determine visibility per view.
     ///
@@ -124,6 +126,7 @@ impl EffectBatches {
                 .collect(),
             handle: input.handle,
             layout_flags: input.layout_flags,
+            alpha_mode: input.alpha_mode,
             image_handle: input.image_handle,
             render_shaders: input.effect_shader.render,
             init_pipeline_id,
@@ -149,6 +152,8 @@ pub(crate) struct BatchesInput {
     pub effect_shader: EffectShader,
     /// Various flags related to the effect.
     pub layout_flags: LayoutFlags,
+    /// Alpha mode.
+    pub alpha_mode: AlphaMode,
     /// Texture to modulate the particle color.
     pub image_handle: Handle<Image>,
     /// Number of particles to spawn for this effect.

src/render/mod.rs

@@ -46,8 +46,9 @@ use crate::{
         effect_cache::DispatchBufferIndices,
     },
     spawn::EffectSpawner,
-    CompiledParticleEffect, EffectProperties, EffectShader, EffectSimulation, HanabiPlugin,
-    ParticleLayout, PropertyLayout, RemovedEffectsEvent, SimulationCondition, ToWgslString,
+    AlphaMode, CompiledParticleEffect, EffectProperties, EffectShader, EffectSimulation,
+    HanabiPlugin, ParticleLayout, PropertyLayout, RemovedEffectsEvent, SimulationCondition,
+    ToWgslString,
 };
 
 mod aligned_buffer_vec;
@@ -1000,6 +1001,8 @@ pub(crate) struct ParticleRenderPipelineKey {
     /// Key: USE_ALPHA_MASK
     /// The effect is rendered with alpha masking.
     use_alpha_mask: bool,
+    /// The effect needs Alpha blend.
+    alpha_mode: AlphaMode,
     /// Key: FLIPBOOK
     /// The effect is rendered with flipbook texture animation based on the
     /// sprite index of each particle.
@@ -1026,6 +1029,7 @@ impl Default for ParticleRenderPipelineKey {
             has_image: false,
             local_space_simulation: false,
             use_alpha_mask: false,
+            alpha_mode: AlphaMode::Blend,
             flipbook: false,
             needs_uv: false,
             #[cfg(all(feature = "2d", feature = "3d"))]
@@ -1213,6 +1217,32 @@ impl SpecializedRenderPipeline for ParticlesRenderPipeline {
             TextureFormat::bevy_default()
         };
 
+        let blend_state = match key.alpha_mode {
+            AlphaMode::Blend => BlendState::ALPHA_BLENDING,
+            AlphaMode::Premultiply => BlendState::PREMULTIPLIED_ALPHA_BLENDING,
+            AlphaMode::Add => BlendState {
+                color: BlendComponent {
+                    src_factor: BlendFactor::SrcAlpha,
+                    dst_factor: BlendFactor::One,
+                    operation: BlendOperation::Add,
+                },
+                alpha: BlendComponent {
+                    src_factor: BlendFactor::Zero,
+                    dst_factor: BlendFactor::One,
+                    operation: BlendOperation::Add,
+                },
+            },
+            AlphaMode::Multiply => BlendState {
+                color: BlendComponent {
+                    src_factor: BlendFactor::Dst,
+                    dst_factor: BlendFactor::OneMinusSrcAlpha,
+                    operation: BlendOperation::Add,
+                },
+                alpha: BlendComponent::OVER,
+            },
+            _ => BlendState::ALPHA_BLENDING,
+        };
+
         RenderPipelineDescriptor {
             vertex: VertexState {
                 shader: key.shader.clone(),
@@ -1226,7 +1256,7 @@ impl SpecializedRenderPipeline for ParticlesRenderPipeline {
                 entry_point: "fragment".into(),
                 targets: vec![Some(ColorTargetState {
                     format,
-                    blend: Some(BlendState::ALPHA_BLENDING),
+                    blend: Some(blend_state),
                     write_mask: ColorWrites::ALL,
                 })],
             }),
@@ -1290,6 +1320,8 @@ pub(crate) struct ExtractedEffect {
     pub inverse_transform: Mat4,
     /// Layout flags.
     pub layout_flags: LayoutFlags,
+    /// Alpha mode.
+    pub alpha_mode: AlphaMode,
     /// Texture to modulate the particle color.
     pub image_handle: Handle<Image>,
     /// Effect shader.
@@ -1518,6 +1550,8 @@ pub(crate) fn extract_effects(
             layout_flags |= LayoutFlags::PARTICLE_TEXTURE;
         }
 
+        let alpha_mode = effect.alpha_mode;
+
         trace!(
             "Extracted instance of effect '{}' on entity {:?}: image_handle={:?} has_image={} layout_flags={:?}",
             asset.name,
@@ -1539,6 +1573,7 @@ pub(crate) fn extract_effects(
                 // TODO - more efficient/correct way than inverse()?
                 inverse_transform: transform.compute_matrix().inverse(),
                 layout_flags,
+                alpha_mode,
                 image_handle,
                 effect_shader,
                 #[cfg(feature = "2d")]
@@ -2073,6 +2108,7 @@ pub(crate) fn prepare_effects(
                 property_layout: extracted_effect.property_layout.clone(),
                 effect_shader: extracted_effect.effect_shader.clone(),
                 layout_flags: extracted_effect.layout_flags,
+                alpha_mode: extracted_effect.alpha_mode,
                 image_handle: extracted_effect.image_handle,
                 spawn_count: extracted_effect.spawn_count,
                 transform: extracted_effect.transform.into(),
@@ -2466,6 +2502,8 @@ fn emit_draw<T, F>(
             let render_shader_source = &batches.render_shaders[draw_batch.group_index as usize];
             trace!("Emit for group index #{}", draw_batch.group_index);
 
+            let alpha_mode = batches.alpha_mode;
+
             #[cfg(feature = "trace")]
             let _span_specialize = bevy::utils::tracing::info_span!("specialize").entered();
             let render_pipeline_id = specialized_render_pipelines.specialize(
@@ -2477,6 +2515,7 @@ fn emit_draw<T, F>(
                     has_image,
                     local_space_simulation,
                     use_alpha_mask,
+                    alpha_mode,
                     flipbook,
                     needs_uv,
                     #[cfg(all(feature = "2d", feature = "3d"))]